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Grounding negative side of power supply?

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Joe Planisky

Grounding negative side of power supply?

Hi folks,

The recent discussions about bonding equipment together to reduce
noise has prompted me to ask a question I've been mulling over for a
few days now.

Should the negative side of a power supply be connected to the supply
chassis (and thus to the "green wire" AC ground), or should it be left
floating? I have heard arguments both for and against floating the
negative terminal, mostly from the fields of industrial control and
precision sensing. The gist seems to be that the negative side of
power supplies are usually connected to chassis or structure ground
except in cases of very sensitive analog sensing where it is sometimes
left floating to help reduce noise. I've heard stories of hum in
repeater systems being cured by floating the negative side of the
supply.

Does whether or not the negative side of the supply is floating affect
the idea of bonding the rig and PS cases to a common point?

73
--
Joe KB8AP

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Don Wilhelm-4

Re: [Elecraft] [OT] Grounding negative side of power supply?

Joe,

The real answer is - it all depends...

It all depends on the equipment that is connected to the power source.
It all depends on how the power supply itself is grounded
It all depends on how the entire group of equipment (your ham station)
is grounded.

There is no one answer - it all depends on the particular situation
where the power supply is employed.

"Sneak" current paths can (and do) exist, and the real answer depends on
where these sneak paths occur. If grounding the negative side of your
supply reduces the 'sneak paths', then grounding is the right thing to
do, but if it makes them worse, floating is the better answer.

Analysis with your particular equipment mix is impossible from this
distance, so just try both scenarios and pick the one that works best
for you. Be aware that your answer to that question will likely be
different than the answer from another installation. It all depends ...

73,
Don W3FPR

Joe Planisky wrote:

> Hi folks,
>
> The recent discussions about bonding equipment together to reduce
> noise has prompted me to ask a question I've been mulling over for a
> few days now.
>
> Should the negative side of a power supply be connected to the supply
> chassis (and thus to the "green wire" AC ground), or should it be left
> floating? I have heard arguments both for and against floating the
> negative terminal, mostly from the fields of industrial control and
> precision sensing. The gist seems to be that the negative side of
> power supplies are usually connected to chassis or structure ground
> except in cases of very sensitive analog sensing where it is sometimes
> left floating to help reduce noise. I've heard stories of hum in
> repeater systems being cured by floating the negative side of the
> supply.
>
> Does whether or not the negative side of the supply is floating affect
> the idea of bonding the rig and PS cases to a common point?
>
> 73
> --
> Joe KB8AP
>
>

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Jim Brown-10

Re: [Elecraft] [OT] Grounding negative side of power supply?

>Should the negative side of a power supply be connected to the supply
>chassis (and thus to the "green wire" AC ground), or should it be left
>floating?

As Don says, it depends -- on what design mistakes the engineers made
who designed the equipment. In other words, there can be a kind of "pin
1 problem" for power wiring, where noise current flowing on power wiring
(the black wire in a red/black pair) wanders around the circuit and
causes mischief.

The MOST important thing is that every chassis have a low impedance bond
to every other chassis, so that leakage currents flow outside the
chassis -- that is, green wire to green wire, chassis to chasssis -- and
that the voltage difference between one chassis and another is small.

Henry Ott has the fundamental answer -- figure out where the current is
flowing by studying the invisible schematic hiding behind the "ground"
symbol, and realize that there can be other current on that DC conductor
besides DC.

Remember -- low impedance means low resistance AND low inductance, and
low inductance means SHORT and STRAIGHT.

73,

Jim K9YC

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Rich

Re: Grounding negative side of power supply?

In reply to this post by Joe Planisky

I had a situation with an older (analog) power supply (that had its negative side grounded to the main AC ground) that tripped the Ground Fault Circuit Interrupter (GFCI) in one of the bathrooms. Eliminating the bond to ground fixed the problem. And, NO there was no problem with high SWR, RFI, etc. on the rig or antenna. It was a new house, it only happened on the whirlpool tub circuit, and since I did not use it that often It took months to determine that use of the transmitter was causing the problem - It tripped off while I was on air and the tub was in use. Only the tub used that circuit, so there was no indication other than it not working after filling up the tub and turning it on. It was a cheap GFI, and I can only assume that a transistor/diode in it was rectifying the signal on the ground line and tripping the circuit.

David Woolley (E.L)

Re: [Elecraft] [OT] Grounding negative side of power supply?

In reply to this post by Joe Planisky

Unless the power supply is a Class II double insulated device and there
are no connections from any of your equipment to true ground, it is
essential that all its exposed metal work is bonded to the mains ground
with a connection that is very low impedance at mains frequency and
capable of carrying the full rated current of the nearest fuse.

If you don't do this, in a fault situation you could get electrocuted
because the chassis is at a large voltage compared with other exposed
metalwork in the building.

Top posted by list policy. Incidentally, this seems to be about an
amateur radio topic, so it is on topic.

Joe Planisky wrote:

>
> Should the negative side of a power supply be connected to the supply
> chassis (and thus to the "green wire" AC ground), or should it be left
> floating? I have heard arguments both for and against floating the

--
David Woolley
"we do not overly restrict the subject matter on the list, and we
encourage postings on a wide range of amateur radio related topics"
List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm>
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David Woolley (E.L)

Re: [Elecraft] Grounding negative side of power supply?

In reply to this post by Rich

Rich wrote:
> I had a situation with an older (analog) power supply (that had its negative
> side grounded to the main AC ground) that tripped the Ground Fault Circuit
> Interrupter (GFCI) in one of the bathrooms. Eliminating the bond to ground

I consider this dangerous advice. If you have an ELCB tripping, you do
not treat the problem symptomatically, by creating an unsafer system,
you find out what the real problem is and you fix it.

I can't tell what the exact wiring configuration is here, but it is very
likely that you have created a situation where there are pieces of metal
in reach which have low impedance paths to very different "earths".

--
David Woolley
"we do not overly restrict the subject matter on the list, and we
encourage postings on a wide range of amateur radio related topics"
List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm>
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Don Wilhelm-4

Re: [Elecraft] Grounding negative side of power supply?

The AC side should always be connected to the power supply chassis -
unless it is of the "double insulated" design where no ungrounded
metallic part can come into contact with the human body. Yes, cutting
the AC "green wire ground" is a dangerous thing indeed - the entire
chassis could rise to the AC mains voltage in the event of a fault.

The power supply negative *can* certainly be floating *if* the designer
made provisions for doing that. It requires that all the common
connections on the secondary side of the transformer are isolated from
ground. As I recall, Astrons are not built that way.

73,
Don W3FPR

David Woolley (E.L) wrote:

> Rich wrote:
>
>> I had a situation with an older (analog) power supply (that had its negative
>> side grounded to the main AC ground) that tripped the Ground Fault Circuit
>> Interrupter (GFCI) in one of the bathrooms. Eliminating the bond to ground
>>
>
> I consider this dangerous advice. If you have an ELCB tripping, you do
> not treat the problem symptomatically, by creating an unsafer system,
> you find out what the real problem is and you fix it.
>
> I can't tell what the exact wiring configuration is here, but it is very
> likely that you have created a situation where there are pieces of metal
> in reach which have low impedance paths to very different "earths".
>
>

Joe Planisky

Re: [Elecraft] [OT] Grounding negative side of power supply?

In reply to this post by David Woolley (E.L)

Correct, and I agree that the power supply chassis should be connected
to the AC (mains) safety ground. But that wasn't the situation I was
asking about. I was asking whether the negative side of the DC output
should be connected to the chassis.

73
--
Joe KB8AP

On Jan 20, 2010, at 2:57 PM, David Woolley (E.L) wrote:

>
> Unless the power supply is a Class II double insulated device and
> there are no connections from any of your equipment to true ground,
> it is essential that all its exposed metal work is bonded to the
> mains ground with a connection that is very low impedance at mains
> frequency and capable of carrying the full rated current of the
> nearest fuse.

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Joe Subich, W4TV-4

Re: [Elecraft] Grounding negative side of power supply?

In reply to this post by Don Wilhelm-4

This creates a situation that is potentially hazardous
to your equipment. The AC "third (green) wire" is supposed
to be connected to ground only at the main panel/service
entrance. However, since it is connected to the chassis
of the power supply, it is also connected through the power
supply and radio to ground via the coaxial cable.

If the point at which the coaxial cables enter the building
is not the same place that power enters the building, any
nearby lightning strike can set up a significant difference
in voltage between the power line "safety ground" and the
RF ground (feedline shields/tower). That difference can
fry any electronics connected to both "grounds."

There are techniques for dealing with this problem ... but
they are not necessarily easy or inexpensive.

73,

... Joe, W4TV

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Don Wilhelm
> Sent: Wednesday, January 20, 2010 8:01 PM
> To: David Woolley (E.L)
> Cc: Rich; [hidden email]
> Subject: Re: [Elecraft] Grounding negative side of power supply?
>
>
> The AC side should always be connected to the power supply chassis -
> unless it is of the "double insulated" design where no ungrounded
> metallic part can come into contact with the human body.
> Yes, cutting
> the AC "green wire ground" is a dangerous thing indeed - the entire
> chassis could rise to the AC mains voltage in the event of a fault.
>
> The power supply negative *can* certainly be floating *if*
> the designer
> made provisions for doing that. It requires that all the common
> connections on the secondary side of the transformer are
> isolated from
> ground. As I recall, Astrons are not built that way.
>
> 73,
> Don W3FPR
>
> David Woolley (E.L) wrote:
> > Rich wrote:
> >
> >> I had a situation with an older (analog) power supply
> (that had its
> >> negative side grounded to the main AC ground) that tripped
> the Ground
> >> Fault Circuit Interrupter (GFCI) in one of the bathrooms.
> >> Eliminating the bond to ground
> >>
> >
> > I consider this dangerous advice. If you have an ELCB
> tripping, you
> > do
> > not treat the problem symptomatically, by creating an
> unsafer system,
> > you find out what the real problem is and you fix it.
> >
> > I can't tell what the exact wiring configuration is here, but it is
> > very
> > likely that you have created a situation where there are
> pieces of metal
> > in reach which have low impedance paths to very different "earths".
> >
> >
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

Don Wilhelm-4

Re: [Elecraft] Grounding negative side of power supply?

Joe,

That is *one* reason *any* ground rod should be tied back to the utility
ground stake. It is as requirement of NEC, and should not be ignored.
If you drive ground rods for the ham station, connect those ground rods
to the utility entrance ground rod - no exceptions. The ideal is #6 or
larger wire, but if you cannot do that use whatever wire you can. Your
safety depends on it. If you cannot connect extra ground rods to the AC
mains entry ground, then do not drive those extra ground rods - they are
*not* an RF ground (see my many posts in the archives on that topic) -
and as Joe points out, in the event of a lightning strike (or equipment
fault), they may create a dangerous condition.

You have 3 "grounds" to consider in the hamshack - 1) The AC safety
ground, 2) The lightning path ground, and 3) The RF ground.
1) and 2) may be one and the same, but 3) is a "horse of a different
color", and has nothing to do with a "mother earth" ground - it is a
point of low impedance at the frequency of interest, and usually exists
at some point in the antenna system, quite apart from "mother earth".
The English folks have the language a bit better and refer to "earthing"
which is often apart from "grounding", but we here in the US use the
same term for all common connections and in the process create confusion
for ourselves.

73,
Don W3FPR

Joe Subich, W4TV wrote:

> This creates a situation that is potentially hazardous
> to your equipment. The AC "third (green) wire" is supposed
> to be connected to ground only at the main panel/service
> entrance. However, since it is connected to the chassis
> of the power supply, it is also connected through the power
> supply and radio to ground via the coaxial cable.
>
> If the point at which the coaxial cables enter the building
> is not the same place that power enters the building, any
> nearby lightning strike can set up a significant difference
> in voltage between the power line "safety ground" and the
> RF ground (feedline shields/tower). That difference can
> fry any electronics connected to both "grounds."
>
> There are techniques for dealing with this problem ... but
> they are not necessarily easy or inexpensive.
>
> 73,
>
> ... Joe, W4TV
>
>
>
>
>
>
>> -----Original Message-----
>> From: [hidden email]
>> [mailto:[hidden email]] On Behalf Of Don Wilhelm
>> Sent: Wednesday, January 20, 2010 8:01 PM
>> To: David Woolley (E.L)
>> Cc: Rich; [hidden email]
>> Subject: Re: [Elecraft] Grounding negative side of power supply?
>>
>>
>> The AC side should always be connected to the power supply chassis -
>> unless it is of the "double insulated" design where no ungrounded
>> metallic part can come into contact with the human body.
>> Yes, cutting
>> the AC "green wire ground" is a dangerous thing indeed - the entire
>> chassis could rise to the AC mains voltage in the event of a fault.
>>
>> The power supply negative *can* certainly be floating *if*
>> the designer
>> made provisions for doing that. It requires that all the common
>> connections on the secondary side of the transformer are
>> isolated from
>> ground. As I recall, Astrons are not built that way.
>>
>> 73,
>> Don W3FPR
>>
>> David Woolley (E.L) wrote:
>>
>>> Rich wrote:
>>>
>>>
>>>> I had a situation with an older (analog) power supply
>>>>
>> (that had its
>>
>>>> negative side grounded to the main AC ground) that tripped
>>>>
>> the Ground
>>
>>>> Fault Circuit Interrupter (GFCI) in one of the bathrooms.
>>>> Eliminating the bond to ground
>>>>
>>>>
>>> I consider this dangerous advice. If you have an ELCB
>>>
>> tripping, you
>>
>>> do
>>> not treat the problem symptomatically, by creating an
>>>
>> unsafer system,
>>
>>> you find out what the real problem is and you fix it.
>>>
>>> I can't tell what the exact wiring configuration is here, but it is
>>> very
>>> likely that you have created a situation where there are
>>>
>> pieces of metal
>>
>>> in reach which have low impedance paths to very different "earths".
>>>
>>>
>>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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> Please help support this email list: http://www.qsl.net/donate.html
> ------------------------------------------------------------------------
>
>
> No virus found in this incoming message.
> Checked by AVG - www.avg.com
> Version: 9.0.730 / Virus Database: 271.1.1/2634 - Release Date: 01/20/10 04:12:00
>
>

Don Wilhelm-4

Re: [Elecraft] Grounding negative side of power supply?

In reply to this post by Joe Subich, W4TV-4

Joe and all,

I would also like to point out that the situation Joe presents can be
the source of "sneak ground path currents" which can contribute to noise
at your station. By all means, connect any ham related ground rods to
the AC mains entry point ground rod. I don't care how you accomplish
that - just "do it". If it reduces noise in your receiver, that is a
benefit, but if not, be assured that your shack will be a more safe
place to inhabit.

73,
Don W3FPR

Joe Subich, W4TV wrote:

rlindzen

Re: [Elecraft] Grounding negative side of power supply?

In reply to this post by Don Wilhelm-4

Dear Don,

This leaves me a bit concerned. I am planning to put up a K9AY
receiving antenna in my backyard and it is supposed to be connected
to a ground rod. I had never seen it suggested that this must be
connected to the utility ground stake. I'm not even sure where the
utility ground stake is. I've never noticed one though I will ask my
electrician. If there is one, it is likely to be pretty far from the K9AY.

73,

Dick, KA1SA

At 10:22 PM 1/20/2010, Don Wilhelm wrote:

>Joe,
>
>That is *one* reason *any* ground rod should be tied back to the utility
>ground stake. It is as requirement of NEC, and should not be ignored.
>If you drive ground rods for the ham station, connect those ground rods
>to the utility entrance ground rod - no exceptions. The ideal is #6 or
>larger wire, but if you cannot do that use whatever wire you can. Your
>safety depends on it. If you cannot connect extra ground rods to the AC
>mains entry ground, then do not drive those extra ground rods - they are
>*not* an RF ground (see my many posts in the archives on that topic) -
>and as Joe points out, in the event of a lightning strike (or equipment
>fault), they may create a dangerous condition.
>
>You have 3 "grounds" to consider in the hamshack - 1) The AC safety
>ground, 2) The lightning path ground, and 3) The RF ground.
>1) and 2) may be one and the same, but 3) is a "horse of a different
>color", and has nothing to do with a "mother earth" ground - it is a
>point of low impedance at the frequency of interest, and usually exists
>at some point in the antenna system, quite apart from "mother earth".
>The English folks have the language a bit better and refer to "earthing"
>which is often apart from "grounding", but we here in the US use the
>same term for all common connections and in the process create confusion
>for ourselves.
>
>73,
>Don W3FPR
>
>Joe Subich, W4TV wrote:
> > This creates a situation that is potentially hazardous
> > to your equipment. The AC "third (green) wire" is supposed
> > to be connected to ground only at the main panel/service
> > entrance. However, since it is connected to the chassis
> > of the power supply, it is also connected through the power
> > supply and radio to ground via the coaxial cable.
> >
> > If the point at which the coaxial cables enter the building
> > is not the same place that power enters the building, any
> > nearby lightning strike can set up a significant difference
> > in voltage between the power line "safety ground" and the
> > RF ground (feedline shields/tower). That difference can
> > fry any electronics connected to both "grounds."
> >
> > There are techniques for dealing with this problem ... but
> > they are not necessarily easy or inexpensive.
> >
> > 73,
> >
> > ... Joe, W4TV
> >
> >
> >
> >
> >
> >
> >> -----Original Message-----
> >> From: [hidden email]
> >> [mailto:[hidden email]] On Behalf Of Don Wilhelm
> >> Sent: Wednesday, January 20, 2010 8:01 PM
> >> To: David Woolley (E.L)
> >> Cc: Rich; [hidden email]
> >> Subject: Re: [Elecraft] Grounding negative side of power supply?
> >>
> >>
> >> The AC side should always be connected to the power supply chassis -
> >> unless it is of the "double insulated" design where no ungrounded
> >> metallic part can come into contact with the human body.
> >> Yes, cutting
> >> the AC "green wire ground" is a dangerous thing indeed - the entire
> >> chassis could rise to the AC mains voltage in the event of a fault.
> >>
> >> The power supply negative *can* certainly be floating *if*
> >> the designer
> >> made provisions for doing that. It requires that all the common
> >> connections on the secondary side of the transformer are
> >> isolated from
> >> ground. As I recall, Astrons are not built that way.
> >>
> >> 73,
> >> Don W3FPR
> >>
> >> David Woolley (E.L) wrote:
> >>
> >>> Rich wrote:
> >>>
> >>>
> >>>> I had a situation with an older (analog) power supply
> >>>>
> >> (that had its
> >>
> >>>> negative side grounded to the main AC ground) that tripped
> >>>>
> >> the Ground
> >>
> >>>> Fault Circuit Interrupter (GFCI) in one of the bathrooms.
> >>>> Eliminating the bond to ground
> >>>>
> >>>>
> >>> I consider this dangerous advice. If you have an ELCB
> >>>
> >> tripping, you
> >>
> >>> do
> >>> not treat the problem symptomatically, by creating an
> >>>
> >> unsafer system,
> >>
> >>> you find out what the real problem is and you fix it.
> >>>
> >>> I can't tell what the exact wiring configuration is here, but it is
> >>> very
> >>> likely that you have created a situation where there are
> >>>
> >> pieces of metal
> >>
> >>> in reach which have low impedance paths to very different "earths".
> >>>
> >>>
> >>>
> >> ______________________________________________________________
> >> Elecraft mailing list
> >> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> >> Help: http://mailman.qth.net/mmfaq.htm
> >> Post: mailto:[hidden email]
> >>
> >> This list hosted by: http://www.qsl.net
> >> Please help support this email list: http://www.qsl.net/donate.html
> >>
> >
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> > ------------------------------------------------------------------------
> >
> >
> > No virus found in this incoming message.
> > Checked by AVG - www.avg.com
> > Version: 9.0.730 / Virus Database: 271.1.1/2634 - Release Date:
> 01/20/10 04:12:00
> >
> >
>______________________________________________________________
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>
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==================================================
Richard S. Lindzen
Alfred P. Sloan Professor of Atmospheric
Sciences

Office: 54-1720, MIT
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1 (617) 253-2432 (voice)
1 (617) 253-6208 (fax)

Temporary Home: 100 Memorial Drive
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1 (617) 945-5784 (voice)
==================================================

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Don Wilhelm-4

Re: [Elecraft] Grounding negative side of power supply?

If *all* connections to the K9AY antenna (including 'sneak' paths) are
isolated from the AC mains ground, the safety factor does not exist.
The ground required by the K9AY antenna is an RF ground which is not
necessarily (but may be) at the same potential as the AC mains ground
and safety ground. BUT, that same isolation may lead to ground currents
that defeat the low noise characteristics of the K9AY antenna. Ideally,
all "mother earth" grounds should be connected to the AC mains ground by
a wire.

Often the building inspector likes to see the AC mains ground buried
beneath the surface of the earth so it is not subject to being hit by
lawn mowers or other instruments of destruction. There will be a bare
#6 (or larger) wire going into the earth at your AC mains entry point -
that is the wire that you must connect to. Look for the type of
connector that is used by the telephone company connection to this
ground wire - it is usually a "U" shaped clamp with a nut for
tightening. Those type clamps are available at your local DIY store in
their electrical department.

73,
Don W3FPR

Richard S. Lindzen wrote:

> Dear Don,
>
> This leaves me a bit concerned. I am planning to put up a K9AY
> receiving antenna in my backyard and it is supposed to be connected to
> a ground rod. I had never seen it suggested that this must be
> connected to the utility ground stake. I'm not even sure where the
> utility ground stake is. I've never noticed one though I will ask my
> electrician. If there is one, it is likely to be pretty far from the
> K9AY.
>
> 73,
>
> Dick, KA1SA
>
> At 10:22 PM 1/20/2010, Don Wilhelm wrote:
>> Joe,
>>
>> That is *one* reason *any* ground rod should be tied back to the utility
>> ground stake. It is as requirement of NEC, and should not be ignored.
>> If you drive ground rods for the ham station, connect those ground rods
>> to the utility entrance ground rod - no exceptions. The ideal is #6 or
>> larger wire, but if you cannot do that use whatever wire you can. Your
>> safety depends on it. If you cannot connect extra ground rods to the AC
>> mains entry ground, then do not drive those extra ground rods - they are
>> *not* an RF ground (see my many posts in the archives on that topic) -
>> and as Joe points out, in the event of a lightning strike (or equipment
>> fault), they may create a dangerous condition.
>>
>> You have 3 "grounds" to consider in the hamshack - 1) The AC safety
>> ground, 2) The lightning path ground, and 3) The RF ground.
>> 1) and 2) may be one and the same, but 3) is a "horse of a different
>> color", and has nothing to do with a "mother earth" ground - it is a
>> point of low impedance at the frequency of interest, and usually exists
>> at some point in the antenna system, quite apart from "mother earth".
>> The English folks have the language a bit better and refer to "earthing"
>> which is often apart from "grounding", but we here in the US use the
>> same term for all common connections and in the process create confusion
>> for ourselves.
>>
>> 73,
>> Don W3FPR
>>
>> Joe Subich, W4TV wrote:
>> > This creates a situation that is potentially hazardous
>> > to your equipment. The AC "third (green) wire" is supposed
>> > to be connected to ground only at the main panel/service
>> > entrance. However, since it is connected to the chassis
>> > of the power supply, it is also connected through the power
>> > supply and radio to ground via the coaxial cable.
>> >
>> > If the point at which the coaxial cables enter the building
>> > is not the same place that power enters the building, any
>> > nearby lightning strike can set up a significant difference
>> > in voltage between the power line "safety ground" and the
>> > RF ground (feedline shields/tower). That difference can
>> > fry any electronics connected to both "grounds."
>> >
>> > There are techniques for dealing with this problem ... but
>> > they are not necessarily easy or inexpensive.
>> >
>> > 73,
>> >
>> > ... Joe, W4TV
>> >
>> >
>> >
>> >
>> >
>> >
>> >> -----Original Message-----
>> >> From: [hidden email]
>> >> [mailto:[hidden email]] On Behalf Of Don Wilhelm
>> >> Sent: Wednesday, January 20, 2010 8:01 PM
>> >> To: David Woolley (E.L)
>> >> Cc: Rich; [hidden email]
>> >> Subject: Re: [Elecraft] Grounding negative side of power supply?
>> >>
>> >>
>> >> The AC side should always be connected to the power supply chassis -
>> >> unless it is of the "double insulated" design where no ungrounded
>> >> metallic part can come into contact with the human body.
>> >> Yes, cutting
>> >> the AC "green wire ground" is a dangerous thing indeed - the entire
>> >> chassis could rise to the AC mains voltage in the event of a fault.
>> >>
>> >> The power supply negative *can* certainly be floating *if*
>> >> the designer
>> >> made provisions for doing that. It requires that all the common
>> >> connections on the secondary side of the transformer are
>> >> isolated from
>> >> ground. As I recall, Astrons are not built that way.
>> >>
>> >> 73,
>> >> Don W3FPR
>> >>
>> >> David Woolley (E.L) wrote:
>> >>
>> >>> Rich wrote:
>> >>>
>> >>>
>> >>>> I had a situation with an older (analog) power supply
>> >>>>
>> >> (that had its
>> >>
>> >>>> negative side grounded to the main AC ground) that tripped
>> >>>>
>> >> the Ground
>> >>
>> >>>> Fault Circuit Interrupter (GFCI) in one of the bathrooms.
>> >>>> Eliminating the bond to ground
>> >>>>
>> >>>>
>> >>> I consider this dangerous advice. If you have an ELCB
>> >>>
>> >> tripping, you
>> >>
>> >>> do
>> >>> not treat the problem symptomatically, by creating an
>> >>>
>> >> unsafer system,
>> >>
>> >>> you find out what the real problem is and you fix it.
>> >>>
>> >>> I can't tell what the exact wiring configuration is here, but it is
>> >>> very
>> >>> likely that you have created a situation where there are
>> >>>
>> >> pieces of metal
>> >>
>> >>> in reach which have low impedance paths to very different "earths".
>> >>>
>> >>>
>> >>>
>> >> ______________________________________________________________
>> >> Elecraft mailing list
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>> >> Post: mailto:[hidden email]
>> >>
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>> >>
>> >
>> > ______________________________________________________________
>> > Elecraft mailing list
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>> >
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>> >
>> ______________________________________________________________
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>
> ==================================================
> Richard S. Lindzen
> Alfred P. Sloan Professor of Atmospheric Sciences
> Office: 54-1720, MIT
> Cambridge, MA 02139 USA
> 1 (617) 253-2432 (voice)
> 1 (617) 253-6208 (fax)
>
> Temporary Home: 100 Memorial Drive
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> 1 (617) 945-5784 (voice)
> ==================================================
> ------------------------------------------------------------------------
>
>
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> Checked by AVG - www.avg.com
> Version: 9.0.730 / Virus Database: 271.1.1/2634 - Release Date: 01/20/10 04:12:00
>
>

David Woolley (E.L)

Re: [Elecraft] [OT] Grounding negative side of power supply?

In reply to this post by Joe Planisky

The safety problem is that, with typical ham radio equipment, that
negative connection is connected to exposed metalwork, e.g. on the K2,
the microphone socket, bezel screws and headphone socket on the front
panel, any morse key and the multiple sockets on the back panel. The
paintwork, also, isn't designed for electrical isolation.

If there is a fault in the power supply transformer, these can become
hot to AC; a Class II power supply addresses this (most amateur radio
supplies are not Class II - any that has an earth wire is not Class II).
If the rig is grounded to the real earth, electrical faults, or
lightning can produce a dangerous voltage between it and other
metalwork, which should be connected to mains earth according to your
NEC/Building Regulations; ensuring that there is no real ground
connected to the rig addresses this one.

It doesn't, of course have to be the negative side; there is no absolute
rule against positive "earth" systems, it is just that valves and
current generation semiconductors are naturally negative "earth"
devices. The original, alloy junction, PNP transistors favoured
positive common systems.

Joe Planisky wrote:
> Correct, and I agree that the power supply chassis should be connected
> to the AC (mains) safety ground. But that wasn't the situation I was
> asking about. I was asking whether the negative side of the DC output
> should be connected to the chassis.
>

--
David Woolley
"we do not overly restrict the subject matter on the list, and we
encourage postings on a wide range of amateur radio related topics"
List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm>
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Jim AB3CV

Re: [Elecraft] Grounding negative side of power supply?

In reply to this post by Don Wilhelm-4

In many US homes the utility ground is found inside the home as it is a
ground rod embedded in the poured concrete foundation immediately below the
power panel.

73

jim ab3cv
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David Christ

Re: [Elecraft] Grounding negative side of power supply?

Another commonly used ground is the water system. Check your water
meter. If there is a heavy jumper around it, chances are the
grounding wire from the service entrance connects to the cold water
system.

David K0LUM

At 7:17 AM -0500 1/21/10, Jim Miller wrote:
>In many US homes the utility ground is found inside the home as it is a
>ground rod embedded in the poured concrete foundation immediately below the
>power panel.
>
>73
>
>jim ab3cv
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Jim Brown-10

Was Grounding negative side of power supply? - CORRECTING A SERIOUS ERROR

In reply to this post by Don Wilhelm-4

NO, NO, NO!

Joe, who rarely ever gets it wrong, has led us down a VERY wrong path,
and you, who also rarely get it wrong, have followed him. :)

It is the NEUTRAL that must be bonded to EARTH and SYSTEM GROUND at the
main panel/service entrance, and ONLY at that panel. An additional
NEUTRAL connection to ground (or the green wire) is what causes an unsafe
condition.

Multiple paths to earth for the chassis of equipment are a GOOD thing, as
long as they are all bonded together. in fact, safety codes and good
engineering practice all say that you can have as many connections to
EARTH as you want, that more connections are better, AND that all of
these earth connections MUST be bonded together by a low impedance path.

On Wed, 20 Jan 2010 22:46:54 -0500, Don Wilhelm wrote:

>Joe and all,

>I would also like to point out that the situation Joe presents can be
>the source of "sneak ground path currents" which can contribute to noise
>at your station.

I suggest study of my power point on Ham Interfacing to understand what
you are calling "sneak ground path currents" -- indeed, they are nothing
more than leakage currents from the hot side of the AC power line through
capactance to the chassis of equipment. This capacitance includes bypass
capacitors (including those in line filters) and the stray capacitance
between the power transformer primary and its frame, which is bonded to
the chassis.

http://audiosystemsgroup.com/HamInterfacing.pdf

For more on power and grounding, see

http://audiosystemsgroup.com/SurgeXPowerGround.pdf

>By all means, connect any ham related ground rods to
>the AC mains entry point ground rod. I don't care how you accomplish
>that - just "do it". If it reduces noise in your receiver, that is a
>benefit, but if not, be assured that your shack will be a more safe
>place to inhabit.

YES!

>73,
>Don W3FPR

>Joe Subich, W4TV wrote:
>> This creates a situation that is potentially hazardous
>> to your equipment. The AC "third (green) wire" is supposed
>> to be connected to ground only at the main panel/service
>> entrance.

WRONG. See above.

73,

Jim Brown K9YC

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Jim Brown-10

Re: [Elecraft] Grounding negative side of power supply?

In reply to this post by rlindzen

On Wed, 20 Jan 2010 23:47:51 -0500, Richard S. Lindzen wrote:

>I am planning to put up a K9AY receiving antenna in my backyard and
>it is supposed to be connected to a ground rod.

That ground rod is isolated by a ferrite core stepdown transformer
from the shack, so it is NOT a part of your house ground.

73,

Jim K9YC

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Joe Subich, W4TV-4

Re: [Elecraft] Was Grounding negative side of power supply? -CORRECTING A SERIOUS ERROR

In reply to this post by Jim Brown-10

Jim,

While the Neutral (the white wire in the US three wire power
cable) must be bonded to ground at the service entrance and
nowhere else, by code the Neutral must ** NOT ** be bonded to
the case/chassis of any equipment (e.g., white should never
be connected to the case) so the neutral is not at issue here.
However, the SAFETY ground (green wire/round pin) is also
bonded to ground at the service entrance - and in most
residential installations ONLY at that point.

It is this situation, where the safety ground (chassis) and
the shield of the coaxial cables (also connected to chassis)
are at different potentials that is potentially unsafe.

First, the "safety ground" conductor in most residential
wiring is no larger than #10. In a lightning strike, currents
WILL flow on the safety ground. Those currents can make the
chassis/cabinet of anything connected to the power lines HOT
and can be dangerous. The ONLY way to prevent this issue is
BOND the coaxial entry window, cable TV entry, satellite TV
entry, telephone entry, and power entry ... in addition, any
other conductor (water lines, gas lines, power to outbuildings
or landscape lighting, etc.) that enter the home should be
bonded to the common point.

Where those items do not enter the building at the same place
it may be necessary to install a ground ring (heavy wire with
multiple ground rods) around the entire structure and tie each
conductor to that ground ring.

Again, the key is to insure that the individual "grounds" rise
and fall together and can not become separated and therefore
pose a danger to either persons or equipment.

73,

... Joe, W4TV

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Jim Brown
> Sent: Thursday, January 21, 2010 12:42 PM
> To: Elecraft List
> Subject: [Elecraft] Was Grounding negative side of power
> supply? -CORRECTING A SERIOUS ERROR
>
>
> NO, NO, NO!
>
> Joe, who rarely ever gets it wrong, has led us down a VERY
> wrong path,
> and you, who also rarely get it wrong, have followed him. :)
>
> It is the NEUTRAL that must be bonded to EARTH and SYSTEM
> GROUND at the
> main panel/service entrance, and ONLY at that panel. An additional
> NEUTRAL connection to ground (or the green wire) is what
> causes an unsafe
> condition.
>
> Multiple paths to earth for the chassis of equipment are a
> GOOD thing, as
> long as they are all bonded together. in fact, safety codes and good
> engineering practice all say that you can have as many connections to
> EARTH as you want, that more connections are better, AND that all of
> these earth connections MUST be bonded together by a low
> impedance path.
>
> On Wed, 20 Jan 2010 22:46:54 -0500, Don Wilhelm wrote:
>
> >Joe and all,
>
> >I would also like to point out that the situation Joe presents can be
> >the source of "sneak ground path currents" which can
> contribute to noise
> >at your station.
>
> I suggest study of my power point on Ham Interfacing to
> understand what
> you are calling "sneak ground path currents" -- indeed, they
> are nothing
> more than leakage currents from the hot side of the AC power
> line through
> capactance to the chassis of equipment. This capacitance
> includes bypass
> capacitors (including those in line filters) and the stray
> capacitance
> between the power transformer primary and its frame, which is
> bonded to
> the chassis.
>
> http://audiosystemsgroup.com/HamInterfacing.pdf
>
> For more on power and grounding, see
>
> http://audiosystemsgroup.com/SurgeXPowerGround.pdf
>
> >By all means, connect any ham related ground rods to
> >the AC mains entry point ground rod. I don't care how you
> accomplish
> >that - just "do it". If it reduces noise in your receiver,
> that is a
> >benefit, but if not, be assured that your shack will be a more safe
> >place to inhabit.
>
> YES!
>
> >73,
> >Don W3FPR
>
> >Joe Subich, W4TV wrote:
> >> This creates a situation that is potentially hazardous
> >> to your equipment. The AC "third (green) wire" is supposed
> >> to be connected to ground only at the main panel/service
> >> entrance.
>
> WRONG. See above.
>
> 73,
>
> Jim Brown K9YC
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

Joe Subich, W4TV-4

Re: [Elecraft] Grounding negative side of power supply?

In reply to this post by Jim Brown-10

> That ground rod is isolated by a ferrite core stepdown transformer
> from the shack, so it is NOT a part of your house ground.

IF you use the transformer version of the schematic and not the
original "auto-transformer" design.

73,

... Joe, W4TV

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Jim Brown
> Sent: Thursday, January 21, 2010 12:46 PM
> To: Elecraft List
> Subject: Re: [Elecraft] Grounding negative side of power supply?
>
>
> On Wed, 20 Jan 2010 23:47:51 -0500, Richard S. Lindzen wrote:
>
> >I am planning to put up a K9AY receiving antenna in my backyard and
> >it is supposed to be connected to a ground rod.
>
> That ground rod is isolated by a ferrite core stepdown transformer
> from the shack, so it is NOT a part of your house ground.
>
> 73,
>
> Jim K9YC
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

123