[KPA500] 240V connection advice

[Matt Murphy]

Hello, I am thinking of connecting my KPA500 to a 240V outlet that is close
to the shack that has a NEMA 10-30 receptacle.  I'm soliciting advice on
how to proceed.

As background, I am looking into this because the lights dim a bit when the
amp is keyed down. It's a bit distracting and while I don't think the
circuit is actually overloaded, it's definitely close to the limit.

I was thinking of making a cable by modifying an IEC power cord (with C13
connector) by connecting the two wires to the two hots of a NEMA 10-30
plug, and ignoring the neutral plug AND ignoring the ground wire in the IEC
power cord.

A few questions about this approach:

- Is it the correct way to wire the connectors together?

- Is it dangerous in any way?

- Is there anything that can be done to reduce/mitigate the danger (if any)
other than having an electrician install a currently-up-to-code 240V
circuit in the shack?

- With respect to safety, assuming it is safe for the KPA500 would it be
safe to run other amplifiers that require 240V? How would I determine
this?  It seems that clothes dryers that are connected via a NEMA 10-30
connector typically have the neutral pin connected to the chassis.

Based on my research, the NEMA 10-30 connector was used widely before it
was declared not up to code for new installations in 1996. Since many homes
were built prior to 1996, I would imagine that others on the reflector
might have encountered this sort of issue when dealing with 240V in the
shack.

Advice appreciated.

73,
Matt NQ6N
______________________________________________________________
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
Message delivered to [hidden email]

[Jim Brown-10]

On Mon,7/11/2016 1:42 PM, Matt Murphy wrote:
> I was thinking of making a cable by modifying an IEC power cord (with C13
> connector) by connecting the two wires to the two hots of a NEMA 10-30
> plug, and ignoring the neutral plug AND ignoring the ground wire in the IEC
> power cord.

Hi Matt,

Good engineering practice as well as all building codes in NA require
that two hots be used to power 240V equipment, and that a green wire be
run with the two hot conductors and bonded to the equipment enclosure.
It is both illegal and very bad practice to use neutral as a ground, or
to bond neutral to ground anywhere but the main entry panel.

I suspect that outlet you have is for an old laundry appliance. If you
can get at the wiring to re-run it, you should pull in a new run to
replace the old one. You should NOT use that outlet without that green
wire run from the panel with the "hot" (phase) conductors.

What WOULD be safe is to rewire the existing wiring on both ends so that
the wire currently connected to neutral in the panel is moved to the
ground bus in the panel, the existing outlet replaced with a 240V
outlet, and that former neutral, now used as the green wire, is
connected to the round "ground" pin in the new outlet. And to satisfy
code, put a piece of green electrical tape on that green wire on both
ends to identify it.

If the circuit is protected by a pair of 20A breakers and the conductor
size is #12 or larger, I suggest that you use a 20A outlet, which allows
you to connect both 15A and 20A plugs.

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
Message delivered to [hidden email]

[k6dgw]

Ummm, not exactly following your description but ...  NA electrical
codes require the two phase conductors [240V between them], after
passing through the breaker(s), to go directly to the equipment.  The
center-tap of your distribution transformer secondary [neutral] is
bonded to earth ground at your service entrance.  The earth ground
becomes the "green wire" [it may be uninsulated and thus the "copper"
wire] and should be bonded to the enclosure of the equipment.  It's the
safety ground and that's all that should power a 240V equipment.  Ugly
things can happen if the neutral gets involved or used as a ground.

If that's what you're describing, exactly, it's probably good.  How long
a run from the outlet to the KPA500?  I'd also make sure the outlet is
wired properly.  If it's an old dryer plug, an electrician with a
license might be in order.

For 120V, the neutral forms one side of the circuit, however the safety
ground [green wire] still should be bonded to the equipment enclosure.
Under no circumstances should you connect the green wire to the neutral
ANYWHERE but the bond in your service entrance.

73,

Fred K6DGW
Sparks NV
Washoe County DM09dn


On 7/11/2016 1:42 PM, Matt Murphy wrote:

> Hello, I am thinking of connecting my KPA500 to a 240V outlet that is close
> to the shack that has a NEMA 10-30 receptacle.  I'm soliciting advice on
> how to proceed.
>
> As background, I am looking into this because the lights dim a bit when the
> amp is keyed down. It's a bit distracting and while I don't think the
> circuit is actually overloaded, it's definitely close to the limit.
>
> I was thinking of making a cable by modifying an IEC power cord (with C13
> connector) by connecting the two wires to the two hots of a NEMA 10-30
> plug, and ignoring the neutral plug AND ignoring the ground wire in the IEC
> power cord.
>
> A few questions about this approach:
>
> - Is it the correct way to wire the connectors together?
>
> - Is it dangerous in any way?
>
> - Is there anything that can be done to reduce/mitigate the danger (if any)
> other than having an electrician install a currently-up-to-code 240V
> circuit in the shack?
>
> - With respect to safety, assuming it is safe for the KPA500 would it be
> safe to run other amplifiers that require 240V? How would I determine
> this?  It seems that clothes dryers that are connected via a NEMA 10-30
> connector typically have the neutral pin connected to the chassis.
>
> Based on my research, the NEMA 10-30 connector was used widely before it
> was declared not up to code for new installations in 1996. Since many homes
> were built prior to 1996, I would imagine that others on the reflector
> might have encountered this sort of issue when dealing with 240V in the
> shack.
>
> Advice appreciated.
>
> 73,
> Matt NQ6N

______________________________________________________________
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
Message delivered to [hidden email]

[Phil Kane-2]

On 7/11/2016 3:58 PM, Fred Jensen wrote:

> Ugly things can happen if the neutral gets involved or used as a ground.

The 1996 Code revision required that the neutral (white wire) be carried
as well and installed on an appropriate three-wire-plus-ground
receptacle on new installations and any substantial rework.  The reason
for this was that many 240V appliances (dryers, ovens, etc) used 120V
for some purpose (lights, fan, controllers, etc) and formerly this was
accomplished by using one "hot" side and ground.  No longer acceptable.

73 de K2ASP - Phil Kane
Elecraft K2/100   s/n 5402

From a Clearing in the Silicon Forest
Beaverton (Washington County) Oregon
______________________________________________________________
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
Message delivered to [hidden email]