Fw: static ground
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My house was built in 1978 before my area was annexed 5 years ago. Bottom line- No inspectors, no city code, I've got 3-wire plugs and 2-wire wiring on every plug I've checked. As I understand the situation, the power company runs 240V lines to the house with a earth ground from the power line transformer and your house to make to split the 240V into two 120V circuits. Hopefully, these 120V circuits have balanced current flow and there is little current flow in the ground, or neutral lead. It appears that the neutral (white) wire and the ground (green) wire eventually meet at the ground rod under your meter base. Assuming that the above is true and that I can verify that the white wire REALLY IS connected to neutral at the circuit breaker panel, can the green screw on the duplex outlet be corrected directly to the neutral at the socket, to ground both my anti-static mat and my Weller soldering station? All opinions welcome. (If this theory is a loser, then I've got a trip through two walls, a closet ceiling, and a long attic to run a station ground that I need anyway. It was almost 100 north of Dallas today and you could probably roast a thanksgiving turkey in my attic. I would prefer that attic trip be in late fall if possible......................) NJ5A <<snip>> I saw a post a few days ago about this. I have a table mat with snap on alligator clip. I do not have unpainted metal ground. How exactly do I do this using a resistor and 3 prong plug ?? 73 de Jesse W6JMM _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In a message dated 6/10/06 11:36:48 PM Eastern Daylight Time,
[hidden email] writes: > As I understand the situation, the power company runs 240V lines to the > house with a earth ground from the power line transformer and your house to > make to split the 240V into two 120V circuits. Hopefully, these 120V > circuits have balanced current flow and there is little current flow in the > ground, or neutral lead. Not exactly. The power co. distribution transformer has a center tapped secondary. That center tap is the neutral, and it has the same current rating as the two 'hot' wires. > > It appears that the neutral (white) wire and the ground (green) wire > eventually meet at the ground rod under your meter base. Sort of. They are supposed to be connected at the 'service entrance'. Usually, that's the panel with the main breaker. The neutral is also grounded at the transformer, but that's the power company's domain. The *only* place in your house that neutral should be connected to ground is at the service entrance. Assuming that the > > above is true and that I can verify that the white wire REALLY IS connected > to neutral at the circuit breaker panel, can the green screw on the duplex > outlet be corrected directly to the neutral at the socket, to ground both my > > anti-static mat and my Weller soldering station? > I wouldn't do that. National Electrical Code specifically states not to do that. The neutral lead (known colloquially as the 'white wire') is not a grounding conductor. That's why a third wire (bare or green) is run - the bare wire is the ground wire. I find it odd that such a new house doesn't have ground wires. Are the boxes and faceplates metal? If so, there should be some form of grounding. One way to test is to make a "test light" of a low-wattage 110 volt bulb and two test leads, and see if the faceplate is grounded by connecting it between the hot prong and the metal faceplate of the outlet. (BE SURE TO TAKE ALL NECESSARY PRECAUTIONS!!) If the lamp works, the faceplate is already grounded. A lamp is used, rather than a meter, to prove that the ground can handle some current. 73 de Jim, N2EY _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Bob Robertson-5
While it is true that the white wire does connect to ground at the service
entrance, that wire should not be considered a ground because it is a current carrying conductor. Figure the voltage drop in one ohm of wire carrying 15 amps - that will produce 15 volts - and that voltage is what makes the white wire 'not a ground'. Additionally, if the white conductor should open at some point between your connection point and the service panel, it can become 'hot' with full line voltage on it. With the sloppy way I have seen some electrical connections done, the possibility of an open circuit is quite high. Re-wiring your home may not be practical at this point (but it would be a wise step), but it would be practical to run a wire from critical places such as the ham shack or the workbench area to the service entrance ground as an added safety ground wire. If you use a separate ground for the shack, that ground should also connect back to the utility service entrance (connect your added safety ground wire to the shack ground). Remember that your safety is at stake anytime you plug an appliance with a 3 prong plug into one of your ungrounded sockets. There is no protection if the appliance should develop an internal fault. 73, Don W3FPR > -----Original Message----- > > My house was built in 1978 before my area was annexed 5 years > ago. Bottom > line- No inspectors, no city code, I've got 3-wire plugs and > 2-wire wiring > on every plug I've checked. > > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Bob Robertson-5
Hi Bob,
Sounds like you live in Texas. Your theory is pretty much correct. I am a professional Engineer, and home inspector in Texas. The default way to deal with (update) a two wire circuit is to install a GFCI in the upstream outlet and slave the GFCI to the downstream outlets. However if there is not a ground available in the box, you must label the outlet "No Equipment Ground". I haven't found the Lutron PDF file on their site that I use as reference, but I found an abbreviated explaination here: See: http://www.codecheck.com/250_50_commentary.html Its very possible that the center screw and the box may not be grounded. If it isn't do not connect the ground screw on the outlet to the neutral. The NEC code is quite confusing. If you need to determine a grounding method I can look it up, but I am sure its not going to be simple. If it’s the first floor it might be best to just drive a ground rod into the earth for your RF and static ground and not wire it directly to the electrical system. Regards, Steve, W2MY -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.1.394 / Virus Database: 268.8.3/360 - Release Date: 6/9/2006 _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Don Wilhelm-3
That's also why the anti-static ground has (must have!) a 1-megohm resistor
in series with it. That way a dangerous amount of current isn't going to flow in any case while the resistance is still low enough to continuously dissipate any static charges that are developed. It doesn't matter whether you accidentally come in contact with the "hot" side of a mains lead or the positive side of some other power source, the resistor should keep the current down to safe levels. So, if you have nothing else, any connection to the earth will work either as a terminal for the anti static pad/strap with their internal 1 meg resistors or as a point you can touch briefly (while not touching anything else) to dissipate any charge on your body just before you handle a static sensitive part. Don makes a good point about running a ground wire through the house, at least to the critical outlets near the ham shack. I'd include, as a minimum, kitchen and bath outlets as well so they can be equipped with ground-fault interrupters. I 'grew up' in the age of exposed AC/DC equipment that had one side of the metal case connected to the mains, and I recall many instances of touching a panel and noting the slight tingle that warned me that I was touching the hot side of the mains line because the plug was in backwards. That was a warning because the next metal panel a few inches away might be grounded and touching both of them at once would put me across the mains power! Millions of people survived such wiring without problem, but many did die. Don't be one of them. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Don Wilhelm-3
Bob:
Your old house wiring may be BX, meaning it is wire in a spiral armored casing, typically made of aluminum. While not ideal, you may be able to gain an independent ground using this casing. It would require (a) that the casing be continuous from receptacle to receptacle, and (b) that it be well clamped with a BX connector to each receptacle. In this case, you can add 3-prong plugs with ground wires firmly connected (under a screw head, for example) to the receptacle. Once you do this, you can get a "tester plug" from you local jobber or hardware that can be used to determine whether all is well. These tester plugs indicate with lights whether the polarity is correct, the common is closed, and the ground exists. best wishes, dave belsley, w1euy On Jun 11, 2006, at 8:24 AM, Don Wilhelm wrote: > While it is true that the white wire does connect to ground at the > service > entrance, that wire should not be considered a ground because it is a > current carrying conductor. Figure the voltage drop in one ohm of > wire > carrying 15 amps - that will produce 15 volts - and that voltage is > what > makes the white wire 'not a ground'. Additionally, if the white > conductor > should open at some point between your connection point and the > service > panel, it can become 'hot' with full line voltage on it. With the > sloppy > way I have seen some electrical connections done, the possibility > of an open > circuit is quite high. > > Re-wiring your home may not be practical at this point (but it > would be a > wise step), but it would be practical to run a wire from critical > places > such as the ham shack or the workbench area to the service entrance > ground > as an added safety ground wire. If you use a separate ground for > the shack, > that ground should also connect back to the utility service entrance > (connect your added safety ground wire to the shack ground). > > Remember that your safety is at stake anytime you plug an appliance > with a 3 > prong plug into one of your ungrounded sockets. There is no > protection if > the appliance should develop an internal fault. > > 73, > Don W3FPR > > >> -----Original Message----- >> >> My house was built in 1978 before my area was annexed 5 years >> ago. Bottom >> line- No inspectors, no city code, I've got 3-wire plugs and >> 2-wire wiring >> on every plug I've checked. >> >> > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com ------------------------------------- david a. belsley professor of economics _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Ron D'Eau Claire-2
Hi Ron and all,
Actually the name GFCI is a bit misleading I think. You don't need a ground for a GFCI to work. That's why they recommend their use in upgrading two wire systems. The GFCI senses a current difference between the neutral and the hot wire. If the difference is greater than 5 milliamps, the GFCI is supposed to trip and disable the circuit. Thus if you get a shock and the GFCI trips you were in essence the "ground fault" in "Ground Fault Circuit Interupter". Having a third wire as ground is nice to have, but it seems that putting a GFCI in a two wire circuit greatly increases the safety of the circuit. Steve, W2MY -----Original Message----- From: [hidden email] [mailto:[hidden email]] On Behalf Of Ron D'Eau Claire Don makes a good point about running a ground wire through the house, at least to the critical outlets near the ham shack. I'd include, as a minimum, kitchen and bath outlets as well so they can be equipped with ground-fault interrupters. -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.1.394 / Virus Database: 268.8.3/360 - Release Date: 6/9/2006 _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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