[GreenKeys] Grounding and GFI's

[Steve Schlink]

At 11:38 AM 2/13/2005 -0500 Bob Camp  wrote:
>I agree with your analysis. All I'm going by is the sheet that comes with 
>some of the Home Depot GFI's these days. They *appear* to have added a 
>neutral sense feature.

                 Neutral sensing for sure, but you said "ground". I suspect 
that it would be against code to put any device in series with the ground 
conductor. Also, the NEC allows GFCI receptacles to be installed in 
locations without a third ground conductor.

>The only correction I would make is that the current limit for a wall 
>mounted unit is 5 ma rather than 40.

                 I thought that we were speaking about breakers.

Steve

>On Feb 13, 2005, at 11:02 AM, Steve Schlink wrote:
>
>>Bob,
>>
>>I'm not sure what you mean by "The other thing that they depend on is a 
>>single path back to ground *through* the GFI."
>>
>>AFAIK, GFCIs work by measuring the current on the line and neutral only. 
>>If there is a 40ma imbalance (which presumes that there is leakage to a 
>>ground, either metallic or earth) then they will trip.
>>
>>Also, GFCIs are NOT recommended for any stationary motor operated 
>>equipment because of inherent leakages.
>>
>>As for single point grounding, that's sort of a law of nature.
>>
>>Steve
>>
>>At 10:37 AM 2/13/2005 -0500 Bob Camp  wrote:
>>>Hi
>>>
>>>GFI's are a significant problem when it comes to older gear. Since they 
>>>trip out on minor current imbalances they are really designed to work 
>>>with gear that has total isolation of the AC line to ground. The other 
>>>thing that they depend on is a single path back to ground *through* the 
>>>GFI. It's this second requirement that often gets messed up. Cross 
>>>grounding gear between different GFI'd circuits is a no-no. Running a 
>>>grounded antenna to the chassis of a GFI'd radio is also against the 
>>>rules. If the Model 28 is on one GFI and the computer is on another GFI 
>>>that's a problem if there is a direct ground connection between the 28's 
>>>keyboard and the frame ground on the RS-232 input on the computer.
>>>
>>>I'm not trying to say that it's time to throw out the GFI's. They could 
>>>save your life. They only will do that if they are being used properly. 
>>>There are ways to break up the direct grounds that work just fine. You 
>>>just have to take the time to build and install them.
>>>
>>>A while back I figured out that I am one of those people who are safer 
>>>if they am more worried about what I am doing. GFI's make me worry less. 
>>>The choice I made was to put the garage/wood working shop on GFI's (no 
>>>down side there). I put the computer/radio/Teletype room on non-GFI 
>>>circuits. I simply could not figure out a way to run GFI's in there and 
>>>have them do what they are supposed to do. I would rather *know* that 
>>>there are no GFI's than *assume* there are working GFI's. My choice may 
>>>not be your choice.
>>>
>>>Of course if you are going the no GFI way you *must* do it all the old 
>>>fashion way. Everything gets three conductor cords. All the chassis are 
>>>checked for grounding (including that 28 ASR cabinet !!!). All the 
>>>grounds on the wall sockets get checked with the little plug in tester. 
>>>The antennas are grounded and surge supressed. Death by electrocution is 
>>>not a good thing ...
>>>
>>>Since a lot of gear has been though multiple owners it's never clear 
>>>what the condition of it's chassis ground is. I certainly have been in a 
>>>rush to get that new toy running. It's only human to want to try a new 
>>>gizmo out. I wish I could say that I always check the ground before I 
>>>fire the gear up, but no I'm far from perfect in that respect. Yes I 
>>>have tripped a breaker that way. So don't do as I do, do as I say. Check 
>>>the ground on that 28 or 15 *before* you plug it in. The wire is simply 
>>>to old on a 15 to be trusted without some basic checks. GFI's don't 
>>>respond to 125 VDC ... If you don't have a simple VOM then skip the 
>>>burger and fries for lunch and get one. It's something the safety guy 
>>>says you should have.
>>>
>>>End of rant ....
>>>
>>>         Take Care!
>>>
>>>                 Bob Camp
>>>                 KB8TQ