[GreenKeys] Grounding and GFI's

[Bob Camp]

Hi

Got twisted on the second post. I should have said they added a ground 
sense feature in addition to the neutral sense.

The last batch I put in were wall socket mount units from Home Depot 
rather than breakers in the breaker box. I have never seen a breaker 
box install unit that you run the ground (as opposed to neutral) 
through.

	Sorry for the mistake.

		Bob

On Feb 13, 2005, at 1:54 PM, Steve Schlink wrote:

> 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
>
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