[GreenKeys] Grounding and GFI's

[Bob Camp]

Hi

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.

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

	Take Care!

		Bob Camp
		KB8TQ


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
>>
>> _______________________________________________
>> GreenKeys mailing list
>> GreenKeys at mailman.qth.net
>> http://mailman.qth.net/mailman/listinfo/greenkeys
>