Re: [VAL] fuse box / grounding questions

[Rick Kunath <k9ao@xxxxxxxxxxx>]

A GFCI (ground fault circuit interrupter) monitors the current coming in the 
hot side of the protected circuit and checks to make sure the same amount is 
returning via the neutral wire (common electrical nomenclature not 
withstanding, the fact is that the 60 Hz AC current reverses direction 120 
times per second .) If it isn't there is either some leakage somewhere or 
someone is getting a shock. At this point, in a very short time, sometimes so 
short that you won't actually feel a shock, the GFCI opens the circuit, 
thereby saving your life.

> Assuming it functions 
> correctly, does it protect me from shock in case of damp/wet conditions
> where my trailer's "shore power cord" connects to the land outlet? (or
> where there might be any damage to the cord itself)
>

No. To protect you from shocks at land outlet, the land outlet would need to 
have GFCI protection on it. Any leakage or shock currents would be flowing 
prior to the breaker panel in your trailer and would be undetectable by any 
GFCI circuit breaker in your trailer's breaker panel. A GFCI device can only 
protect downstream from itself. The land outlet is upstream from the 
trailer's breaker panel.



> Question #2 - how do I tell if I have a GFI breaker? How do I know it
> works?
>

GFCI breakers and receptacles have a test button on them. Press it to cause a 
trip and then reset the device. If you have a GFCI breaker in a circuit, 
there won't be GFCI receptacle on the circuit. You use one or the other on a 
given circuit. And a GFCI receptacle protects other receptacles downstream 
from it. 


> Question #3 - how do I know what size any of the breakers are and how do I
> confirm that rating?
>

Circuit breaker current ratings are marked on the breaker trip lever. If you 
had access to a clamp-on AC ammeter and a series of loads you might attempt 
to check breaker calibration. This is not an exact trip point in most 
breakers and is almost always above the marked rating. Common circuit 
breakers  are of the eutectic type and respond to heat generated by some 
circuit element in the breaker. Some melt small assemblies filled with solder 
and allow a rod to rotate to cause the trip, some are of bimetallic strips 
and springs, the best (I'd bet that you don't have these) are magnetic 
breakers and actually measure the current, then cause an electrically 
operated forced circuit trip (these are very accurate.)

If you are unsure about the safety and effectiveness of your breakers, it 
might be safer to just replace them with new units and be sure. There are 
breakers that offer GFCI protection that can probably be placed in your 
existing breaker panel. These then protect every outlet wired off of that 
circuit breaker. Breakers do need replacement with age, and repeated trips 
shorten their life.

> Question #4 - when somebody refers to an electrical outlet/switch as being
> grounded, is that the same as GFI?
>

No. 

> I notice that dust etc. sticks via static electricity to the hard plastic
> housing on my compact vacuum cleaner. Is this necessarily indicative of
> lack of grounding? Or is it indicative of the climate (dry, 12" rain per
> year)? OR ??? (It is not unusual to experience static shock when wearing
> rubber soled shoes and touching car door, for example, in this same
> climate.)
>

You are seeing the effects of static electricity. The presence of static 
electricity on the *plastic* portions of your vacuum cleaner would not be 
affected by grounding the vacuum. Your cleaner may not have a three-prong 
plug on it. Most I have seen have a polarized plug with one blade wider than 
the other, insuring that the plug will be inserted with the correct prong 
connected to the receptacle's neutral wire.

> Clearly, I am a novice when it comes to BOTH Airstreams AND electricity.
> Scarey thought.
>

Electricity is one of those things that can be a lot more dangerous that one 
might think when it runs amok. If you have any doubts, professional advice 
and repairs are really a bargain. After all, your life is priceless, isn't 
it?

Ask away if you have more questions.

Rick Kunath
WBCCI #3060