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GFI as a stop-gap?

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itsmoked

Electrical
Feb 18, 2005
19,114
Barely makes the grade as "power" but here it is.

What are your thoughts on the following?

I live in a 1947 house. All the original wiring is flex steel armor. You know, the stuff that when shorted limits the current to 14A while turning a dull red in the walls.

As I have made improvements I replace the stuff with romex with grounds etc. etc.

As a temporary measure I have pulled some of the ancient ungrounded receptacles and replaced them with GFIs (three terminal). My thought is that if a three pronged load is plugged into one of these GFIs, a fault in the load that would normally be expected to trip out the circuit's breaker thru excess ground current will instead trip out the GFI, when the current reaches the paltry GFI trip level, thereby protecting the armor.

Am I overlooking something? While this is not the same as a nicely installed new circuit is it not an improvement over the two wire or three wire with a ground wire hooked to the box?
 
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Boy, if it wan't you itsmoked, I'd RF this for being residential in nature (read the rules), but you've earned a freebie.

The GFCI receptacle will not necessarilly protect you from an insulation fault inside the armored cable (BX) feeding the receptacle because the GFCI can only remove the load downstream of itself. If the conductor insulation within the BX faults and grounds to the armor, it will continue to burn in the wall long after the GFCI has tripped the original load fault off line. The only thing a GFCI might do it prevent some of the causes of overloading the wires inside the BX in the first place, but not all of them.

What you might want to consider is changing your circuit breakers to GFI breakers, because they will react to any ground fault downstream of the BREAKER, which would include any insulation fault in the BX. More expensive, but that is the only thing worth doing IMHO. If you have a fuse box, just add a small load center downstream and move your remaining BX lines into it until you get to all of them. I had a 100 year old house in Seattle with BX and knob-and-tube wiring, and that's what I did until I had time to open up the walls and replace it with Romex.

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Thanks for the tolerance[sadeyes].

Thanks jraef for the info.

Since I have a new load center that I gradually add new and upgraded circuits to/at I can actually replace the existing old load center(8 ckts) with a newer one that can accept GFIs.

Thanks agiain.
 
The use of a three prong GFCI as a replacement of a two prong receptacle is one of the approaches specifically permitted in the NEC as a way of dealing with two prong receptacles that need to be replaced where a ground is not available. So you aren't in trouble code wise.
 
Very good that! It improves MHO of the NEC code.[atom]

Thank you davidbeach.
 
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