GFCI wiring question

[schmism]

its been my experience trying to wire new GFCI recepticals into older houses with shared nutrals that they usually dont work right.

 

[JoeL4330]

why not use a 220V GFCI breaker and have the whole cable and everything connected to it protected? i know most folks know how those things work, but just in case, its kinda like a water line: it looks at how much water(current) goes out and how much water(current) comes back, and if theres a difference, it shuts off. i have a couple circuits that use the GF recept: and some that use GF breakers: i have never had to change a breaker, but have changed the recepts several times over the past 10-15 years. and i do test all of them yearly.
heehaw

GFCI works, as you say, by comparing current out vs current back ...if they are different, there is a "leakage" path somewhere and GFCI trips. If you were to use a 220V GFCI breaker (with which I am unfamiliar) it would be looking for the current out on, say, the black, to equal the current back on, say, the red. However, if the two legs of the 220v split into two 110v circuits with a common neutral (the third, white wire) then if either circuit were in use, there would be an imbalance, no? Or, perhaps I don't understand.

 

[heehaw]

i have a 220V GFCI, with lots of sub-ckts off of it, both 220 and 110: and it works with no problems at all: or has for almost 3 years now: all i know is it has to be lot smarter than the ones that are just 110: because at times there is no current in the neutral wire: even though there may be a lot going out both hot legs: so it must be looking at a lot more variables than the 110 style.
heehaw

 

[JimMorrissey]

Joe,

Not sure I fully undertand what you're saying so let me try again.....Yes, it appears that they ran one three wire to feed two circuits, likely to save time and money....not how I would have done it, but the work is done and there's no way I'm re-running new romex up three flights in an old house. To be clear, the black wire connects to one 15 amp breaker and the red wire connects to another breaker with a shared ground and netural. This is why I can't use a arc-fault or a GFCI breaker. I'll use GFCI recepticles where possible ($15 each), but I think I'm out of luck on the arc-fault end on those shared circuits.

I did want the arc-fault just for protection regardless of the code, which there is none in VT. I try to follow the NEC rules the best I can. Also I've gotten rid of almost all the old BX cables, but not sure if there might be a segment here or there in the walls and it would be nice to have arc protection with the possibility of old BX somewhere.....make sense?

 

[JoeL4330]

Did a little research: I believe you can do what you want ...yes, gfci receptacle ...but, check out <http://www.arcadvisor.com/afci.html>

See two attached diagrams from that URL

Does that scratch your itch?

 

[JimMorrissey]

Joe,

Cool. I guess what I need is a double pole arc-fault breaker for the two seperate circuits and then they can share neutral and ground. Excellent find. I bet the breaker will cost 2/3 the price of the whole load center! I'm thinking if this works for arc-fault then it should work the same for GFCI......

Thanks so much for the research.

 

[Inspector507]

I'm thinking if this works for arc-fault then it should work the same for GFCI......

No, they are different animals.

 

[heehaw]

different, but i think they hook up the same way? i've never installed an arc fault, so i'm not sure about that, just guessing: the best buy i found for a 50amp 2 pole gfci breaker was at lowes: they had them for swimming pools, like everything else, they have gone up a lot in the last 3 years.
heehaw

 

[JimMorrissey]

Yeah, like the small container (200 or so) wire nuts I bought the other day for $22! I couldn't believe it. I know copper has gone way up too. I paid over $100 for a 250' roll of 12/2. Just nuts...The guy at the counter said "if you think this is bad, just wait until the price increases coming after the New Year"....well I can't hardly wait.

 

[JimMorrissey]

Although wired the same......no? Inspector, will I be able to wire a dual circuit off three wire in a similar fashion, or will this only work on GFCI cicuit? The basic wiring design is the same for both GFCI and Arc.