GFI Caused a Fire!

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wrote:

Right, the usual GFCI does not against electrical arcs. The National Electrical Code now requires arc fault circuit interrupters (AFCI) in certain rooms of homes to reduce such fires. Wikipedia has a good summary of what GFCIs can and cannot do at: http://en.wikipedia.org/wiki/Arc-fault_circuit_interrupter Arcing that results from loose connection at outlets and switches or broken wires are a major cause of house fires.
Tomsic
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So it seems like the ground fault is especially useful near water faucets and wet places.
But the arc fault seems especiallly useful everywhere, not just bedrooms. Does that mean every circuit breaker should be arc fault?
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*Article 210.12 in the 2011 National Electrical Code requires them for almost every circuit in a home.
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On Wed, 26 Jun 2013 10:12:30 -0400, "John Grabowski"

That's great for new houses. But my house was built back in 1998.
me
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On 6/26/2013 8:47 AM, snipped-for-privacy@b.c wrote:

You can likely add them one way or another. If circuits are multiwire branch circuits with a common neutral that is a problem.
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On 6/26/2013 6:01 PM, bud-- wrote:

I don't advise trying to use current technology on older wiring systems. Aside from Edison circuits, you find anomalies caused by mixed neutrals and the like. You certainly could test each circuit with an AFCI, and if it holds, you're good to go
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Even after looking it up last year, I never did understand what an Edison circuit is or how it's different from any other circuit.

I know approximately what a mixed neutral is. I don't think my home described below is likely to have the anomalies you speak of.
My house is from 1979, has quite a bit of empty space in the breaker box, and there has only been one change, one added circuit, to the attic to power the attic ceiling light (with receptacle), the roof fan, and the outdooor floodlight. Along the way it goes by the far wall of the laundry room where it powers a ceiling light and 5 double receptacles (no more than 2 sockets are used at any one time, a lamp and one power tool or another.) The circuit breaker has never tripped.
Do you think it's likely I'll have problems changing to AFCI?
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On 6/26/2013 9:39 PM, micky wrote:

I think you'd be OK, it's houses that predate the 50's where I find all manner of rube wiring. In your case the only probable issue would be 3 wire circuits, which are two circuits which share a common neutral. AFCI breakers can't be connected to these circuits. If you open your panel and find any cables that have a red, black, and white wire, you won't be able to protect them with an AFCI.
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Thanks. I"m saving this for next summer, when I'll have time.
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wrote:

Aha! Now I understand what 'common ground' means. My former house was built in 1980, and had common grounds (3-wire) circuits. I understood how they worked, but I did not realize the danger involved. Thanks
me
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On 6/27/2013 6:32 AM, snipped-for-privacy@b.c wrote:

These circuits, which are called multiwire branch circuits, three wire circuits, or Edison circuits, are common "neutral" in that two hot legs, of different potential share one neutral. Your typical residential electric service, which is 120/240 is an Edison circuit. When installed properly, they're no more dangerous than a two wire circuit
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<stuff snipped>

Are you sure that's still true?
http://w3.usa.siemens.com/powerdistribution/us/en/product-portfolio/circuit-breakers/residential-circuit-breakers/2-pole-afci/pages/2-pole-afci.aspx
<<The 2-pole device can reduce wiring costs and installation time by enabling contractors to use multi-wire branch circuits, commonly known as "shared neutrals". When using single pole CAFCIs, a dedicated neutral is required for each circuit. The new 2-pole CAFCI allows electricians to share neutrals between the two circuits fed by the breaker.>>
--
Bobby G.



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On Wednesday, June 26, 2013 9:39:36 PM UTC-4, micky wrote:

An Edison circuit allows you to save running one neutral wire. Let's say I'm putting in new outlets, a long run from the panel. There are enough outlets that I would need to pull two romex cables, ie one hot, one neutral, one ground. Each cable would serve half those outlets.
With an Edison, I can pull one romex with two hots, one neutral, one ground. The one neutral is shared by the two groups of outlets. I've traded two cables for one and reduced the number of conductors by one, all of which save some $$.

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On Thu, 27 Jun 2013 06:27:09 -0700 (PDT), " snipped-for-privacy@optonline.net"

It also reduces combined voltage drop by up to half if both circuits are equally loaded because the current on the neutral is virtually zero. That is another reason to use them on long runs.
They do make 2 pole AFCIs now to replace the two pole breaker you should be using on a multiwire circuit.
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On Thu, 27 Jun 2013 06:27:09 -0700 (PDT), " snipped-for-privacy@optonline.net"

Thanks. This all seems so simple now, I wonder why I didn't understand it the last time. ~~~~~!

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<stuff snipped>

From my understanding of MWC's (which could easily be wrong) if the shared neutral fails for any reason, you can potentially end up with much more than 120VAC where you don't want it. If a neutral fails in normally wired pair of outlets, there's usually no risk of voltage escalation or imbalance. However a failer neutral in a MWC can play out like this:
http://www.ecmweb.com/images/archive/205ecm18fig1.gif
There are a couple of other considerations that affect the cost analysis, too. I have always been able to buy 12/2 w/g Romex on sale for much less than 12/3 w/g. So much less, in fact, that there was no difference in the price between running two 12/2 cables and using a MWC using 2/3. I assume that's a function of how much more 12/2 is manufactured than 12/3. It took a little longer to install and staple, but I really prefer separate neutrals. I assume that the different in installation time is a much bigger concern to builders of large tracts of homes.
MWC's require (at least I am pretty sure NEC and CEC say so) a double pole breaker requiring de-energizing both circuits to do repairs. Not a big issue, but at times it's been nice to have a nearby live outlet to plug tools into when I am working on a different circuit in the room. Not sure if the DP breakers with a single handle for MWC's come in "dual skinny" format, either, which is another concern for folks wanting to add new circuits to an older box.
I do have one multiwire circuit in the panel to power my XTB X10 repeater/coupler/amplifier but nothing else is plugged into that outlet, which has about 6' of wire running to the nearby circuit panel. Even that outlet is wired with two separate runs of 12/2 w/g Romex.
I am sure there are labor cost savings for developers building a series of houses, but in my case MWC's didn't make much sense except for the special case of the X10 device that by design has to straddle both hots to communicate between the phases.
--
Bobby G.



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On Fri, 5 Jul 2013 14:58:35 -0400, "Robert Green"

Split circuit receptacles were required by code in kitchens before GFCIs were required - and the ONLY way to put GFCI protection on these split kitchen outlets is to use a 2 pole panel mounted device.
Current code prefers non-split 20 amp GFCI outlets within a 59 inch radius of the sink, but still allows split 15 circuits
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On 07/05/2013 11:06 PM, snipped-for-privacy@snyder.on.ca wrote:

That's a Canadian thing... it is not required in the US and appears not to be common practice although it would still make sense to do it that way in many situations.
nate
--
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On 06/26/2013 09:39 PM, micky wrote:

It's basically a 120/240 two-phase circuit with two hots and a neutral. The advantage of using it is that it requires two less wires to be pulled than two separate 120VAC circuits, because only one neutral and one ground is required rather than two of each. The reason that you can get away with it is that if you are only using 120VAC loads, but they are evenly split between the two hot legs, the current in the neutral will actually be zero! This is because the two 120VAC hots are 180 degrees out of phase (they add to a potential of 240VAC) it's very similar to the way a three phase system works with 480VAC/277VAC if you are familiar with that but with only two "phases."
Apparently this was devised by Edison as a means to provide two DC circuits with only three wires (I guess the two "phases" in that case would have been one wire at the positive nominal voltage relative to ground and the other would be at negative nominal voltage relative to ground) and someone appropriated the terminology to include the analogous AC configuration... which makes sense as we all know that Edison was a proponent of DC not AC. (Tesla and Westinghouse were the AC guys...)
The problem with using an AFCI on an Edison circuit is that you would need a two pole breaker, which do exist but are unsurprisingly more expensive than a single pole unit (or even two single pole units!) An alternative would be two single pole breakers, but the manufacturer would have to list them as being acceptable to use with a handle tie and I haven't researched it enough to determine if there are any like that or not.
https://www.platt.com/platt-electric-supply/Circuit-Breakers-Residential-Arc-Fault-Breakers/Eaton/CH220AF/product.aspx?zpidG3677

I'm assuming what he means by a "mixed neutral" is one where neutrals from one circuit are cross-connected to another circuit. That would be a code violation and has been for ages - when neutrals from different circuits are connected together you can no longer assure that the currents in a cable sum to zero which has been a requirement for a very long time.
So... you shouldn't have that situation, and if you do, might as well find out about it now and fix it (should not require opening any walls unless you have hidden splices which would be another violation...)
nate
--
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On 7/9/2013 7:11 AM, Nate Nagel wrote:

A handle tie might be acceptable if AFCI breakers only detected arc faults. But they also include ground fault protection, which requires the neutral to go through the breaker, which means you need a 2-pole breaker for an Edison circuit.
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