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KingsX · Jan 22, 2010, 11:21 AM

As some of you might remember, I have knob and tube in my house. I just had a new panel installed, but the knob and tube remains. I am in the process to change that over, but in the meantime, would an AFCI breaker protect from arcs that might happen in the wall cavity? My wife heard a story of a house in town, where the wires inside the wall were old and knob and tube, and started a fire. I do know that inside the walls, the neutral and hot run separately, so I'm not sure how you could have an arc inside the walls. But regardless of that, if there was an arc in any switch or outlet, the breaker would trip. So would this put our fears to rest? Thanks!

KISS · Jan 22, 2010, 12:34 PM

It might protect against a burn through, but it might not

The biggest problem is that there is no protective ground nearby. If you have plaster, I doubt the backing metal is grounded.

GFCI's most of the time are combined in the AFCI breaker as well, so that gives you added protection. In the states it is permissible to use an unconnected 3 wire plug with a GFCI as long as the outlets are labeled "No equipment ground".

Certain devices need the ground. Some computers with 3 prong plugs, for instance.

AFCI's are going to be required nearly everywhere for the latest NEC code.

We know your in Canada.

donf · Jan 22, 2010, 02:17 PM

Beg to differ. But not disagree with KISS.

A combined GFCI and Arc Fault is a rather expensive device because it is looking for two different electrical traits.

A GFCI is looking for a current difference between hot and neutral. If the current is greater than 0.6 amp difference, it will open to prevent any one from being electrocuted.

An Arc Fault is a device that is looking for the electrical signature of an arc failure. Short pulses of electrical bursts on its circuit. Its purpose is to prevent fires from loose connections or worn and frayed wiring.

As of the 2008 code, All bedrooms (210.12) are required to be on Arc Fault Breakers. In fact so are most other rooms and halls.

Since you are installing a new main service panel and rewiring, I believe that you would be required to follow current level code.

Personally, I believe that knob and tube is a very well designed system and if I didn't need to change it out I would leave it alone. However, that said, the electrical wire may be big concern because of the insulation wearing down and cracking.

tkrussell · Jan 22, 2010, 03:45 PM

Who makes a combination AFCI and GFCI device?

KISS · Jan 22, 2010, 10:28 PM

Tk:
Cutler Hammer

Click on the catalog page link on this link: CH120AFGF, Cutler Hammer - Circuit Breaker Service

donf:

Originally Posted by donf

A GFCI is looking for a current difference between hot and neutral. If the current is greater than 0.6 amp difference, it will open to prevent any one from being electrocuted.

Your off my at least two orders of magnatude. ~6 mA or 0.006 Amps.

tkrussell · Jan 23, 2010, 05:05 AM

Thanks, heard of it but did not know who was making them. Easier to ask than search.

Since I don't do residential as a rule, so much stuff comes out I need to catch up on.

KingsX · Jan 23, 2010, 10:44 AM

Ya, in Canada code required AFCI's installed for bedroom outlets in new construction. I'm assuming as a fire prevention method. But that's essentially why I'm looking for my knob and tube. But you think that without a ground, it won't work? I know, like you said, GFCI's will work for ground fault, but will that protect against fire?

KISS · Jan 23, 2010, 01:26 PM

Take a look here:

http://www.cpsc.gov/CPSCPUB/PUBS/afcifac8.PDF

What it seems to suggest is that AFCI's can help, but not ELIMINATE fires caused by arcs.

So, I have to ask:

With knob and tube are splices allowed within walls. If so an AFCI would be useful.

AFCI's seem to detect bad switches and frayed insulation in things such as lamp cords and intermittant connections.

If a wire can touch another wire then an AFCI could help.

GFCI's would allow grounded outlets without a ground if properly labeled.

KingsX · Jan 24, 2010, 01:45 PM

I'm thinking it couldn't hurt anyway. I only have two circuits on knob and tube. One runs the all the lights on the main floor and the other runs all the plugs (except new stuff installed) on the main floor, plus all the lights in the basement. So as I convert over to new wiring in the house, I can then use those two AFCI's for the two bedrooms in the house, as per code. And then just leave the old know and tube as it won't be in use anymore.

KISS · Jan 24, 2010, 02:22 PM

True.

Why not consider 1 AFCI for the lights and a combo AFCI+GFCI for the outlets if you can get one?