Installation of Arc Faults with old wiring

[Tetra]

I was working in a house with recently updated panels, the electricians replaced the old panels with new ones and brought it up to code. Without getting into useless info they put AFCI breakers on the bedroom circuits.

I was going through the bedrooms replacing the receptacles and switches.
I had the circuit for the bedrooms shut off at the breaker, and I was checking each with my tictester before getting to work. I got to a receptacle in one of the bedrooms and when i pulled it out i got shocked pretty good, confused I put my tictester to it and it didn't go off, grabbed my meter and checked hot to ground, nothing, checked neutral to ground got 120v (it was actually two neutral wires spliced together I undid them before i got 120v to ground on one of them, and noticed the hallway light turned off when i seperated them!
Long story short the old neutral to the hallway light was damaged so someone ran a length of romex from the hallway light and tied into the neutral of the bedroom circuit, even had the ground and common wires snipped off at each end.

This is where my confusion comes in, the bedroom circuit is protected by an arc fault combo breaker, I thought AFCI's and GFCI's operated by measuring the balance between the hot and the neutral wires, but how come the AFCI never tripped with the neutral from a different circuit piggybacked onto that circuit? Am I to assume the AFCI breaker is faulty? Or am I misunderstanding how an AFCI breaker works? Or was the neutral from one light not enough to make a difference?

 

[jumper]

I was working in a house with recently updated panels, the electricians replaced the old panels with new ones and brought it up to code. Without getting into useless info they put AFCI breakers on the bedroom circuits.

I was going through the bedrooms replacing the receptacles and switches.
I had the circuit for the bedrooms shut off at the breaker, and I was checking each with my tictester before getting to work. I got to a receptacle in one of the bedrooms and when i pulled it out i got shocked pretty good, confused I put my tictester to it and it didn't go off, grabbed my meter and checked hot to ground, nothing, checked neutral to ground got 120v (it was actually two neutral wires spliced together I undid them before i got 120v to ground on one of them, and noticed the hallway light turned off when i seperated them!
Long story short the old neutral to the hallway light was damaged so someone ran a length of romex from the hallway light and tied into the neutral of the bedroom circuit, even had the ground and common wires snipped off at each end.

This is where my confusion comes in, the bedroom circuit is protected by an arc fault combo breaker, I thought AFCI's and GFCI's operated by measuring the balance between the hot and the neutral wires, but how come the AFCI never tripped with the neutral from a different circuit piggybacked onto that circuit? Am I to assume the AFCI breaker is faulty? Or am I misunderstanding how an AFCI breaker works? Or was the neutral from one light not enough to make a difference?

The best I can figure is that you have violations of 300.3(B) and 240.15(B)(1). Maybe more.

GFCIs measure imbalance, I am not so sure about AFCI.

 

[Dennis Alwon]

The best I can figure is that you have violations of 300.3(B) and 240.15(B)(1). Maybe more.

GFCIs measure imbalance, I am not so sure about AFCI.

Most brands of afci do have gfci built in so....I think they are 30 ma instead of 5ma required for gfci protection.

 

[Tetra]

The best I can figure is that you have violations of 300.3(B) and 240.15(B)(1). Maybe more.

GFCIs measure imbalance, I am not so sure about AFCI.

I don't doubt this house violates plenty of codes, doing our best to rectify it, house was wired in the early 80's, soldered neutrals wrapped in vinyl tape, and the tape is dry and brittle as paper now, wire nuts were rarely used. I'm beginning to find burnt up neutrals more and more as i go along, at first thought they were burnt from when they soldered the neutrals together but after looking at it some more I'm beginning to think some of these neutrals were simply overloaded, as best as I can tell there are some areas where two or even three circuits meet with all the neutrals tied together, so with shared neutrals I'm wondering if the AFCI's are even able to work properly.

Actually the hallway light that caused my original problem had an abandoned nuetral wire in it, it was chared all to hell and the insulation was so brittle I could break it off with my bare fingers, the wire was obviously fried but from what is hard to say.

That is what has gotten me so concerned about the AFCI breakers that were installed, I'm starting to wonder if they are working (or can work) properly with this old wiring. Just as Dennis pointed out, I was under the assumption AFCI breakers had GFCI capabilities as well, but from looking it up with good old google I can't find a clear explanation of AFCI's having GFCI capabilities as well.

 

[Sierrasparky]

If you have shared neutrals the AFCI's will never work, they work just like a GFCI in that respect.

Besides you need to get rig of the overloaded neutrals unless they are a proper multi wire branch circuit 2 hots from different phases and a neutral. You can get AFCI for this application in some panels these days.

 

[ELA]

That is what has gotten me so concerned about the AFCI breakers that were installed, I'm starting to wonder if they are working (or can work) properly with this old wiring. Just as Dennis pointed out, I was under the assumption AFCI breakers had GFCI capabilities as well, but from looking it up with good old google I can't find a clear explanation of AFCI's having GFCI capabilities as well.

AFCI's I have worked with have a GFI feature that trips from 30-50ma.
To assure yourself that the AFCI's do have this feature, and work, do a test.

Put a small load (possibly a wiggy) or a small lamp ( > 50ma load) from the breakers hot leg to ground. Do this at the service cabinet. The breaker should trip if GFI protection is included.

 

[Tetra]

I tried the test you recommended ELA and the breakers tripped as I hoped they would.
I also went through and separated all the shared neutrals, and everything is now balanced.

But now the AFCI's are humming...

Is that a bad thing? I actually went an looked at some AFCI's in a different house and they were completley silent, is humming normal for these breakers? These breakers come with two tests on the breaker and both tests seem to work fine, and they are cool to the touch. And the ones that are humming aren't carrying a significantly high load (~4 amps on one ~2 amps on the other, and the rest of the AFCI's aren't humming).

BTW i'm thinking 'humming' is a vague term but I don't know how else to describe it, in this sense i mean the sort of humming you'd hear from a small transformer except a little more high pitched.