splain it to me lucy

[stew]

can anyone tell me why we can use gfcis on shared neutrals but not afcis. ?

 

[iwire]

Not sure I understand.

GFCIs and AFCIs must be wired in the same ways.

On the load side of either device the neutrals must be dedicated if the units are single pole or if they are two pole you can share neutrals.

On the line side a shared or dedicated neutral makes no difference.

 

[tonyi]

There's at least a couple of vendors making 2-pole AFCI that I've used. GE and Cutler Hammer.

I bet if copper prices stay this high, there may be more economic pressure for the others RSN.

 

[stars13bars2]

Because you can put the GFCI receptacle downstream of the shared neutral whereas the AFCI breakers pretty much have to go in the panel. One solution would be two pole AFCIs. Where are all the AFCI receptacles?

 

[jeff43222]

Siemens also makes a two-pole AFCI breaker.

 

[stew]

I had heard(but didnt know for sure) that if you used a shared neutral on an afci circuit like to feed 2 bedrooms with say a 14/3 and 2 afcis that the afci would trip and not function properly. am I wrong on this then I wire? it would mean of course that you would have to connect the afci load side neutrals together in the panel and then out to the load. willl or wont work?

 

[LarryFine]

I had heard(but didnt know for sure) that if you used a shared neutral on an afci circuit like to feed 2 bedrooms with say a 14/3 and 2 afcis that the afci would trip and not function properly. am I wrong on this then I wire? it would mean of course that you would have to connect the afci load side neutrals together in the panel and then out to the load. willl or wont work?

It will definitely not work. There is no way the two AFCI breakers can proportionately split the current between them. GFCI breakers have this same linitation.

Since code requires the entire circuit be protected, and not just the outlets, the breakers themselves must be the protective device. The only option is individual 2-wire circuits.

 

[al hildenbrand]

Stew,

If you understand why two single pole GFI breakers will always trip when you try to protect 120/240 volt single phase load on 3-conductor circuit (common neutral), then, you have the essential reason that two single pole AFCI breakers will also trip.

Part of the AFCI breaker is a GFP sensor that trips at a 30 to 50 milliamp ground fault current (depending upon manufacturer and model).

Now, the actual arc fault sensing part of the AFCI breaker may also have an interactive conflict with another AFCI sharing a common neutral, but it is not clear because the manufacturers have been stonewalling describing the actual circuitry they incorporate in their individual solutions to the Big Concept AFCI.

 

[stew]

gotcha thx

 

[tom baker]

Manufactures have not disguised how the AFCIs work, its well known:

An AFCI has a GFCI type circuit, but set at 50 mA, so its a GFPE, all AFCI's are dual listed as GFPE.
An GFCI/AFCI/GFPE have two separate sensing circuits
Ground Fault
Grounded Neutral
A grounded neutral is what makes a GFCI/AFCI trip, for afcis its the cause of 95% of the trips.
Unless designed for the purpose a 2 pole AFCI will trip, due to the grounded neutral sensing.
Cutler Hammer makes a listed AFCI 2 pole breaker.

 

[ramsy]

On the load side of either device the neutrals must be dedicated if the units are single pole or if they are two pole you can share neutrals.

Can someone explain how we can share neutrals with a 2-pole AFCI breaker? If one phase draws more doesn't the other pole detect an imbalance and trip?

 

[don_resqcapt19]

Roger,

Can someone explain how we can share neutrals with a 2-pole AFCI breaker? If one phase draws more doesn't the other pole detect an imbalance and trip?

The GFP part of the AFCI looks at the current on the two hots and the grounded conductor. This will always sum to zero unless there is a ground fault. If the sum is 30-50 mA above zero the breaker trips.
Don

 

[ramsy]

The GFP part of the AFCI looks at the current on the two hots and the grounded conductor. This will always sum to zero unless there is a ground fault.

Thanks Don, now I see this working for a 240vac circuit, since the single (line-line) circuit load is balanced. Getting two seperate 120vac phases synchronized and balanced with perfect timing might be more difficult.

 

[don_resqcapt19]

Roger,

Getting two seperate 120vac phases synchronized and balanced with perfect timing might be more difficult.

The current that goes out on one hot returns on the other hot or the neutral. The current on all three wires must sum to zero unless there is another path. There is no need for any type of timing or synchronization.
Don

 

[ramsy]

The current on all three wires must sum to zero unless there is another path.

Ahh, I see the breaker is comparing the neutral current to both poles summed, so the two poles can draw different currents as long as they sum the neutral current?