2 pole 20 amp afci on multi wire branch circuit

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
Try replacing with a true GFCI breaker. If it does not trip a neutral ground fault is not the problem.
[HR][/HR]Then put back the AFCI and plug in something at the end of the run and load it up. See what happens
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
The microwave may be the source of the arc signature, or the arc signature may be coming intermittently from something else (not even on the same circuit) and all the microwave is doing is bringing the circuit current above the serial arc detection threshold (~7A?)

Or the microwave may be on the threshold of the 30ma GF trip of the AFCI breaker.
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
The microwave may be the source of the arc signature, or the arc signature may be coming intermittently from something else (not even on the same circuit) and all the microwave is doing is bringing the circuit current above the serial arc detection threshold (~7A?)

Or the microwave may be on the threshold of the 30ma GF trip of the AFCI breaker.
The more I read up on these things , the more I see what you are saying about the Arc signature. If these devices can see Arc signature up stream/ downstream then why not from another circuit? ( I think that is mostly series arc) whos to say differently.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
The more I read up on these things , the more I see what you are saying about the Arc signature. If these devices can see Arc signature up stream/ downstream then why not from another circuit? ( I think that is mostly series arc) whos to say differently.
Precisely. To trip on what it thinks is a parallel arc there would have to be well over 20A on the breaker in question. That is, into the low mag trip range.
 

crtemp

Senior Member
Location
Wa state
The microwave may be the source of the arc signature, or the arc signature may be coming intermittently from something else (not even on the same circuit) and all the microwave is doing is bringing the circuit current above the serial arc detection threshold (~7A?)

Or the microwave may be on the threshold of the 30ma GF trip of the AFCI breaker.
Im thinking it has to be the microwave. It will trip in a matter of seconds with nothing else in the house on.
It's before anyone moves in (at least the ones I find). Otherwise it will just be random tripping whenever the microwave is running
 

user 100

Senior Member
Location
texas
Im thinking it has to be the microwave. It will trip in a matter of seconds with nothing else in the house on.
It's before anyone moves in (at least the ones I find). Otherwise it will just be random tripping whenever the microwave is running
If you have tried out everything mentioned previously more than likely you have compatibility issues going on.

Now plug microwave afci is protecting you from into standard non afci ct, and you could run it until the motor craps out and know what would happen?: absolutely nothing.:happyno:
 

jap

Senior Member
If you could read continuity with your meter between the neutral and the ground the breaker would trip immediately and there would be no delay like your describing.
Based on the simple concept of a GCCI monitoring what goes out to what comes back I'd try to rule out a problem in the shared neutral.

I'd take the multi wire branch circuit out of the equation to see if the symptoms changed at all.
Maybe there's some small residual return current that the breaker doesn't like since it's monitoring not only the microwave circuit but another one also that doesn't have a load on it.

For a test, Tie the 2 hots together and bring them to a single pole arc fault breaker in the panel and see if the problems still exists.

I've never been a fan of using a shared neutral for the type of scenario your describing but that's just me.
I've always pulled dedicated circuits with dedicated neutrals to 1p breakers.

JAP>
 

crtemp

Senior Member
Location
Wa state
If you could read continuity with your meter between the neutral and the ground the breaker would trip immediately and there would be no delay like your describing.
Based on the simple concept of a GCCI monitoring what goes out to what comes back I'd try to rule out a problem in the shared neutral.

I'd take the multi wire branch circuit out of the equation to see if the symptoms changed at all.
Maybe there's some small residual return current that the breaker doesn't like since it's monitoring not only the microwave circuit but another one also that doesn't have a load on it.

For a test, Tie the 2 hots together and bring them to a single pole arc fault breaker in the panel and see if the problems still exists.

I've never been a fan of using a shared neutral for the type of scenario your describing but that's just me.
I've always pulled dedicated circuits with dedicated neutrals to 1p breakers.

JAP>
I have tied it down to one circuit and it does not trip on a single pole eaton br breaker but it does still trip with only one leg tied into the 2 pole Murray breaker.
 

curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
If the same circuit holds on an Eaton breaker but trips on a Siemens (Murray) breaker it sounds like a ground fault issue. Eaton BR breaker no longer have GF protection but Siemens breakers do.
 

crtemp

Senior Member
Location
Wa state
If the same circuit holds on an Eaton breaker but trips on a Siemens (Murray) breaker it sounds like a ground fault issue. Eaton BR breaker no longer have GF protection but Siemens breakers do.
They don't say they are combo breakers (Murray). It just says afci combination. Another weird thing that happens is no matter if I put the microwave wire on phase a or phase b of the Murray breaker it will always say that phase a has tripped on the LED indicator.
 

curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
They don't say they are combo breakers (Murray). It just says afci combination. Another weird thing that happens is no matter if I put the microwave wire on phase a or phase b of the Murray breaker it will always say that phase a has tripped on the LED indicator.
All Siemens AFCI breakers have 30-50ma GF protection. Eaton removed the GF protection from their BR line a while back similar to GE. The Eaton CH line still has GF protection.

Since you are using Siemens breakers what do the indication lights show on the breaker? They have lights showing the cause of the last trip. AF or GF
 

crtemp

Senior Member
Location
Wa state
All Siemens AFCI breakers have 30-50ma GF protection. Eaton removed the GF protection from their BR line a while back similar to GE. The Eaton CH line still has GF protection.

Since you are using Siemens breakers what do the indication lights show on the breaker? They have lights showing the cause of the last trip. AF or GF
It's just one LED light that indicates an arc fault. But why would it always say the fault is on phase a when it trips no matter what phase I hook it up to?
 

kwired

Electron manager
Location
NE Nebraska
Is the power source a 120/240 or is it two 120/208?

Seem to recall a discussion where it was concluded that 2 pole AFCI's don't work on 120/208 systems.
 
Top