Combo AFCI Issue Please Help

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C3PO

C3PO

Senior Member
Location
Tennessee
I have an interesting situation that I would like to get some intput on. A good friend of mine who is also a EC had a house "hotwired" off of a portable generator so he could check everything and the inspector could do the final.

There is four combination type AFCI's in the panel. They will not trip when the test button is pushed.

The inspector did not like this so my friend ran a wire out to the temporary pole and the AFCI's trip/test just fine running off of the temp.

Branch/feeder type AFCI's will test/trip off of both the generator and the temp.

Does anyone have any reasons/ideas as to why this is happening?
Has anyone else had a problem like this?
 
Afci

Afci

Can't say I have had this specific problem but I offer this thought: AFCI use a computer algorithm to look at current and determine if there is an arc. Every AFCI manufacturer MUST use a different algorithm because of patent issues. Were all devices by the same manufacturer and same vintage? Perhaps the algorithm used in one device was different from another and, as a result, they operated differently.
 
All four of the combo AFCI's are Square D Homeline HOM115CAF. Everything on these circuits worked find, but they would not trip when the test button was pushed. Then when we found out that they did trip off of the temp we swapped out all four for the branch feeder type (HOM115AF) and they tripped off of both the generator and the temp.

I called Square D's tech support and they did not have an answer but are supposed to get back with me.
 
I often use a generator to "circuit test" houses on inspections and have found that AFCIs will occasionly not trip on the generator test but when I make it a point to go back once utility power has been connected, they work.
I will be interested in what the SquareD rep advises
 
These AFCI's sure seem to be a strange implementation. It seems very strange to me to have allowed introduction of them before a standardized external test method was commonly available.

From what I have read the only approved test method is the test button. I have not been able to locate anything that explains exactly what the test button on a combination device actually tests. (e.g. what factors is it dependent upon).

Is the ground bounding the same for the generator as the temporary service?
One thought was that it could be a difference in the the bonding resistances?

If not that then could it be a frequency sensitivity depending upon how accurate the generator frequency is?

My last guess was noise from the generator affecting its ability to distinquish an arc?

I will also be very interested in hearing the factory response.
 
Could it be that the Grounds and Neutrals were isolated at the generator meaning that there really was no return path for fault current on the grounding conductor? Would this cause the AFCI's to act strangely? Just a thought...
 
haskindm said:
Could it be that the Grounds and Neutrals were isolated at the generator meaning that there really was no return path for fault current on the grounding conductor? Would this cause the AFCI's to act strangely? Just a thought...
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Unless the transfer switch isolates the neutral, its still bonded to the EGC @ the service. With a portable generator plugged in, I don't see how the neutrals could've been isolated.
 
brantmacga said:
Unless the transfer switch isolates the neutral, its still bonded to the EGC @ the service. With a portable generator plugged in, I don't see how the neutrals could've been isolated.
Click to expand...

My understanding is that some portable generators are set up just that way, with the neutrals isolated from ground. I think I read someplace about one manufacturer having a label to that effect and instructions on how to tie the neutrals and grounds together if that was desired.

I can't quite get my head around how it would cause a problem, but I would be willing to bet that the neutral/ground bond at the generator is the culprit. 1. Either the neutrals and grounds ARE bonded together and should not be, or 2. they ARE NOT bonded together and should be...
 
haskindm said:
I can't quite get my head around how it would cause a problem, but I would be willing to bet that the neutral/ground bond at the generator is the culprit. 1. Either the neutrals and grounds ARE bonded together and should not be, or 2. they ARE NOT bonded together and should be...
Click to expand...

I thought this as well. The generator's neutral is not bonded at the generator, but it was hooked up with four wires at the panel. What makes it more confusing is why would do the branch/feeder type test out but not the combo's.
 
augie47 said:
I often use a generator to "circuit test" houses on inspections and have found that AFCIs will occasionly not trip on the generator test but when I make it a point to go back once utility power has been connected, they work.
I will be interested in what the SquareD rep advises
Click to expand...

Is there any certain brand that you have had more trouble with?

When you had trouble was it all of the AFCI's in a panel or just some?
 
haskindm said:
My understanding is that some portable generators are set up just that way, with the neutrals isolated from ground. I think I read someplace about one manufacturer having a label to that effect and instructions on how to tie the neutrals and grounds together if that was desired.
Click to expand...

The grounded conductor and EGC are still bonded at the service in this scenario. They will remain bonded unless physically or mechanically disconnected from the panelboard being fed by the generator.
 
brantmacga said:
The grounded conductor and EGC are still bonded at the service in this scenario. They will remain bonded unless physically or mechanically disconnected from the panelboard being fed by the generator.
Click to expand...

That is correct they are bonded at the service.
 
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