afci tripped by coax

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mikeys68

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i have a new house that has a afci tripping issue. I discovered it when i tried to plug my cable coax into my computer for tv. It tripped the rooms afci. Of course, right away the electrician tells me it's a problem with my computer, but after many hours of testing i discover that if anything is plugged into any outlet on the afci circuit, then a coax touches the item, such as a surge protector with coax protection....the afci trips. It only happens on this circuit. I have plugged the same surge protector into other rooms with afci breakers and connected the coax to it with no trouble. To make things more confusing...I have an external hard drive that when it is plugged (three prong plug) into the room with the afci problem and connected to the usb port of the computer all is okay, but if the ext hard drive is plugged into the other rooms circuit (different afci breaker than problem one), then the afci breaker trips in the computer room when the usb touches the computer. The electrician has replaced the afci breaker with the issue, but wants to replace it with a regular breaker that doesn't trip when coax attached to items.

Anyone have thoughts on this. An help would be appreciated. I really don't want to just "bypass' the issue with a regular breaker since something is different about this circuit. I have opened the outlets and light switch to see if any neutrals may be touching grounds or issues, but have not come up with anything yet!
Thanks,
Mike
 
If I am reading your post correctly, there is an electrician involved in this work, so I will respond under the understanding that you will pass this along to the electrician, and discontinue testing and whatnot on your own. I see you are an engineer, but it is still considered giving "how-to" advice if we give it to you and you proceed on your own.

It sounds to me as though you have a neutral touching ground somewhere on the circuit, IMO. So, when you touch the grounded sheathing of the coax to something else grounded, the resistance of the EGC drops even further, allowing more neutral current to flow, tripping the GFPE of the breaker.

As unhelpful as your electrician seems to be, you hinder his progress by troubleshooting this when he's not around. AFCI's can be a bear to troubleshoot, and if variables change from one visit to the next, that difficulty is compounded. Force the electrician to honor his warranty.

If there are no bootleg grounds, have him swap the AFCI one more time. Sometimes we get two that are more troublesome in a row.

Is this room even being used as a bedroom? It could be that he could remove the AFCI protection for this room under the guise that it's an office. It would be better to find out the problem, because this shouldn't happen.
 
If I were troubleshooting this, I would swap the problem AFCI with the one that is working OK. If the problem moves with the breaker, it's the breaker. If the problem stays with the circuit, it's the circuit.

I don't understand why the electrician just swapped out the AFCI w/out doing some investigation.
 
LarryFine said:
Another possibility is that there is voltage on the coax shield.
Click to expand...

If that was so, wouldn't it have tripped the other AFCI breaker?


...but after many hours of testing i discover that if anything is plugged into any outlet on the afci circuit, then a coax touches the item, such as a surge protector with coax protection....the afci trips. It only happens on this circuit. I have plugged the same surge protector into other rooms with afci breakers and connected the coax to it with no trouble.
Click to expand...
 
hardworkingstiff said:
If that was so, wouldn't it have tripped the other AFCI breaker?
Click to expand...
Okay, I'll buy that. :roll: Maybe there's voltage on the EGC. :roll:

I would check for voltage between that circuit's EGC and the coax shield. Use a third ground (such as the EGC on an extension cord plugged into a known-good receptacle) as a reference to check for voltage on either, and maybe resistance as well.

How about one experiment more: Unplug everything on that circuit, and see what happens if you touch the coax shield to a receptacle EGC (or use a piece of wire, of course). If that trips, try it against another AFCI circuit, again using the cord.

The point is that something is not at the potential which it should be.
 
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