Interesting electrical failure

Started by davidj, May 23, 2011, 09:25:09 PM

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davidj

Had an interesting electrical failure this weekend.  Suggestions welcomed...

The electrical system on our off-grid cabin is basically complete, and we've been using it thanks to my trusty 5KVA Honda EM5000is Inverter generator.  Pretty much everything was working perfectly - lights, outlets, 220V well pump.  However, this weekend, it failed when I was trying to use a compressor plugged into one of the interior AFCI-protected outlets.  I started the gennie, the compressor started up, then a light that had been left on flickered, and everything died.  At first I thought this was because the well pump had kicked in at the same time - trying to start the generator and the compressor doesn't work with just 5KVA and the generator overloads.  However, the generator overload light wasn't on, and when I went to the box many of the breakers (probably just the AFCI breakers - didn't note which at the time) had tripped (but the main breaker hadn't tripped).  There was burnt electrical smell in the cabin, and also in the breaker box.

I switched everything off, then gingerly started trying to bring stuff back up.  The generator worked fine and ran directly-connected tools .  I could run the well pump through the box with all other breakers off.  Flipping the GFCI or refrigerator breakers (with no load on either circuit) worked fine. But whenever I tried to flip any AFCI breaker it made fizzling sounds, smoked and, more often than not, tripped.  I tried several AFCI breakers and they all did the same, even if there was no load on the connected circuit.  Checking the wiring, everything looks fine between the gennie and the box (and there isn't much to check - a sealed 220V plug, wire nuts to a some 10AWG in a conduit and a direct connection from there to the breaker box).  And whatever I do the gennie doesn't seem to be overloaded - even when the AFCI breakers are looking seriously scary the gennie isn't loading down at all.

Any ideas?

bayview

#1
    Groung fault?

http://www.thecircuitdetective.com/afci_circuit_breakers.htm

   Do you have two breakers sharing a common neutral?

/.
    . . . said the focus was safety, not filling town coffers with permit money . . .


davidj

Quote from: bayview on May 24, 2011, 06:33:08 AM

   Do you have two breakers sharing a common neutral?

It's possible I do have two AFCI-protected circuits where the neutrals are joined.  I've got a couple of boxes where there are switches for lights from two different circuits - I wouldn't be suprised if I tied all of the neutrals in the box together.  I'll check that out first at the weekend as that should be an easy fix.

I guess another option is neutral->ground arcing.   Apparently some of these AFCI breakers can spot upstream arc faults, and a neutral->ground arc anywhere in the system might look like an upstream fault and wouldn't necessary be removed by switching off regular breakers.

Finally I'm gonna try is eliminating the possibility of a generator issue.   Given the generator has an inverter, I guess it's not impossible that something noisy in the inverter circuit could produce a waveform that looks like an upstream arc.  Hopefully I can borrow a neighbors gennie to make sure it's not that.

Thanks for the ideas.

davidj

So the net damage from the electrical failure was:

- 2 dead AFCI breakers - they smoke and fizzle if switched on and the test switch doesn't work
- all four fluorescent ballasts in the cabin dead
- one electronic fan timer smoked (literally - black smudges everywhere). Probably the cause of the burning smell in the cabin.

Once I'd replaced the breakers and disconnected the dead stuff everything else worked fine - no problems on the circuits with blown breakers.

My guess is that there was a significant voltage surge that resulted in all of the fried stuff. Not sure how it happened - I guess it was some combination of the well pump, compressor and inverter generator that caused it (could two inductive loads and a bunch of smart power electronics do that??).  Does this sound like a reasonable diagnosis?

The plan to avoid another $150 of fried parts is to only plug the compressor into the small, portable, gennie in future.

Is there such a thing as a whole-house surge protector?

Tickhill

Power companies install these if the customer's request it, so they should be available for purchase from an online vendor. The surge/lightning suppressor attaches parallel to the incoming service lines, usually at the weatherhead.
"You will find the key to success under the alarm Glock"  Ben Franklin
Forget it Ben, just remember, the check comes at the first of the month and it's not your fault, your a victim.

Pray while there is still time


rocking23nf

I paid 90$ alone for a square D AFCI breaker last year, they are expensive.    I would only use them as a bare code minimum in bedrooms outlets due to the cost.

davidj

I used AFCIs everywhere that doesn't need GFCI.  This was slightly more than necessary for the code I built under (I may have been able to squeeze in maybe 1 regular breaker) but it was simpler just to use them everywhere and not worry about which outlet ended up on which circuit.  I figured it wasn't too bad as I only needed to buy the breakers once, but I guess I was wrong!  The Siemens version (which is identical to the Murray - Siemens own Murray) come in at $37 each in HD.