[Hillbilly]

House is 2 yrs old. Things were fine for over a year,then last Fall,Homeowner called and said the Mast. Bed breaker trips......but only during a Thunderstorm,or sometimes when there's Lightning visible in the distance.

We went back,changed the breaker. Happened again in a Month or so.Went back again,checked all switches,receps,and wires in the boxes etc in the bedroom,and closet. No visible problems.

Next Thunderstorm,same thing....tripped. Went back,and as an experiment,changed to conventional breaker. No problems. Thunder,lightning didn't affect it.

Put AFCI back in,and of course over the winter,no thunderstorms,so no problems. Since Spring has arrived,it's happening again.

There's 4 AFCi breakers in the panel. None of the others trip in a Storm. This came about after about 16 months of normal usage.

After going over things with the Homeowner,the only thing that changed was that they put a Computer in the bedroom right before this started happening. Is there any possibility that the AFCI is seeing somethin' it doesn't like coming thru the Computer thru the Phone connection during a Storm?????

This one has me stumped. Any ideas?????????

 

[MDShunk]

Yes, there are a couple of quick steps that will sort out a tripping AFCI in a hurry. First, remove all loads from the circuit... unplug everything, unscrew all lamps, but turn switches on, remove GFCI's and wire nut line to load. Then, megger the circuit at the panel and check hot to neutral, hot to ground, neutral to ground, and neutral to hot. I want to see greater than 100 megohms at 500 volts. Anthing less, and you better start isolating parts of the circuit to find the offending conductor to conductor leak. This has found the problem for me each and every time. I normally isolate it to a piece of romex that appears perfectly fine and undamaged, or a receptacle that looks completely normal.

 

[brian john]

Marc: That would have been by suggestion, though I know nothing about GFCI's. Guess I really should get off my tushie and investigate these buggers.

So many electricians utilize a continuity tester for trouble shooting, and while they will show a dead short, they are no good for leakage currents minimal insulation break downs.

 

[MDShunk]

Thought I should add to remove and jumper any dimmers.

 

[MDShunk]

So many electricians utilize a continuity tester for trouble shooting, and while they will show a dead short, they are no good for leakage currents minimal insulation break downs.

RIGHT!

If you're on a trouble call for an AFCI or GFCI that intermittantly trips, you will probably never find the problem with an ohm meter. Throw a little juice to the situation, and the problem will show itself front and center.

Case in point... Went on a trouble call several weeks back for a garage GFCI that was tripping from time to time. Didn't seem to be weather or use related. Just tripped sometimes. I determined that this GFCI did all the garage recs, all the outdoor recs, and the post light. The megger test at 500 volts showed less than 20 megaohms between any of the three conductors, no matter how I tested. AH! Problem found. Just a matter of unhooking sections of the circuit until it was pinned down. Turned out to be the little single receptacle with a flipper lid in the post light. I ran to the supply house and got one, and put it in. Megger check now, over 1000 megohms between any conductor. No reported problems since. Took the receptacle apart, just out of curiosity, and found a spider's nest type deal inside the guts of the post receptacle. That's all it takes, sometimes. Get a little morning dew or dampness on that spider web mess in there, and you've got yourself a fine little low level short.

 

[Hillbilly]

Thanks Fellas! We'll Megger things next week and I'll tell ya what we come up with.

 

[MDShunk]

A cheap, every-day megger for the electrician would be Supco's M-500. It is designed for the HVAC trade to check compressor windings. It uses a series of idiot lights, so you don't get a precise megger reading, but perfectly good enough for troubleshooting. It does a 500V check with 2 'C' batteries. They're less than 100 bucks, and available at HVAC supply houses.

 

[Hillbilly]

A cheap, every-day megger for the electrician would be Supco's M-500. It is designed for the HVAC trade to check compressor windings. It uses a series of idiot lights, so you don't get a precise megger reading, but perfectly good enough for troubleshooting. It does a 500V check with 2 'C' batteries. They're less than 100 bucks, and available at HVAC supply houses.

Thanks MD. The one we have at the Shop is a bit old,and sometimes unreliable.

That one looks like somethin' I could buy and keep on the Truck. Thanks again.

 

[MDShunk]

http://www.supco.com/images/04 test instruments.pdf

or, they're $121 bucks at Grainger, if you have one of those nearby:

http://www.grainger.com/Grainger/wwg/itemDetailsRender.shtml?ItemKey=3T105&BaseItem=4LW54

 

[MDShunk]

Thanks MD. The one we have at the Shop is a bit old,and sometimes unreliable.

That one looks like somethin' I could buy and keep on the Truck. Thanks again.

Yeah, it's not something you're going to be commissioning new switch gear with, but an excellent, low-cost troubleshooting tool.

 

[brian john]

Marc:

I have a small (8" long X 2 X 2) digital perfect for a tool box I'll post tomorrow.

went to a service call GFP tripped switchboard looked a mess and the electrician was going to close the main. I told him on the phone NO WAY WAIT FOR ME. He had used a ohm meter and it read clear, megger the board and it meggered less that .3 megohms. I always try to tell them they need a little UMPH. 1000 VDC versus 9 VDC of a typical ohm meter.

 

[MDShunk]

MArc:

I have a small (8" long X 2 X 2) digital perfect for a tool box I'll post tomorrow.

Looking forward to it. I looked into "beater" meggers several years back, and the Supco one was about all I could come up with. I really didn't want to go with the old high-school type hand crank jobbies, since you can sorta create readings with those.

 

[Hillbilly]

Yeah, it's not something you're going to be commissioning new switch gear with, but an excellent, low-cost troubleshooting tool.

Looks fine for Residential stuff MD.

 

[MDShunk]

Looks fine for Residential stuff MD.

That's what I thought, too :thumbsup:

I'm interested to see what Brian's got. If he's got a little digital, I will own one. I'll pass my Supco down the line to someone that might have a clue what to do with it.

 

[Hillbilly]

Looking forward to it. I looked into "beater" meggers several years back, and the Supco one was about all I could come up with. I really didn't want to go with the old high-school type hand crank jobbies, since you can sorta create readings with those.

The hand crank is what we have at the Shop. I don't like that one much.:no:

 

[MDShunk]

The hand crank is what we have at the Shop. I don't like that one much.:no:

I think you need some finesse to work those successfully. Finesse that I think I lack. I'd rather just press the red button on the Supco.

 

[MDShunk]

went to a service call GFP tripped switchboard looked a mess and the electrician was going to close the main. I told him on the phone NO WAY WAIT FOR ME. He had used a ohm meter and it read clear, megger the board and it meggered less that .3 megohms. I always try to tell them they need a little UMPH. 1000 VDC versus 9 VDC of a typical ohm meter.

Yep!!! Every service electrician should have some form of megger available to him. Preferrably, on the truck. Twice operating voltage is just about the rule of thumb, if you're dealing with more than 120/240. 120 and 240 normally get meggered at 500 volts. I know Brian starts with a 100 volt megger to make sure there's nothing on the line he missed (load wise) so he doesn't blow it up. I normally just use my regular OHM meter first, to make sure I didn't miss unplugging something. A megger will normally toast whatever you missed, so keep that in mind.

 

[RCG]

Supco's M-500
I am buying one!!