circuit breaker popping once every 24 hrs

Hello all
I have a dedicated 20 amp circuit that feeds 4 outdoor recepticals spaced around my yard. There is probably a total of 300 feet of 12 AWG Romax underground wire used, burried about a foot deep in our (very) sandy soil. This setup has been working fine for years, until the other day when the circuit breaker popped. We reset it, and things were fine until the middle of the next night...I thought we had a power failure... turns out the circuit breaker popped again, along with the upline main breaker that has all the 110v stuff going through it for the whole house. The only time I've ever seen this upline breaker go was when we had a lightning strike a few years back. Since then, the upline breaker has not popped again, but the 20 amp breaker pops about once every 24 hours. When the breaker is reset, things appear normal. A clamp on AC ammeter shown 0 amps when nothing is plugged in, and reads correctly (4 amp) when the normal load is connected (a couple of pond pumps that run 24-7). I've checkec the voltage at all the outlets with a volt meter and all looks fine. I even swapped the circuit breaker with another thinking maybe it was just a bad breaker.
Anyone got an idea of what could be going on? I'm stumped.
Thanks
Dan
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Dan Kuechle wrote:

I assume by Romax (sic) you mean NM / NMW non-metallic wire rated for direct burial?
Is it a GFI breaker? It should be, if it feeds an outside circuit. The breaker may be tripping because of a small current leak caused by degraded or damaged undergroup wire. However, if you swapped it with a non-GFI breaker (it sounds like you did) and still have the same problem, then it may be something else.
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On Wed, 4 Aug 2004 10:07:51 -0500, "Dan Kuechle"
Yep, you got an electrical problem. Call a licensed plumber.

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snipped-for-privacy@ma.us.gov wrote:

Call a what? Now that's funny :) Why not call a licensed house painter or automobile mechanic to fix electrical problems.
Too bad we can't edit our typos.
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wrote:

Ah! Mr. chevelless does not recognize sarcasm......
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Yeah right
Red Neckerson wrote:

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If it is fairly regular, is there an event that happens that may trigger it such as sprinklers coming on, or maybe an hour after they come on?
Wayne

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Outdoor receptacles and pond pumps gives me a clue that your problem may be with water. I suggest opening up each receptacle to inspect their condition and to see if any water has come in contact with the wiring. Look for any indication of burning or charring on the receptacles. Water is a conductor which will allow current to flow and usually not enough to trip a circuit breaker immediately, but enough to burn up wiring devices.
When you get this problem resolved you should change the circuit breaker to a GFI type. That will provide better protection for human life. It is also required by the National Electrical Code for direct buried residential wiring 12" deep. The downside of installing a GFI circuit breaker is that it will cause more nuisance tripping. If your wiring was 18" or deeper the code permits GFI receptacles which tend to experience less nuisance tripping.
John Grabowski http://www.mrelectrician.tv

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I just had a similar problem where a wore electric wire to the outside AC box was shorting out and taking its 30 amp breaker out as well as the 100 amp breaker. Would only happen once in a while and made tracing difficult.
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On Wed, 4 Aug 2004 10:07:51 -0500, "Dan Kuechle"

I am going to go with ground water rising as a first choice.
But check these other two for 'strange events' that I have had to investigate in the past. An old house which was originally wired in VRI (a rubber based insul) and 'modernised' with CB's and RCD's (I think equivalent to those GFI devices that USA guys mention) kept having 'ghost trips' of a CB . Turned out it was the cable stretched over a gal iron water pipe that was being stressed as the house moved from AM to PM on +30C days. A brand new condo had a similar problem but different in that there was no consistent pattern to the tripping. That problem proved to be caused by the field setup from the UHF Security System transmitter which was mounted adjacent the modular switchboard. Each time (maybe) the System 'phoned home' to Central Control one or more RCD's would trip.
Check the innocuous things,, maybe your answer lies there?
cheers
BTZ
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A trifle unlikely for tripping a 20A breaker. But...

Given that the OP's situation seems very simple with nothing exotic, a temperature dependency like you suggest and a very worn cable sheath seems most likely to me.
Ie: when you install a buried cable, where it exits the house (or enters receptacle "standards" buried in the yard), there should be a few inches of slack. Ie: a small loop of cable before penetrating the house foundation.
If you don't provide such slack, repeated expansion/contraction cycles could cause the cable insulation to degrade (ie: pressure from the rim of the hole in the concrete), and the conductors touch at certain times of day.
That said, I'm going to throw out another - do you have any groundhogs or squirrels digging holes nearby? Could be something like a a chewed chunk of cable shorting periodically (due to temperature cycling, or another animal brushing the cable nearby on their nightly rounds).
And another: a wire inside a receptacle so close to shorting that temperature cycling (or brushing past by above animal ;-) causes it to ground short.
I'd start with killing the power, and inspecting the inside of every box on the circuit very carefully. Then, if that doesn't yield anything, carefully dig out where the circuit exits the house and check the condition of the cable.
In any event, I believe you should be changing the circuit over to GFCI protection (breaker or upstream outlet). The circuit is already dubious, and the GFCI will probably help you find the problem faster while making it safer in the meanwhile.
And of course, the breaker may simply be just about kaput.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
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