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post #11 of 24 Old 06-26-2013
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Re: tips needed to chase dc short

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Originally Posted by chucklesR View Post
I'm not buying the 'slow load' causing a short eventually.

I'd call this an intermittent short, very hard to find because you can test and test and if it's not shorting at the moment you won't find it. Electricians that charge by the hour love these kinds of shorts.

You're going to have to trace every wire and wiggle it while you do. Hopefully since you say it's the 'port side breaker' you are talking a couple of loads - not dozens.
You make (honestly) be better off just replacing the wiring of one load at a time, that depends on the age of the boat, your budget and your time.

On the other hand, you could just transfer one load at at time to the starboard breaker. When it trips off you know you've found the faulty load - replace every inch of that circuit and you may be done.
It's not intermittent, though. The breaker trips every time and within 30 seconds of turning on the breaker and his ammeter always shows current with all loads off.
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post #12 of 24 Old 06-26-2013
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Re: tips needed to chase dc short

Not familiar with your circuitry but it may be simpler to find...

-if the port DC breaker supplies a bus that loads are powered individually from you can lift ALL the leads from the bus and check the current through the breaker (mark the leads before removing them from the bus unless they have wire markers or unless color coded and then draw a simple diagram of the bus for use in reattaching)...

-and then replace them one at a time until the culprit is found.

Even if a a couple of systems that are powered off that breaker aren't on the bus it may still be useful to do this...

-if after lifting the leads from the bus the breaker still trips it is likely one of the directly powered loads. They should be individually fused so you can pull fuses to further isolate.
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post #13 of 24 Old 06-26-2013 Thread Starter
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tips needed to chase dc short

Lots of great ideas here - I'm working through them and will spend some quality time chasing it this weekend. Some clarification : In my panel the tripping breaker is connected to a bus bar with a total of six other breakers. None of the others have any issues. The breaker in question powers the starboard (don't know why I said port before) side cabin lights and two small fans. The lights and fans work when the breaker is first turned on and then it flips off. Even with all lights and fans switched off, the breaker will still flip. On the panel there is a cumulative analog ammeter that shows the total load across all breakers. This appears to be working properly as I can watch the load build as I turn circuits on, and the bigger items like the icebox show a bigger load etc. for regular usage it stays between 5 and 10 amps. However, as soon as I turn on the starboard breaker switch the meter goes above 20 and stays there until the breaker flips off.
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post #14 of 24 Old 06-27-2013
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Re: tips needed to chase dc short

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Lots of great ideas here - I'm working through them and will spend some quality time chasing it this weekend. Some clarification : In my panel the tripping breaker is connected to a bus bar with a total of six other breakers. None of the others have any issues. The breaker in question powers the starboard (don't know why I said port before) side cabin lights and two small fans. The lights and fans work when the breaker is first turned on and then it flips off. Even with all lights and fans switched off, the breaker will still flip. On the panel there is a cumulative analog ammeter that shows the total load across all breakers. This appears to be working properly as I can watch the load build as I turn circuits on, and the bigger items like the icebox show a bigger load etc. for regular usage it stays between 5 and 10 amps. However, as soon as I turn on the starboard breaker switch the meter goes above 20 and stays there until the breaker flips off.
Do what I suggested above and you will locate your problem. You can skip the pigtail suggestion if you wish and work through the circuit in the same way as I suggested and then reset the beaker each time until you get it to stay on. . I check with the fans first. From your description of the problem they appear to be the more likely suspects.
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post #15 of 24 Old 06-27-2013
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Re: tips needed to chase dc short

Sounds like an easy fix to me. Just turn everything off that's connected to that particular breaker circuit. Then, disconnect the positive wire going to the breaker, place an ammeter in the line. Now, turn the breaker on. If you get any current reading at all, begin disconnecting the wires from the individual items, fan, light, etc..., until there is no reading. When you get to where there is NO current flowing, you've narrowed down the culprit. I suspect it one of the fans - they tend to do some nasty things if they've been onboard for more than a decade.

Good Luck,

Gary
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post #16 of 24 Old 06-28-2013
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Re: tips needed to chase dc short

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Sounds like an easy fix to me. Just turn everything off that's connected to that particular breaker circuit. Then, disconnect the positive wire going to the breaker, place an ammeter in the line. Now, turn the breaker on. If you get any current reading at all, begin disconnecting the wires from the individual items, fan, light, etc..., until there is no reading. When you get to where there is NO current flowing, you've narrowed down the culprit. I suspect it one of the fans - they tend to do some nasty things if they've been onboard for more than a decade.

Good Luck,

Gary
This is basically what I suggested but using a 12v pigtail light in line instead of a ammeter. The problem with an ammeter in this particular instance is that it has very low resistance and the breaker will trip within 30 seconds of turning it on. I also like the light because it's a quick an easy visual reference. Usually on a boat you can see the light at all times.
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post #17 of 24 Old 06-29-2013 Thread Starter
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tips needed to chase dc short

Got it! Ceiling light in forward head. (Just used for storage right now, don't go in there much. )
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post #18 of 24 Old 06-29-2013
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Re: tips needed to chase dc short

Congratulations!!! What method of isolating it did you use?

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post #19 of 24 Old 06-29-2013
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Re: tips needed to chase dc short

Was it the bulb or the light itself?

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post #20 of 24 Old 07-02-2013 Thread Starter
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tips needed to chase dc short

i used analog ammeter which is already in the panel and just kept disconnecting loads until i found it. It is the light itself - original to boat 1985 - and corroded. Of course I started aft and worked forward, so it took awhile. .
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