Circuit Breaker Tripping Randomly

[Dmeistar]

Hey guys,

I am preparing to head down the West Coast from Washington to San Fransisco. For the past 2 weeks I have been struggling with an electrical issue on board.

The "Electronics" circuit breaker randomly will trip, killing power to my chartplotter, AIS, depth-sounder, and knot-meter. There are two hot wires connected to the breaker--one that goes to the AIS, and another that leads to a busbar in the cockpit where it splits out to the other equipment.

The breaker seems to trip more often when the boat is moving a lot (rough seas or rough idle). The tricky part is that its so inconsistent. Sometimes the circuit will stay on for hours at a time, and sometimes it will trip within seconds. My first though that a short circuit. I have traced both of the hot wires leading from the distribution panel and cannot find and breaks or bad connections (thats not to say that there aren't any, access is very limited). I have tried turning on the circuit but leaving off the AIS, and the breaker still trips. I have tried leaving the chartplotter off and it still trips. The same happened for the depth sounder.

I have spent hours buried in Nigel Calder's electrical/maintenance manual, but cant pinpoint the short because it is so intermittent. Whenever I try to troubleshoot the circuit I cant get the breaker to trip! Its like as soon as I turn my back it will trip, but when I try to pop the hood and take a look everything works fine!

I think my next step will be replace the hot wire leading out to the cockpit. If anyone has any advice or recommendations on troubleshooting this I am all ears!

Thanks in advance,

Daniel

[barnakiel]

My guess is that when the boat moves, something shorts and the breaker trips.


Another guess but I think less likely is a bad breaker. They sometimes go bad. I had this on one boat too.


b.

[gsuescum]

Try replacing the circuit breaker. I was having trouble with my genset. Breaker kept shutting it down. Tried to track down the bad wiring/short with no luck. Got a diesel mechanic to come look at it. He noticed that the breaker was old and worn out (13 years old). Put a new one in and zero problems. Took him about an hour to diagnose and fix.

[Panama Red]

Originally Posted by gsuescum

Try replacing the circuit breaker. I was having trouble with my genset. Breaker kept shutting it down. Tried to track down the bad wiring/short with no luck. Got a diesel mechanic to come look at it. He noticed that the breaker was old and worn out 13 years old). Put a new one in and zero problems. Took him about an hour to diagnose and fix.

My first thought. I have had same problems with old breakers.

[ohgary]

A breaker is going to trip for 2 reasons, One there is a short or two you have used it for a swtich to long and you have warn it out. I would replace the breaker first and if it continues to trip the only option is to find the short.

[wingless]

A very handy tool is a DC ammeter.

Usage of that instrument would permit measurement of the actual current passing through the breaker. It would remove lots of guessing.

A second handy tool is an adjustable DC load. That device would permit determination of the current / time required to trip the breaker. I have used both electronic loads and carbon pile loads. Either would be appropriate for this test.

[Dmeistar]

Guys,

Thanks for all the replies.

There's one detail I forgot to add-- my girlfriend was in front of the distribution panel one time, right as the breaker tripped. She saw the needle on the DC ammeter jump up from about 6A into the 20-25A range and start dancing around right before the breaker tripped. The spike in current makes me think its a short. The part that has got me stumped is how to track it down. I have a little experience with a multimeter and am familiar with a continuity test, but the problem is the intermittent nature of the short. Should I just start replacing wires and see what makes it work?

[Panama Red]

Originally Posted by Dmeistar

Guys,

Thanks for all the replies.

There's one detail I forgot to add-- my girlfriend was in front of the distribution panel one time, right as the breaker tripped. She saw the needle on the DC ammeter jump up from about 6A into the 20-25A range and start dancing around right before the breaker tripped. The spike in current makes me think its a short. The part that has got me stumped is how to track it down. I have a little experience with a multimeter and am familiar with a continuity test, but the problem is the intermittent nature of the short. Should I just start replacing wires and see what makes it work?

Start with the simplest solution first:
1. Replace breaker
2. then replace wiring attachments/connectors
3. finally replace hot wire
4. Replace black wire

[Tellie]

Originally Posted by wingless

A very handy tool is a DC ammeter.

Usage of that instrument would permit measurement of the actual current passing through the breaker. It would remove lots of guessing.

A second handy tool is an adjustable DC load. That device would permit determination of the current / time required to trip the breaker. I have used both electronic loads and carbon pile loads. Either would be appropriate for this test.

For the DC amp meter. This tool is invaluable for 12 volt systems.

[Wotname]

Originally Posted by Dmeistar

Guys,

Thanks for all the replies.

There's one detail I forgot to add-- my girlfriend was in front of the distribution panel one time, right as the breaker tripped. She saw the needle on the DC ammeter jump up from about 6A into the 20-25A range and start dancing around right before the breaker tripped. The spike in current makes me think its a short. The part that has got me stumped is how to track it down. I have a little experience with a multimeter and am familiar with a continuity test, but the problem is the intermittent nature of the short. Should I just start replacing wires and see what makes it work?

Eyeballs are the best way to find an intermittent short but you can make things easier.

You have several circuits feed by this one circuit breaker. You can add a temporary in line fuse (rated say at 50% or less of the circuit breaker) at all the busbar distribution points mentioned in your opening post.

Wait until a fuse blows instead of the circuit breaker and you have isolated the section of faulty wiring considerably.

[Tellie]

Originally Posted by Dmeistar

Guys,

Thanks for all the replies.

There's one detail I forgot to add-- my girlfriend was in front of the distribution panel one time, right as the breaker tripped. She saw the needle on the DC ammeter jump up from about 6A into the 20-25A range and start dancing around right before the breaker tripped. The spike in current makes me think its a short. The part that has got me stumped is how to track it down. I have a little experience with a multimeter and am familiar with a continuity test, but the problem is the intermittent nature of the short. Should I just start replacing wires and see what makes it work?

I doubt it's a short. Usually dead shorts will trip your breaker instantly and won't let you re-set it. Get the DC amp meter as suggested by wingless. This is in Nigels book as well. It's a must on any boat in my humble opinion. This will tell you where the loads are on your wires. Sounds more like you have something else on that circuit that randomly starts on it's own, water pump, bilge pump AC unit etc. Before you replace anything you need to trace all the wires coming off that breaker, especially for bad fittings that may be loose, wicked, or corroded. Flex the wire as well, it should be supple, listen and feel for any cracking or crunching noise when doing this. Also, what size is the breaker and have you checked all your electronic equipment on the circuit for their individual amp draw?

[Wotname]

If you replace the circuit breaker and the fault persists then I would assume it's an intermittent short. Also assuming there is no additional unknown circuit connected to the circuit breaker.

While Tellie is spot one with using an ammeter, it is only good for trouble shooting an intermittent fault during the times the fault exists.

What your girlfriend saw suggests (to me) there is a intermittent short.

[smac999]

How big is the breaker and do you have fuses on all the devices attached to it? You should have fuses on each thing. . Then A short should be blowing a fuse. Not tripping the whole thing. Unless it’s the wire from breaker to bus bar. But that’s probably only a few feet.

The electronics breaker should be feeding something like a Bluesea 5025. Then you can make the electronics breaker big like 30a. And it should never blow.


You need an amp meter to see what you are drawing compared to breaker size. If it has max holding ability. You can leave it on. And see if it’s blowing due to an amp spike. = Breaker acting normal. And other problem. Or blowing at a low constant amps. = Bad breaker.

[garychurch]

Plenty of good advice.

I had an identical problem of intermittently tripping a 24V DC breaker dedicated to a vent fan.

I check the nominal Amos on the circuit measured about 8 amps. Replaced the 10 amp fuse with a 15 amp fuse... problem solved.

You may have added a lot of electronics to the one protected circuit and the breaker is no long able to support transient loads.

Suggest you check the load and replace the breaker with a larger capacity if needed to give you greater margin. Big however you need to be sure the wiring can accommodate and additional load without overheating.

If the breaker is not the problem and your breaker feeds multiple devices you need to isolate each load using a temporary fuse as suggested to fine the problem.

Good luck.

[Dmeistar]

Great advice everyone, thanks! I am going to be digging into this the next few days and will let ya'll know what turns up