Hot Wire at 30amp Breaker

[Head Sail]

During a weeklong cruise in the chili Pacific Northwest where my 30amp system was taxed creating hot water running an electric heater and occasional hair dryer I noticed the neutral wire leading out of the main 30amp Blue Sea breaker was getting hot enough to melt insulation on the 12AWG wire in the proximity of the connection to the beaker. The neutral coming in and both hot wires showed no signs of getting hot. Should not the main breaker have tripped before the insulation started to melt?

 

[centerline]

During a weeklong cruise in the chili Pacific Northwest where my 30amp system was taxed creating hot water running an electric heater and occasional hair dryer I noticed the neutral wire leading out of the main 30amp Blue Sea breaker was getting hot enough to melt insulation on the 12AWG wire in the proximity of the connection to the beaker. The neutral coming in and both hot wires showed no signs of getting hot. Should not the main breaker have tripped before the insulation started to melt?

Not if it was due to a loose or incomplete connection.

An amp draw trying to get thru a necked down/restricted connection will create acute heat.. the connection inside the breaker was obviously adaqate for the task, but not where the wire attached to the screw.

If all the connections in the system are secure and the wire is sized proper, then its the circuit breaker that is the weak link... and will trip as designed.

This is why its so important to have no corrosion or loose connections in anything electrical..

 

[Head Sail]

Thanks for the response CL. I should add that the breaker shows signs of heat damage in the area of the connection (photo below). I replaced the breaker.

 

[John Nantz]

Head Sail - Thanks for the (original) post and it makes for a good reminder to check those connections. While I can’t answer your question I’ll volunteer a little editorial comment.

For some of us it seems there’s never enough time in a day so we tend to do those things higher up on the squeaky-wheel list. “If it ain’t broke don’t fix it” so looking for potential trouble items tends to be at the bottom of anyone’s list.

Checking electrical connections is probably not the highest item on anyone’s list; however, a 30 Amp AC circuit carries a lot of power and some of the DC circuits also carry a lot of power. Four golf carts wired for 50 Amp DC with 00 cables can put out a lot of power too.

The problem with our boats that run using a diesel engine is the engine really vibrates. Even with good motor mounts there is still vibration that is transmitted to everything throughout the boat - including the electrical conductors. This constant vibration causes a certain amount of vibration in conductors and in the case where they terminate at, say, a screw, this can eventually cause the screw to loosen or at least the pressure of the screw on the terminal to loosen.

One place where a loose contact happens a lot is at the boat’s shore power connection. The early result here is usually a sign that the shore power cable end shows some sign of melting and it it’s not caught early it gets pretty ugly.

Over the years I’m had various wire terminal screw connections become loose (mostly in the main panel) resulting in some device not working or only functioning with a problem. One major malfunction was while running though pea soup fog in an area with lots of rocks (north side of Prince of Whales Island) and both the autopilot and the radar started having weird problems. The culprit was a loose jumper cable connection from the main breaker bank (with the incoming cable from the battery) to the second breaker bank (with the radar and the autopilot). The fix was something like a 1/4 turn on the screw. Lesson learned: Check those cable and wire connections to make sure the screws are tight.

Phil: the original title seems to have disappeared.

 

[Head Sail]

Thanks John. Loose connection seems to be the consensus so far. This is the second time this has happened at the same location so I suspect the problem may be other than a loose connection. The first time I spliced in a new wire. This time I replaced the breaker and wire.

 

[uncledom]

During a weeklong cruise in the chili Pacific Northwest where my 30amp system was taxed creating hot water running an electric heater and occasional hair dryer I noticed the neutral wire leading out of the main 30amp Blue Sea breaker was getting hot enough to melt insulation on the 12AWG wire in the proximity of the connection to the beaker. The neutral coming in and both hot wires showed no signs of getting hot. Should not the main breaker have tripped before the insulation started to melt?

HS for starters a 30 amp circuit should be carried on no less than 10 awg wire. If it were larger wire which is a smaller number, ie 8 or 6 that would be ok. 12 gauge wire is only rated for 20 amps. Make sure of the size.

 

[kloudie1]

About every 5-6 years, I think about tightening mine.. The ones on the air conditioner seem to get loose more often than the others. The high ampere looads seem to loosen more than the low amp loads do.. I don't have 'em on a schedule, I always check/tighten if I open the breaker panel for any reason.

 

[woodster]

HS for starters a 30 amp circuit should be carried on no less than 10 awg wire. If it were larger wire which is a smaller number, ie 8 or 6 that would be ok. 12 gauge wire is only rated for 20 amps. Make sure of the size.

absolutely correct

 

[Maine Sail]

#1 12GA wire is not correct for a 30A AC system.

#2 No 30A shore power system on a boat should be loaded at more than 80% of its rating but preferably never more than 20A unless you want to burn your boat. This is especially true if you have "twist-lock" shore power cords and sockets. Even when brand new 24-25A should be max as the boat ages 18-20A max.

Rx; Turn off water heater when using hair dryer & check, clean all tighten all terminations..

 

[Stu Jackson]

Rx; Turn off water heater ...

All the time except for the 15-20 mins you're heating the water.

 

[Bill Roosa]

try blue (not red) locktight on the bolts/nuts (a tiny amount is all that is needed)nand a generous mitten-full of battery terminal protector spray. Be sure you have a good electrical connection that does not rely on the bolt/nut threads as the locktight will not conduct.

 

[Marc14857]

Hot Water Breaker

I posted this about 2 years ago.

DJust wanted to share this weekend's close call with shorepower AC connection. We were onboard tied up to the slip with a single 30 Amp Shorepower line coming into the boat. We had the water heater powered up all day as well as the battery/inverter with no apparent problems. Both of these are on AC Line 1. We started the microwave on the same bus to heat some water up (done this many times before) and while the microwave did run we started to smell that acrid odor indicative of something electrical burning. No breakers tripped but I did manually trip the main AC breaker onboard. Opened up the AC distribution panel at the Nav station and while I did not see any smoke the acrid smell was definately coming from behind the panel and there was definately some fairly significant heat coming from behind the panel. We let everything vent and air out and didn't see any apparent wire damage though did not have a great view of all the wires under the bundle. Thinking that the problem was limited to the microwave circuit, we reennergized the AC distribution panel powered up the battery/inverter and hot water heater with no apparent problem. We left the microwave deenergized and was planning on having the yard look it over the next day. Next morning some dockmates came over and we deceided to do some trouble shooting. We opened up the AC panel which was live and switched on the microwave with no discernable problem. When the microwave actually started however we saw sparks flying somewhere underneeth the wiring bundle in the vicinity of the neutral busbar on the AC distribution panel. Turned the microwave off and the sparking stopped. Started to remove some wires to get a clearer view of what was sparking which turned out to be unrelated to the microwave. Apparently there is a larger gauge white neutral wire that is the neutral return from the AC distribution panel busbar for all the circuits that had become loose and was arching whenever the load on the bus increased above a certain threshold. It must have been going on for quite some time as the wire was severly burned as well as some of the neighboring wires. We also found some other terminations to the busbar that had become loose over time. Had the yard replace the burned terminations and tighten up all the connections and everything is fine now.

I suspect that no one ever checks the electrical terminations on the backside of their AC distribution panels and just opening up the panel may cause some wires to become loose. Not sure what if anything to recommend here but wanted you all to perhaps tuck this away somewhere in case you are inclined to check the terminations or ever are in the position where you have that acrid electrical smell on your boat.


ShareThis