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Weird Electrical Fault, 30a circuit breaker tripping with 12A and wire getting warm.

Jgrov2

Jgrov2

Member
Joined
Aug 6, 2020
Member Number
2554
Messages
22
Bit of a weird one but here's the setup. power runs to a 20A circuit breaker than through a relay into a connector into the intank fuel pump. The relay is controlled by the ecu relay via its secondary output which turns on with key set to on. The other day circuit breaker tripped twice. I measured the current draw and its only 12A at 13.4V. The wire going from the circuit breaker into the relay was hot to the touch as was the relay and the cable running to the pump but only near the relay end. I swapped in different breakers and a 30A breaker which didnt trip but still got pretty hot.

Im guessing its probably shitty contact on the terminals or wires frayed internally but everything looks and feels rock solid I even yanked on the bastards to try and loosen them and nothing. Ive switched out the relay and the new one still seems to be getting warm. Ive measured resistance all through the circuit and its pretty minimal so Im not sure whats causing the heat. Update, Ive forced and rammed everything together as a temp fix and so far so good only thing is the wire is getting hot and new relay gets warm. Im thinking of getting a new fuse and relay housing a rewiring it.
 
Lose connections get hot. I would imagine inside that wire there is damage, or the connection to the relay is dirty.

Just a guess. I think you are in the right spot though.
 
Voltage drop test the wire.
In case that doesn't make sense:
Hook up your voltmeter to both ends of the same wire, one lead at each end. In theory, this should show you 0V.
Put it "in service", run power through it.
Watch what the voltmeter does.
If the voltmeter shows >0.5V, you have a problem: that much voltage is being "consumed" by the wire. In general, a >10% voltage drop in the wiring of a circuit is bad news.
You can have a wire that will show good on resistance, but will fail a voltage drop test. Imagine a starter cable with 100 strands of wire. Can carry 400 amps, no problem. Now cut away 85 of those strands. Resistance still shows good, 15 strands out of 100 will give you continuity. But put a load to it, and you'll see a big voltage drop. You can voltage drop test connections, wires, etc., you're just looking for the difference in voltage from one side of "suspect part" to the other side, if you find voltage drop, move your leads closer together along the circuit until you narrow it down to the problem item.
 
sounds like your relay is not rated for what you want it to do. what guage wire are you running? whats the rated amp draw on the pump?

i hate relays
 
relay is rated for 40 Amps, pump draw is 12A and the graph shows it should be between 10-14A depending on voltage and load. The wire gauge is AWG 6 power feed to a bussed bar inside fuse box and AWG 12 to relay and on to pump. I have noticed the power windows are more reliable since I rammed the connections home and they are on the bussed fuse block...
 
Relays create heat when the magnet is pulling the contacts closed via electric magnet. Is the circuit breaker and relay located under the hood?
 
no they are in the cab on the side of the passenger foot well. This relay gets significantly hotter than the other two with it and seems to be regardless if i swap the relays over etc. Im starting to think there maybe a loose connection in the bussbar or power feed into. That seems to be where the heat originates.
 
Jgrov2 said:
relay is rated for 40 Amps, pump draw is 12A and the graph shows it should be between 10-14A depending on voltage and load. The wire gauge is AWG 6 power feed to a bussed bar inside fuse box and AWG 12 to relay and on to pump. I have noticed the power windows are more reliable since I rammed the connections home and they are on the bussed fuse block...
Click to expand...

got a link to the cut sheet or make and model?
 
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