Combining 2 fused power supply circuits in parallel

Thread Starter

bsellers89

Joined Dec 28, 2018
5
In my motorhome, I am wiring an inverter. A convenient spot to mount the inverter places it near 2 power supply lines from 2 circuit breakers, which I believe are 15 amp each. The gauge of the wire is small for the application - looks to be stranded 12 or 14 gauge.



Can I connect both power supply lines in parallel to the inverter for increased power when needed? Google searches show power supply redundancy to be suitable as long as the supply voltage is the same, so that the current is shared across both supply lines. In this case, the battery feeds equal voltage to both 15 amp breakers, so by summing the 2 15 amp circuits, do I in effect have a "thicker" power supply line to the inverter, capable of 30 amps?
 

crutschow

Joined Mar 14, 2008
25,120
The problem is that any slight difference in wire/connection resistance between the two circuits will cause more current to go through one of the paths.
When that current exceeds 15A it will trip the breaker, dumping all the load to the other breaker, which will then also trip.

But you could try it and see how it works. There's no danger to doing that.
 

Thread Starter

bsellers89

Joined Dec 28, 2018
5
Very good point - the differing resistance of the paths would not allow the paths to share the load. I suppose this is 2 15 amp lines, then!

Thank you very much for your reply
 

crutschow

Joined Mar 14, 2008
25,120
Here's a thought.
You could connect both sets of wires to one 30A breaker.
Even if there's a slight imbalance, it shouldn't be a problem.
If one wire starts carrying too much current it would heat up more than the other, which would cause its resistance to increase, reducing the imbalance.
But any load would need to be connected to both sets of wires.
 

ebp

Joined Feb 8, 2018
2,332
If the circuit breakers are adjacent, it may be possible to "gang" the handles to assure that if one trips both turn off. Some breakers have a hole through the handle so a pin can be inserted to tie two together (very common for AC mains breakers in North America, less common for DC breakers). A piece of stiff wire will do the job. If you did this and also connected the two breakers in electrical parallel, you would get very close to what crustschow suggested at very little expense (barring possible frustration trying to do the electrical paralleling).
 

crutschow

Joined Mar 14, 2008
25,120
If you did this and also connected the two breakers in electrical parallel, you would get very close to what crustschow suggested
But that wouldn't prevent a small imbalance in resistance causing one breaker to trip, (and thus both breakers) as I noted in post #2.
Better to run both sets of wires through one breaker.
 
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Thread Starter

bsellers89

Joined Dec 28, 2018
5
The double wire to a 30A breaker sounds best to me. It's like having a single large stranded wire, just separated down the middle. Thank you all for your input. Cool to learn about the handle-gang method as well. This forum is great
 
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