combining electrical breakers

[Georgesalmon]

OK, some background: I restored a boat last winter and of course did a major rewiring. Everything new and protected with breakers.

I have found only one problem; when I try and trim the engine at speed I blow a 20amp breaker, works fine on the trailer or idling in the water. Did some research and found the 20amp is not big enough I should have a 40amp breaker. Over the years I have acquired a box of 12vdc breakers from 3amp to 20amp nothing bigger. Here comes the dumb question:

Is there any way to use two breakers in either series or parallel to get a higher rating? I'll buy a 40amp breaker if I have to but I have looked and can't find one that matches all my other ones. I know it sounds silly but it would be really nice to have everything match. I suspect that I can't make this work but it would be really nice if I could.



The pictures show a couple of my power panels that have yet to be painted.

 

[Don S]

Re: combining electrical breakers

What are you trimming? Small outboard? IO?

 

[Georgesalmon]

Re: combining electrical breakers

old 1979 1/2, 115 inline 6. external trim pump.

 

[Don S]

Re: combining electrical breakers

Merc ????????

 

[Georgesalmon]

Re: combining electrical breakers

Duhhhhhhhhhh, yeah, sorry Don, its a merc, slapping myself for not including that little bit of important info.

 

[Silvertip]

Re: combining electrical breakers

You need one 40 amp breaker. Electricity doesn't care what breakers or fuses look like.

 

[Georgesalmon]

Re: combining electrical breakers

Yeah, I guess I knew that, just wanted to work with what I had and somehow combine two 20amp breakes to be electrically the same as one 40amp breaker. I know I can add resisters and capaciters in parallel and series to come up with a new rating. Like R1 + R2 + R3 in series = the total or one over R1 + R2 in parallel. Oh well.

 

[Grandad]

Re: combining electrical breakers

Is there any way to use two breakers in either series or parallel to get a higher rating? I'll buy a 40amp breaker if I have to but I have looked and can't find one that matches all my other ones. I know it sounds silly but it would be really nice to have everything match. I suspect that I can't make this work but it would be really nice if I could.

Hey George, there's no way to double up your two 20 amp breakers. In series, they'll still trip at 20 amps, the "weaker" one first. Theoretically in parallel, precisely matched breakers with interconnections exactly matched for resistance would share up to 20 amps each for a total of 40 amps, but I think the independent trip curve characteristics of each breaker will cause you unpredictable nuisance tripping. You might also run into some dangerous overheating issues at the terminals as any slight imbalance between the load shared between 2 breakers could have one breaker running hot at continuous full load, while the other gets off easy carrying the remaining balance.
- Grandad

 

[UncleWillie]

Re: combining electrical breakers

Yeah, I guess I knew that, just wanted to work with what I had and somehow combine two 20amp breakers to be electrically the same as one 40amp breaker. I know I can add resisters and capacitors in parallel and series to come up with a new rating. Like R1 + R2 + R3 in series = the total or one over R1 + R2 in parallel. Oh well.

Your logic is sound except that with a breaker that is "ON", R= Zero!

This is Not actually correct but it illustrates the concept.
Breakers in series buys you nothing. 0+0=0
Breakers in Parallel is undetermined. 1/(0+0)= Division by Zero = Undetermined

Breakers have some very small resistance, but if the breakers and the associated wiring are not EXACTLY Equal, down to the micro-Ohm, the current will divide unequally.
You start with 30 amps flowing in the system. 21 amps goes through one and 9 through the other.
The first breaker trips on the 20+ amps. All 30 amps divert to the other breaker and it trips also.

 

[Georgesalmon]

Re: combining electrical breakers

guess i'm buying a 40 amp breaker. thanks all

 

[gm280]

Re: combining electrical breakers

guess i'm buying a 40 amp breaker. thanks all

After reading the problem, question and replies, yes buy the correct breaker and your problem and peace of mind will be solved. Unlike electronic components, fuses and circuit breakers don't add or subtract or combine like any of those parts for this simple situation. Without getting into needless explanation of closed circuit contact resistances and micro-ohm situations, let’s for the sake of conversation just say it doesn’t work that way. “UncleWillie” gave a quite good and quick explanation and an equally good example, and I completely concur with his suggestion as well. So a simple 40 amp breaker IS your only serious and correct choice...