Replacing ganged DC breakers

[Corvidae]

In the midst of a fairly aggressive electrical refit and I've been kind of stumped by the breaker set up. The original panel has 3 60amp breakers connected, in parallel, to a bus bar for the house DC circuit. And for the life of me, I'm not really sure what amperage breaker to replace them with to match the original sizing with a single breaker. The simple answer is a 60amp breaker, but a parallel circuit like that should be able to handle 180 amps, except there's no way the power would be distributed evenly so the actual rating would be far lower, but I'm not sure how much lower.

Any suggestions?

[smac999]

the problem is you won't find a 180a breaker that fits in a standard DC panel. that is why they put 3 in parallel.

IE the blueseas A series goes to 50a and the C series goes to 100a. above that they sell them as 2 or 3 pole ganged breakers.

that seems way too high for a DC panel. windlass and other high loads should have own feeds / fuses. and a panel really should not have that kind of draw on it.

[Jammer]

Originally Posted by Corvidae

In the midst of a fairly aggressive electrical refit and I've been kind of stumped by the breaker set up. The original panel has 3 60amp breakers connected, in parallel, to a bus bar for the house DC circuit. And for the life of me, I'm not really sure what amperage breaker to replace them with to match the original sizing with a single breaker. The simple answer is a 60amp breaker, but a parallel circuit like that should be able to handle 180 amps, except there's no way the power would be distributed evenly so the actual rating would be far lower, but I'm not sure how much lower.

Any suggestions?

The parallel breakers for high loads are sold as a set of two or three breakers, with a rated trip current at 2x or 3x the rating of individual breakers. You can take a look at the Blue Sea Systems catalog to see for yourself. The idea is that the very small internal resistance of each breaker, combined with a low-resistance busbar connecting them, is enough to ensure that the current flow is even amongst them. Since they will all trip if one trips, any uneven distribution of current would serve to cause them to trip earlier.


So, in your situation, a 180 amp breaker would be a suitable replacement. DC breakers in that size are uncommon, at least in a configuration that will fit a standard panel along with other breakers, but are available for freeform mounting. Depending on the nature of the load, you may also be able to use a fuse, which would be cheaper and less likely to fail closed.

[Dulcesuenos]

Dealing with bad breakers on a customers cat. At first glance it looked like 3x30 amp breakers with single switch, in actuality it was 2 30 amp breakers and one 65 Volt breaker all tied together as one, the 65 Volt breaker to protect against incorrect / faulty shore power wiring, also there is a special motor start delay built into the breakers.

[Corvidae]

My plan is to remove the entire panel. So a surface mount breaker would work just fine. Thank you all for the info.

[billknny]

Originally Posted by Corvidae

My plan is to remove the entire panel. So a surface mount breaker would work just fine. Thank you all for the info.

Don't forget, when changing the size of the breaker to be sure that you match it to the wire that it is protecting.

If sized properly, the 60AMP breakers could have been connected with wire as small as AWG 10. If you bump to a 180 Amp breaker or fuse you'll need to go to at least an AWG 2--or larger depending on the physical setup.

[Corvidae]

The wire on both sides is 4/0, it's the main feeder wire to the DC panel. The panel it's in is going to go away. Because it's the housing for the ac transfer switch, that's been replaced elsewhere, the battery charger transfer switch that's been replaced elsewhere, the generator control circuits for a generator that is no longer there, and the electrical harnesses for the two diesel engines that are no longer there.

At the moment, the only thing still active in the 2' by 2' panel is the main breaker for the AC and DC circuits. Which I plan on putting in a much, much smaller enclosure.

[stormalong]

Originally Posted by Dulcesuenos

Dealing with bad breakers on a customers cat. At first glance it looked like 3x30 amp breakers with single switch, in actuality it was 2 30 amp breakers and one 65 Volt breaker all tied together as one, the 65 Volt breaker to protect against incorrect / faulty shore power wiring, also there is a special motor start delay built into the breakers.

Your OP says DC and this post says it is for the AC circuit. The C/B you describe in your second post is typical for an A/C mains circuit.

If you cannot tell the difference you need to bring in a professional.

[Dulcesuenos]

Originally Posted by stormalong

Your OP says DC and this post says it is for the AC circuit. The C/B you describe in your second post is typical for an A/C mains circuit.

If you cannot tell the difference you need to bring in a professional.

Thanks for catching that, for some reason I thought the post said AC I hadn't had my coffee yet[emoji12]
Clearly I knew I, was speaking about AC breakers, unless for some reason you've seen shore power in DC

[Cadence]

The hole post is confusing, AC or DC The OP sounded like DC then one came in that was a post of AC.

[james247]

Originally Posted by smac999

the problem is you won't find a 180a breaker that fits in a standard DC panel. that is why they put 3 in parallel.

IE the blueseas A series goes to 50a and the C series goes to 100a. above that they sell them as 2 or 3 pole ganged breakers.

that seems way too high for a DC panel. windlass and other high loads should have own feeds / fuses. and a panel really should not have that kind of draw on it.

I agree can't see why you could possibly need 3 times 60 you can weld with that amperage - and that's undesirable

[stormalong]

Originally Posted by james247

I agree can't see why you could possibly need 3 times 60 you can weld with that amperage - and that's undesirable

Read responses eight and nine.

[Corvidae]

Just to clarify, it's a DC circuit. As to why it's so large of a circuit, my guess is that you could conceivably be starting both motors, and the generator, while the radar and refrigerator was on, the davit winch was lifting the outboard, and the windlass is raising the anchor. It's very unlikely, but if you're going to plan a circuit, you plan for full use. It's also a 40 year old boat, so adding up every incandescent light comes out to a decent load as well.

Honestly I may down size the circuit a bit. The windlass is the only big thing on it any more, and it draws less than 60. The starters are gone with the engines, and the generator is off on it's own now. The fridge is also running on 110 now, instead of the ancient 12v system that was in there.