Paralleling circuit breakers

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dacflyer
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Paralleling circuit breakers

Post by dacflyer » Fri Jul 24, 2020 1:01 pm

I have seen fuses doubled up to get higher amperage.. mostly used on Inverters and car Amps.
is it a must that the paralleled fuses or breakers be same values, or can they be different..
Example if i need a 65A breaker, Can a 50A and 15A be paralleled to make 65A ? same situation with a circuit breaker. or will 1 trip before the other?
I'm just thinking of my resistor knowledge...

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Re: Paralleling circuit breakers

Post by dyarker » Fri Jul 24, 2020 1:17 pm

The resistances of the breakers is not directly related to current ratings. So, for example, with a 60A load the 15A breaker may pass 20A. The 15A breaker will trip. That leaves the 50A breaker with the whole 60A, it will trip too.

Equal rating, same part number breakers will share the load more evenly.

If this is for AC mains power, I do not think UL allows doubled up breakers.

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Re: Paralleling circuit breakers

Post by jwax » Fri Jul 24, 2020 6:00 pm

I had a vehicle winch that came with three paralleled 50 Amp breakers. If they were of different values, no I don't think they would just add up. The lowest rated would blow first, then the other.

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Re: Paralleling circuit breakers

Post by dacflyer » Fri Jul 24, 2020 8:28 pm

Ya, ok,, i thought so...

Ok,, now another question..
I'm looking at some ANL type fuses..
From what I find, they are only good for 32V , but i see the holders are rated for 48V... so how do i find 48V rated fuses ?
I'm looking at this for my solar project. Would putting 2 100A in series work ?
I want to make sure i have something safe so that there is no sustained arc if the fuse happens to blow.
I contacted the maker of the inverter that recommended the fuse type.
I questioned this, and they said that their fuses are designed for 48V. Isn't there an industry standard for fuses ?

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Re: Paralleling circuit breakers

Post by dacflyer » Fri Jul 24, 2020 8:35 pm

Never mind... After a few hours I finally found something to use..

https://www.littelfuse.com/products/fus ... _5701.aspx
special made fuses...

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Re: Paralleling circuit breakers

Post by haklesup » Mon Jul 27, 2020 2:05 pm

its always better to use one protection device, they aren't resistors and one should not design like they are in a resistive network. Breakers cannot be used in parallel unless the datasheet for it indicates that it is allowed. Placing them in series is no better than having only one. As you indicated, sometimes manufacturers get away with it with fuses but I still feel it is a poor design practice

The voltage rating on the fuse is more related to the construction and spacing of the electrodes to guarantee there will never be arc over after it blows. The size of the fuse is probably based on an industry specification so holders and fuses of matching size should match voltage rating for the most part. Of course current is the working variable but so is the time to blow chart.

Glad you found a fuse form you can use, these days there should be a wide range of choices. One could debate when a breaker is better than a fuse, there are various factors that may direct the choice. I think for battery systems, fuses near the cells and breakers near the main output make sense. The virtue of a fuse is that it disables the equipment until a more invasive look is made, users can reset breakers too easily while ignoring the root cause of the fault.

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Re: Paralleling circuit breakers

Post by dacflyer » Mon Jul 27, 2020 5:07 pm

Right... and with my solar project, i want everything to be right..
i'll be fusing the solar input , fuses at the combiner box on the roof and where it is on my wall before it goes into my solar charge controller
and the inverter input will also be fused.
and fuses for each battery string.

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Re: Paralleling circuit breakers

Post by haklesup » Tue Jul 28, 2020 11:53 am

Sounds good, Fuses anywhere a hardware failure could cause high current. Breakers anywhere the load could overburden the source system, that's technically not a failure, more of an application problem.

That addresses overcurrent, you should also monitor battery temperature if you want to maximize life of the pack. The inverter and charge controller probably have internal thermal protection, the charge controller may have external thermal protection inputs. You can do that passively with thermal fuses or actively with a more complex setup. Are you using lead acid or something else?

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Re: Paralleling circuit breakers

Post by dacflyer » Tue Jul 28, 2020 12:31 pm

I am still searching for a multi point temp sensor module..
I am using Li-ion pack from BMW.
I'll have 6 strings of 14s ( 14s6p) should yield me about 660AH Not sure i'll be able to use them all, but the BMW was a 96s pack,, several 3s, 4s, and 5s packs. What ever i can't use, i'll probably resell, or buy more solar panels.
I have a nice AIMS Inverter/charger 2Kw with 6Kw surge good for 20 seconds,
Also have a Epever solar charge controller.

I also acquired 6 other BMW batteries, i think they came out of an i3 or an i8 hybrid, but the packs are about almost 60v 16s1p config,, i'll be selling them.. no use to me, but they have value.. sell em and then buy more stuff for projects.

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Re: Paralleling circuit breakers

Post by Joseph » Tue Jul 28, 2020 7:22 pm

Something that could allow effective paralleling of circuit breakers is seperate wiring for each breaker. The key to best current sharing would be to make the gauges of wires in each breaker's circuit the minimum size you can use.

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Re: Paralleling circuit breakers

Post by dyarker » Tue Jul 28, 2020 7:33 pm

Nonsense, he said non equal current rated breakers.

And even if they were equal breakers, and the wires were just large enough not to overheat, they are not a load balance resistor.
Dale Y

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Re: Paralleling circuit breakers

Post by Joseph » Wed Jul 29, 2020 1:13 pm

Oh I thought the breakers were equal. I was only considering it for equal breakers and the following would only apply if the beakers have the same trip rating.

So if the wires were minimum acceptable size, and the breakers have the same rating, as they carry current closer to the breaker trip point their resistance would increase a lot, and themselves would act as resistors in series with the breakers. Their resistances would doninate in the series resistance that is composed of a breaker and the wire in series with it. So yes they would act as load balancing resistors if the breakers are the same.

I'm done here.

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Re: Paralleling circuit breakers

Post by Lenp » Wed Jul 29, 2020 6:17 pm

Here's my take on this discussion!

First, about wire. We consider wire size based on the current anticipated in the circuit, or the guidance from approved codes. For example, it is common that 14 AWG copper wire is used for 15 amp household circuits. Why? will the wire explode at 16 Amps? No. Will it catch fire at 17 Amps? No. Look up the fusing current of #14 AWG copper wire..It is 166 Amps! That's the point where the wire will melt and interrupt the circuit. The reason that a maximum of 15 Amps is used for #14 gauge wire is that wire is a resistor, which has a voltage drop.
At at the end of the wire, under a full load, the voltage drop must not be excessive. A 250 foot run of #14 AWG wire (2 wires going 125 feet) with a 15 amp load may have a 30% voltage drop at the end! That means 80 volts...NOT 120 Volts is delivered.
Many appliances have a much smaller gauge wire internally than the supply cable. That's because the manufacturer controls the length of the wire, knows the current and is not too concerned about voltage drop because most internal wiring is short. The fusing current would be more important, and a small gauge wire still has a surprisingly high fusing current. I've see PCB's with a small wire jumper as a fuse. A #30 wire jumper has a fusing current of around 10A!

Any over current device is used because it is supposed to be the weakest link in the wiring system, to protect the connected load, wiring, components from an overload condition and possible fire. Usually, operation of an overload device indicates abnormal operation or failure.

There are considerable differences between fuses and breakers. The are fast blow and time delay blow fuses. Inside a fusible link opens at a certain current, or in the case of a time delay , temperature, to interrupt the flow of electricity. A simple fuse operates almost instantaneously and a time delay fuse takes a bit longer, so in effect, any wire can be a basic 'fuse'. If fuses are paralleled, they may carry more current but what about the wire? All that additional current capacity may easily exceed the capacity of the wire and then It will become the fuse, right after it lets out the smoke and fire, and parallel fuses do not address the voltage drop issue. Parallel fuses are not precision voltage dividers, so one may carry more current than the other, so in a 20 Amp circuit, two parallel, 10 amp fusees, may not carry 10 amps each. Maybe 12 and 8 Amps. Wwho knows or can predict that easily.

It's a dangerous and unprofessional solution to parallel any over current protection devices, except under special circumstances, to solve any problem. Some people are of the impression that a fuse restricts the current and a bigger fuse pushes more current through. The load draws the current, it IS NOT pushed! These same people would also put a penny behind an old plug fuse since the fuse was 'weak', smoke in bed, and are known to say 'I've done this a hundred times before'! Pure nonsense. Right size wire, right size fuse or breaker, right answer. End of that story.

Like a fuse, a breaker also interrupts the current flow during an overload but it is more complex. Some breakers operate on the current creating heat, a magnetic field, or both that trips the circuit opening device. This feature allows a time delay factor so a load that draws a normally large starting load will not 'nuisance' trip the breaker. So the thermal effect provides a time delay, tolerant of the expected higher currents, and the magnetic feature provides quicker action for large overload. If the overall current increases over a longer time the heat accumulates and the thermal feature eventually opens the circuit. A high fault current causes the magnetic feature to more rapidly open the circuit. That is dual protection, for two characteristically different loads. Many industrial breakers are adjustable for the load's current to optimize the protection of the load.
Yes, circuit breakers are more convenient, and also serve a a more tamper proof disconnecting means, but are usually not the primary protection for solid state or fault intolerant circuits because their reaction time is much slower, by design, than a fuse. Some equipment manufacturers may require a circuit breaker at the distribution panel but a fused disconnect at the site of the machinery.
Just try to use the right protection for the load and don't cut corners since It's for your own protection as well.

Sorry for the long dialogue.
It's my 'Cabin Fever Psychosis' :eek:
Len

“To invent, you need a good imagination and a big pile of junk.” (T. Edison)
"I must be on the way to success since I already have the junk". (Me)

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Re: Paralleling circuit breakers

Post by dacflyer » Fri Jul 31, 2020 4:40 am

Boy!...Didn't think I'd open such a big can of worms.
it was mostly a curiosity question. i figured i knew my answer, but just wanted clarity of it.

As far as ANL type fuses, i'm still on the fence about voltage ratings. most say 32Vdc rating, and some say up to 80vdc.
I was looking for something i could use with my 48V system.
I finally did find the ones I wanted, from Littlefuse.com
But I would have thought that 1 type of fuse would have just 1 voltage rating for it's type.
DC power is easier to create an arc than AC, especially with solar and batteries.

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