DC Breakers

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DC Breakers

Postby jimbo » Sat Jun 10, 2017 9:18 am

Solar output started dropping substantially and it turns out one of the DC breakers just b4 the charge controller kept tripping. I was away with work so called in a sparky and he said its just faulty and needs replacing EASY.
5 days later the breaker has still not been replaced. I rang the sparky and he said he had to order one in (50 amp double poll) I rang a few places and sure enough no one has them in stock around Ballarat. Why not? What do people use?
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Re: DC Breakers

Postby davidg » Sat Jun 10, 2017 9:21 am

jimbo wrote:Solar output started dropping substantially and it turns out one of the DC breakers just b4 the charge controller kept tripping. I was away with work so called in a sparky and he said its just faulty and needs replacing EASY.

Is it one directly on a string or ?? and what's the peak voltage or VOC it has to handle?
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Re: DC Breakers

Postby jimbo » Sat Jun 10, 2017 9:42 am

Not sure what you meant by first question "directly on string" There are breakers on the roof and then breakers next to the charge controller. My system is only 24v and panels are wired in parallel.
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Re: DC Breakers

Postby Gordon-Loomberah » Sat Jun 10, 2017 10:00 am

What is Isc of the panel array connected to the breaker? Perhaps it could be high current due to cold weather and bright sun+cloud edge effect?
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Re: DC Breakers

Postby jimbo » Sat Jun 10, 2017 10:11 am

Can't remember off the top of my head (i'm not there) but i think its a fair bit under the rating and it has been doing it outside those conditions.

So why don't people stock DC breakers?
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Re: DC Breakers

Postby davidg » Sat Jun 10, 2017 7:26 pm

jimbo wrote:So why don't people stock DC breakers?

Because they don't use them generally. Grid systems or AC coupled are typically long strings of higher voltages and generally only single run strings. These don't require CB's at all, their a current limited source that will not cause the wire insulation to melt just run a bit warm in a worst case scenario so not required. There simply is not enough current to get them to trip.

However for 48Vdc you can use ABB CB's or the Teraski series from NHP they are both rated for DC as single pole CB's if using 2 poles connected together then twice that and so on.
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Re: DC Breakers

Postby Warpspeed » Tue Jun 20, 2017 1:11 pm

That is an interesting point, and quite correct.

A solar panel is a current source, and it has a maximum rated short circuit current which can never be exceeded. So its impossible to fry the wiring from an overload or a short. That is the usual function of a fuse or a circuit breaker, to protect wiring.

The main purpose of a circuit breaker for a solar installation is to isolate the panels from the system for maintenance purposes, especially for electrical safety reasons for higher voltage arrays.

Now if you use just a straight switch, or an AC breaker in a high voltage dc system, it will arc over if you try to open the circuit under load. This can quickly destroy the switch or breaker, even melt down the breaker and start a fire.
DC breakers are much safer, because they usually have special provisions for extinguishing dc arcs.
Maybe vacuum contacts, or magnets to blow out the arc, a feature ac breakers do not have.

Many people laugh at all this and say its crap, they have been using ac breakers for years in their 48v system without any trouble. Sure, no problem at 48v.

But if you have a grid tie system that works at 200v or 450v you are going to have problems with dc arcing for certain.

Most electrical suppliers do not carry dc breakers, they are a specialist item with very low demand.

There are some 63 amp dc breakers on e-bay that I have used successfully on a 250 to 300v dc system.
And yes I found out all this the hard way after burning down several ac breakers.

http://www.ebay.com.au/itm/63A-DC-2P-250V-C65H-DC-Circuit-Breaker-MCB-PV-Solar-Energy-Air-Switch/281750604673?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649
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