DC Breaker in AC Circuit

Well, surely the best people to ask are those that manufacture it? The 'phone number is on the webpage.

I highly doubt they are the manufacturer of that circuit breaker, but thank you for your insight

Never use a DC breaker for AC, unless it is dual rated.

Do you have an explanation as to why this is? Or some reference I can look at explaining so?

The breaker serves as the circuit interrupting mechanism specifically during fault conditions.

Unlike AC fault current that cycles from zero to maximum magnitude in the positive and negative quadrant with the voltage; DC voltage is of constant magnitude which causes the DC fault current to be more of a steady state and therefore is not ever reduced by the system.

DC fault current is only limited by the maximum current available by equipment design limitations.

Therefore the resultant arc flash that occurs during a DC circuit fault is much harder to control and extinguish.

This means a circuit breaker that is used in a DC circuit of the same amperage rating as in an AC circuit must be capable of opening extremely more current and much faster than when used exclusively in an AC circuit.

The size of the contact surfaces are normally larger, the speed of contact opening is higher/faster, and the arc extinguishing components of the breaker contact must be larger and/or have more diffusing fins.

All major manufacturers of circuit breakers provide information and training on breaker application and operation that is normally free of charge.

Blue Sea makes both AC and DC breakers

I'm not trying to get caught up in the technicality of what this website offers. I was merely providing a visual example of the circuit breaker I am looking for that would operate in the 175 amp range for AC. A lot of what I have found it not the same form factor as this one.

My main question really revolves around the use of DC circuit breakers in AC circuits without any regard for what the breaker looks like or who sells it.

Don't do it. AC breakers must be de-rated to 1/5 the power if used in a DC circuit.

What does your code say? Don't know the code? Then stop right now and hire an electrician to keep you out of trouble.

The house you save, may be your own.

Thank you for the info lyn, but again where is this documented?

How about checking the NEC.

You'll find it all there.

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In the overcurrent section pertaining to circuit breakers of the NEC 240.80 and beyond I don't see anything regarding 1/5 power rating of the breaker. Please forgive me I am not fully familiar with all the ins and outs of the NEC. Perhaps I am looking in the wrong location?

How did the phone call to the breaker manufacturer go?

They just referred me to a different AC breaker that wasnt high enough amperage because they didn't have an answer for me.

So what is the next step towards a result?

Lyn, actually it's the other way around, interrupting duty is much more severe for DC because there's no zero crossing to extinguish the arc every half cycle, hence the need for big arc chutes, magnetic blow-out coils, etc. to quench the arc. None dual-rated breakers go by the 20% of AC rating rule of thumb, dual-rated are often 50% of the AC rating. But it's still a good idea to use the breaker matched to the duty to which it wil be exposed, so using a 12 VDC breaker on a 120 VAC circuit would always be a bad idea, even if the current rating is the same.

I thought that was what I said. Oh well.

It was...

DC rated breakers generally do just fine in an AC application.

What exactly are you wanting to use this for and what voltages are you working with?

I would have an AC input coming into a box and wanted to run it through a switched breaker and then it goes to a contactor that is controlled by a PLC. Now if i see the current get above 130A I would open the contactor. The switched breaker I wanted as a second layer of safety as well as a physical disconnect of the AC input. It would be 120 60Hz voltage also.

I should probably also state that this is really experimental not anything I intend to install in any location so NEC considerations aren't necessarily something I am concerned with conforming to.

Given the 120 VAC power source I doubt that would be a problem for the breaker to deal with

Also being that you are not planning to go above 130 amps peak you could also use most any common 150 amp home breaker box main breaker as well.

Take your pick. Menards. Main breakers. $45 - $90 for ones rated in the ranges you are looking for and they can be found at most every home building supply center.

The issue I have with those Menards breakers is that they are not a panel mount. The one I originally posted can be mounted to a panel so that the switch is on one side and the body is separated if that makes sense.

A little epoxy and some brackets and they become panel mount breakers without problems.

Haha true I found some larger size ones from carling was just hoping to not get one thy big

There are some DC breakers which use permanent magnet blowouts. These may be polarised, ie, sensitive to +ve and -ve connections. Obviously, these are not suitable for AC application. All other types of DC breakers should be ok. Though, why would one use a more expensive, more elaborate (with blowouts etc) DC breaker when AC breakers are ubiquitous...

I wouldn't use a more expensive elaborate DC breaker because I dont want to spend a fortune. The form factor from my initial post was the style and mounting type of breaker I wanted which is not easy to find at 150 or 175AAC. They all cap out at 100 for that style. All the other common breakers that size are made for rear mounting into a house panel. I was hoping to find something that would let me cut a hole and panel mount from the from without any Jerry rigging as suggested in another post

Generally speaking, DC breakers need to be sturdier, as a DC arc is more difficult to extinguish. For a non-type approved application: If the peak voltage and peak current is within spec., it will work right in AC.

Jxm1092

You might look at a Square-D QDL22175 breaker. It's 3" wide, 2-pole, lug-lug and might be mounted to the cover of your enclosure after wiring the lugs. Generally, applying AC breakers on DC is a problem, as others have said, due to the lack of a zero crossing of the voltage to assist in arc extinguishing. Therefore, many manufacturers have a limit to the applied voltage for AC breakers on DC circuits or require wiring them with the contacts in series. The opposite application is less of a problem. You will learn a lot when you work on a development project--have fun but be safe.

--JMM