Breaker AC to DC ???

System
System Posts: 2,511 admin
in General Solar Power Topics #1
Hi
I have a stock of breakers (10/20/30/40 ... A - 230vac). I thought to use them as PV-DC breakers in a connect-box.

Questions :
  • I don't know weither I could use them under VDC. Is it possible ?
  • Their voltage trip tolerancy would change. What could be the convert rates VAC to VDC depending of the voltage (12/24/48v) ?

Thks, Jacques


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Comments

  • System2
    System2 Posts: 6,290 admin
    #2
    Re: Breaker AC to DC ???

    What make and model are they?
    I've read on here that Square D makes breakers for AC that are also rated for DC, up to a max 24 or 48 VDC, can't remember which. I believe they are "QO" model.
    Wayne
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  • System2
    System2 Posts: 6,290 admin
    #3
    Re: Breaker AC to DC ???

    Hi
    brand MERLIN-GERIN from France. with rail DIN support. But all European Thermo breakers are egal
    jacques
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #4
    Re: Breaker AC to DC ???

    All things being equal--the voltage (AC or DC) will not affect the trip CURRENT of the breakers. It is the amount of current plus the time that will trip the breaker (rms-AC or DC will be the same). (by the way, RMS is Root Mean Square measurement for AC voltages and current--basically mathematically converts the AC sinusoidal wave form peaks and valleys into their DC equivalent energy).

    Two things that people typically forget about safety devices (breakers and fuses) is 1) DC current is harder to interupt than AC current (typically breakers and fuses, if DC rated, the same devices are rated at lower voltages than AC). And 2) breakers/fuses are rated to stop a certain amount of current (in the US, the typical home breakers are rated to interrupt 10,000 amps--because that is the maximum amount of current a pole transformer will output before it saturates).

    If you exceed the maximum interrupt current or rated voltage (AC or DC), you run the risk of the interrupting device not stopping the current flow (continuous arcing). A DC battery bank with with large copper busbars and wiring can easily exceed the max-interrupting current for many fuses and breakers if there was a dead short.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #5
    Re: Breaker AC to DC ???

    Bill,

    Your concerns about breakers and battery banks is well founded. However, Jacques is looking for breakers to use for his PV array. Nonetheless, here's a link to the maximum current rating specs for QO, QOB and QOU breakers.

    Jacques,

    You'll need to check with your European source for the DC specifications. Here in the U.S., Square D makes a line of commonly available AC breakers (i.e., QO, QOU) that are also good for up to 48 VDC. However, many of their AC breakers are not rated for DC use.

    HTH,
    Jim / crewzer
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  • System2
    System2 Posts: 6,290 admin
    #6
    Re: Breaker AC to DC ???

    Thks all
    Unfortunatly the stock i have is of AC breakers  :cry:... I have not yet found a such FAQ SQUARE-D, in European Manufacturer. I'll persever.
    The funny thing, is that, both Merlin-Gerin and Square-D are both subsidiary of a French Group SCHNEIDER.

    Bye Jacques
    By the way, is the problem different with FUSES ?
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