DC Breaker : 1Pole vs 2Pole

ChanChan Registered Users Posts: 45 ✭✭
I was wondering how does a 1pole DC breaker compare with a 2pole DC Breaker?

I have a few 1pole dc breaker, and comparing it to 2pole, the 1pole only has top + and - bottom... now if I use the 1pole via my solar pv wiring... can I use the FIRST(POSITIVE) wire 1pole on the POSITIVE and the other 1pole Second(NEGATIVE) wire as my second dc breaker...

attached is the i

Comments

  • BB.BB. Super Moderators, Administrators Posts: 30,634 admin
    OK... The answer is a bit more complicated.

    First, is your DC battery bus grounded? If so, then you really do not need a two pole switch to turn off your solar array. The grounding of the battery bank (bonding the negative battery terminal to ground rod/cold water pipe/rest of building's green wire grounding) is done so that you only need a single pole breaker (or fuse) on the + wiring from battery bus (you cannot get a high current short circuit between negative and ground as an example).

    Next, if you use a pair of breakers on a circuit (a common requirement for floating power systems), you should have the two handles tied together (pin through the holes in the handles or a clip that connects the two handles). That way, if a one side of the circuit trips, the other breaker is tripped too.

    Your circuit breakers appear to be polarized. If you high short circuit current is expected to come from the solar array, then the wiring for the "red" breaker should be reversed. right now, if the red breaker is turned off, the current through the breaker is reversed and can cause the breaker to fail from arcing.

    Is this for a Grid Tied solar power system or an Off Grid solar power system? If this is a Grid tied inverter system, you generally do not need any circuit breakers on the input to the inverter--Unless you want a convient on/off switch. Otherwise, you could just use a properly rated knife switch.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ChanChan Registered Users Posts: 45 ✭✭
    The manual state that a DC breaker is a must along with a SPD to protect the INVERTER from LIGHTNING SURGES. - GRID TIE setup.

    What I am confuse about is that, since the + is only connected to the BREAKER, my SPD  has a + and - ....  also, will touching either of the + or the - side of the PV causes electric shock?
  • BB.BB. Super Moderators, Administrators Posts: 30,634 admin
    I would guess that, if you have a DC SPD, that you will have three wires. +/- from the battery/array and a green wire to go to ground.

    In theory, Array->breakers->SPD->Panel input to GT inverter would work like this. If you get a surge, it goes to the SPD which shunts the excess current/voltage to ground, which (if enough current and long enough time, will trip the breakers).

    Remembering that the lightning strike just took a 3 mile path through the air to get to your array, a 1/2 inch gap in a circuit breaker is not really going to slow down the energy from a direct strike.

    In any case, you asked another question--Can you get a shock from the solar array + and - connections. Depends on a lot of conditions... If the voltage is under 12 volts, not usually. If the voltage is 12-60 volts (depending on which section of code you are complying with), you can get a shock. And over 60 volts is considered hazardous.

    There is also the fact you need two connections to get a shock. Obvioulsy, if you have a Vmp-array of 300 VDC, touching + and - from the array will give you a shock (or worse).

    But there is the other hazard--You touch ground and + or - wiring. That, to a degree, depends on the wiring of the GT inverter. Older inverters would ground the negative wire to green wire safety ground. But that is not required (and in some cases, there is a small fuse/breaker in the white to green wire connection to detect earth faults). It would normally be expected that you would get a shock from + to earth and no shock from - to earth (that earth ground). However, with a DC Ground fault detection (that small fuse/breaker in the negative to green wire connection), a + to earth fault blows the ground bonding fuse/breaker, and now the negative wiring becomes "hot" (with respect to ground).

    The short answer is to assume that any wiring in a system of unknown condition can shock you until you have measured the potentials and prove otherwise.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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