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    Solar DC question

    Hello all,
    We have a 175 Kw 1500Vdc string inverter. It has 12 mppt channels with 2 inputs each. Each channel (you can have 1 or 2 strings per "chanel") has 1 DC contactor for the positive and 2 DC contactors for the negatives.
    Does anyone know the specific UL requirements for this and where to find it? The requirement being referred to, I believe is breaking the negative twice in a DC circuit. I just cannot find the reference for that.

    I tried to attach a picture but was unable. Basically just shows the positive having one contactor and the negative having two.

    Thank you!

    #2
    Originally posted by Greenautomator View Post
    Hello all,
    We have a 175 Kw 1500Vdc string inverter. It has 12 mppt channels with 2 inputs each. Each channel (you can have 1 or 2 strings per "chanel") has 1 DC contactor for the positive and 2 DC contactors for the negatives.
    Does anyone know the specific UL requirements for this and where to find it? The requirement being referred to, I believe is breaking the negative twice in a DC circuit. I just cannot find the reference for that.

    I tried to attach a picture but was unable. Basically just shows the positive having one contactor and the negative having two.

    Thank you!
    It might be a three-pole contactor. They are more common than two-pole. It's something we have done. To break DC you need quite a lot more clearance than on AC. Placing the contacts in series is one way of doing this.

    I'm from across the pond. We don't normally have to be UL compliant so I can't comment on that.

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      #3
      There is no UL requirement to have two poles in a DC circuit but many manufacturers have to have two poles to get the disconnect to pass the UL listing for use in DC circuits. It's just harder to break the arc in a DC circuit and it's cheaper to have two poles than to have an expensive arc extinguishing system and one pole.

      Comment


        #4
        Originally posted by pv_n00b View Post
        There is no UL requirement to have two poles in a DC circuit but many manufacturers have to have two poles to get the disconnect to pass the UL listing for use in DC circuits. It's just harder to break the arc in a DC circuit and it's cheaper to have two poles than to have an expensive arc extinguishing system and one pole.
        And in some cases getting the required DC voltage rating will require 3 contacts in series. No reason not to split them between + and - if you are not worried about manually breaking a ground fault. No special reason (IMHO) to put the two contacts in the - side instead of the + side. I assume this is an ungrounded array?

        Comment


          #5
          Originally posted by GoldDigger View Post

          And in some cases getting the required DC voltage rating will require 3 contacts in series. No reason not to split them between + and - if you are not worried about manually breaking a ground fault. No special reason (IMHO) to put the two contacts in the - side instead of the + side. I assume this is an ungrounded array?
          You can get two-pole DC rated contactors. We made a lot of DC variable speed drives, mainly for paper making machines. Often DC contactors were specified by the old school customers. These DC contactors were "bar and shaft". Cumbersome beasts. And very expensive.

          https://www.schneider-electric.co.uk...e/667-tesys-b/

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