Breaking negative DC twice in disconnect

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.



Thank you!

Ok, I've looked through my copy of UL508A, there is nothing in it that even references the setup you currently have.

Are you sure that they are 3 separate contactors? I don't see any tag identification on the drawing.

Are you sure they aren't just utilizing 3 poles on 1 standard contractor? This is quite common with DC due to it being more difficult to quench an arc breaking DC current.

Rob,
Thank you for your reply and looking it up!

The inverter is an ABB PVS175 - US version. I tried putting in the link but it would not allow.

I think that they were referring to is UL 1699B, UL Standard for safety Photovoltaic DC Arc-Fault Circuit Protection. That reference is used in the technical documents of the inverter. Says that those requirements cover devices rated 1500 volts or less. I do not see where it calls for double breaking but I am guessing this is where it is. I will try to dig more.

In this inverter, there are 12 inputs, so technically there are 3 DC contactors for each input - 1 DC+, 2 DC-. All in the same inverter. These are internal to the inverter. 36 small DC contactors.
I will be able to get in front of one soon to physically see the contactors and circuitry. I have looked at European schematics of the same inverter and they only show one one DC contactor for the negative, so apparently it is resulting from a UL Standard.


Thanks again for your comments!

Rob said:

Ok, I've looked through my copy of UL508A, there is nothing in it that even references the setup...

Click to expand...

Was there any spec for minimum contact separation ?
( wondering if shorter throw "contactors" need a helping hand )

I imagine it is to do with breaking distance. An am wondering if the -ve is connected to the metal chassis of the unit.

Will take a look at the UL standard tomorrow that was posted.

Quite handy being a UL member, unlike the IET, I have access to all their standards for free.

suttonnc said:

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.



Thank you! View attachment 51722

Click to expand...

To get the 600 Volt DC rating, 3 poles are typically wired in SERIES.
For grounded PV systems all three poles break the ungrounded wire.
For Ungrounded PV Systems then one Pole breaks the (+) wire and 2 Poles in series break the (-) wire = 3 poles total

Search "Eaton 600 VDC 30 Amp Fusible Solar Disconnect DH161NRK"



Features:

• NEC 690 PV compliant up to 600 V DC
• UL 98 listed
• NEC 690.17–compliant labeling warning that the switch terminals may be energized in the open position
• NEC 690.14.(C) 2 required “PV System Disconnect” label included