Breaking negative DC twice in disconnect

[suttonnc]

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!

 

[Bobster]

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.

 

[suttonnc]

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!

 

[static zap]

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

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

 

[Bobster]

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.

 

[mvas-sti]

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

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