PS2DC & Array breakers

Discussion about OutBacks "PS" enclosures

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PS2DC & Array breakers

Post by bflusche »

I am planning on having two parallel strings of solar arrays with a single MX-60. I know I need a breaker for each string and that I have to combine the two strings into a single input into the MX-60. I want to be NEC compliant, but would like to avoid the expense of a PSPV if possible.

Can I just put two OBDC-10 breakers in the PS2DC to isolate each string?

Can I put in a simple bus bar to combine the breaker outputs into a single input for the MX-60?

Kent Osterberg
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Post by Kent Osterberg »

Since NEC 690.14 (C) (5) says that a PV disconnecting means shall not be required at the PV location, I believe your proposal could be compliant with the NEC. Futhermore, since the two 10-amp breakers do not exceed the capacity of the MX-60 you could do away with the OBDC-60 that is usually put on the input of the MX-60.

That said there are more things to consider:
  • While the PSPV doesn't meet all of the requirements of a disconnect, it serves well enough in that capacity for service purposes. Having one near the PV array is really useful if there ever is any troubleshooting to do. In general, the code requires a disconnect for service purposes near the load for all dedicated circuits. The exception for PV arrays is because they are still energized when disconnected. A disconnect near the PV array is still a good idea; it may even be required in a future version of the code.

    NEC 690.14 (C) requires the PV disconnect to be grouped with other disconnects for the building. That may or may not be where the PS2 is located. Also, depending on your location, it be necessary for the PV disconnect to be outside. That may throw a wrench in your plan, especially if the system were to ever grow to more than three parallel strings.
When you only have two parallel strings, it may not be necessary to have series breakers in each string. Unless the MX-60 contributes to the DC fault current (I'm pretty sure that it doesn't) there is no fault condition that could ever cause one of the series breakers to trip. That means for two parallel strings the series breakers are pointless.
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Post by ryanmayfield »

The way you described using the two breakers and bus bar will work just fine. As Kent mentioned there may be some additional Code requirements that may alter the install a bit. Another part of code that may be a factor is the maximum number of disconnects allowed which is 6 (doesn't sound like an issue here but something to be aware of).
That means for two parallel strings the series breakers are pointless.
I don't think this is correct. The MX60 probably doesn't/won't contribute any fault current or backfeeding to the array but there is no UL listing to verify that.

Since there is a huge current source avaialble, batteries, ready to send that current where ever it sees a load, I would say there is an extremely important point to the series breakers.
Ryan Mayfield
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