Disconnect requirements in a Solar PV system

philly

Senior Member
Can someone explain the DC disconnect requirements for the DC side of a Solar PV system.

Can the disconnect(s) be be located inside the inverter?

Do they have to be in sight of the PV arrays, combiner boxes, or inverter?

Can one disconnect be used for all the PV arrays or must one DC disconnect be used for each combiner box or array?
 

Smart $

Esteemed Member
Can someone explain the DC disconnect requirements for the DC side of a Solar PV system.

Can the disconnect(s) be be located inside the inverter? Yes

Do they have to be in sight of the PV arrays, combiner boxes, or inverter? In sight of inverters.

Can one disconnect be used for all the PV arrays or must one DC disconnect be used for each combiner box or array?
Yes, but depends on circumstances... as more than one may be required. Disconnecting means is more based on conductors entering a building and location of inverter(s) rather than the number of arrays or combiner boxes... and you may need to have isolation switches on the array side of the disconnecting means.
 

philly

Senior Member
Yes, but depends on circumstances... as more than one may be required. Disconnecting means is more based on conductors entering a building and location of inverter(s) rather than the number of arrays or combiner boxes... and you may need to have isolation switches on the array side of the disconnecting means.
O.k. the layout has (14) arrays and combiner boxes coming down from the rooftop into a room on a lower level where the inverter is located. The inverter has an internal DC disconnect with a handle that is external to the cabinet. From what I gather out of NEC 690 section III is that the disconnct internal to the inverter is all that is required to disconnect the PV system wiring from all other conductors in the building structure. This means that there does not have to be a DC disconnect at each combiner box although sometime I know they are put there fore convenience.

The only question I have about the inverter disconnect is 690.14(1) which states the disconnect should be at the nearest point of entrance of the PV system conductors. In my case the conductors enter the building from the roof but may have to travel inside the parking garage for a little bit before they get to the inverter on the lower level. Is there a maximum distance that the circuits can run inside before they must hit a disconnect. (Nearest can be loosely defined as written in the code)

Aso what is meat in 690.16(A) regarding fuses? Does this simply mean that each PV source circuit should be capable of being independently disconnected from the other source circuits, thus the purpose of the fuses in the combiner box? What about section (B) for fuse servicing?
 

Smart $

Esteemed Member
O.k. the layout has (14) arrays and combiner boxes coming down from the rooftop into a room on a lower level where the inverter is located. The inverter has an internal DC disconnect with a handle that is external to the cabinet. From what I gather out of NEC 690 section III is that the disconnct internal to the inverter is all that is required to disconnect the PV system wiring from all other conductors in the building structure. This means that there does not have to be a DC disconnect at each combiner box although sometime I know they are put there fore convenience.
Don't forget that if your inverter is tied into any of the structure's utility or other power source's AC system, you need an AC disconnecting means, too.

The only question I have about the inverter disconnect is 690.14(1) which states the disconnect should be at the nearest point of entrance of the PV system conductors. In my case the conductors enter the building from the roof but may have to travel inside the parking garage for a little bit before they get to the inverter on the lower level. Is there a maximum distance that the circuits can run inside before they must hit a disconnect. (Nearest can be loosely defined as written in the code)
Since subject to interpretation, mounting outside or immediately inside is always the non-debatable option... but its equal is asking the AHJ and knowing beforehand if an inside location beyond immediate is acceptable. Two disconnecting means may be required because of your inverter's location and routing of supply conductors.

Aso what is meat in 690.16(A) regarding fuses? Does this simply mean that each PV source circuit should be capable of being independently disconnected from the other source circuits, thus the purpose of the fuses in the combiner box? What about section (B) for fuse servicing?
Simply put, any fuse in the PV system must have zero voltage when accessible by other than qualified personnel. The key words in this requirement are "accessible" and "qualified". A locked fuse box (e.g. fused combiner) would limit access, but assuring a person accessing the locked box is qualified is always open to debate :roll::roll::roll: Perhaps a "qualified personnel only" label would be acceptable the AHJ... either that or a disconnect on both sides of the fuse(s).
 

philly

Senior Member
Since subject to interpretation, mounting outside or immediately inside is always the non-debatable option... but its equal is asking the AHJ and knowing beforehand if an inside location beyond immediate is acceptable. Two disconnecting means may be required because of your inverter's location and routing of supply conductors.)
It would be difficult to put a 2nd disconnect at the building entrance due to the fact that the disconnect in the drive has the capability of combining all of the combiner box outputs into one DC disconnect. If I had to put a disconnect at the building entrance as well this would require some sort of disconnect that would be capable of combining all the combiner box outputs as well.

Unless I put each of the each of the combiner box DC disconnects at the building entrance. If I put the 14 combiner box DC disconnects at the building entrance would this satisfy the requirement of having the DC disocnnet nearest the conductor entrance?


Simply put, any fuse in the PV system must have zero voltage when accessible by other than qualified personnel. The key words in this requirement are "accessible" and "qualified". A locked fuse box (e.g. fused combiner) would limit access, but assuring a person accessing the locked box is qualified is always open to debate :roll::roll::roll: Perhaps a "qualified personnel only" label would be acceptable the AHJ... either that or a disconnect on both sides of the fuse(s).
So I guess the convenience of having a DC disconnect after each combiner box allows the capability to shut off the souce circuits for one array in order to work on them without having to shut down the rest of the PV system. Would having a DC disconnct at this location be simply a convenience thing?

I dont think just the one disconnect after each combiner box would satisfy the "non qualified personel" requirment since the combiner box fuses could still be energized from the PV source circuit side. Is this correct?
 

Smart $

Esteemed Member
It would be difficult to put a 2nd disconnect at the building entrance due to the fact that the disconnect in the drive has the capability of combining all of the combiner box outputs into one DC disconnect. If I had to put a disconnect at the building entrance as well this would require some sort of disconnect that would be capable of combining all the combiner box outputs as well.

Unless I put each of the each of the combiner box DC disconnects at the building entrance. If I put the 14 combiner box DC disconnects at the building entrance would this satisfy the requirement of having the DC disocnnet nearest the conductor entrance?
I believe so.

So I guess the convenience of having a DC disconnect after each combiner box allows the capability to shut off the souce circuits for one array in order to work on them without having to shut down the rest of the PV system. Would having a DC disconnct at this location be simply a convenience thing?
The requirement is based on safety. Convenience is merely circumstantial.

I dont think just the one disconnect after each combiner box would satisfy the "non qualified personel" requirment since the combiner box fuses could still be energized from the PV source circuit side. Is this correct?
That is correct. Where a fuse is (or can be) energized from both directions, there must be a disconnect to each side of the fuse (if the fuse is accessible to non-qualified persons).
 

tallgirl

Senior Member
That is correct. Where a fuse is (or can be) energized from both directions, there must be a disconnect to each side of the fuse (if the fuse is accessible to non-qualified persons).
"Maybe". PV sources have no disconnecting means other than "wait until the sun goes down." In those instances, "touch safe" fuse holders should be used.
 

Smart $

Esteemed Member
"Maybe". PV sources have no disconnecting means other than "wait until the sun goes down." In those instances, "touch safe" fuse holders should be used.
I don't believe the sun counts as a disconnect :roll::);)

...but if it does count, don't forget LOTO :cool:
 
Last edited:

Jraef

Moderator
Staff member
"Maybe". PV sources have no disconnecting means other than "wait until the sun goes down." In those instances, "touch safe" fuse holders should be used.
As funny as that sounds, I have heard that discussed in meetings. the issue at hand was the cost of a 400A 600VDC rated disconnect switch feeding the combiner boxes. The people footing the bill were questioning the rather extreme cost of the switches (there were 50+ in the farm) and were told they were necessary because of the fuse issue. Each individual fuse was only 20A and they were using those new IEC style finger safe DIN rail mount fuse holders that look like a switch. But if you look closely at the specs, they ALL say very clearly that you CANNOT open those "switch" style handles when they are energized. People do it all the time, but they have ZERO switching rating. ZERO! So the discussion switched to them saying they were going to eliminate the 400A disconnects in each combiner box be establishing a procedure that said they were not allowed to change fuses when the sun was out! Their plan was to lock each combiner box and only allow access to the keys when the power output of the array was zero.

Go figure.
 

tallgirl

Senior Member
So the discussion switched to them saying they were going to eliminate the 400A disconnects in each combiner box be establishing a procedure that said they were not allowed to change fuses when the sun was out!
It's for this reason that G-d invented the blanket.

Seriously -- I know installers who carry very heavy blankets in their trucks so they can toss them over an array and work on an array when the sun is shining. The alternative approach, used by the guy who worked on my system years ago, is to work after dark ...
 
Top