solarken
NABCEP PVIP
- Location
- Hudson, OH, USA
- Occupation
- Solar Design and Installation Professional
I posted initial questions for this originally in the PV forum but still would like clarification on a few things. I am interconnecting two solar PV systems (two 60A AC disconnects from the inverters) to a separately derived system (SDS) at the Y secondary of a 480 to 208V 3phase transformer. When I quoted the job, the building plans showed the SDS had the system bond made at the transformer and not at the secondary panelboard. When I opened up the transformer there was not a N-Gnd bond in it, and instead the main bonding jumper was installed between N and Gnd at the secondary panelboard. I opened the panelboard and verified the bonding jumper was there but there is no GEC in the panelboard. It is my understanding is that the GEC must be made at the same point as the N-G system bond per 250.30(A)(5).
Attached is a dwg I made of the connectivity. The solar interconnection is made at the transformer in the center of the dwg. I connected EGC's from the solar disconnects to lugs on the transformer sheet metal chassis. I connected the line and neutral connections to the transformer secondary lugs.
The secondary panelboard is at lower right in the dwg. It has 2x300AL parallel line and neutral conductors, and a 400A main breaker. It has a 2/0cu wire type main bonding jumper installed. It has 2x#1AL parallel EGC's from it's ground bar to individual lugs on the transformer sheet metal chassis. The conductors to the transformer are in flexible metal conduit. There is not a GEC in the panelboard. I read 250.30(A)(1) to mean that the system bonding jumper for this SDS can be installed at the transformer secondary or the secondary panelboard, and 250.30(A)(2) to mean that the ground conductor between the panelboard and transformer is then actually a supply side bonding jumper (SSBJ) and sized per 250.102(C).
The transformer 480V delta primary has 3/0AL line conductors to a 175A breaker in the main service panelboard, in flexible metal conduit. There is a #4AL ground wire in the conduit between a lug on transformer sheet metal chassis to the ground bar in the Main panelboard. This looks to me to serve just as an EGC, but maybe this could also serve as a GEC?
I don't believe the current connectivity meets NEC, as there is no one place where a GEC and system bonding jumper connect to Neutral for the Separately derived system. I can't make the solar interconnection in the secondary panelboard because My questions:
1. Without regard to adding the solar, is the existing installation with the system bond for the SDS made at the secondary panelboard, and with no GEC in that panelboard and with a SSBJ of size 2x#1 between panelboard and transformer chassis sheetmetal in compliance with NEC?
2. Would the existing installation without regard to adding the solar be corrected by simply adding a GEC to the panelboard? And would this need to be sized per 250.66 as 3/0 AL?
3. Would a second option for correcting the existing system be to remove the main bonding jumper in the secondary panelboard and make the system bond in the transformer? If so, the 2 sets of #1AL between the panelboard are then considered as EGC and sized properly per 250.122, correct? But it seems to make the system bond at transformer, all the individual lug to sheetmetal chassis connections would need to change to landing on an actual groundbar that is sized sufficiently, and there would need to be a GEC added to the transformer, correct? Would an added GEC in this case be sized per 250.66 as 3/0AL?
3. If the GEC were added in the panelboard to correct the existing system, would there be any way to keep the solar interconnections made at the transformer? Like if I treated the solar disconnects with the same approach as panelboard, and installed the system bonding screw in the disconnects, and then considered the #8cu ground conductors between the disconnect and the transformer as a SSBJ?
4. Are there any exceptions that would come into play for this situation? For example, Exception 2 in 250.30(A)(5), which I am not really understanding.
I need to finish this solar project and want to make sure it is safe and to code. It seems to me the electrician that installed the existing system made changes to the bonding and grounding from the plans and did not do it completely right.
I appreciate any insight and advice!
Attached is a dwg I made of the connectivity. The solar interconnection is made at the transformer in the center of the dwg. I connected EGC's from the solar disconnects to lugs on the transformer sheet metal chassis. I connected the line and neutral connections to the transformer secondary lugs.
The secondary panelboard is at lower right in the dwg. It has 2x300AL parallel line and neutral conductors, and a 400A main breaker. It has a 2/0cu wire type main bonding jumper installed. It has 2x#1AL parallel EGC's from it's ground bar to individual lugs on the transformer sheet metal chassis. The conductors to the transformer are in flexible metal conduit. There is not a GEC in the panelboard. I read 250.30(A)(1) to mean that the system bonding jumper for this SDS can be installed at the transformer secondary or the secondary panelboard, and 250.30(A)(2) to mean that the ground conductor between the panelboard and transformer is then actually a supply side bonding jumper (SSBJ) and sized per 250.102(C).
The transformer 480V delta primary has 3/0AL line conductors to a 175A breaker in the main service panelboard, in flexible metal conduit. There is a #4AL ground wire in the conduit between a lug on transformer sheet metal chassis to the ground bar in the Main panelboard. This looks to me to serve just as an EGC, but maybe this could also serve as a GEC?
I don't believe the current connectivity meets NEC, as there is no one place where a GEC and system bonding jumper connect to Neutral for the Separately derived system. I can't make the solar interconnection in the secondary panelboard because My questions:
1. Without regard to adding the solar, is the existing installation with the system bond for the SDS made at the secondary panelboard, and with no GEC in that panelboard and with a SSBJ of size 2x#1 between panelboard and transformer chassis sheetmetal in compliance with NEC?
2. Would the existing installation without regard to adding the solar be corrected by simply adding a GEC to the panelboard? And would this need to be sized per 250.66 as 3/0 AL?
3. Would a second option for correcting the existing system be to remove the main bonding jumper in the secondary panelboard and make the system bond in the transformer? If so, the 2 sets of #1AL between the panelboard are then considered as EGC and sized properly per 250.122, correct? But it seems to make the system bond at transformer, all the individual lug to sheetmetal chassis connections would need to change to landing on an actual groundbar that is sized sufficiently, and there would need to be a GEC added to the transformer, correct? Would an added GEC in this case be sized per 250.66 as 3/0AL?
3. If the GEC were added in the panelboard to correct the existing system, would there be any way to keep the solar interconnections made at the transformer? Like if I treated the solar disconnects with the same approach as panelboard, and installed the system bonding screw in the disconnects, and then considered the #8cu ground conductors between the disconnect and the transformer as a SSBJ?
4. Are there any exceptions that would come into play for this situation? For example, Exception 2 in 250.30(A)(5), which I am not really understanding.
I need to finish this solar project and want to make sure it is safe and to code. It seems to me the electrician that installed the existing system made changes to the bonding and grounding from the plans and did not do it completely right.
I appreciate any insight and advice!