690.64 (B)(2) limits the sum of the ampere ratings of OC devices on a bus to the rating of the bus (with the exception of +20% for dwellings). This makes retrofitting for solar quite difficult and expensive in many instances. Why does this rule exist in the first place? We routinely design systems where the sum of all the OC devices add to more than the rating of the bus, for example, a main-lug switchgear bus may be rated for 1000A but have 1200A worth of breakers. We simply show that the sum of all loads (and 125% of continuous loads) is less than 1000A. Why not the same for solar systems?
Why does 690.62(B)(2) limit total breaker sum for solar, but no limit for non-solar?
- Thread starter donw
- Start date
- Status
- Location
- Illinois
- Occupation
- retired electrician
In normal systems the line side device limits the maximum current that can flow on the panel bus. In the case of solar, you have two "line side" OCPDs that can supply current to the panel bus and you could overload the bus. The code rule permits a 20% overload of the bus. Note that the 20% applies to all occupancies in the 2008 code.
- Location
- Illinois
- Occupation
- retired electrician
It would be the service OCPD if you are conecting the solar to the service panel. The utility OCPD would never enter into this issue.
- Location
- Illinois
- Occupation
- retired electrician
Sorry, I didn't really understand your question. In that case, I don't see any rule as to the size of the OCPD. The rule in 690.64(B)(2) only applies to solar connections on the load side of the service disconnect. 690.(B)(1) applies where the output of the solar system in connected on the line side of the service disconnect. The rule only refers you to 230.82(6) but gives no guidance as to the size of the OCPDs.
Wait a minute, I don't think that's right. What I'm talking about is a main-lug-only service equipment with multiple (6 or less) disconnects/OC devices. Lets say 5 are service disconnects, and one is the solar disconnect. They still combine on the load side of the disconnects.
- Location
- Illinois
- Occupation
- retired electrician
The panel bus is on the line side of the service disconnects so the solar system connection is on the line side of the service disconnects. With a MLO panel the breakers are the service disconnects and the load side of the breaker is the load side of the service disconnect.
fcfjr
Member
- Location
- Santa Rosa, California
- Occupation
- Electrical Contractor
I'm not sure if I'm doing this according to the rules so please bear with me. I understand 690.64 (B)(2) limits the sum of the ampere ratings of OC devices on a bus that are feeding the bus. I would think the 5 OCPDs on the bus with the solar OCPD would not count because they are not feeding the bus they are on.
crossman gary
Senior Member
fcfjr:
You are correct. And I think there was some misunderstanding of the point in this thread.
You are correct. And I think there was some misunderstanding of the point in this thread.
BillK-AZ
Senior Member
- Location
- Mesa Arizona
PV with main-lug-only service equipment with multiple (6 or less) disconnects
PV with main-lug-only service equipment with multiple (6 or less) disconnects
If you have main-lug-only service equipment with multiple (6 or less) disconnects, the PV breaker can be up to the rating of the bus. PV breaker must be on the opposite end of the bus from the utility feed.
PV with main-lug-only service equipment with multiple (6 or less) disconnects
If you have main-lug-only service equipment with multiple (6 or less) disconnects, the PV breaker can be up to the rating of the bus. PV breaker must be on the opposite end of the bus from the utility feed.
- Location
- Illinois
- Occupation
- retired electrician
For installations where the PV breaker is on the line side of the service disconnect(s), there is no code rule that says the PV breaker must be on the opposite end of the bus. That rule only applies to PV breakers that are installed on the load side of a service disconnect.
- Status