branch circuit ampacities

[Jraef]

Interestingly enough I just had a very similar conversation today. The owner of my company is having a solar PV system installed. He has a very big house and being that we are an electrical engineering company with a distribution branch, he has really good equipment installed and LOTS of electrical circuits. He has a 200A service and has it split into 2ea 42 circuit panelboards with a total of 60 pole spaces filled. Most of them are going to unused outlets in living spaces, I guess he didn't want anything tripping off anything else. So he almost literally has one breaker per duplex!

The contractor he had come and do the estimate for installing the PV system told him he is going to have to upgrade his service to 400A, because the AHJ is going to add up all the breakers and see that it will come to more than 200A! When my boss challenged him on that assertion (he is after all an EE), the contractor said that's what the inspectors are doing now.

Maybe this guy had no idea who he was dealing with and thought he could punch up the job costs, maybe he really is that dumb, but I fear that just maybe he DID get that kind of a write-up from an AHJ on another project and so now believes it to be true! My boss was running it by me for a reality check because I used to be a contractor. I told him the contractor was nuts and he needed to find someone else.

 

[iwire]

Interestingly enough I just had a very similar conversation today. The owner of my company is having a solar PV system installed. ...............................

The contractor he had come and do the estimate for installing the PV system told him he is going to have to upgrade his service to 400A, because the AHJ is going to add up all the breakers and see that it will come to more than 200A!

This one may be legitimate as long as he is only adding the source breakers.

2008 NEC

690.64 Point of Connection.

The output of a utilityinteractive
inverter shall be connected as specified in
690.64(A) or (B).

(B) Load Side. The output of a utility-interactive inverter
shall be permitted to be connected to the load side of the
service disconnecting means of the other source(s) at any
distribution equipment on the premises. Where distribution
equipment, including switchboards and panelboards, is fed
simultaneously by a primary source(s) of electricity and
one or more utility-interactive inverters, and where this distribution
equipment is capable of supplying multiple branch
circuits or feeders, or both, the interconnecting provisions
for the utility-interactive inverter(s) shall comply with
(B)(1) through (B)(7).


(2) Bus or Conductor Rating. The sum of the ampere
ratings of overcurrent devices in circuits supplying power
to a busbar or conductor shall not exceed 120 percent of the
rating of the busbar or conductor. In systems with panelboards
connected in series, the rating of the first overcurrent
device directly connected to the output of a utilityinteractive
inverter(s) shall be used in the calculations for
all busbars and conductors.

(7) Inverter Output Connection. Unless the panelboard
is rated not less than the sum of the ampere ratings of all
overcurrent devices supplying it, a connection in a panelboard
shall be positioned at the opposite (load) end from
the input feeder location or main circuit location. The bus
or conductor rating shall be sized for the loads connected in
accordance with Article 220. A permanent warning label
shall be applied to the distribution equipment with the following
or equivalent marking:
WARNING
INVERTER OUTPUT CONNECTION
DO NOT RELOCATE
THIS OVERCURRENT DEVICE