Elexit
Member
- Location
- Austin, Texas
Hello All. This is my first post on this forum.
The rules for supply-side interconnection of a PV system have been moved, from 690.64(A) in the 2008 NEC, to 705.12(A) in the 2011 NEC. The reason for the move is simple, since the same rule ought to apply to wind turbines, gas microturbines, and any other generator that might be paralleled with the utility on the customer side of the meter.
So far, so good. But along with the move, a sentence was added which I feel is too vague and could lead to misinterpretation:
705.2 defines Power Production Equipment, so it is quite clear that this definition excludes the utility. No confusion there.
But what does connected to mean? I interpret it to mean that one or more service disconnecting means (that is what a supply-side PV disconnect is, even though the NEC doesn't explicitly call it that) each of which is dedicated to power production equipment.
In other words, if you had two PV inverters, and each one was connected to a bussed service gutter through a 200A safety switch fused at 175A, and one or more service disconnecting means for the building loads, your service conductors and gutter busbars would have to have an ampacity not less than 350A. The minimum ampacity is the larger of the two: calculated load or installed PV OCPD.
But the phrase connected to doesn't say all of that. One could very easily interpret it in light of the old song "Dem Bones": The knee bone connected to the thigh bone, the thigh bone connected to the hip bone, etc, etc. In this interpretation, the service conductors would require sufficient ampacity for the sum of all service OCPD. After all, they are all connected, right?
I feel strongly that the former interpretation is correct, but it has sparked arguments within our office. Sooner or later, we will encounter an AHJ who uses the latter interpretation.
I am interested in other people's opinions on this subject.
The rules for supply-side interconnection of a PV system have been moved, from 690.64(A) in the 2008 NEC, to 705.12(A) in the 2011 NEC. The reason for the move is simple, since the same rule ought to apply to wind turbines, gas microturbines, and any other generator that might be paralleled with the utility on the customer side of the meter.
So far, so good. But along with the move, a sentence was added which I feel is too vague and could lead to misinterpretation:
The sum of the ratings of all overcurrent devices connected to power production sources shall not exceed the rating of the service.
705.2 defines Power Production Equipment, so it is quite clear that this definition excludes the utility. No confusion there.
But what does connected to mean? I interpret it to mean that one or more service disconnecting means (that is what a supply-side PV disconnect is, even though the NEC doesn't explicitly call it that) each of which is dedicated to power production equipment.
In other words, if you had two PV inverters, and each one was connected to a bussed service gutter through a 200A safety switch fused at 175A, and one or more service disconnecting means for the building loads, your service conductors and gutter busbars would have to have an ampacity not less than 350A. The minimum ampacity is the larger of the two: calculated load or installed PV OCPD.
But the phrase connected to doesn't say all of that. One could very easily interpret it in light of the old song "Dem Bones": The knee bone connected to the thigh bone, the thigh bone connected to the hip bone, etc, etc. In this interpretation, the service conductors would require sufficient ampacity for the sum of all service OCPD. After all, they are all connected, right?
I feel strongly that the former interpretation is correct, but it has sparked arguments within our office. Sooner or later, we will encounter an AHJ who uses the latter interpretation.
I am interested in other people's opinions on this subject.