Residential-400 amp sub panel fed off 200 amp service

[electrofelon]

Well, the thread may now be well hijacked, but I can't resist a discussion.



Yes we agree.

(Sorry if you read my previous response, I misread your #1).



There's no important difference between a main breaker panelboard and a separate disconnect with panelboard. However in either case the disconnecting means ahead of the busbar changes the rules which apply to the busbar.

Right I agree, an OCPD ahead if the busbar effects the rules that apply to the busbar. What I am trying to get at is: considering this concept of applying 230.40 ex 2 instead of calling it a supply side connection, doesn't that mean there is ambiguity as to whether it is a supply side connection or a load side connection? For example my #2 in post 14: Cant I correctly call that a supply side connection OR a 230.40 exception #2 install with a load side PV connection?

 

[jaggedben]

So, as a related question, other than the issue of a 7th "service breaker", would there be any substantive change in what configurations are and aren't allowed if we just deleted (2020) 705.11 and put in an informational note directing the reader to 230.40 Ex 2?

It wouldn't change anything about overcurrent protection or conductor/busbar size. But it would affect a number of things about bonding, grounding, grouping, and the length of conductors.

 

[jaggedben]

Right I agree, an OCPD ahead if the busbar effects the rules that apply to the busbar. What I am trying to get at is: considering this concept of applying 230.40 ex 2 instead of calling it a supply side connection, doesn't that mean there is ambiguity as to whether it is a supply side connection or a load side connection? For example my #2 in post 14: Cant I correctly call that a supply side connection OR a 230.40 exception #2 install with a load side PV connection?

I don't think there's any ambiguity. All of your examples in post #14 have three load side connections in series with one supply side connection, whether or not you call the supply side connection a 'service disconnect' or a 'PV disconnect'.

The real significance enters when you want to add loads. Let me see if I can explain the difference as it relates to the 'sum of all breakers' rule.

Let's say you want to add a new set of service entrance conductors, to which you are going to add a 100A PV breaker and a 100A load breaker:
- If you're not yet on the 2020 NEC, you'd be allowed to use an MLO panel with each 100A breaker as a new additional service disconnect. You'd be allowed to use a 100A panel because the busbar, which is a service conductor, only has to be sized for the greater of the load or the PV.
- If you add any kind of disconnect ahead of the breakers, (be it separate fused, separate circuit breaker, or main breaker in the same panel) you are now obligated to use a 200A panel. Because now the load side rules apply to the busbar.

 

[wwhitney]

- If you add any kind of disconnect ahead of the breakers, (be it separate fused, separate circuit breaker, or main breaker in the same panel) you are now obligated to use a 200A panel. Because now the load side rules apply to the busbar.

FWIW, I submitted a public input to modify the "sum of all breakers" rule to allow excluding from the sum one breaker of the smallest size present. That would allow using only a 100A busbar in the above case. Which is obviously sufficient, as the 100A busbar is sufficient in your first case.

Given that 2020 now requires a single service disconnect per enclosure, do you have an example of a significant difference under the 2020 NEC?

Cheers, Wayne

 

[electrofelon]

I don't think there's any ambiguity. All of your examples in post #14 have three load side connections in series with one supply side connection, whether or not you call the supply side connection a 'service disconnect' or a 'PV disconnect'. in the

Now I am confused. I thought a PV "system", if connected line side was just a line side connection. You are saying we (usually) have a load side connection after the line side connection? So the only time we would have only a line side connection is if there is a single inverter that connects to directly to the "PV disconnect"?

 

[wwhitney]

So the only time we would have only a line side connection is if there is a single inverter that connects to directly to the "PV disconnect"?

[emphasis added]

Yes, the only time you could ignore (2020) 705.12 and just care about (2020) 705.11 would be a system like this:

Utility conductors -- PV disconnect -- Inverter

As soon as you add any further equipment connected between the PV disconnect the Inverter, those further connections are subject to the "load side" rules in 705.12.

Cheers, Wayne

 

[jaggedben]

I agree with Wayne.

 

[electrofelon]

All of your examples in post #14 have three load side connections in series with one supply side connection, whether or not you call the supply side connection a 'service disconnect' or a 'PV disconnect'.

Now I am confused. I thought a PV "system", if connected line side was just a line side connection. You are saying we (usually) have a load side connection after the line side connection? So the only time we would have only a line side connection is if there is a single inverter that connects to directly to the "PV disconnect"?

Been thinking about this a bit. I am not sure I like the part in red. I have never heard anyone say such a thing. To elaborate, in my experience a PV system is either a supply side connection or a load side connection. I am certainly aware there are "load side rules" and "supply side rules" and that there will be "load side rules" within/after a supply side connection. Perhaps this is a semantics discussion.
Thoughts?

 

[jaggedben]

Been thinking about this a bit. I am not sure I like the part in red. I have never heard anyone say such a thing. To elaborate, in my experience a PV system is either a supply side connection or a load side connection. I am certainly aware there are "load side rules" and "supply side rules" and that there will be "load side rules" within/after a supply side connection. Perhaps this is a semantics discussion.
Thoughts?

While it is true that it is rarely if ever discussed as if all PV systems have a supply side connection, I think it is ultimately the most sensible way to apply the rules.

For example, suppose you have a service with two MCB panels under the 230.40 exception. Both panels have both loads and PV systems. How to make sense of the rule, which has always been in the supply side section of 705, that the sum of the PV sources output shall not exceed the rating of the service? You would agree that this rule makes sense regardless of how the systems are connected, right? One should not make the argument that because the systems are connected load side, the supply side rule limiting total output does not apply. Right?

(And this is not all that far fetched. Imagine a 200A service, with two 100A main breakers, but someone uses 200A panels, thus allowing up to 280A of backfeed according to the load side 120% rule.)

The best way to make sense of it is to treat the installation as if there are two supply-side connections. Hence my contention that there is a supply-side connection for every system, whether it is the only one or whether it is in series with load side connection(s).

Another point: if load side connections in series each need to be considered under 705 at each point along the way (as many of us here have argued and which was corroborated by past code language) then so does the supply side connection.

In the past, the definition of inverter output circuit corroborated this interpretation, because it said (more or less) that inverter output circuit conductors were all the conductors between the inverter and the service point. Hence you still have inverter output 'connections' all along the way in series. In the last cycle they removed that language and essentially made the definition meaningless, in my opinion. I just noticed that recently. In my opinion it was a mistake.