AC PV disconnect count towards six service disconnect rule

Status
Not open for further replies.
hhsting said:
In the MLO service switchboard post #1 picture:

First 4000A section has 2x1200A breaker going to building load

Second 4000A section has 2x1200A breaker going to building load

1200A section has 2x600A breakers going to building load


Based on 700.12(A) the total overcurrent is 5000A and thats Without counting the solar breaker. The rating of service is 4000A. The sum of all overcurrent protection size exceeds utility rating which is 4000A. I dont see how engineer can even put 800A space and any solar breakers on line side of the switchboard. Am I correct or incorrect?
Click to expand...
See 230.90(A) Exception 3.
 
jaggedben said:
See 230.90(A) Exception 3.
Click to expand...

What does 230.90(A) exception no. 3 has to do with pV Solar breakers install line side? I dont get it

Lets say I am going to install 800A breaker where it says note #29 in that MLO service switchboard pictured in post#1.

But in order for me to do that i have to comply with 705.12(A):

Supply side.. the sum of ratings of all overcurrent protection connected to power production sources shall not exceed the rating of the service

Total sum of rating of all overcurrent protection connected to power production source: 5000A (sum of all breakers in MLO switchboard without solar breakers of 800A)

Rating of utility service: 4000A

How can solar breaker be installed in the MLO switchboard?
 
Last edited:
jaggedben said:
The PV isn't a load. Max amps the busbar can see is the sum of the load breakers regardless of whether the PV is there or not. This is why 705 has nothing to say about it, it's considered not to matter.
Click to expand...
If you don't mind, teach me something. 705.12 goes into length on a load side buss stating:(a) The sum of 125 percent of the power source(s) output circuit current and the rating of the overcurrent device protecting the busbar shall not exceed the ampacity of the busbar. but I don't need to consider that on a "line buss". Why, pl;ease ???
 
Okay, for both of you...

A PV source on the line side of all load breakers cannot increase the maximum current that the loads draw. That current is limited by the load breaker(s), whether that current is supplied by the utility, the PV or some combination of both.

Further, the service conductors cannot carry current in two directions at the same time. The maximum current that can be 'imported' is the maximum load. And the maximum that can be 'exported' is the PV max output if there is zero load. Article 230 sections mentioned above covers overload protection for import current. Article 705 language mentioned above provides protection against 'export' overload. In other words, as long as the service is rated for the larger of the 'import' or 'export' need then it is protected, and these two requirements never add to each other.

hhsting, the PV in this case is fine because it is less than the service rating. The sum of the load breakers exceeds the service rating, but this may be allowed by the above mentioned exception in 230.90(A). It is completely legitimate to ask an engineer to provide documentation that the calculated load (per Art. 220) is less than the service rating. However the PV does not add to the load, and has nothing to do with that. If the loads are all existing and were compliant when installed then the PV changes nothing about them.

augie, on the load side of the service disconnect means it is possible for an interactive source to defeat upstream overcurrent protection in various ways by possibly adding to the max current that can be provided by the utility through that overcurrent protection. Hence the complicated 705 rules for load side connections. This isn't possible for supply side connections because there is no upstream overcurrent protection to defeat. Hope that makes sense.
 
Last edited:
jaggedben said:
This is controversial under the 2017 code. Mike Holt once put out an opinion that it does not count because the powerflow direction doesn't accord with the definition of a service in that cycle, therefore it is not a service disconnect. However the definition of a service changed in 2020 to take away that argument. From a common sense point of view, I see no reason it shouldn't be counted.
Click to expand...

What does NEC 2017 say about counting towards six rule? Of its controversial then can you please let me know what are both sides arguments based on NEC 2017? Only item I see is NEC 2017 section 705.31.
 
hhsting said:
Can the seventh solar breaker in the MLO switchboard be violation of NEC 2017 section 230.40 exception no. 2?
Click to expand...
In the 2017 code a supply side connection for a power production source is not a service disconnect and does not count as such.
 
I hope this helps OP:

6 handle rule and PV SSC

Hello, I have a question I’m hoping to get answered here. Looking for a theoretical scenario. Any thoughts are appreciated! I have a MSP with 6 breakers. Can I ssc the PV and get away with the 6 handle rule? Does the (fused) PV disconnect count as #7 = violation? 2017 NEC Part IV...
forums.mikeholt.com

Anyways I did like to know what is the big controversy in NEC 2017 that jaggedben is saying in this thread and in one link is posted if he/she doesn’t mind explaining that is.
 
Thanks, my local AHJ considers them a service disconnect and thus one of the 6.
 
In the 2020 NEC the definition of a service was changed from

The conductors and equipment for delivering electric energy from the serving utility to the wiring system of the premises served.
Click to expand...
To
The conductors and equipment connecting the serving utility to [same].
Click to expand...
This more or less completely demolishes the argument that Mike Holt made years ago, which pretty much relied solely on that definition. So if AHJs say that under the 2020 NEC the PV disco meets all the definitions of a service disconnect, there's not really any counterargument.
 
jaggedben said:
In the 2020 NEC the definition of a service was changed from


To

This more or less completely demolishes the argument that Mike Holt made years ago, which pretty much relied solely on that definition. So if AHJs say that under the 2020 NEC the PV disco meets all the definitions of a service disconnect, there's not really any counterargument.
Click to expand...
While the definition has changed there is nothing in the 2020 code that treats a line side disconnect for solar as a service disconnect.
 
don_resqcapt19 said:
While the definition has changed there is nothing in the 2020 code that treats a line side disconnect for solar as a service disconnect.
Click to expand...
Not sure if I have the full picture, but doesn't (2020) 250.25(A) require the PV line side disconnect to be earthed in the same manner as a service disconnect would be?

Cheers, Wayne
 
don_resqcapt19 said:
While the definition has changed there is nothing in the 2020 code that treats a line side disconnect for solar as a service disconnect.
Click to expand...
But with the definition change it is indistinguishable from a 230.40 Exception 3 disconnect.

The only thing the 'anti' service disconnect side still has going for it is the reading-between-the-lines interpretation that 'on the supply side of the service disconnecting means' implies that the 'normal' service disconnecting means is the only service disconnecting means and the PV disco is somehow 'other'. But this is logically very weak, because even if the PV disco is considered a service disconnect, the 'connection' is still on the supply side of all service discos.
 
Last edited:
You must mean exception 230.40 No.5 that allows another set of service entrance conductors for stuff like PV and sprinkler systems.
But if I have a disconnect for a fire system its one of the 6 no?
 
jaggedben said:
In the 2020 NEC the definition of a service was changed from


To

This more or less completely demolishes the argument that Mike Holt made years ago, which pretty much relied solely on that definition. So if AHJs say that under the 2020 NEC the PV disco meets all the definitions of a service disconnect, there's not really any counterargument.
Click to expand...
It's been years since I saw that Holt video, but I thought that the central point of the argument was that the six handle rule applied to six handles controlling the flow of power from a single source, and since the PV is a different source it doesn't count toward handles connected to the utility.
 
tortuga said:
You must mean exception 230.40 No.5 that allows another set of service entrance conductors for stuff like PV and sprinkler systems.
But if I have a disconnect for a fire system its one of the 6 no?
Click to expand...
Sorry, I meant exception 2. Yes there's also Exception 5, but what it is about choosing one or the other that makes it a service disconnect or not?
 
ggunn said:
It's been years since I saw that Holt video, but I thought that the central point of the argument was that the six handle rule applied to six handles controlling the flow of power from a single source, and since the PV is a different source it doesn't count toward handles connected to the utility.
Click to expand...
Perhaps, but first, that isn't how the code puts it. Second, it's always been a tortured argument, since we all know that what matters is where conductors are energized from, not which direction power flows. And in interactive systems the conductors are for all practical purposes energized from the utility side.
 
Status
Not open for further replies.
Top