Residential Critical Loads Panel Connected to Line Side of Service Disconnect

[Rick Malone]

2020 NEC 230.82 - Equipment Connected to the Supply Side of Service Disconnect regarding solar PV systems allows the following to be connected to the line side:
(6) Solar photovoltaic systems, fuel cell systems, wind electric systems, energy storage systems, or interconnected electric power production sources, if provided with a disconnecting means listed as suitable for use as service equipment, and overcurrent protection as specified in Part VII of Article 230

My question is would a critical loads panel connected to a Sol-Arc type inverter, enphase system controller 2, etc., connected to the line side of a service be allowed.

If generation is not underway, the critical loads panel would be an additional load to the main panel and main circuit breaker. I don't see a way to insure the meter / service conductors are not overloaded and/or protected. Also, an exact reading of 230.82 would seem to indicate you cannot have loads connected to the line side of the service.

Any thoughts?

 

[jaggedben]

Just invoke 230.40 Exception 2 instead.

 

[Rick Malone]

2020 NEC 230.40 is the requirement that a service drop or service lateral supply only one set of service conductors. Exception 2 allows two to six service disconnecting means. 230.2 through 230.10 shows examples of permitted service configurations. 230.2(A) Allows certain additional services including...... (5) Parallel power production systems.

Except for (1) fire pumps and (2) emergency systems, I don't see loads being allowed to connect on the line side.

I don't think a critical loads panel was intended to be considered an emergency system. I'm still not on solid ground trying to support the installation of a critical loads panel (connected via inverter or controller) on the line side of a PV connection.

Any other ideas or clarifications? I appreciate your comments. Thanks,

 

[jaggedben]

... Exception 2 allows two to six service disconnecting means. ...

There you go. Done. Everything else you said is irrelevant.

You have one regular service disconnect. You want another. That's allowed. (You could still add four more.) A service disconnect may serve loads as well as an interconnected power source, which is what you want it to do. Don't over-complicate it. There's no need to call it a supply-side connection for anything. Physically it's the same installation by a different name that just happens to meet code language.

Just be aware the 2020 code requires the separate disconnect to be in it's own enclosure. But that's a bit of a side issue.

 

[Rick Malone]

All loads (including line side loads) must be considered when specifying building service equipment and service conductor size from the utility, or coordinate with the utility with total load information for them to specify the service conductor size.

PV systems connected to the supply side of a service disconnecting means (230.82) have fewer considerations……Is the kVA generation output less than the utility transformer rated kVA and is the PV OCP within 10ft of the line side tap less than the service disconnect. If so, then the service conductor size and transformer from the utility are adequate. PV generation effectively reduces the current flowing on the conductor from the utility so it all comes together safely.

Adding a critical loads panel to the supply side with no PV generation (perhaps at night) has the potential of increasing current flowing on the conductor from the utility. A 200A service with a 60A fused disconnect for PV and critical loads panel could end up with a 200A rated utility conductor protected by 260A worth of OCP. Therefore, this would not be a safe installation.

Inquiries made to inverter / controller manufacturers indicate that they are unable to limit current flow to a critical loads panel in the line side configuration we are discussing.

Also, since at least 2014, the NEC does not consider a PV line side connection a service….I’m copying a few references for this below

2014


2017 NEC 690.13


2017 NEC 100

 

[wwhitney]

Adding a critical loads panel to the supply side with no PV generation (perhaps at night) has the potential of increasing current flowing on the conductor from the utility.

Not compared to those same loads being on the primary service disconnect.

A 200A service with a 60A fused disconnect for PV and critical loads panel could end up with a 200A rated utility conductor protected by 260A worth of OCP. Therefore, this would not be a safe installation.

For better or worse, it has long been the case that with multiple service disconnects, the service conductors are protected only by load calculation, not via the sum of the service OCPDs. See (2017) 230.90(A) Exception (3).

Also, since at least 2014, the NEC does not consider a PV line side connection a service….I’m copying a few references for this below

That information is out of date as of the 2023 NEC, where they are explicitly service conductors.

Cheers, Wayne

 

[ggunn]

Also, since at least 2014, the NEC does not consider a PV line side connection a service….I’m copying a few references for this below

That isn't precisely true; many AHJs have been considering line side PV interconnections to be services (except for conductor length considerations, which are changing in the 2023 NEC) for many years, and previous versions of the NEC support their position by interpretation. I haven't seen the text of the 2023 code yet, but I think the point of the changes is to remove the ambiguity surrounding this issue. I hope it accomplishes that.

 

[Rick Malone]

Nice reference. (2017) 230.90(A) Exception (3) ...also the same verbiage in (2020) 230.90(A) Exception (3).....
This would then support locating an inverter / critical loads panel on the line side of the main breaker provided all calculated loads were less than the rating of the utility conductor.

(2017NEC 310.15(B)(7) 83% of service rating rule) For a residential 200A MCB, 0.83 x 3/0 CU (200A) is 166A or 2/0 CU minimum conductor size. So if we can show that the entire demand load of the residence were less than 200A, we are good to go.

If consensus now is that the line side PV connection is a service, then there should be no ambiguity that the above design configuration meets code requirements. Does anyone know the article in the 2023 NEC that explicitly calls the line side pv connection service conductors?

Very helpful. Thanks,

 

[jaggedben]

...

Adding a critical loads panel to the supply side with no PV generation (perhaps at night) has the potential of increasing current flowing on the conductor from the utility. A 200A service with a 60A fused disconnect for PV and critical loads panel could end up with a 200A rated utility conductor protected by 260A worth of OCP. Therefore, this would not be a safe installation.

...

If it really concerns you, downsize the original 200A breaker to 150A. At least in my area, many residences with 200A services don't actually need anything close to that, even with people electrifying. In any case, a proper load calculation will tell you what the NEC does and doesn't allow.

...

If consensus now is that the line side PV connection is a service, then there should be no ambiguity that the above design configuration meets code requirements. Does anyone know the article in the 2023 NEC that explicitly calls the line side pv connection service conductors?
...

Article 705.11 has significant changes which now refer back to article 230 and 250 such that a line side pv connection is treated mostly the same as an additional service disconnect in all important respects. This is very clarifying after years of ambiguity.

That said, if the additional disconnect serves both loads and power sources, then it's just an additional service disconnect anyway.

 

[Rick Malone]

Found the 2023 NEC 705.11 reference regarding calling the PV line side connection a service. I was previously relying on the 2014 NEC 270.31 and 2017 NEC 690.13 (above) that explicitly indicated that the PV connection was not a service. With all these several references calling the PV connection a service, and services can supply both loads and generation, a critical loads panel connection on the line side of an MCB would be allowed........provided calculations or a rational is provided showing loads do not exceed service conductor size from the utility. The article is copied below for reference:
705.11 Source Connections to a Service.
(A) Service Connections.
An electric power production source shall be permitted to be connected to a service by one of the following methods:

• (1) To a new service in accordance with 230.2(A)
• (2) To the supply side of the service disconnecting means in accordance with 230.82(6)
• (3) To an additional set of service entrance conductors in accordance with 230.40, Exception No. 5

These connections shall comply with 705.11(B) through (F).
(B) Conductors.
Service conductors connected to power production sources shall comply with the following:

• (1) The ampacity of the service conductors connected to the power production source service disconnecting means shall not be less than the sum of the power production source maximum circuit current in 705.28(A).
• (2) The service conductors connected to the power production source service disconnecting means shall be sized in accordance with 705.28 and not be smaller than 6 AWG copper or 4 AWG aluminum or copper-clad aluminum.
• (3) The ampacity of any other service conductors to which the power production sources are connected shall not be less than that required in 705.11(B).

(F) Overcurrent Protection.
The power production source service conductors shall be protected from overcurrent in accordance with Part VII of Article 230. The rating of the overcurrent protection device of the power production source service disconnecting means shall be used to determine if ground-fault protection of equipment is required in accordance with 230.95.