OEM generator interlock versus after-market

[RustyShackleford]

I'm curious about peoples' experiences and thoughts about generator interlock kits, specifically the OEM ones such as:

Product Details - Industry Mall - Siemens USA

... versus the several aftermarket ones such as:

Generator Interlock Kit / OEM Model Siemens 150 and 200 Amp Panels POST March 2020 | GenInterlock

7/8 spacing for Plug on Neutral Panels 1 1/4 spacing for NON Plug on Neutral panels

www.geninterlock.com

The price of the OEM version is not significantly higher (at least for this manufacturer), so I wonder why the after-market ones exist, unless they have some advantage.

 

[don_resqcapt19]

Right now there is actually no language in 702.5 that permits the use of interlock kits as they are not listed as transfer equipment. Yes, I am well aware that the use is a common practice that is acceptable to most AHJs. Technically the AHJ would need to give a written 90.4 permission.

This should change in the 2026 code as it is likely the term "interlock kit" will be added to 702.5, but even then there may be an issue with the type of device used.

The UL Marking Guide for Panelboards (QEUY) says the following:

Some panelboards, constructed with interlocked main switching and overcurrent protective devices, have been investigated for use in optional standby systems in accordance with Article 702 of the NEC and are marked "Suitable for use in accordance with Article 702 of the National Electrical Code ANSI/NFPA 70," or, if provided within kit form, "Suitable for use in accordance with Article 702 of the National Electrical Code ANSI/NFPA 70 when provided with interlock kit Cat No. ____

I see that as a 110.3(B) listing and labeling instruction that only permits the use of OEM interlock kits.

 

[infinity]

Around here this is something that inspectors look for. If you buy an interlock kit on Interlockkit.com you'll get a red sticker.

 

[micabay]

Around here this is something that inspectors look for. If you buy an interlock kit on Interlockkit.com you'll get a red sticker.

What difference would it make, if said interlock is preventing the main, and generator breakers from being closed at the same time?

 

[RustyShackleford]

Around here this is something that inspectors look for. If you buy an interlock kit on Interlockkit.com you'll get a red sticker.

So they're making a kit that does the same thing, for roughly the same price - the only bonus is, you get a red sticker. Doesn't quite make sense.

 

[GoldDigger]

So they're making a kit that does the same thing, for roughly the same price - the only bonus is, you get a red sticker. Doesn't quite make sense.

I would guess that one deciding factor could be availability. Suppliers like Interlockkit.com can generally ship anything in a few days while you might have to wait a much longer time to get an equivalent part from the manufacturer.

 

[infinity]

What difference would it make, if said interlock is preventing the main, and generator breakers from being closed at the same time?

I would guess that one deciding factor could be availability. Suppliers like Interlockkit.com can generally ship anything in a few days while you might have to wait a much longer time to get an equivalent part from the manufacturer.

I agree that these should be allowed especially for old panels where the panel manufacturer doesn't even sell an interlock kit because the panel is ancient. IMO any decent inspector should be able to look at the interlock kit and see if it will actually do its job regardless of a listing.

 

[LarryFine]

Interlockkit just happens to be right here in Richmond, so i can just run down and pick up one.

 

[infinity]

Interlockkit just happens to be right here in Richmond, so i can just run down and pick up one.

Do inspectors in your area except them without being listed?

 

[LarryFine]

Do inspectors in your area except them without being listed?

It has never been mentioned either way. Maybe they're used to seeing them here.

 

[RustyShackleford]

I can't tell for sure (from the links in te OP) but it looks like the OEM one works even if the panel cover is absent. The after-market ones definitely do not.

 

[RustyShackleford]

I can't tell for sure (from the links in te OP) but it looks like the OEM one works even if the panel cover is absent. The after-market ones definitely do not.

So, following up on this, yes it certainly appears that it works even if the cover is removed. That's a great thing, and should eliminate the primary objection an AHJ might have (although mine seems fine with the aftermarket kind that bolts to the cover, as well).

There's just one problem: you can't get the damn cover on !!

Check out the attached photos. The twin arrows indicate tabs that stick outwards from the panel and are used to shift the configuration for entering/exiting generator mode. The single arrow points to sheet metal in the cover that will not fit between those tabs (and even if it could, it would probably render the thing inoperable.

The only solution I can see is to use a feintool to remove that piece of sheet metal, which is almost certainly code a violation and bush league at best.

 

[Eddie702]

I have never seen one that did not bolt to the cover.

What are you supposed to do with an older panel that no kit is available for it except an aftermarket kit, and you want to add a generator?

Put a new subpanel in with an interlock, I guess.

 

[RustyShackleford]

I have never seen one that did not bolt to the cover.

Yeah, it's pretty cool. And little, if any, more expensive than the bolt-ons. And doesn't require any drilling. There's GOTTA be a way to get the cover back on ...

What are you supposed to do with an older panel that no kit is available for it except an aftermarket kit, and you want to add a generator?

Put a new subpanel in with an interlock, I guess.

Well, like I said, our AHJ is cool with the bolt-on. Dunno how unusual that is ...

 

[RustyShackleford]

Research elsewhere (not the Siemens instructions) ....

It appears you have to turn off the main breaker (to remove or replace the cover). Then those tabs slide over the top of that (arrow) spot on the cover.

People are also saying you can't use slots 2 and 4, because the interlock intrudes (except possibly by taking tin snips to the interlock). Doesn't look that way on mine - maybe they fixed it - but I haven't tried yet.

 

[jim dungar]

The only solution I can see is to use a feintool to remove that piece of sheet metal, which is almost certainly code a violation and bush league at best.

How does it cause a violation or bush league while a field punched conduit isn't?

 

[RustyShackleford]

It all makes sense now. Siemens might've thought about putting this in their instructions for the part ...

 

[don_resqcapt19]

From the UL Marking Guide for Panelboards.

"Some panelboards, constructed with interlocked main switching and overcurrent protective devices, have been investigated for use in optional standby systems in accordance with Article 702 of the NEC and are marked "Suitable for use in accordance with Article 702 of the National Electrical Code ANSI/NFPA 70," or, if provided within kit form, "Suitable for use in accordance with Article 702 of the National Electrical Code ANSI/NFPA 70 when provided with interlock kit Cat No. ____."

This really says you can only use the interlock kit specified by the panel manufacturer, and if no such kit is specified, you can't use an interlock kit with that panel.

Note, the language of the current NEC does not even permit the use of interlock kits as 702.5 specifies transfer equipment and interlock kits are not listed as transfer equipment. However they are very commonly used. The First Draft of the 2026 code shows that interlock kits will be added to 702.5 to make it clear that you can use those to prevent the inadvertent interconnection of multiple sources when using an optional standby source of power.

 

[RustyShackleford]

This really says you can only use the interlock kit specified by the panel manufacturer, and if no such kit is specified, you can't use an interlock kit with that panel.

That's why I was psyched to find this OEM device, especially now that I figured out how to get the cover back on.

Note, the language of the current NEC does not even permit the use of interlock kits as 702.5 specifies transfer equipment and interlock kits are not listed as transfer equipment. However they are very commonly used.

Probably said before, but the great thing about this Siemens kit is that it works even when the cover is off the panel, unike the bolt-on ones . Although arguably a non-issue, since if the panel cover is off you have exposed energized parts, at least as dangerous as backfeeding the grid.