Generator interlock is this safe??

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
This is a very common type of generator interlock. Yes, it can be defeated if the dead front is removed.

IMHO it is sufficient to prevent accidental connection of the generator to the mains, which is the purpose of an interlock.

-Jon
 

Srv52761

Member
Location
lowa
Occupation
Energy Manager
That is how all interlocks operate.
But, you are correct. If you don’t feel good about it as is, you could switch out the screws on the interlock and the panel cover with tamper resistant or security screws. The next EC that works on that panel will probably cuss you, though.
Edit: Never mind, I see I type too slowly. winnie just said this...
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
I found this that can be installed on a SQUARE-D meter main that one can hook up a generator to the main service. But I just don't feel safe about it. If the dead front cover is removed then the safety goes away.

Your thoughts please.

GENERATOR INTERLOCK
These things have been around for decades and many AHJs are fine with them. I have always had reservations about them due to them relying on the cover for the interlock. The 2017 and prior editions of the NEC have never required listing for Article 702 transfer equipment. However the 2020 edition now requires transfer equipment to be listed. The one you posted does have a listing but I don't think it is valid to meet the requirements for the 2020 NEC as that listing is very limited in scope and not listed as transfer equipment. I have not yet had a chance to research the history of this change in the code but I sense this is what they were getting at.
 

edward

Senior Member
Thank you all for your replies. I never knew these things existed. I am a bit concerned about it, then again it is the same situation the homeowner replaced a 15A breaker with 60A breaker and creates an issue.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
It's not legal to energize a panel with a cover not in place (other than for testing), so the fact that the interlock can be defeated by removing the cover is a moot point.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Are these things really listed for use with the panels covers they actually fit on?
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
"If" the dead front cover is removed then the safety goes away.

GENERATOR INTERLOCK
IF - one of the smallest words in the English language but one that carries a ton of weight depending how it is used. IF I hit the lottery for 100 million $$$ would I still do electrical work ? Maybe - but I wouldn't HAVE TO to stay alive.

All joking aside, think about safety and the unsuspecting utility user. When we install these devices on main breaker panels we are preventing the every day utility user from back-feeding generated power onto the utility grid. IF someone like one of us or someone that has some knowledge of the workings of these devices wants to compromise the integrity of the interlock device it can be done.
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
Are these things really listed for use with the panels covers they actually fit on?
When you buy the ones that are manufactured by the panel maker like this one :


most EI's will accept them (if you're getting the installation inspected). However, if you use one like the one in the OP, most EI's will not accept them even though they have a MET sticker on them.

Just an FYI and a side bar to this thread (sorry), when I upgrade an electric service and include an (approved) interlock kit and power inlet port at the same time I am being charged a separate fee for that portion of the job.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
When you buy the ones that are manufactured by the panel maker like this one :


most EI's will accept them (if you're getting the installation inspected). However, if you use one like the one in the OP, most EI's will not accept them even though they have a MET sticker on them.

Just an FYI and a side bar to this thread (sorry), when I upgrade an electric service and include an (approved) interlock kit and power inlet port at the same time I am being charged a separate fee for that portion of the job.
We had a good discussion at an inspector CEU seminar about those with the MET stickers and the somewhat shady language they use to say they're compliant. I would never use one for that reason and stick with the listed ones made by the panel manufacturer. I could see an inspector allowing one of those when you had an old panel and no OEM interlock for that panel.
 

paulengr

Senior Member
When you buy the ones that are manufactured by the panel maker like this one :


most EI's will accept them (if you're getting the installation inspected). However, if you use one like the one in the OP, most EI's will not accept them even though they have a MET sticker on them.

Just an FYI and a side bar to this thread (sorry), when I upgrade an electric service and include an (approved) interlock kit and power inlet port at the same time I am being charged a separate fee for that portion of the job.
Whether it comes from the manufacturer or not is immaterial. If I buy 508A parts and build a panel, I AM the “manufacturer” if it’s a 508A panel. If my shop rebuilds a motor with a UL sticker, it’s Listed. And as far as field installs go if I buy crimped on lugs and crimp them following manufacturer instructions (correct die and crimper), EVEN if it’s a T&B lug crimped with a Greenlee crimper using the correct Milwaukee U series due, it’s a Code legal crimp. If you read the T&B catalog they only state their lugs are Code with specific T&B crimpers. But many crimpers are multi-brand and tested under UL and many use U series universal dies which are interchangeable amongst crimpers. It doesn’t matter that T&B only Listed with their crimpers. Actually it does because that relieves T&B of testing everyone else’s crimpers and relieves Greenlee and Milwaukee for instance of having to sell lugs.

To suggest otherwise means you can only use manufacturer specified lugs, wiring, etc., is simply not correct. Are you saying you cannot drill mounting holes or drill holes for 2 screws let alone EMT fittings? There is a big difference between a Listed field installable modification where you are following the instructions on the field installable component as opposed to say drilling and tapping the bus in a Siemens panel to accept a Square D QOB breaker because the QOB was not Listed this way. The only time this gets this utterly stupid is that UL.com only tests to UL.org standards and only assemblies with UL Listed components (RU or UL) while EVERYONE else tests to a variety of Codes and accepts components from anybody. It’s an advertising scheme (I’d say strong arm tactic) from UL.
 
Thank you all for your replies. I never knew these things existed. I am a bit concerned about it, then again it is the same situation the homeowner replaced a 15A breaker with 60A breaker and creates an issue.
I would say having an interlock is far safer than not having one. Without one, when that time comes, home owner Harry could rig up any number of improper backfeeds.
 

ActionDave

Moderator
Staff member
Location
Durango, CO, 10 h 20 min without traffic from wing
Occupation
wire pulling grunt
We had a good discussion at an inspector CEU seminar about those with the MET stickers and the somewhat shady language they use to say they're compliant. I would never use one for that reason and stick with the listed ones made by the panel manufacturer. I could see an inspector allowing one of those when you had an old panel and no OEM interlock for that panel.
In my experience the after market kits were better quality than the ones sold by the name brand electrical manufactures.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
In my experience the after market kits were better quality than the ones sold by the name brand electrical manufactures.
You might be right. IMO the OEM ones work well enough to keep someone from closing both breakers at the same time. If you can't pass an inspection with the "better" after market device what good is it. :unsure:
 

ron

Senior Member
I will admit that I personally have a Reliance panelboard with an interlock between the main and positions 2&4 in my own residence.

Hence, I think it is code compliant.

I hesitate to tell this story, but ....
A few years ago, I had the deadfront off for testing during a storm and was negligent in putting it back on before going out for work with the generator running. While I was out, the utility returned and my wife, feeling very capable, took it upon herself to perform the transfer that she has watched me do many times. After opening the generator breaker, she went to operate the 200A main, and after having difficulty getting enough leverage to close the handle, she put 2 fingers on the top of the main breaker which happened to be the incoming energized conductors. After about 30 minutes of tingly and numbness, we are lucky that there are no lasting "physical" deficiencies.

Clearly it may have been worse if she closed the main without opening the generator, or just the shock hazard from the main from my own negligence, but I still think it is a code compliant installation.
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
One of the gripes an EI had was that the after-market devices come with a cable tie (or two) that holds the generator breaker and the adjacent breaker in place. He claimed that the cable tie could become compromised over time, crack and fall off. I don't see it that way but it wasn't worth arguing the point. The Sq D Homeline (or QO) interlock kit that I posted has a metal frame that holds the generator breaker in place and that seems to be a more secure way to accomplish the same thing.

As Infinity stated, if you can't pass an inspection what's the point of installing an after-market device. My opinion is that many HO's have older breaker panels that either wouldn't have an approved interlock kit made for it or do not warrant a full replacement. After-market manufacturers like Interlock kit.com and Geninterlock.com have done a lot of research on older panels and their devices work well. While I am a proponent of 3rd party inspections I believe you shouldn't bother getting the installation inspected. I'd rather get hired to do it the right way than have a HO do it the wrong way. I'm sure I'll get a lot of push-back on this. :cool:
 

480sparky

Senior Member
Location
Iowegia
If we start down the rabbit-hole of "what if"s, we'll end up with nothing to install.

Take a standard device like a receptacle or switch. "What if the homeowner takes the cover off? Then they can reach the bare terminals!" What if someone puts 100w lamps in a luminaire marked 60w max? What if I install AWG 12 for voltage drop on a 15a breaker and someone decides to install a 20a breaker?

Oh, the horror!
 
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