Generator Interlock

mkgrady

Senior Member
Location
Massachusetts
I have a customer that wants a portable generator connection. I typically install a gen breaker in the main panel and interlock it with the main breaker. In this case he does not have a main in the panel. It is out at the meter. There isn't enough room in the panel to add a main.

I'm hoping to install a breaker between the outside main and the inside panel. I'm picturing a 3R enclosure main lug with a 100 amp and a 30 amp breaker and interlock. I'm not sure I will find a four space 100 amp panel that can accommodate an interlock. Any ideas?
 

hillbilly1

Senior Member
Location
Atlanta,Ga
A lot of manufactures use the same can for the mlo and breaker type load centers, if the panel is new enough, I just buy the main breaker version and swap out the guts and the cover. Then an interlock kit can be used inside. Just done that last year with a Siemens loadcenter.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
Why aren't you going to use a main breaker panel? They make interlocks for them and some manufacturers make a panel designed with an interlock built in.
 

mkgrady

Senior Member
Location
Massachusetts
The panel inside does not have a main breaker and there is no room to add one. The main breaker for the service is a combo meter socket/main breaker so there is no place to put a gen breaker and interlock. I plan to put a mlo panel outside and interlock it with a gen breaker. I just can’t picture a 3R four circuit panel that will accept an interlock.
 

mkgrady

Senior Member
Location
Massachusetts
We usually end up doing a Sq D HOM816M200FTRB with a gen interlock in a situation like this.

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Thanks. That looks like it would work. I don’t need the 200 amp rating but it can’t hurt. I was thinking something more compact but it doesn’t look like I will find anything
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Engineer
The QO line has a QO1DM10030TRBR: 100A main interlocked with a 30A gen breaker, subfeed lugs, and space for 4 branches, probably still bigger than you need.
 

Eddie702

Licensed Electrician
Location
Western Massachusetts
Occupation
Electrician
I have done it with older panels with no interlock available by installing a sub panel with a main and an interlock. Move the 'emergency circuits into the new sub panel
 

GerryB

Senior Member
I have a customer that wants a portable generator connection. I typically install a gen breaker in the main panel and interlock it with the main breaker. In this case he does not have a main in the panel. It is out at the meter. There isn't enough room in the panel to add a main.

I'm hoping to install a breaker between the outside main and the inside panel. I'm picturing a 3R enclosure main lug with a 100 amp and a 30 amp breaker and interlock. I'm not sure I will find a four space 100 amp panel that can accommodate an interlock. Any ideas?
How about just the old style 100 amp manuel generator bypass switch. Did one years ago for a friend, I would say you can still get them but I don't know. The 200 amp is pricey but the 100 amp is not. (just looked online, saw one for $153.00, not available for 4 weeks because of the storm on the east coast.)
 

Todd0x1

Senior Member
Location
CA
The QO line has a QO1DM10030TRBR: 100A main interlocked with a 30A gen breaker, subfeed lugs, and space for 4 branches, probably still bigger than you need.
I was just going to post this after confirming it comes with the 100A main, the datasheet isn't 100% clear but sqd confirms it in a faq, but you beat me to it.

This is probably the most cost effective option as the whole thing is only around $100 and includes both breakers.

Datasheet: https://www.se.com/us/en/product/download-pdf/QO1DM10030TRBR
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor

mkgrady

Senior Member
Location
Massachusetts
Coulda saved you about $100. Above SqD interlock, two breakers, and this or similar:

Yes $100 is nothing to sneeze at but I avoid square D because my local supplier charges crazy prices and I’m not sure what I can find at big box stores for interlock hardware. I once paid about $200 for a panel that Big Box sold for $80.
 
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