View Single Post
Old 11-21-2018, 09:25 PM   #16
Senior Member
Join Date: Oct 2010
Posts: 2,028
Thanks: 603
Thanked 686 Times in 424 Posts

Originally Posted by panjumbie View Post
The mechanical (sliding plate) interlock mentioned by several here and pictured in one of the posts would appear to be absent when the cover to the breaker panel is removed.

For that reason and others, it has not been permitted in some jurisdictions and by many utilities.

Backfeeding the utility can be fatal to a utility worker restoring service. The transformer feeding your property works in both directions. It will step up the 120/240 volts from your generator to the thousands of volts on the primary side. And if the outage is local and there is little other load on the primary side of the transformer, it is quite possible that the external load will be insufficient to trip the breaker on the generator.

I'm interested in whether that interlock is UL (or other listing agency) approved for that application.

John Schmidt, PE (retired)
Could you give me the "jurisdictions" and "utilities" that don't allow an interlock on the panel cover. Also do you know of any cases where someone removed the panel cover and caused damage to anything while operating a portable generator.

I do agree that an interlock that is under the cover is better and real easy to put on.
It's never crowded along the extra mile.
Rusty is offline   Reply With Quote