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Old 11-21-2018, 05:55 PM   #15
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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)
Here’s the MET certification for the Square D kit:

Mine was installed by a licensed electrician with a permit from the town. The town then inspected and approved the work. Yes, removing the panel cover could defeat the system. I do not have any plans to do that.
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