Service and generator question.

[Strife]

I have a residential job with a 400A service feeding two 200A main breakers in separate enclosures. Someone did a generator job on this service by installing a 200A Single Throw disconnect and feeding the load side of each breaker. To me it was always a given that double throw would be required. But I can not find it in the code, least not in the service part.
So my question is? where can I find in the code the part that deals with this? Another question is, if I change this to a double throw switch, fed from the meter then use three wire lugs ( I have to add another main disconnect) and feed the three mains from the disconnect does the disconnect has to be fusible? and if not I assume the tap rule applies from the load side of the disconnect to the mains. The meter, mains and disconnect are all grouped.
Thank you.

 

[qcroanoke]

I have a residential job with a 400A service feeding two 200A main breakers in separate enclosures. Someone did a generator job on this service by installing a 200A Single Throw disconnect and feeding the load side of each breaker. To me it was always a given that double throw would be required. But I can not find it in the code, least not in the service part.
So my question is? where can I find in the code the part that deals with this? Another question is, if I change this to a double throw switch, fed from the meter then use three wire lugs ( I have to add another main disconnect) and feed the three mains from the disconnect does the disconnect has to be fusible? and if not I assume the tap rule applies from the load side of the disconnect to the mains. The meter, mains and disconnect are all grouped.
Thank you.

I don't have my code book with me right now but I can tell you that if the generator is hooked to the load side of those 2 disconnects without a Manual Transfer Switch between them someone has a very good chance of being killed! If those 2 disconnects are left on the generator will feed back out on to the grid and endanger a lineman working on it.
Sounds like you ran up on a hack job.
Ideally the MTS (which should be 400 amp) would be behind the meter and then feed the 2 disconnects.

 

[augie47]

NEC 700.6 and 702.6 require that transfer equipmemt prevent back-feeding onto utility systems.
Any equiupment that you connect ahead of the existing service equipment would need to be "service rated".

 

[esobocinski]

What he said. Note that NEC doesn't require a double-throw switch, only that both sources can't be energized at the same time. For example, there are many solutions for smaller installations within a single panel that use a bar, lever or slider plate between two breakers to ensure that only one breaker can be on at a time. I expect that for 400A/200A you'll be forced back to a "real" transfer switch because the switch needs to be rated as service equipment and the interlock needs to be "permanent", but it's possible that someone makes an interconnect between levers of two single disconnects should you have a reason to go that route. Just sayin' to keep an open mind and not automatically think double-throw.

Prep the customer for some sticker shock for any of these solutions.

If cost is a problem, it might be viable to put a slider solution (like Square D QOCGK2) in both panels so that each panel is 200A utility or 100A generator, manually switched. However, if they have that big of a generator, cost shouldn't be the big driver, and I'm really wondering why they didn't go all the way and use an automatic transfer switch when the generator was installed.