Advice on conflict between generator interlock kit and subpanel requirements (Siemens Panel)

[jasonvr]

I recently had my 50yr old 100A main panel replaced with a 200A Siemens panel (MC2040B1200EFC). It is the incarnation with the 200A main breaker at the bottom (earlier versions were center fed which would have alleviated my problem). At the same time I had the electrician add a 50A inlet for a generator (because SoCal Edison likes to turn off my power any time the wind blows, like 29 hours on Thanksgiving) and a 100A subpanel in the garage for future electric vehicle charging.

This was all done with permits and the inspector has signed off on it, but I currently have no generator interlock kit. This is because the panel label states that:

Any 80-100 Amp max. circuit breaker must be installed in the lowest position in the branch panel. All other positions are limited to 70 Amp max. circuit breakers.

As such, the 100A breaker feeding the subpanel is immediately above the main breaker. This means the 50A breaker for the generator inlet can't be placed next to the main breaker meaning there is no way to add an interlock kit.

I'm not sure what to do about this. I have considered moving the 50A breaker next to the main breaker and then moving the 100A breaker up above it, but that violates the panel label. But which is worse - violating the panel label, or not having an interlock kit which, if my wife or I mess up, could electrocute, injure, or even kill a lineman?

My guess is the restriction on the panel label is to prevent too much current having to flow up the panel bus bars and past all the other in use breakers. However, in this case, the 50A breaker would be off in most cases (except when on generator power) and if I were on generator power, the main would be off as well as the subpanel (not gonna charge an EV off my generator). So the additional current would only be flowing past a turned off breaker connected to nothing in the nominal use case.

What would you do in this situation?

 

[jasonvr]

Anyone have any ideas or thoughts on this?

 

[Megawatt]

I recently had my 50yr old 100A main panel replaced with a 200A Siemens panel (MC2040B1200EFC). It is the incarnation with the 200A main breaker at the bottom (earlier versions were center fed which would have alleviated my problem). At the same time I had the electrician add a 50A inlet for a generator (because SoCal Edison likes to turn off my power any time the wind blows, like 29 hours on Thanksgiving) and a 100A subpanel in the garage for future electric vehicle charging.

This was all done with permits and the inspector has signed off on it, but I currently have no generator interlock kit. This is because the panel label states that:


As such, the 100A breaker feeding the subpanel is immediately above the main breaker. This means the 50A breaker for the generator inlet can't be placed next to the main breaker meaning there is no way to add an interlock kit.

I'm not sure what to do about this. I have considered moving the 50A breaker next to the main breaker and then moving the 100A breaker up above it, but that violates the panel label. But which is worse - violating the panel label, or not having an interlock kit which, if my wife or I mess up, could electrocute, injure, or even kill a lineman?

My guess is the restriction on the panel label is to prevent too much current having to flow up the panel bus bars and past all the other in use breakers. However, in this case, the 50A breaker would be off in most cases (except when on generator power) and if I were on generator power, the main would be off as well as the subpanel (not gonna charge an EV off my generator). So the additional current would only be flowing past a turned off breaker connected to nothing in the nominal use case.

What would you do in this situation?

That sounds ridiculous you can in stall your generator breaker any where you want to in your panel. It puts out the same power whether it’s the bottom or top. It sounds like you have a bottom fed panel. You will as you stated have to have a tie down kit for your generator breaker.

 

[jasonvr]

That sounds ridiculous you can in stall your generator breaker any where you want to in your panel. It puts out the same power whether it’s the bottom or top. It sounds like you have a bottom fed panel. You will as you stated have to have a tie down kit for your generator breaker.

Maybe I wasn't clear in my original post. I realize that I can put the 50A breaker for the inlet anywhere, but the panel label says any breaker over 70A needs to be at the lowest position. You are correct that the panel is bottom fed which means the 200A main is at the far bottom. So, the lowest position, which according to the label, is the only place I can place the 100A breaker for the sub-panel is right above the main. That means I can't place the 50A next to the main to put the interlock in. If I do put the 50A next to the 200A, it means I can put the interlock in, but the 100A for the sub-panel won't be at the lowest position which violates the panel label. Seems like a rock and a hard place situation

 

[packetrat]

Consider changing out the 100A subpanel breaker for now with a 70A, after ensuring the 70A breaker will accept the larger wire size (1/0 Cu?) feeding your 100A subpanel. Typical EV level-2 chargers (EVSE) draw no more than 32A @ 240V, recommending a 40A circuit, so even two vehicles charging at once would be pulling 64A or less. This would exceed the 80% continuous duty rating of a 70A breaker (at 91.4%), but with the wire and everything downstream sized for 100A, there'd be no safety issue, only a minor risk of nuisance tripping. EVSEs and vehicles can also be dialed back manually to a lower amperage, and some advanced EVSEs can communicate to share limited current (e.g. fall back to 25A whenever both are in use at once). With only one EV to charge, it would never be a problem. Hold onto the 100A breaker in case you ever want to swap it back in.