Split Bus Panelboard for a hybrid inverter with NEC compliance?

[poldim]

I'm curious if anyone has used a split bus panel and had it pass inspection. The interwebs points to 408.36 of the NEC but I don't see any issues with this setup so long as the backfed breaker has an additional fastener per (D) and confirmed by the manufacturer.

This configuration would give you the benefit of a single panelboard to function as the main panel and the critical loads panel. If you need to do maintenance on the inverter, you use the maintenance bypass breaker by shutting off the inverter output breaker and turning on the bypass breaker.

 

[sunshine_eggo]

no idea.

@timselectric ?

 

[zanydroid]

Potentially galaxy brain assuming stuff like busbar rating passes for 705.12. Is a split bus considered two separate busbars/subpanels in one enclosure by code?

Is the M an interlock plate?

There might be some code violations on how the panels is energized/not energized. Or tricky explanations for why this is OK.

You would likely have to write out a state table and exhaustively analyze all combinations of breakers. And I’m not sure a plan checker will bother to read it, or is legally required to.

 

[zanydroid]

I think another combination is to move the interlock plate down to bottom bus and two breakers there. And then the lug to the top bus.

That would arguably make the interlock less confusing to understand.

You also need a split bus where the built in bus connection can be removed.

 

[poldim]

Is the M an interlock plate?

yes

 

[poldim]

I think another combination is to move the interlock plate down to bottom bus and two breakers there. And then the lug to the top bus.

The mechanical interlock needs to sit between the two breaker's its interlocking, so this means it has to straddle the split with the two breakers on either side.

LMK if I've missed what you were suggesting.

 

[zanydroid]

The mechanical interlock needs to sit between the two breaker's its interlocking, so this means it has to straddle the split with the two breakers on either side.

LMK if I've missed what you were suggesting.

You have the interlock on a forward feeding breaker on the top bus and a backfeed breaker on the bottom, which is confusing (and makes it harder to understand IMO) because usually interlocks are on two backfeed breakers.

I think if you reverse the lug and breaker: lug on top bus feeding a backfeed breaker on bottom bus. Then the top two breakers on the bottom bus (interlocked) would both be backfed.

In other words, reverse the lug and breaker on that jumper between top and bottom bus.

 

[hwy17]

Potentially galaxy brain

Yup.

Thing is, can you still get split bus panels?

 

[zanydroid]

There might be some code violations on how the panels is energized/not energized. Or tricky explanations for why this is OK.

Another question is whether splitting the bus is considered a valid field modification.

 

[zanydroid]

Yup.

Thing is, can you still get split bus panels?

Another question is, if you have a nice modern main that isn’t split, why would you take the pain to switch to a split…

This is presuming that there are no convertible split panels (IE either come as subpanel or have removable N-G bond). If there are, then maybe doing funky stuff with split subpanels is going to be the new DIY solar meme.

I think this idea is super cool if it works and you have such a panel already (and probably just do this without permits to avoid the plan check pain)

 

[hwy17]

the new DIY solar meme.

Reject Modernity. Embrace the ancient wisdom.

HOM1427X2242M200PC

 

[zanydroid]

Discontinued last year. Put in your order NOW.

It looks potentially convertible. The PON and neutral bars are on black plastic. Haven't found a closeup photo of the top / front or the wiring diagram (and I should probably stop with this madness LOL)

 

[poldim]

You have the interlock on a forward feeding breaker on the top bus and a backfeed breaker on the bottom, which is confusing (and makes it harder to understand IMO) because usually interlocks are on two backfeed breakers.

I think if you reverse the lug and breaker: lug on top bus feeding a backfeed breaker on bottom bus. Then the top two breakers on the bottom bus (interlocked) would both be backfed.

In other words, reverse the lug and breaker on that jumper between top and bottom bus.

Thanks for the suggestion:

 

[poldim]

Discontinued last year. Put in your order NOW.

It looks potentially convertible. The PON and neutral bars are on black plastic. Haven't found a closeup photo of the top / front or the wiring diagram (and I should probably stop with this madness LOL)

Yea, this is basically what I'm thinking





Looks like one of the few still available: QOGP3P604436200P

 

[zanydroid]

Thanks for the suggestion:

View attachment 207208

Yup, this is what I had in mind. Feels a lot less like a rebel, although you are now definitely modifying the panel. What you had previously did not require reversing the lug and breaker.

What software are you using to draw these?

 

[poldim]

Another question is, if you have a nice modern main that isn’t split, why would you take the pain to switch to a split…

This is presuming that there are no convertible split panels (IE either come as subpanel or have removable N-G bond). If there are, then maybe doing funky stuff with split subpanels is going to be the new DIY solar meme.

I think this idea is super cool if it works and you have such a panel already (and probably just do this without permits to avoid the plan check pain)

I've looked at my QO panel and it looks like 2 min with a grinding wheel can make it split bus, just need to remove the plastic, cut, then reassemble.

 

[zanydroid]

I've looked at my QO panel and it looks like 2 min with a grinding wheel can make it split bus, just need to remove the plastic, cut, then reassemble.

Well in that case you can forget about passing inspection :laugh:

 

[poldim]

Yup, this is what I had in mind. Feels a lot less like a rebel, although you are now definitely modifying the panel. What you had previously did not require reversing the lug and breaker.

What software are you using to draw these?

Need to find out how willing the SF DBI are to things like these.......

AutoCAD

 

[Shimmy]

Discontinued last year. Put in your order NOW.

Plenty of options outside of Homeline style though.

 

[timselectric]

I'm curious if anyone has used a split bus panel and had it pass inspection. The interwebs points to 408.36 of the NEC but I don't see any issues with this setup so long as the backfed breaker has an additional fastener per (D) and confirmed by the manufacturer.

This configuration would give you the benefit of a single panelboard to function as the main panel and the critical loads panel. If you need to do maintenance on the inverter, you use the maintenance bypass breaker by shutting off the inverter output breaker and turning on the bypass breaker.


View attachment 207199

Perfectly fine as long as you install a breaker interlock. So that the two breakers feeding the secondary bus can not be turned on simultaneously.
I have installed several emergency portable generator systems this way.