Split Bus "Subpanel" Grounding

[hitehm]

These split bus panels always get me. Please refer to the 2 pics. The "main panel" has a split bus with 2 breakers - 1 feeding the local enclosure's bus and the other feeding a second "remote panel", which btw is just on the other side of the wall but not sure the distance is relevant here. So I have 2 questions:

1- Is the 2nd panel a subpanel or just a second service equipment enclosure? It's got it's own service disconnect which is by code, grouped together in the main panel with the other. It's not being fed from a feeder however they ran an EGC with the conductors to the subpanel per feeder rules and as expected, did not bond it to the neutral bus in the 2nd panel.

So my second question is, was it necessary to run the EGC into the remote panel at all, or could they have just ran the N to the 2nd panel and bonded it to the EGC bar as a main bonding jumper? I believe 250.28 allows this. It seems to me it's a second service panel but with an EGC brought to it I'm not sure. And Is one way better than the other here?

If anyone is wondering why it matters, this is a solar design issue with load calc and 120% bus rules, etc. so knowing exactly what were dealing with is important.

 

[augie47]

FWIW this does not fit the classic definition of a split buss panel i don't believe but regardless, Panel 2 is simply a "sub-panel" and the supply to it would be a feeder and require a separate equipment ground from the neutral.

 

[infinity]

I agree with Augie. This is not a split-bus panel. It's a service with two service disconnects feeding two panelboards with one being a sub-panel remote from the other.

 

[hitehm]

FWIW this does not fit the classic definition of a split buss panel i don't believe but regardless, Panel 2 is simply a "sub-panel" and the supply to it would be a feeder and require a separate equipment ground from the neutral.

I agree except the 100A breaker feeding the sub is clearly labeled on the main panel as a "service disconnect" and it's feeding a MLO panel. Clearly, you would have to disconnect BOTH service breakers to kill service to the premises so it's definitely not a feeder breaker in that sense. So can a service disconnect be the sole protection for a feeder circuit with no dedicated OCPD on either end other than a main breaker, or can a service disconnect also simultaneously serve as the OC protection for a feeder?

 

[hitehm]

To me it's a "split-bus" panel in the sense that it definitely splits the main busbar coming from the meter to 2 separate panelboards with 2 separate busbars. The wire conductors feeding the remote panel are simply an extension of the remote panels bus.

 

[infinity]

It's

The wire conductors feeding the remote panel are simply an extension of the remote panels bus.

Traditional split-bus panels have a very consise configuration and this is not it. The conductors after the OCPD to the sub are feeder conductors.

 

[hitehm]

It's

Traditional split-bus panels have a very consise configuration and this is not it. The conductors after the OCPD to the sub are feeder conductors.

So if you were landing a solar breaker in the subpanel, would you consider the main panels busbar to be part of the busbars needing protection per 705 rules? You would if it was a feeder feeding back on the main's busbar, but it doesn't in this case. It has an isolated busbar that's fed from an isolated section of the main bus separate from the load side of the local enclosures bus. To me, that's at least similar enough to a split-bus to call it one. I understand how the traditional split-bus panels are constructed but I've never scene a "concise" definition to exactly what they are. The label is attached if interested.

Not trying to be argumentative, just looking for detailed clarity. Thanks for all your help as always.

 

[LarryFine]

That is clearly not a split-bus panel, because the bus is intact. Plus, there is no split bus where the two main breakers are. Granted, it could be said that the entire installation electrically resembles one.

It's really more of a two-panel installation with the two main breakers grouped in one panel. The remote panel is definitely a sub-panel, just as it would be with two separately-enclosed main breakers.

 

[don_resqcapt19]

I agree except the 100A breaker feeding the sub is clearly labeled on the main panel as a "service disconnect" and it's feeding a MLO panel. Clearly, you would have to disconnect BOTH service breakers to kill service to the premises so it's definitely not a feeder breaker in that sense. So can a service disconnect be the sole protection for a feeder circuit with no dedicated OCPD on either end other than a main breaker, or can a service disconnect also simultaneously serve as the OC protection for a feeder?

All service disconnect breakers supply feeders on the load side of of the service disconnect. In many case the feeder on the load side is simply the panel bus.

 

[don_resqcapt19]

So if you were landing a solar breaker in the subpanel, would you consider the main panels busbar to be part of the busbars needing protection per 705 rules? You would if it was a feeder feeding back on the main's busbar, but it doesn't in this case. It has an isolated busbar that's fed from an isolated section of the main bus separate from the load side of the local enclosures bus. To me, that's at least similar enough to a split-bus to call it one. I understand how the traditional split-bus panels are constructed but I've never scene a "concise" definition to exactly what they are. The label is attached if interested.

Not trying to be argumentative, just looking for detailed clarity. Thanks for all your help as always.


View attachment 2565441

No. None of the solar current would ever be on the panel bus bars. It would go from the sub panel to the service disconnect to the service conductors.

 

[busman]

It looks like an unusual configuration of what I would call a panel with sub-feed breaker.

 

[Little Bill]

That panel is just a meter-main. Normally what we see is a 200A with the meter in one section and the panel in the other. This one is a 400A with the same setup but has a separate breaker to feed another panel not in the enclosure. Also, instead of 200A breakers, they chose to have a 175A and 100A. These are fine as the unit is rated 400A max, which means you can have smaller than 400A.

 

[hitehm]

It looks like an unusual configuration of what I would call a panel with sub-feed breaker.

It's definitely not a traditional sub feed breaker that matches your green image. However, I think don's point (and others) is correct in that, the wiring for the remote panel is on the load side of a service disconnect and therefore, regardless of what we call it, it can no longer be considered service wiring/equipment and therefore must be feeder wiring.

My follow-up question is: When doing the load calcs and comparing the total loads for the property to the service OCP, do you add the 2 main breakers together for your total service OCP? This is where a panel like this gets tricky. Normal panels with bus-fed feeders, the feeders are part of the main loads, really no different than the branch circuits. They all add together and are not to exceed the service rating, the panel and main breaker rating. With these multiple and isolated enclosures that's not the case. The loads for this property are 246A total. This panel divides these loads on 2 isolated mains: 175A + 100A for what I consider, a total of 275A of service OCP. However, if an inspector looks at the load calcs and then applies them against just the main breaker where the solar is landed, he's gonna say it exceeds the rating and now I have an uphill battle on my hands.

BTW, the main panel supply side is rated at 400A and so is the service to the house, so that's not an issue.

 

[Joethemechanic]

I understand what a split bus panel is and how they work. What I never really understood is why they were used. What are the advantages?

 

[infinity]

I understand what a split bus panel is and how they work. What I never really understood is why they were used. What are the advantages?

The only real advantage was that you didn't need a single main breaker which could in theory save you a few bucks when you purchased the panel. You still had a sub-feed breaker for the lower portion of the panel so that would deduct from the savings of no main by a few bucks.

 

[Joethemechanic]

The only real advantage was that you didn't need a single main breaker which could in theory save you a few bucks when you purchased the panel. You still had a sub-feed breaker for the lower portion of the panel so that would deduct from the savings of no main by a few bucks.

So they used the 6 hand operations rule to get around not having a main breaker? I'm not seeing the savings.

 

[infinity]

So they used the 6 hand operations rule to get around not having a main breaker? I'm not seeing the savings.

That's correct. This was back in the day when you had branch circuit appliance panels and power panels.

 

[Stuff]

So they used the 6 hand operations rule to get around not having a main breaker? I'm not seeing the savings.

The factory could ship a 200 amp panel with a single 60 amp breaker feeding the lighting and appliance bus instead of having a 200 amp main breaker feeding a single bus. Today that is $15 vs. $100 so a $85 savings.

 

[jaggedben]

It looks like an unusual configuration of what I would call a panel with sub-feed breaker.

View attachment 2565447

No, it's not any kind of sub feed. And it's the most typical configuration for a 400A resi service. Just today I happened to be looking at a recent Eaton version of this panel which is very little changed from the Cutler Hammer model in the pics.