# Split Bus Panel Feed



## acebradley (Mar 1, 2012)

Man, I couldn't get any takers when I posted something similar in the alternative energy topic section, so I thought I'd try my luck in the code section here. This one will be in reference to the 2011 NEC.

Here is the scenario: Split bus panel, (5) 2-pole breakers in main section including 40A, 20A, 50A, 50A, and 60A. The 60A feeds the lower bus section. PV installer installed the PV breaker in the last remaining space in the upper bus section (at the opposite end of the main lugs) with a 50A breaker. Panel rating is 150A with the lower section shown as 100A max OCPD rating. Installer says this is a supply side connection since there is no single main OCPD. 

Seems to me this is almost no different than a load side connection at opposite ends of the busbar, the only difference being that there is no single main OCPD protecting the busbar. However, the (5) breakers in the upper section are considered the disconnecting means per 230.71. So in my mind, 705.12(D)(2) would apply and the sum of the ampere ratings of the overcurrent devices would exceed the 120% rule for the ampacity of the busbar.

It seems to me that the installer could have avoided any issues by doing a true supply side connection and not installing a breaker on the busbar. Has anybody ran into this scenario before or have any opinions on the matter?


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## Black Dog (Oct 16, 2011)

acebradley said:


> Man, I couldn't get any takers when I posted something similar in the alternative energy topic section, so I thought I'd try my luck in the code section here. This one will be in reference to the 2011 NEC.
> 
> Here is the scenario: Split bus panel, (5) 2-pole breakers in main section including 40A, 20A, 50A, 50A, and 60A. The 60A feeds the lower bus section. PV installer installed the PV breaker in the last remaining space in the upper bus section (at the opposite end of the main lugs) with a 50A breaker. Panel rating is 150A with the lower section shown as 100A max OCPD rating. Installer says this is a supply side connection since there is no single main OCPD.
> 
> ...


Where does the Bus-bar originate?


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## zen (Jun 15, 2009)

What does pv mean. What size breaker did he install? Recently I was looking at a federal pacific panel that sounds the same. 6 spaces for 240v on top which is 5 and 1 to feed lower half. If I remember correctly. Really im not understand the question. There are many older panels that have no main only main lugs and it was up to the electrician and inspector to ensure the feeders were properly sized. Then the next thing others have done is to putting the feeders on a breaker on the bus which seems better than no ocpd at all.

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## acebradley (Mar 1, 2012)

It is a split bus panel, MLO with 5 main breaker section at top that feed the big appliances, and one of which feeds the lower bus section with a 60A. The PV system feed is a 50A breaker. I am wondering if this is basically considered a load side connection. In my mind it is, even though there is no single main breaker to kill power to the entire bussing.

PV = photovoltaic system


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## zen (Jun 15, 2009)

I have seen many of these type panels. My concern with them is that they can get over loaded. If its a 125 amp panel what size wire is feeding it

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## wildleg (Apr 12, 2009)

I have not installed any PV, or even grid tie meters. but let's read what the section you mentioned says:



> (2) Bus or Conductor Rating. The sum of the ampere ratings
> of overcurrent devices in circuits *supplying power to a
> busba*r or conductor shall not exceed 120 percent of the rating
> of the busbar or conductor.



the sum of the overcurrent devices supplying power to the busbar is just the one 50a breaker you mentioned, no ? the other ones are receiving power from the busbar.


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## don_resqcapt19 (Jul 18, 2010)

This is a supply side connection. No different than if you tap the service conductors.


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## zen (Jun 15, 2009)

So the installer installed the breaker on the bus as a new main and the pv is now the feeder?. For u guys who have forgotten more than I may ever know tollerate me if u can. There are panels like 100 amp main breaker and the breaker is on the bus the sane as a breaker so is a pv a line side to split bus or a load from the split bus. 

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## don_resqcapt19 (Jul 18, 2010)

If there is a main breaker connected to the service conductors, then the PV breaker would not be a supply side connection.

Typical split bus panels do not have a main breaker that is connected to the service conductors. The service conductors are most often directly connected to the panel bus when you have a split bus panel.


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## zen (Jun 15, 2009)

I would think that it would be a good idea to update that panel just to avoid any headaches later. New expensive equipment connected to outdated equipment isnt a goid idea

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## don_resqcapt19 (Jul 18, 2010)

zen said:


> I would think that it would be a good idea to update that panel just to avoid any headaches later. New expensive equipment connected to outdated equipment isnt a goid idea
> 
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I don't see any issues using the existing split bus panel for a connection to a new PV system.


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## zen (Jun 15, 2009)

Maybe I mean as an electrician I wouldnt push a new panel in a customer if it was fine. Now if I was a homeowner spending alot of money on a upgrade to my home , then yes id think I need a new panel

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## zen (Jun 15, 2009)

Like this

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## acebradley (Mar 1, 2012)

My main concern is that the location of the PV breaker is creating an installation that is essentially the same as a load side connection. The nature of the split bus panel and the number and size of the breakers in the top section of the panel creates a potential to overload the bus, and by adding another 50 amp load to the bus that was not previously there, there is even more of a problem in my mind. And since there is no main breaker to protect the bus in the event of an overload situation, there is nothing to stop it from overheating. And I am now even rethinking the supply side connection. Even with a supply side connection on this particular split bus panel, there still exists the potential to overload that bus and not have any way of disconnecting power to it because there is no single overcurrent device protecting it.


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## don_resqcapt19 (Jul 18, 2010)

acebradley said:


> My main concern is that the location of the PV breaker is creating an installation that is essentially the same as a load side connection. The nature of the split bus panel and the number and size of the breakers in the top section of the panel creates a potential to overload the bus, and by adding another 50 amp load to the bus that was not previously there, there is even more of a problem in my mind. And since there is no main breaker to protect the bus in the event of an overload situation, there is nothing to stop it from overheating. And I am now even rethinking the supply side connection. Even with a supply side connection on this particular split bus panel, there still exists the potential to overload that bus and not have any way of disconnecting power to it because there is no single overcurrent device protecting it.


If the section the breaker is being installed in, has only service disconnects, it is a line side connection. There is no potential to overload the panel unless the rating of the PV breaker exceeds the rating of the panel bus. The PV is not a load, it is a supply. Installing it does not increase the load on the service or the panel bus. The current supplied by the PV system is just current that will not be supplied by the utility supply.

The potential to overload a service that has multiple service overcurrent protective devices always exists if additional loads are added. The service entrance conductors and panel bus for a service with multiple service over current devices is only protected by design, not by an overcurrent protective device.


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## zen (Jun 15, 2009)

Thats what I was trying to say. These type panels are feed straight from the meter load side. Some will sure add things to these panels til the amps are graeter than the feeder size and if pv at that connection is a feeder for that panel then I dont see how a 50 or 60 amp is gonna be enough. .. So id get a real 125 amp main breaker panel . .

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## acebradley (Mar 1, 2012)

OK. For comparison, let's say you have a main breaker installed now instead of the main lug attachment. Why then would you be required to follow the bus ampacity rules of 705.12? Essentially the current flow will be exactly the same as a supply side connection to a busbar with no main breaker, yet we are required to limit the amount of PV load installed and locate it on the opposite end of the bus to limit the current flow, as some articles I have read are suggesting. The only difference is that now you have a main breaker which will at least limit the amount of utility current that can flow onto the bus in the case of an overload situation.

In reality, if the service size was calculated correctly to begin with, then we would really never see a situation to cause overheating of the bus because the PV system would essentially just replace some of the utility load when it is producing. But, the code still tells us that we have to limit the PV supply on the bus for a load side connection. 

Seems to me that if this situation of feeding a bus with no main overcurrent protection is not an issue because it is a supply side connection, even though the current will flow the same as a load side connection in my mind, then why would we be limited to the amount of PV supply installed as a load side connection? Then it seems to me that we should feasibly be allowed to have a PV supply rated up to the rating of the main OCPD. I really just don't see the logic in the differentiation of Supply Side or Load Side connection if connecting directly to the bus. 

Still trying to wrap my head around why the code addresses the issue in this manner.


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## RIVETER (Sep 26, 2009)

acebradley said:


> Man, I couldn't get any takers when I posted something similar in the alternative energy topic section, so I thought I'd try my luck in the code section here. This one will be in reference to the 2011 NEC.
> 
> Here is the scenario: Split bus panel, (5) 2-pole breakers in main section including 40A, 20A, 50A, 50A, and 60A. The 60A feeds the lower bus section. PV installer installed the PV breaker in the last remaining space in the upper bus section (at the opposite end of the main lugs) with a 50A breaker. Panel rating is 150A with the lower section shown as 100A max OCPD rating. Installer says this is a supply side connection since there is no single main OCPD.
> 
> ...


Respectfully, you are thinking too much.:thumbsup:


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