Cutler Hammer panels

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
It doesn't.

It applies to using something that you know is the same but not listed as such in that application.

Can you use a Murray breaker in a Siemens panel, even though they are the same? No.

Can you treat the busbar in a 150A panel as if it's a 225A panel even though it's the same? No.
You can use a Murray breaker in a Siemens panel and vice versa. If you look at the sticker in a Murray panel it says to use Siemens breakers.
 

kwired

Electron manager
Location
NE Nebraska
Not sure how that applies to bus bar ampacity...?:?
No.

Busbars and other conductors, internal to listed equipment, are typically sized based on heat rise not cross sectional area.
Kind of what I was going to reply with - they can do testing and get a listing on anything they can conclude passes any testing for conditions they are concerned about. Build it without testing and getting that listing, you are stuck with general listing requirements for same kind of item you are building.
 

jaggedben

Senior Member
You can use a Murray breaker in a Siemens panel and vice versa. If you look at the sticker in a Murray panel it says to use Siemens breakers.
It depends on the panel. Especially the other way around (i.e. some Siemens do not list Murray). PITA when an inspector flags it and you know it really. just. doesn't. matter.
 

Strathead

Senior Member
One of our master electricians did some research and got confirmation of something I have long suspected. For Cutler-Hammer panels (and I suspect for others as well) they don't make differently rated busbars for every different panel. Specifically, and he got it in writing, all 150A - 225A CH panels have 225A rated busbars.

I am confused here. I have always known that panel manufacturers make panels in "frame sizes" similar to disconnects. For Square D the frame sizes are 125, 225, 400, 600, 800,and then I think 1200 and 2000, not sure there may be same in between but I don't think so. All you have to do is look at all of the part numbers that make up an assembly to know that a 60 amp MLO or MCB panel has a 125A bus. What am I missing?
 
I am confused here. I have always known that panel manufacturers make panels in "frame sizes" similar to disconnects. For Square D the frame sizes are 125, 225, 400, 600, 800,and then I think 1200 and 2000, not sure there may be same in between but I don't think so. All you have to do is look at all of the part numbers that make up an assembly to know that a 60 amp MLO or MCB panel has a 125A bus. What am I missing?
Mostly this discussion is about "loadcenters" where there are more sizes at the lower end. The case I mentioned a few posts back was three phase panelboards. I just remembered another case where I ordered a 200 amp I line, but it had a 400 amp buss, so there is definitely some standardization of parts going on where it might have a higher bus rating then they say.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Can you treat the busbar in a 150A panel as if it's a 225A panel even though it's the same? No.
I disagree. The code refers to the rating of the busbar, not the rating of the panel. In the absence of documentation that says otherwise, we have taken the busbar rating to be the same as the main breaker, but when we have documentation from the manufacturer that a 200A panel has 225A busbars, that's different. We have yet to face our first AHJ challenge on this issue; I'll let you guys know how it turns out.
 

pv_n00b

Senior Member
Location
CA, USA
I disagree. The code refers to the rating of the busbar, not the rating of the panel. In the absence of documentation that says otherwise, we have taken the busbar rating to be the same as the main breaker, but when we have documentation from the manufacturer that a 200A panel has 225A busbars, that's different. We have yet to face our first AHJ challenge on this issue; I'll let you guys know how it turns out.
It looks like it would pass the letter of the NEC with documentation showing the rating of the busbar. It would be interesting to know if the CMP considered this and approved it or if this loophole just kind of slipped into the code because they made an assumption that the panelboard rating and busbar rating would always match. Anyone know someone on the CMP they can ask?
 

kwired

Electron manager
Location
NE Nebraska
I am confused here. I have always known that panel manufacturers make panels in "frame sizes" similar to disconnects. For Square D the frame sizes are 125, 225, 400, 600, 800,and then I think 1200 and 2000, not sure there may be same in between but I don't think so. All you have to do is look at all of the part numbers that make up an assembly to know that a 60 amp MLO or MCB panel has a 125A bus. What am I missing?
When you get into ~8 spaces or less sometimes you run into 100, 70, 60, 40 and 30 amp rated loadcenters, that is what I recall from the QO line, there may be others out there.

I disagree. The code refers to the rating of the busbar, not the rating of the panel. In the absence of documentation that says otherwise, we have taken the busbar rating to be the same as the main breaker, but when we have documentation from the manufacturer that a 200A panel has 225A busbars, that's different. We have yet to face our first AHJ challenge on this issue; I'll let you guys know how it turns out.
:thumbsup:
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
It looks like it would pass the letter of the NEC with documentation showing the rating of the busbar. It would be interesting to know if the CMP considered this and approved it or if this loophole just kind of slipped into the code because they made an assumption that the panelboard rating and busbar rating would always match. Anyone know someone on the CMP they can ask?
Loophole? I'm certainly not looking for loopholes that will allow me to design unsafe systems. If a 200A panel has a 225A busbar, there is no difference between a 200A panel and a 225A panel with a 200A main breaker changeout. We have been replacing CH 200A/200A panels with 255A/200A panels in jurisdictions where line side connections are disallowed or made difficult/expensive when we didn't need to.
 

pv_n00b

Senior Member
Location
CA, USA
There is much more that goes into panelboard design than just the basic ampacity of the components. One of the big design issues is heat rise inside the panelboard under full load. Circuit breakers have a temperature rating and panelboards have to operate within that rating. The end result is that panelboards are rated and listed for what the manufacturer rated them at, not based on the ampacity of the internal components. If a 200A rated MLO panelboard has a 225A busbar it can't have a 225A feeder.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
There is much more that goes into panelboard design than just the basic ampacity of the components. One of the big design issues is heat rise inside the panelboard under full load. Circuit breakers have a temperature rating and panelboards have to operate within that rating. The end result is that panelboards are rated and listed for what the manufacturer rated them at, not based on the ampacity of the internal components. If a 200A rated MLO panelboard has a 225A busbar it can't have a 225A feeder.
OK, but the code specifically applies its rules to busbar ratings, and "gut swapping" where we put, say, a 225A busbar set into a 200A panel and keep the 200A main breaker in order to give us more headroom in 705.12(B)(2)(3)(b) is fairly routine. What we have found out is that the busbars we have been replacing are the same as what we have been replacing them with. Since the main breaker remains the same, any heating from loads will not change.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
If a 200A rated MLO panelboard has a 225A busbar it can't have a 225A feeder.
That's not what we are doing. We wouldn't put a 225A main breaker in a 200A panel and run a 225A feeder to it just because it has 225A busbars.
 

pv_n00b

Senior Member
Location
CA, USA
OK, but the code specifically applies its rules to busbar ratings, and "gut swapping" where we put, say, a 225A busbar set into a 200A panel and keep the 200A main breaker in order to give us more headroom in 705.12(B)(2)(3)(b) is fairly routine. What we have found out is that the busbars we have been replacing are the same as what we have been replacing them with. Since the main breaker remains the same, any heating from loads will not change.
Is this "gut swapping" a manufacturer approved modification of listed equipment?

Increasing the power in a panelboard increases the heat. So if you have a 200A 240V panelboard and you add an allowed 40A PV backfeed now you go from a full load of 48kW to 57.6kW with an increase in heating (20%), if the loads draw that much. Now if it has a 225A bus and that is used in the calcs then you go up to a possible 63.6kW. That's a 32.5% increase. People making up the NEC decided 20% was acceptable but that was the limit.
 
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ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Is this "gut swapping" a manufacturer approved modification of listed equipment?
That's a non-issue now because we won't need to do it any more; the 200A panelboards already have 225A busbars. Actually, I may have misspoken on that issue; I specified "replace 200A panel with 225A panel with 200A main breaker" on the plans; I don't know for sure what the guys in the field were doing.

Increasing the power in a panelboard increases the heat. So if you have a 200A 240V panelboard and you add an allowed 40A PV backfeed now you go from a full load of 48kW to 57.6kW with an increase in heating (20%), if the loads draw that much. Now if it has a 225A bus and that is used in the calcs then you go up to a possible 63.6kW. That's a 32.5% increase. People making up the NEC decided 20% was acceptable but that was the limit.
The NEC settled on 120% of the busbar rating, specifically. BTW, the door stickers (enclosure rating) on these 200A panels say "Maximum mains 225A".
 
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