I have a bit of a situation. I have (3) 400-amp rated panelboards, each on seperate floors above each other. First panel on level 7, up to 8 and then to 9. 120/240-volt, 3-phase, 4-wire. I have (1) 250-amp main breaker in the panel on level 7, lugs out of that panel up to 8 and lugs into the buss, then lugs off the buss up to level 9 and lugs onto the buss. 250MCM to each panel. Is this a code violation or would it fall under the tap rule? Recently had an occupancy inspection and this was stated in the report as needing a main breaker installed.
Feed thru panels on seperate floors
- Thread starter ericl22
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- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Code issues aside, every component in this set will be protected at, or below, its ampacity or rating. So if there are any real and present dangers in this installation, I do not know what they are.
On the other hand, if there are code issues to be resolved, I can say that the tap rules are not going to help your situation. The notion of the tap rules is that you can sometimes protect a conductor at its load end, rather than at the point at which it receives power. All such rules require protection to be installed at the load end. So if neither the floor 8 panel nor the floor 9 panel has a breaker, then their respective feeders do not meet the tap rule requirements.
My basic problem with this installation is in establishing the point at which a conductor receives its power. Consider the feeder to the floor 9 panel. It originates on floor 8, and there is no breaker on floor 8 to protect it. So the issue boils down to this: can we say that the feeder to the floor 9 panel gets its power from floor 7, and that the 250 amp main breaker on floor 7 is protecting it at its point of origin?
I think not. I think this violates the first paragraph of 240.21, and it does not meet the sub-paragraphs that follow.
One solution would be to install a 250 amp breaker within the floor 7 and floor 8 panels, to supply the feeders going up from those two points. Then you would not need main breakers at the upper panels.
On the other hand, if there are code issues to be resolved, I can say that the tap rules are not going to help your situation. The notion of the tap rules is that you can sometimes protect a conductor at its load end, rather than at the point at which it receives power. All such rules require protection to be installed at the load end. So if neither the floor 8 panel nor the floor 9 panel has a breaker, then their respective feeders do not meet the tap rule requirements.
My basic problem with this installation is in establishing the point at which a conductor receives its power. Consider the feeder to the floor 9 panel. It originates on floor 8, and there is no breaker on floor 8 to protect it. So the issue boils down to this: can we say that the feeder to the floor 9 panel gets its power from floor 7, and that the 250 amp main breaker on floor 7 is protecting it at its point of origin?
I think not. I think this violates the first paragraph of 240.21, and it does not meet the sub-paragraphs that follow.
One solution would be to install a 250 amp breaker within the floor 7 and floor 8 panels, to supply the feeders going up from those two points. Then you would not need main breakers at the upper panels.
Thanks alot. I have been beating my brain around all day. Well, the only down side to installing the main si that they are Federal Pacific panels. Good luck finding a main for that. Also, there is no room in the electrical room to add a main breaker enclosure. I'll have to change out the entire panel, which is good for me but not the customer. I should be able to get away with changing the panel out on level 8 and having a 250-amp main in and 250-amp main out, correct? If not I will have to change 2 of the panels out. Thanks again for your input.
- Location
- New Jersey
- Occupation
- Journeyman Electrician (retired)
charlie b said:
Panel "7" has a feed through bus that connected 250 kcmil conductors up to panel "8". Panel "8" has feed through bus and 250 kcmil conductors up to panel "9". All panels and conductors are protected according to their ampacity.
But since he already has a 250 amp CB protecting pael "7" why would another breaker be required?
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Let me offer the minor correction: a 250-amp main in, and a 250-amp feeder breaker out. Yes, that would be OK.ericl22 said:
But back to my earlier suggestion. Is there room on the floor 7 and floor 8 panels for a 250 amp feeder breaker? If so, then that would solve your problem, with minimal impact.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
I did say that I saw no dangers in doing that. But the issue is this: At what point does the feeder to the floor 9 panel get its supply? Look at the wording of the first paragraph of 240.21, and those are the words you will find.infinity said:
If you say that this feeder gets its supply from the floor 7 panel, then all is well. If you say that this feeder gets its supply from the lugs on the floor 8 panel, then you have a violation of 240.21.
- Location
- New Jersey
- Occupation
- Journeyman Electrician (retired)
charlie b said:
OK, I missed that part. So you're saying that this setup is fine with 2 panels (7 & 8) but not 3 (7 & 8 & 9).
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
No, the two-panel version has the same problem. Or I should say that it boils down to the same question. So how about giving me your answer to the question (i.e., what is the point at which the feeder gets its supply?)?infinity said:
- Location
- Illinois
- Occupation
- retired electrician
Charlie,
I see no code issue with the installation. The panels and conductors are all protected at or below their ratings. I think you can say that the bus in panel 7, the conductors to panel 8, the bus in panel 8 and the conductors to panel 9 are all the same conductor just with splices.
If for some reason I had a run protected with a 250 amp OCPD that started out with 250 kcmil, had a splice to parallel 1/0s and then back to 250 kcmil, would you be asking the same question? I don't see the panel bus as anything other than a splice in a conductor.
Don
I see no code issue with the installation. The panels and conductors are all protected at or below their ratings. I think you can say that the bus in panel 7, the conductors to panel 8, the bus in panel 8 and the conductors to panel 9 are all the same conductor just with splices.
If for some reason I had a run protected with a 250 amp OCPD that started out with 250 kcmil, had a splice to parallel 1/0s and then back to 250 kcmil, would you be asking the same question? I don't see the panel bus as anything other than a splice in a conductor.
Don
- Location
- New Jersey
- Occupation
- Journeyman Electrician (retired)
Feed through bus panels are very common in commercial installations. There are tens of thousands of them out there. I agree with Don but find the wording of 240.21 somewhat confusing.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
I don't have a problem with that interpretation. I did say that the question of "is it compliant" turns upon that very point. I just don't know whether the AsHJ around the country will treat the panel bus as a splice point, or as the point of origin of a brand new conductor.don_resqcapt19 said:
- Location
- Windsor, CO NEC: 2023
- Occupation
- Hospital Master Electrician
If the installation described were not acceptable per 240.21, then neither would receptacles where the conductors are landed on the screws instead of pigtailing the receptacles. There is no OCPD between the first and second receptacle either.
Edit to add: I am working on a five-story office building where all five floors' panelboards (480 and 208 alike) share a common feeder and are fed through as described. It can't be wrong, it was engineered.
Edit to add: I am working on a five-story office building where all five floors' panelboards (480 and 208 alike) share a common feeder and are fed through as described. It can't be wrong, it was engineered.
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