Cable protected by a breaker 2 levels upstream?

[mull982]

Can a cable be protected by a breaker that is located two levels upstream.

For instance lest say that in panel A there is a 600A breaker that feeds (2) sets of 350MCM cables which terminate in panel B. From panel B there is than an 800A breaker which feeds (2) sets of 350MCM cables which feed a panel C.

No I know that the (2) sets of 350MCM cables between panels B and C are not adequately protected by the 800A breaker in panel B. But can these cables be considered adequately protected by the 600A breaker two levels upstream of the cables in panel A?

Or does 240.21 imply that the conducotrs should be protected at the point in which they recieve their supply which would not allow the upstream 600A breaker to provide protection?

 

[charlie b]

Or does 240.21 imply that the conducotrs should be protected at the point in which they recieve their supply which would not allow the upstream 600A breaker to provide protection?

It does not "imply" that, it explicitly states that. The key word is "shall," not "should." I would say that your suggested installation would be non-compliant.

 

[don_resqcapt19]

While it doesn't meet the letter of the code rule, the cables are protected at their ampacity.

 

[mull982]

While it doesn't meet the letter of the code rule, the cables are protected at their ampacity.

So would you cite this as a code violationi although they are technically protected?

 

[charlie b]

So would you cite this as a code violation although they are technically protected?

I would. I know that if panel C had a load in excess of 600 amps, the breaker in panel A would trip before any damage would be done to the cables between B and C. But this is just plain wrong. For one thing, it is a bad design choice, in that under certain circumstances you could unnecessarily lose power to panel B. Also, why would anyone want to do this? Wouldn't it be cheaper to buy a 600 amp breaker, instead of an 800 amp breaker?

 

[ritelec]

Nice question.

What if it where one of them main lug out panelboards.

Would that comply.

Would not the feed out of the 800 protected by the 600 upstream kinda be the same?

 

[kenaslan]

Code Violation!

The 800A panel could be refed at a later date with a 1000A feed. The wires must be protected with the OCPD closest to the wire.

 

[ritelec]

Code Violation!

The 800A panel could be refed at a later date with a 1000A feed. The wires must be protected with the OCPD closest to the wire.

That turns into a different job.

No more 600 a ......no more paralleled 350's.......completely different.
IMHO (first time I ever wrote IMHO.thank you...that was fun)

 

[Strathead]

I would. I know that if panel C had a load in excess of 600 amps, the breaker in panel A would trip before any damage would be done to the cables between B and C. But this is just plain wrong. For one thing, it is a bad design choice, in that under certain circumstances you could unnecessarily lose power to panel B. Also, why would anyone want to do this? Wouldn't it be cheaper to buy a 600 amp breaker, instead of an 800 amp breaker?

I don't think it is a question of why would it be done, it seems to be a question of it is done but is it legal. I contend that it is, and, while I wouldn't design a system this way, I wouldn't spend the money to fix it. If the 800A breaker didn't exist at all, and the panel was a main lug only panel, the question wouldn't even be coming up.

The code does not say that the breaker attached to the wires needs to by sized right, it says the supply side breaker, which I interpret to mean "as opposed to a breaker on the load side."

Just my opinion. I can clearly see the other side of this argument.

 

[don_resqcapt19]

So would you cite this as a code violationi although they are technically protected?

I wouldn't. I know that it is poor design, as Charlie said, but I don't see any type of saftey hazard.

 

[mull982]

Let me take the example a step further. We still have the 600A feeder breaker in panel A. Panel B is actually a UPS bypass cabinet with the UPS input, output, and bypass breakers rated at 800A. From the UPS bypass cabinet we still have the (2) Sets of 350MCM however at panel C they terminate into a 600A Main breaker.

Does this change things any. I woulnd't think so as others have said the cables are still protected by the upstream 600A breaker. The 600A main breaker at panel C doesnt really come into play since we cant apply the tap rule seeing that the cable lenght between panels B and C is 50' indoors.

 

[charlie b]

The code does not say that the breaker attached to the wires needs to by sized right, it says the supply side breaker, which I interpret to mean "as opposed to a breaker on the load side."

Now I am going to call you on a violation - - - of "Charlie's Rule"! :happyyes: The code says neither of those two things. :happysad: What it says is that ". . . overcurrent protection . . . shall be located at the point where the conductors receive their supply. . . ." In the installation described in post #1, the conductors serving panel C receive their supply from the 800 amp breaker. That makes the installation a violation.

That said, I agree with Don that this does not present a safety hazard. I also agree that any future design changes are the responsibility of the designer and installer of those changes. We don't need to account today for the errors that someone else might make later.