OCP protection question

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A touch off topic.
Is there a wire type EGC with this feeder.
I bring it up because of the 3/0 to the 200 with a 225 OCPD.
The EGC if a wire type was installed.
It may be under sized per NEC if was size off of the 200.
Even if a tap.

Great discussion by the way.
 
jim dungar said:
He is feeding a 200A breaker with a 225A breaker. What part of the code prohibits this? The issue is the protection of the conductors between these breakers.
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I guess I was just stuck on this part of the Article

a panelboard shall be protected by an overcurrent
protective device having a rating not greater than that of
the panelboard.
Click to expand...
 
Tulsa Electrician said:
A touch off topic.
Is there a wire type EGC with this feeder.
I bring it up because of the 3/0 to the 200 with a 225 OCPD.
The EGC if a wire type was installed.
It may be under sized per NEC if was size off of the 200.
Even if a tap.

Great discussion by the way.
Click to expand...
The EGC is always sized off the upstream OCPD.
 
PD1972 said:
The general rule is that overcurrent protection needs to be upstream of whatever it is protecting (ie, at the point of supply)

There are two different systems that require overcurrent protection in the scenario you're providing - the feeder conductors (art. 215) and the panelboard (art. 408). The feeder OCPD is the 225A circuit breaker in the switchboard. In my opinion, the panelboard OCPD is the 200A MCB at the panelboard. If there wasn't a MCB, I would then say that the 225A OCPD at the switchboard would be the panelboard OCPD. However, just based on nominal mains ratings of panelboards, I don't think this matters as either nominal mains/bus rating (225A @ 208Y/120V or 250A @ 480Y/277V) may be protected by either a 200A or 225A breaker.

As stated by other posters, the #3/0 feeder conductors need to match the OCPD size unless it's a tap. The point of supply for the feeder is at the switchboard and not at the panelboard so the 200A MCB doesn't provide overcurrent protection for that feeder.
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So in conclusion we can say that the 200A feeder isn't protected by the upstream 225A breaker, correct? I was discussing this issue with a fellow engineer and they mentioned that the feeder could be protected, by a 225A breaker because of the 80% rule, but I countered stating that the NEC does not state a breaker cannot be loaded to 100%, its the manufacturer who sets that limitation. Now if we split the loads from continuous to non-continuous there could be a situation where the breaker could be loaded to 100% and the feeder would be pulling more then 200A and not trip.

Can anyone confirm if my logic makes any sense at all?
 
Dengineer said:
So in conclusion we can say that the 200A feeder isn't protected by the upstream 225A breaker, correct? I was discussing this issue with a fellow engineer and they mentioned that the feeder could be protected, by a 225A breaker because of the 80% rule, but I countered stating that the NEC does not state a breaker cannot be loaded to 100%, its the manufacturer who sets that limitation. Now if we split the loads from continuous to non-continuous there could be a situation where the breaker could be loaded to 100% and the feeder would be pulling more then 200A and not trip.

Can anyone confirm if my logic makes any sense at all?
Click to expand...
whether it is continuous or noncontinuous load has no effect on the sizing of the OCPD rating to protect the conductors.

tap conductors are protected for short circuits by the upstream OCPD and for overloads by the downstream OCPD. your situation seems likely to be a tap conductor situation if the tap rules were followed.

motor circuit conductors are typically protected for short circuit by the upstream OCPD and for overload by the overloads.

most other conductors are protected by the upstream OCPD for both short circuits and overloads.
 
Dengineer said:
So in conclusion we can say that the 200A feeder isn't protected by the upstream 225A breaker, correct? I was discussing this issue with a fellow engineer and they mentioned that the feeder could be protected, by a 225A breaker because of the 80% rule, but I countered stating that the NEC does not state a breaker cannot be loaded to 100%, its the manufacturer who sets that limitation. Now if we split the loads from continuous to non-continuous there could be a situation where the breaker could be loaded to 100% and the feeder would be pulling more then 200A and not trip.

Can anyone confirm if my logic makes any sense at all?
Click to expand...
No the feeder can be protected by the 225 amp breaker under two conditions. One; where the feeder conductors have an ampacity of 225 amps or more, or two, where the feeder has an ampacity of 200 amps or more and is installed in accordance with 240.21(B)(1) or (B)(2).
 
Dengineer said:
So in conclusion we can say that the 200A feeder isn't protected by the upstream 225A breaker, correct? I was discussing this issue with a fellow engineer and they mentioned that the feeder could be protected, by a 225A breaker because of the 80% rule, but I countered stating that the NEC does not state a breaker cannot be loaded to 100%, its the manufacturer who sets that limitation. Now if we split the loads from continuous to non-continuous there could be a situation where the breaker could be loaded to 100% and the feeder would be pulling more then 200A and not trip.

Can anyone confirm if my logic makes any sense at all?
Click to expand...
Both the 200A and 225A breakers have been tested by UL to carry 100% of their rating in open air, with all of their connections exposed. Likewise both breakers are reduced to 80% load when installed inside of electrical enclosures, like they are in the real world, when the load exceeds 3 hours. This loading matches up exactly with the NEC for conductor sizing. This is a code and standards issue, it is not manufacturer dependent.

So the 225A breaker can have 200A conductors feeding a 200A main breaker if the rules of 240.21(B) are followed.
 
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