overcurrent protection

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Chris Rankin

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Question, 225 amp breaker from a main switchboard feeds a 200amp main breaker panelboard with 3/0 feeder conductors, are the 3/0 conductors protected or does the 225 amp breaker have to be replaced. I found in article 240 tap rules that might apply but none of them deal with a main breaker panelboard, any suggestions?
 
Re: overcurrent protection

The 200 amp #3/0 feeder and the 200 amp panelboard are OK. It's the 225 amp OCPD for the feeder that needs to be 200 amps also.
 
Re: overcurrent protection

But why> The 200 amp main breaker on the secondary side of the feeders will not allow more than the rating of the conductors anyway, or am I missing something?
 
Re: overcurrent protection

But because the breaker on the secondary side is 200 amps how would the conductors be exposed to more than that?
 
Re: overcurrent protection

If I read the OP correctly, there is 225 amp with 3/0 feeding a 200 amp breaker. It is the 3/0 between the 225 and the 200 that is the issue. 3/0 is only rated at 200 amp @75 degree.

[ February 17, 2006, 12:17 PM: Message edited by: 1793 ]
 
Re: overcurrent protection

Chris,
But because the breaker on the secondary side is 200 amps how would the conductors be exposed to more than that?
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Unless you are using the "tap" rules or some other special rule, then first part of 240.21 applies.
Overcurrent protection shall be provided in each ungrounded circuit conductor and shall be located at the point where the conductors receive their supply ...
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Don
 
Re: overcurrent protection

Yup! Replace the breaker at the gear or.....4/0 at 75c.....(IMO $) I would change the 225 at the gear.
 
Re: overcurrent protection

Originally posted by Chris Rankin:
But because the breaker on the secondary side is 200 amps how would the conductors be exposed to more than that?
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What if someone came along behind you and tapped that feeder ?
 
Re: overcurrent protection

Note; that the code says that conductors may be tapped WITHOUT overcurrent protection at the tap under these conditions. So it is ok to not have a breaker ahead of this but since there is one there I have to change it? from a practical stand point why???
 
Re: overcurrent protection

Chris:

You are right this is fun.

Do you REALLY have a "tap"? Is a "tap" not utilizing a Split Bolt "Kearney" connection to a "run"? Illustration can be found on page 11 of the Code Check-Electrical book

The OP reads as a "feeder". As a feeder the "tap" rules do not apply; just a thought.
 
Re: overcurrent protection

Chris:

You have a feeder. You do not have a tap. Your feeder is rated for 200 amps using the 75 deg. column of 310.16. You must install an OCPD rated for the ampacity of your wire, which is 200 amps. Since 200 amps is a standard fuse or breaker size, that is what you must use.

Now, there is nothing to prevent someone (even you) from installing a tap to that feeder to supply something else. Of course the tap rules have to be observed. But your feeder will still be protected according to it's ampacity.
 
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