Distribution Service - Feeder Circuits-Code compliance 1

[NAZ55]

I have a project where I am trying to install equipment for distribution service to two different buildings in a substation facility.

The distribution service from a normal and alternate source will be fed via ATS (located on the inner wall of first kysor building- Control Center#2) to two 225A panels via 225A breakers. The service cable from ATS will also be fed to the second building (Control Center #1)150A breaker via a 225A breaker located isnde CC#2.

Please refer to the attached drawing. (service side of ATS not shown)

My question for you all is, do you see any code violation?

Does it comply with NEC 230.3? If not, what is the reasoning behind complying with NEC 230.3?

Also, most importantly are you aware of any breaker panel, which would carry all three 225A breakers within one assembly (items inside dashed line) and has a small form factor to be mounted inside control center 2?

I will appreciate your advice.

 

[davidbeach]

Feeders, not service conductors. Different definitions, different rules.

Define "small form factor".

 

[NAZ55]

That's where the problem is. I am making it a feeder.
The service is fed from ATS, where it's switched between distribution service provider and emergency generator.
Since the ATS is going to be in CC#2 then in order to provide service to CC#1 I will have to reroute the conductor from load side of ATS to CC#1. I am trying to figure out if the way I proposed is ok.

 

[davidbeach]

Your only service is ahead of the ATS. From there on in all you have are feeders and branch circuits. Service rules don't apply when the second building is fed by a feeder, only when fed by a service.

 

[NAZ55]

Thanks davibeach. That was my assumption, but I figured I would rather not assume and get advice from the experts here. Appreciate your comment. Also, are you aware of any panel designed for three feeder circuits only with 225A breakers? My service is 120/240 single phase.

 

[davidbeach]

As I said, define "small form factor". Yes, there are panels, probably by many different manufacturers, that will allow installation of multiple 225A breakers, but small enough, I have no idea.

 

[rbulsara]

If you are feeding a structure which already has a service and you are adding new panelboard from a different service, you may have code issues as more than one service is only permitted under special circumstances. Also a main disconnect is required at each structure.

At the least, you will need to clearly identify number and location of the main disconnects that need to be opened to cutoff total power to a structure in case of an emergency.

Rafiq Bulsara

http://www.srengineersct.com

 

[NAZ55]

davidbeach,
to answer your question. I am looking for a panelboard that only has a place for three or four 225A thermal magnetic breakers that's it. You got any that comes to mind?

rbulsara,
we don't have a dual service issue here. Only one service will be fed to all structures at a time, whether it be distribution service or emergency generator.
Could you advise which code requires main disconnect at each structure? Also, does the code identify the location of this disconnect? (inside/outside)
The breakers are supposed to be serving as overcurrent protection and emergency disconnect.

 

[davidbeach]

The smallest of the Square D I-Line panelboards will take 6 3-phase 250A frame breakers. Probably the smallest I know of, there may be others.

 

[rbulsara]

zazm:

Look (read) up NEC articles 220, 225 and 230 in their entirety. It is there.

Rafiq Bulsara

http://www.srengineersct.com

 

[erickench]

My only question is this. Why do you have two circuit breakers in series and why are they different ratings? Usually a main breaker would feed a minimum of two smaller breakers.

Eric Kench, P.E.

 

[NAZ55]

Eric,

How else would you protect the feeder going to CC#1?
If there's a Short Circuit on the line going to CC#1 then you will end up taking out the AC to CC#2 as well if it were not for the breaker at CC#2 protecting that feeder. The 150A breaker at CC#1 is to be used as an overcurrent protection and emergency disconnect for the building load.

Now my question to you would be, why did this occur as odd to you?

 

[erickench]

You're describing selective coordination. That's not what you have set up here. You have two circuit breakers in series. That 225A breaker is not feeding CC2 it's in the CC1 circuit. It does'nt seem to accomplish any real purpose. Selective coordination is when you have one main breaker feeding a group of smaller breakers in parallel. The smaller breakers trip first thus isolating the fault from the rest of the system.

Eric Kench, P.E.

 

[davidbeach]

Wow, taking something so simple and making it so complex.

The source is ahead of the ATS. The panel is the dashed line inside Control Center 2. There is a 225A breaker that feeds over to Control Center 1, a separate building. In Control Center 1, there is a building disconnect. Why 225A and 150A? That doesn't matter if the conductors between the buildings are protected by the 225A breaker. Without the 225A breaker the conductors to Control Center 1 would have to be large enough to be protected by whatever is protecting the ATS, and that would undoubtedly cost more than the 225A breaker. If the feed between Control Center 2 and Control Center 1 were protected ahead of the ATS, any problem in that circuit would take out both sources to Control Center 2, not a very good design.

I see no practical scenario under which either breaker could be removed. I'd expect a better understanding of the situation from somebody with a PE.

 

[NAZ55]

I agree with davidbeach's comments. david thanks for your detail explaination to eric. I tried to explain the same thing in brief wording. To add to that 150A breaker is sized for the load and the 225A breaker ahead of 150A is protecting the conductors. This way if you have an overload it wouldn't take out the feed from CC#2 going to CC#1. If both breakers are sized the same then unless there is a way to change the protection curve it will be a race b/w which breaker will take out the overload.

 

[davidbeach]

I think you're being overly optimistic though. Unless there is more to it than you show, the outage is the same regardless of which breaker trips, and for any fault downstream of the 150A breaker you are likely to trip both it and the 225A. You may get some selectivity for true overloads but that depends on the breaker curves.

 

[rbulsara]

ZAZM:
I don't want to be designing for you, but there are other issues with your apparent design. The "star" connection shown below ATS is worriesome. The ATS ideally should be feeding a panelboard with a MCB and then branch breakers in that panel feeding the subpanels.

Also coordinating 150A and 250A breakers in series is futile as they won't. Plus the feeder needs to be sized for 250A and not 150A, etc. I hate to do this but you need some other expert eyes in your organization to look at your design.

The lack of comments here by others does not amount to approval of your design, not is this place to get your design checked.



Rafiq Bulsara

http://www.srengineersct.com

 

[NAZ55]

rbulsara,

My post here is not to get some kind of approval or reassurance from you or any other expert in this forum. The purpose of the post was to generate constructive criticism and evaluate and learn from others thought process.
Also, please define your ideal world? The situation you described may be ideal for building internal circuits, with one feeder and multiple branch circuits. I don't see how it's ideal for multiple feeders application.

Oh! by the way, If you don't have any constructive ideas or thoughts please refrain from chipping in.


davidbeach,
you are correct, there is a little bit more to the story.
The AC to the whole substation is being fed by a plant which is going away. We are establishing a new service to replace plant supply. 150A breaker is already present at CC#1 , which is currently being fed by the plant. I don't think it's cost effective to change the breaker at CC#1 since it's already sized properly for the load.

 

[erickench]

Why not just have one circuit breaker sized for both the load and the conductor in circuit CC1? Surely a 150A circuit breaker would protect a feeder sized for 225A if you chose to make it that large. NEC 430.31 to 430.63 describes Motor and Branch Circuit protection. Two different protection devices are required for a motor circuit in that one acts as the overload and the other acts as the short circuit protection. If this is what you are trying to accomplish then I suggest you read that article of the code. There is no separate protection for the motor and the conductor.
As for my explanation of selective coordination the main circuit breaker would be protecting the feeder connected to the ATS. That circuit breaker would open last if a fault occurs in one of the parallel branches that it feeds. The smaller circuit breakers are faster and would open for any fault that occurs in the branch that it protects. I thought I made this clear.

Eric Kench, P.E.

 

[burnt2x]

ZAZM,
When you said

" I don't think it's cost effective to change the breaker at CC#1 since it's already sized properly for the load. "

did you mean that the 150A breaker is also properly sized with the new source's available short-circuit capacity? The 150A breaker might be okay with the old source but exceeded with the new SCMVA available from the new source.