Circuit Breaker Coordination

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Brien Bradley

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Is there a number/percentage used to size feeder breaker that feeds various 1200A panel breakers (one 3000A bkr. feeding seven 1200A bkrs.). I looked in the code book but have been unable to find any info.
 
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C.b.

See art 215.3, the main breaker will only handle its rating. In your own house you might haver a 200A service, but if you added up all your breaker values you most likel would find it to total over 200A. So in your scenario the 7 1200A panels is quite a bit over 3000A. You"ll have to calculate your loads, to get the real picture.
 
I would call the manufacturer of the breaker or a local Electrical Distributor that carries that brand breaker. It sounds like you are looking for a "fully-rated" combination.
Just my $.02
 
Or is he asking the ratio of the current rating of the upstream circuit breaker in relation to downstream breakers to coordinate their time current characteristics to minimize (so called) nusiance trips?
 
If there is a set of plans for the original installation handy, it might make determining the calculated load at a glance a bit easier.

Depending on what your role is with the installation, it may be a good idea to do your own load calculation, if you suspect that the feeder is overloaded.

It would be a good idea to keep the conversation public (on this thread), as there's a lot of people here with more experience on such a large installation than me. :)

Can you provide more details as to what led you here? :)
 
brian john said:
Or is he asking the ratio of the current rating of the upstream circuit breaker in relation to downstream breakers to coordinate their time current characteristics to minimize (so called) nusiance trips?
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I hope not, because one does not exist.
 
Whether it is lower stream or higher stream, feeder sizes will be based on the load connected and adjustment factor , can be done if you go through NEC or u can find @ cooper bussmann.......
 
georgestolz said:
If there is a set of plans for the original installation handy, it might make determining the calculated load at a glance a bit easier.

Depending on what your role is with the installation, it may be a good idea to do your own load calculation, if you suspect that the feeder is overloaded.

It would be a good idea to keep the conversation public (on this thread), as there's a lot of people here with more experience on such a large installation than me. :)

Can you provide more details as to what led you here? :)
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I thought this was a public forum. I've looked through countless articles in the NEC and haven't found any answer remotely close to the situation I have here.
 
Brien Bradley said:
Is there a number/percentage used to size feeder breaker that feeds various 1200A panel breakers (one 3000A bkr. feeding seven 1200A bkrs.). I looked in the code book but have been unable to find any info.
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Based on the wording in your question, this is not an NEC issue. It is a design issue based on your connected loads.

The NEC only cares that each breaker is sized to protect the conductors (which are sized to the total load) applied to it. The only time that the "sum of breaker handle ratings" is used is with some tap rules contained in article 240 and for muliple main services in article 230. In general the NEC does not even care about the coordination of devices (there are some requirements for elevators, hospitals, and some life safety circuits).
 
lowdry has a good analogy here (#2)

Let's say this was a simple single family home (SFH) with a 50A service and MCB.
The home owners (HO) want to add a hot tub.

See where it's headed?
No one cares "how many breakers" are in that 50A panel.
One only cares can the panel supply the new load (the hot tub) while sustaining the existing load.

Your situation is exactly the same, just on a larger scale.
 
Brien Bradley said:
I thought this was a public forum.
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Yes, Brien, it is - I think you misunderstood what I said. By private messaging me about the subject, then our replies are only seen by you and me.

I am not as versed on an installation as big as the one you are dealing with, as the rest of the forum is. This forum consists of hundreds and hundreds of engineers, inspectors and electricians with more experience than I have. By asking for my opinion privately, then what I say isn't being scrutinized by the more experienced, for any mistakes that I make.

A service/feeder/branch circuit situation like you are describing should not get an ampclamp (amp-meter) and a nod, IMO. A full load calculation should be done to determine how many amps are currently left over in the installation.

If you begin doing the load calculation and start getting hung up, trying to determine how to calculate it, by all means, return to this thread with your numbers and let us look them over for you.

Please don't be frustrated with the replies you get: every reply I've seen on this thread have been more or less right on the money.

Trying to figure out a shortcut is not a good idea with an installation of this magnitude. Whoever has requested that the system be added to ought to have the money to pay for your time to do it safely. :)
 
Brien Bradley said:
Is there a number/percentage used to size feeder breaker that feeds various 1200A panel breakers (one 3000A bkr. feeding seven 1200A bkrs.). I looked in the code book but have been unable to find any info.
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Brien !

You have a incomer of 3000A & outgoing of 7 X 1200 A..

It might have designed by somone who arrived all connected load based on the client requirement before they start the construction.. If you provide us the load on each 1200A feeder, we can say whether it is safe or over loaded.

Hope you got an answer , if you want more provide us with more data.

Thanks
 
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