Distribution Panel Size

lookin2pass

Member
Location
Oklahoma
I am currently wiring a commercial building for a national chain of fast food resturaunts. The panels are part of a package that they send out with all of the other materials for the store. they have sent me a distribution panel that has the main breakers for 4 other panels and 2 A/C units. The "DP" panel is a three phase/800amp and the breakers that are in it feeding the other panels are: (1) 400A, (1) 200A, (2) 150A, and (2) 60A (A/C units). They add up to 1020Amps. Is this legal? I can not find anything that says that I can have 1020 amps feeding out of an 800Amp panel in the code book. Am i overlooking something?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Have you ever filled a panel with 20 amp breakers? What is the total as compared to the panel rating?

As long as the calculated load is less than 800 amps, there is no issue with what you are installing. I assume this is the main service and if so the service conductors are sized on the calculated load and not on the total of the breakers in the panel.
 

lookin2pass

Member
Location
Oklahoma
Thanks Don

Thanks Don

I left out an important part of the question. The bussing is rated for 800 amps. There is no 800 amp main breaker in the "DP' panel. if the other panels feeding out of it were to pull the max load of 1020 amps the buss and wire in the "DP" panel wouldn't be big enough to handle it. I'm going to put a 800 amp dissconnect on the feeders to "DP" and it will be protected at that point. Thank you again for your help.
 

texie

Senior Member
I left out an important part of the question. The bussing is rated for 800 amps. There is no 800 amp main breaker in the "DP' panel. if the other panels feeding out of it were to pull the max load of 1020 amps the buss and wire in the "DP" panel wouldn't be big enough to handle it. I'm going to put a 800 amp dissconnect on the feeders to "DP" and it will be protected at that point. Thank you again for your help.
You don't need an 800 amp disconnect ahead of the panel. I'm confident that the panel they gave you is SUSE rated using the 6 circuit rule. This is easy to check. This is one situation where you don't need to protect the panelboard at it's rating. Common application in light commercial.

You really think they are going to give you an extra for that?
 

texie

Senior Member
You don't need an 800 amp disconnect ahead of the panel. I'm confident that the panel they gave you is SUSE rated using the 6 circuit rule. This is easy to check. This is one situation where you don't need to protect the panelboard at it's rating. Common application in light commercial.

You really think they are going to give you an extra for that?
I might add: see 230.71 Informational Note and 408.36 Exception 1.
 

Smart $

Esteemed Member
Location
Ohio
... They add up to 1020Amps. Is this legal? I can not find anything that says that I can have 1020 amps feeding out of an 800Amp panel in the code book. Am i overlooking something?
...

As long as the calculated load is less than 800 amps, there is no issue with what you are installing. I assume this is the main service and if so the service conductors are sized on the calculated load and not on the total of the breakers in the panel.
Currently don't have access to Code but IIRC, the sum of multiple service disconnecting means ratings cannot exceed the ampacity of the service conductors. Are not te panel busbars service conductors? If "DP" is in fact the service equipment, the panel rating cannot be less than the sum of its ocpd ratings.
 
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pete m.

Senior Member
Location
Ohio
230.90 Where Required. Each ungrounded service conductor
shall have overload protection.
(A) Ungrounded Conductor. Such protection shall be provided
by an overcurrent device in series with each ungrounded
service conductor that has a rating or setting not higher than
the allowable ampacity of the conductor. A set of fuses shall
be considered all the fuses required to protect all the ungrounded
conductors of a circuit. Single-pole circuit breakers,
grouped in accordance with 230.71(B), shall be considered as
one protective device.

Exception No. 3: Two to six circuit breakers or sets of fuses
shall be permitted as the overcurrent device to provide the
overload protection. The sum of the ratings of the circuit
breakers or fuses shall be permitted to exceed the ampacity of
the service conductors, provided the calculated load does not
exceed the ampacity of the service conductors.


Is this what you are after?

Pete
 

kwired

Electron manager
Location
NE Nebraska
230.90 Where Required. Each ungrounded service conductor
shall have overload protection.
(A) Ungrounded Conductor. Such protection shall be provided
by an overcurrent device in series with each ungrounded
service conductor that has a rating or setting not higher than
the allowable ampacity of the conductor. A set of fuses shall
be considered all the fuses required to protect all the ungrounded
conductors of a circuit. Single-pole circuit breakers,
grouped in accordance with 230.71(B), shall be considered as
one protective device.

Exception No. 3: Two to six circuit breakers or sets of fuses
shall be permitted as the overcurrent device to provide the
overload protection. The sum of the ratings of the circuit
breakers or fuses shall be permitted to exceed the ampacity of
the service conductors, provided the calculated load does not
exceed the ampacity of the service conductors.


Is this what you are after?

Pete
Sure hope it is. This is type of thing Smart normally does not miss on - must have had a rough night:)
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Engineer
Currently don't have access to Code but IIRC, the sum of multiple service disconnecting means ratings cannot exceed the ampacity of the service conductors. Are not te panel busbars service conductors? If "DP" is in fact the service equipment, the panel rating cannot be less than the sum of its ocpd ratings.
This is basically true for all other applications of a '6 disconnect rule', but service entrances (subject to article 230) are different.
 

Smart $

Esteemed Member
Location
Ohio
Now have access and can't seem to find it...
...Is this what you are after?
Not exactly :p

Sure hope it is. This is type of thing Smart normally does not miss on - must have had a rough night:)
The evidence is irrefutable :ashamed1:

This is basically true for all other applications of a '6 disconnect rule', but service entrances (subject to article 230) are different.
At least it wasn't totally my imagination :roll:
 

kwired

Electron manager
Location
NE Nebraska
Perhaps in the future, when loads are added and only feeder calc's are done.
But how are we to know now if someday only 20 amps will be added or if 400 amps will be added? If and when load is added - especially if something like 400 is added then a new load calculation needs done and appropriate action taken if what is existing is not enough to add it to.
 

lookin2pass

Member
Location
Oklahoma
I am completely convinced

I am completely convinced

I have no worries about installing it without the disconnect now. I have been an electrician for 23 years and have never ran into this exact situation before. I still wasn't sure how, or if, the 6 disconnect rule applied to my situation until 230.90 exception 3 was pointed out. I just joined the site yesterday and I have to say I love it. I spent a few hours today reading other peoples problems and questions and reading all of the great responses. Thank you again for all the help you guys gave me and I look forward to visiting this site often.
 

Smart $

Esteemed Member
Location
Ohio
But how are we to know now if someday only 20 amps will be added or if 400 amps will be added? If and when load is added - especially if something like 400 is added then a new load calculation needs done and appropriate action taken if what is existing is not enough to add it to.
I know this and agree with it in general. However, I see the potential for problems in certain situations. Perhaps, and I hope, those situations will never occur.

Consider a scenario where the Service Panel is 800A as above and feeding six (6) 200A subpanels. Your calculated load is, say 760A. The general purpose receptacles were divided up at 6 per 20A circuit and contribute 6 ? 180VA ? 120V = 9A per circuit and calculated load. Somewhere in the future the consumer loads these receptacle outlets to an average 15A per circuit during business hours. That's an increase of 67% over calculated load. If the calculated load for these receptacles was anything greater than 60A (40 receptacles), the actual load would go over over 800A... and no one really added any load as far as required calculations are concerned. What protects the service conductors???
 

lookin2pass

Member
Location
Oklahoma
this exception has been bothering me too

this exception has been bothering me too

I don't see how having 6 breakers in this panel can possibly be considered overcurrent protection. If we use the line of reasoning that it can't be overloaded because we did the load calculation and it is less than the panel and conductor rating, then that can be said for every panel. You have to know the load calculation to size the panel and the conductors feeding it. By that reasoning we don't need a main on any panel because we already know that it pulls less than what it is rated for. We coud just start bolting lugs onto the busses in every switchgear and distribution panel without fear of ever going high enough for it to be a problem. Add to that. the fact that there is no way to shut the DP down to do any type of service work and you have a major flaw in the electrical system. Now if I have a breaker that quits working properly, I can't just turn the main off and replace it, I have to call the power company to send a bucket truck out to pull the fuses on the pole to kill the power to the primary on their transformer. Every reason for having a main breaker or disconnect on any other panel would apply to the distribution panel for the same reason. I can't figure out any good reason why this exception exsists. It's driving me crazy thinking about it. I noticed a quote that somebody has at the bottom of their post and couldn't hep thinking how well it fit this rule. "just because you can do something, doesn't mean that you should" Thanks Smart $, i'm glad I'm not alone on this.
 
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