230.90(A) and 230.80 I'm a little confused

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wawireguy

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I'm reading those sections trying to decipher what exactly is says.

230.80 makes it sound like if you have more than one service disconnect it they must add up to the capacity of the feeder. IE: 200 amp service. 150amp breaker and a 50amp breaker.

230.90(A) Exception 3 says the sum of multiple over current devices can exceed the feeder capacity.

So one says that the disconnecting means cannot exceed the feeder capacity while the other says the overcurrent protection can. I need help here.
 
Here is the NECHB commentary following 230.80.

Section 230.71(A) permits up to six individual switches or circuit breakers, mounted in a single enclosure, in a group of separate enclosures, or in or on a switchboard or several switchboards, to serve as the required service disconnecting means at any one location. Section 230.80 refers to situations in which more than one switch or circuit breaker is used as the disconnecting means and indicates that the combined rating of all the switches or circuit breakers used cannot be less than the rating required for a single switch or circuit breaker.
Section 230.90 requires an overcurrent device to provide overload protection in each ungrounded service conductor. A single overcurrent device must have a rating or setting that is not higher than the allowable ampacity of the service conductors. However, Exception No. 3 to 230.90(A) allows not more than six circuit breakers or six sets of fuses to be considered the overcurrent device. None of these individual overcurrent devices can have a rating or setting higher than the ampacity of the service conductors.
In complying with these rules, it is possible for the total of the six overcurrent devices to be greater than the rating of the service-entrance conductors. However, the size of the service-entrance conductors is required to be adequate for the computed load only, and each individual service disconnecting means is required to be large enough for the individual load it supplies. See the commentary following 230.90(A), Exception No. 3.
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Sounds to me that you can have up to 6 disconnects that summed, are rated for more than the service entrance conductors can carry. I just don't understand how 230.80 says you can't do that but then in 230.90 it turns around and says you can.
 
wawireguy said:
I'm reading those sections trying to decipher what exactly is says.

230.80 makes it sound like if you have more than one service disconnect it they must add up to the capacity of the feeder. IE: 200 amp service. 150amp breaker and a 50amp breaker.

230.90(A) Exception 3 says the sum of multiple over current devices can exceed the feeder capacity.

So one says that the disconnecting means cannot exceed the feeder capacity while the other says the overcurrent protection can. I need help here.
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I don't think 230.80 says the multiple disconnects must add up to the capacity of the service conductors, as you have stated.

It says the ratings of the multiple disconnects must be "not less than" the calculated load to be carried. It doesn't mention the size of the conductors at all, only the load to be carried, and it can be greater than that load, but not less than.
 
How about this scenario:

400 amp meter can with lugs. Feed two 200 amp panels inside a house. Also feed a detached shop with a 200 amp feed from meter can. Mains are located in the panels. Load calculation shows 215 amps total.

Does it fly? Yay or nay?
 
wawireguy said:
How about this scenario:

400 amp meter can with lugs. Feed two 200 amp panels inside a house. Also feed a detached shop with a 200 amp feed from meter can. Mains are located in the panels. Load calculation shows 215 amps total.

Does it fly? Yay or nay?
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I think this might violate 230.40.
 
Consider the panelboard in any home. If you add up all the branch circuits they exceed the single Main Breaker rating, yet all ungrounded conductors are protected.

Exception 3
The service conductors protection can be split up into 2 to 6 OCPDs. If one of these becomes overloaded or a fault developes it will trip to protect the downstream conductors & the upstream service conductors.
 
wawireguy said:
What exactly does 230.90(A) mean and when do you apply it?
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The rating of the service OCPD must protect the the ungrounded conductors feeding it from either overload or a fault that occurs on the OCPD's load side. ( It cannot protect them against a fault on it's line side. )

If 2 to 6 OCPDs are used, the total sum of their ratings may exceed the the ampacity of the service conductors ( just like in your panelboard ) so long as the calculated load does not exceed the ampacity of the service conductors.
 
I don't see any conflict between 230.80 and 230.90(A). 230.80 says that the breakers have to add up to at least the calculated load. It doesn't prohibit the sum being higher than the calculated load. 230.90(A) exception 3 is saying that it is ok for the sum to be higher than the ampacity of the service conductors.
 
So is this example legal:

400 amp service with no disconnects feeds three 200 amp panels inside a house. Load calc is under 300.
 
I'm just not quite getting exactly what these code sections are saying and how to apply them. I'm close though. I've almost got it.
 
wawireguy said:
So is this example legal:

400 amp service with no disconnects feeds three 200 amp panels inside a house. Load calc is under 300.
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I believe it is (if these are main breaker panels). The sum of the breakers exceeds the calculated load and exceeds 100 amps (230.79(C)), so that takes care of 230.80.

The sum of the breakers probably exceeds the ampacity of the the service conductors, but that is ok per 230.90(A) exception 3 as long as the ampacity of the service conductors meets or exceeds the calculated load.
 
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