Question on total branch circuit breakers adding to more than the main breaker

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Little Bill said:
One thing that might be a problem is the two 150A breakers. The stab/bus rating might not allow 150A, especially if the breakers are side by side, which makes both on the same stab. ...
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This was my thought as well. Often we hear "I was told ______________________" when it's a paraphrasing and critical details may be missing.
 
So what is the deal with that Exception #2?

So what is the deal with that Exception #2?

So what is the deal with this? Is this a panelboard with a single bus but fed by parallel breakers? Or a panelboard with two bus sections? When would one use this?

Exception No. 2: Individual protection shall not be required for a
panelboard protected on its supply side by two main circuit breakers or
two sets of fuses having a combined rating not greater than that of the
panelboard. A panelboard constructed or wired under this exception
shall not contain more than 42 overcurrent devices. For the purposes of
determining the maximum of 42 overcurrent devices, a 2-pole or a
3-pole circuit breaker shall be considered as two or three overcurrent
devices, respectively.
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I may well be dating myself by speaking of "checking accounts." But I will take the risk.

Suppose you open a new checking account at the bank, and ask the banker to send you a box of 100 checks pre-printed with your name and address. Suppose the banker replies that they can only issue you a box of 50 checks, because you didn't deposit enough in your new account to cover the amount of money that could be written on 100 checks. That is the essence of your situation. It does not matter how many checks you have available to use. What matters is whether the total amount of the money written on the checks is less than the amount of money in your account.
 
Most times, when I have the opportunity to put an ammeter on a service conductor to a dwelling, it doesn't exceed 20 amps.
 
How do protect a panelboard with a common bus by (2) overcurrent devices on it's supply side ?

That was the point of my happy no in the first place, so, I'm thinking about reinstating it. :)


JAP>
 
electrofelon said:
So what is the deal with this? Is this a panelboard with a single bus but fed by parallel breakers? Or a panelboard with two bus sections? When would one use this?
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In the old days, it was not unusual to find manufacturers paralleling small protective devices, particularly 400A fuses. Maybe this is left over code language (not like that ever happens;)).
 
charlie b said:
I may well be dating myself by speaking of "checking accounts." But I will take the risk.

Suppose you open a new checking account at the bank, and ask the banker to send you a box of 100 checks pre-printed with your name and address. Suppose the banker replies that they can only issue you a box of 50 checks, because you didn't deposit enough in your new account to cover the amount of money that could be written on 100 checks. That is the essence of your situation. It does not matter how many checks you have available to use. What matters is whether the total amount of the money written on the checks is less than the amount of money in your account.
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I'd get a different banker because he didn't know that the box of 50 checks is not going to keep you from breaking the bank either.

If going by that logic, a good banker would only send you (1) pre-printed check. :)


JAP>
 
My bank just told me that my automatic check refills will now be only 80 checks instead of the usual 100. I'll just have to write them for more money! :)
 
jap said:
How do protect a panelboard with a common bus by (2) overcurrent devices on it's supply side ?

That was the point of my happy no in the first place, so, I'm thinking about reinstating it. :)


JAP>
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jim dungar said:
In the old days, it was not unusual to find manufacturers paralleling small protective devices, particularly 400A fuses. Maybe this is left over code language (not like that ever happens;)).
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So per that exception, can I take, say, two 50 amp feeders (two 50 amp breakers) both to double lugs in a 100 amp MLO panelboard? Seems like that is what it is saying.....Or is this exception talking about "special" equipment that might not exist anymore?
 
electrofelon said:
So per that exception, can I take, say, two 50 amp feeders (two 50 amp breakers) both to double lugs in a 100 amp MLO panelboard? Seems like that is what it is saying.....Or is this exception talking about "special" equipment that might not exist anymore?
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According to NEC 240.8, you can not create your own paralleled protective device.
 
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