service equipment protection

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mwm1752

mwm1752

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I have a 1200 amp rated service equipment - six switches as the service disconnecting means -- calculated load is under 1200 amps -- the disconnecting means sum is 1600 amps
I understand 230.80 conductor sizing in relationship to calculated load but still looking for code allowing equipment that has the bus bar rated below the disconnecting means sum This would follow an example of having a calculated load for an 100 amp rated panel @ 80 amps while using 125 Amp OCPD for the disconnecting means -- 408.36?
 
combination of 230.42 (conductor size must carry load) and 230.71 (up to 6 disconnects permitted) and 230.79 (service disconnect must be rated as high as load)
 
If panel is only listed as service equipment with a main breaker installed, then that breaker will protect the bus.

If panel is listed as service equipment as main lug fed with multiple mains, then your bus ampacity is not really being treated any differently then your service conductor ampacity

Not sure what or if there is code section to cite, just my opinion.

Have done similar before and was never questioned about it, one I do recall was 800 amp bus, two 400 amp and two 125 amp breakers. Total load calculation probably under 400 amps - but one 400 amp breaker was a spare for future use and anticipated load when that happens was to likely be less then 300.
 
Thanks for commenting to conversation
Panelboard. A single panel or group of panel units designed for assembly in the form of a single panel, including buses and automatic overcurrent devices, and equipped with or without switches for the control of light, heat, or power circuits; designed to be placed in a cabinet or cutout box placed in or against a wall, partition, or other support; and accessible only from the front.
-- 408.30 clearly states "panelboard shall be protected by an overcurrent protective device having a rating not greater than that of the panelboard"
408.36 Overcurrent Protection
In addition to the requirement of 408.30, a panelboard shall be protected by an overcurrent protective device having a rating not greater than that of the panelboard. This overcurrent protective device shall be located within or at any point on the supply side of the panelboard.

Exception No. 1 & 230.80 both refer to 230.71 Maximum Number of Disconnects
Exception No. 1: Individual protection shall not be required for a panelboard used as service equipment with multiple disconnecting means in accordance with 230.71. In panelboards protected by three or more main circuit breakers or sets of fuses, the circuit breakers or sets of fuses shall not supply a second bus structure within the same panelboard assembly.
230.80 Combined Rating of Disconnects
Where the service disconnecting means consists of more than one switch or circuit breaker, as permitted by 230.71, the combined ratings of all the switches or circuit breakers used shall not be less than the rating required by 230.79.

230.79 which only calls out minimum for OCPD as a disconnecting means
230.79 Rating of Service Disconnecting Means
The service disconnecting means shall have a rating not less than the calculated load to be carried, determined in accordance with Part III, IV, or V of Article 220, as applicable. In no case shall the rating be lower than specified in 230.79(A), (B), (C), or (D).

I do not interprete (as of this moment) that the initial statement of 408.30 clearly states "panelboard shall be protected by an overcurrent protective device having a rating not greater than that of the panelboard" has been nullified with an exception.
 

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If there is one main breaker than the overcurrent protective device must be rated no larger than the panelborad. There are 6 overcurrent protective device's in your scenario. You do not add up the breaker sizes.


As David posted

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.
Click to expand...
 
Dennis Alwon said:
If there is one main breaker than the overcurrent protective device must be rated no larger than the panelborad. There are 6 overcurrent protective device's in your scenario. You do not add up the breaker sizes.



where does the equipment buss get referenced -- service conductors is stated

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 theampacity of the service conductors, provided the calculated
load does not exceed the ampacity of the service
conductors.
Click to expand...
 
mwm1752 said:
...
I do not interprete (as of this moment) that the initial statement of 408.30 clearly states "panelboard shall be protected by an overcurrent protective device having a rating not greater than that of the panelboard" has been nullified with an exception.
Click to expand...
The individual protection noted in 408.36 Exception No. 1 is the protection noted in the general statement. I realize you are saying the multiple protection afforded by the up-to-six disconnecting means exceeds the panelboard [bus] rating. However, if the protection device is not required the condition it not be greater than the panelboard rating is rendered moot by logical deduction.

Requirements for equipment on the supply side of service disconnecting means relies solely on they be rated not less than the calculated load. No overcurrent device will protect service conductors during a fault condition on the supply side.
 
Dennis Alwon said:
If there is one main breaker than the overcurrent protective device must be rated no larger than the panelborad. There are 6 overcurrent protective device's in your scenario. You do not add up the breaker sizes.


As David posted
Click to expand...

Which is correct but something I've never understood.
Calculations done at the time of install may be greatly exceeded as load is added to a service over the years.
Not sure if anyone ever actually thinks about the service conductors until they burn up from an overload.

JAP>
 
jap said:
Which is correct but something I've never understood.
Calculations done at the time of install may be greatly exceeded as load is added to a service over the years.
Not sure if anyone ever actually thinks about the service conductors until they burn up from an overload.
Click to expand...
As I understand it, the CMP will not entertain any change unless empirical evidence can be shown that a significant number of fires or deaths have resulted from such.
 
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