service conductor protection

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vanwalker

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I know it is here somewhere?
In what code section does it allow you to size service conductors by calculated load only.( ex 200 amp main breaker panel with 150 amp calculated load , allowing you to use conductors for load only instead of normal 200 amp conductors?)hope this makes sense? THANKS GEO
 
This wouldn't apply to a service with a single main service OCPD. For example a service in a single family dwelling. You could not install a panel with a 200 amp main and then size the service entrance conductors for the connected load.
 
Here is the code reference:


VII. Service Equipment ? Overcurrent Protection
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. 1: For motor-starting currents, ratings that conform with 430.52, 430.62, and 430.63 shall be permitted.
Exception No. 2: Fuses and circuit breakers with a rating or setting that conforms with 240.4(B) or (C) and 240.6 shall be permitted.
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.
Exception No. 4: Overload protection for fire pump supply conductors shall conform with 695.4(B)(1).
Exception No. 5: Overload protection for 120/240-volt, 3-wire, single-phase dwelling services shall be permitted in accordance with the requirements of 310.15(B)(6).
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THANKS FOR THE REPLY !!
(A)
Does this mean ?____ that as long as the breaker does not exceed conductor ampacity , that it is not required to match breaker to conductor or panel size if you know the load? (EX smaller conductors to match panel loads)
 
vanwalker said:
THANKS FOR THE REPLY !!
(A)
Does this mean ?____ that as long as the breaker does not exceed conductor ampacity , that it is not required to match breaker to conductor or panel size if you know the load? (EX smaller conductors to match panel loads)
Click to expand...

Geo, I am not sure I understand your question. For a dwelling you would first calculate the load. This will determine the minimum size service. If for example your calculated loaded required a 100 amp service and you installed a 200 amp service, the 200 main OCPD would require conductors based on 200 amps not the calculated load of 100 amps.
 
THANKS
I have been told that on a 200 amp (commercial) breaker, that 200 amp wire is not required if the calculated load is less than the normally required (3/0 - 4/0 cu)size. This will be my last try, sorry as i do not understand this reasoning.
 
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