Sizing of service lateral conductors

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travski06

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The Power company is making me provide the wire from the transformer to a 800 amp switch gear. The calculated load is 395 amps. I was going to pull parallel 500 mcm's based off of 310.16, and 240.4b however there is no overcurrent device. Is there any code reference's that would allow me to do so or would the calculated amperage of my wire have to be 800 amps or more. Thanks
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
The Power company is making me provide the wire from the transformer to a 800 amp switch gear. The calculated load is 395 amps. I was going to pull parallel 500 mcm's based off of 310.16, and 240.4b however there is no overcurrent device. Is there any code reference's that would allow me to do so or would the calculated amperage of my wire have to be 800 amps or more. Thanks

You have a service disconnect, right? Just one or multiple?

99% of the time we pull parallel 500 copper for our 800 amp services.
 

travski06

Member
Cow this goes from the transformer to our gear. Our gear has 4 200 amp breakers and 2 60 amp breakers. Other than the transformer no disconnecting means.
Thanks
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Cow this goes from the transformer to our gear. Our gear has 4 200 amp breakers and 2 60 amp breakers. Other than the transformer no disconnecting means.
Thanks

I think your answer can be found in 230.42 but beware if someone wants to increase the load then you may have some issues. If my customer were expecting an 800 amp service I believe I would give them the appropriate service conductors for future use.

230.42 Minimum Size and Rating.
(A) General. The ampacity of the service-entrance conductors before the application of any adjustment or correction factors shall not be less than either (A)(1) or (A)(2). Loads shall be determined in accordance with Part III, IV, or V of Article 220, as applicable. Ampacity shall be determined from 310.15. The maximum allowable current of busways shall be that value for which the busway has been listed or labeled.
(1) The sum of the noncontinuous loads plus 125 percent of continuous loads
(2) The sum of the noncontinuous load plus the continuous load if the service-entrance conductors terminate in an overcurrent device where both the overcurrent device and its assembly are listed for operation at 100 percent of their rating
(B) Specific Installations. In addition to the requirements of 230.42(A), the minimum ampacity for ungrounded conductors for specific installations shall not be less than the rating of the service disconnecting means specified in 230.79(A) through (D).
(C) Grounded Conductors. The grounded conductor shall not be smaller than the minimum size as required by 250.24(C).
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I agree with Dennis. With no single OCP device, your conductors only need to meet the calculated load.
Contractually might be a different issue.
 

iwire

Moderator
Staff member
Location
Massachusetts
Depending on where the legal service point is the NEC may not apply at all to these conductors even if the power company has you install them.

If the NEC does apply to these you would have to apply 240.21(C)(4).
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
If these are customer owned cables, and that is becoming the case more and more often around here, then the rules in the NEC apply. In addition to the conductor having to have an ampacity equal to or greater than the calculated load, these conductors will have to have overload protection per 230.90. Assuming that there is a single main disconnect, then the service conductors for this service with a calculated load of 395 amps will have to have an ampacity of at least 701 amps.
 
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