Next-Size Up Rule for Equipment or Conductors or Both?

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xptpcrewx

Power System Engineer
Location
Las Vegas, Nevada, USA
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Licensed Electrical Engineer, Licensed Electrical Contractor, Certified Master Electrician
Hi,

I am wondering if section 240.4(B)'s "Next Size Rule" also applies to equipment (as in 240.3) instead of conductors alone?
Also what are we supposed to do when section 240.4(B) and 240.4(G) conflict with one another? Do you take the more restrictive rule?

Thanks in advance!
 

augie47

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Location
Tennessee
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State Electrical Inspector (Retired)
240.4(B), being a part of 240 applies to over-current devices in general.
210.19 & 215.2 cover conductors and require that the conductors be sized for the load
110.3(B) as well as specific Articles regulate equipment protection.
I think 240.4(G) stands alone in that those Articles included provide you with specifics directing you as to the allowance of "next size up"
 

don_resqcapt19

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Location
Illinois
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240.4 only applies to the protection of conductors per the parent text in the section. (B) and (G) are not in conflict with each other...(G) is just a special case that works as an exception to the parent text in 240.4 which requires conductors to be protected at their ampacity.
(2020 code)
240.4 Protection of Conductors. Conductors, other than flexible cords, flexible cables, and fixture wires, shall be protected
against overcurrent in accordance with their ampacities specified in 310.14, unless otherwise permitted or required in
240.4(A) through (G).
Even (B) is an exception to the parent text as it permits the conductors to be protected using the next standard size OCPD rating greater than the conductor ampacity.
 

xptpcrewx

Power System Engineer
Location
Las Vegas, Nevada, USA
Occupation
Licensed Electrical Engineer, Licensed Electrical Contractor, Certified Master Electrician
(B) and (G) are not in conflict with each other...(G) is just a special case that works as an exception to the parent text in 240.4 which requires conductors to be protected at their ampacity.

There are maximum OCPD settings/ratings that must not be exceeded in some sections under (G). For example, look at 430.62.
It seems to me like permitting (B) could create a conflict with (G) since 430.62 has a "not greater than" requirement.
 

don_resqcapt19

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Location
Illinois
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retired electrician
There are maximum OCPD settings/ratings that must not be exceeded in some sections under (G). For example, look at 430.62.
It seems to me like permitting (B) could create a conflict with (G) since 430.62 has a "not greater than" requirement.
The rating of the OCPD permitted by (G) will always be greater than the rating permitted by (B).

Remember for a motor feeder you start with the largest permitted setting for the largest motor served by the feeder. That is 250% of the motor current, plus the full load currents of the other motors. The feeder conductor is sized at 125% of the largest motor current plus the full load currents of the other motors.
 

xptpcrewx

Power System Engineer
Location
Las Vegas, Nevada, USA
Occupation
Licensed Electrical Engineer, Licensed Electrical Contractor, Certified Master Electrician
The rating of the OCPD permitted by (G) will always be greater than the rating permitted by (B).

Remember for a motor feeder you start with the largest permitted setting for the largest motor served by the feeder. That is 250% of the motor current, plus the full load currents of the other motors. The feeder conductor is sized at 125% of the largest motor current plus the full load currents of the other motors.

Thanks don_rescapt19. As you mentioned, 430.62(A)'s setting is only based on the largest motor OCPD plus the remaining motor FLC's; whereas 240.4(B)'s setting is based on the conductor ampacity. If you consider over sized feeder conductors, (B) can actually be greater than (G).
 

xptpcrewx

Power System Engineer
Location
Las Vegas, Nevada, USA
Occupation
Licensed Electrical Engineer, Licensed Electrical Contractor, Certified Master Electrician
Ok, just to summarize:

I am wondering if section 240.4(B)'s "Next Size Rule" also applies to equipment (as in 240.3) instead of conductors alone?

Anything in 240.4 does NOT apply to equipment. Therefore, the "Next Size Rule" does not apply to equipment protection, only conductors.

Also what are we supposed to do when section 240.4(B) and 240.4(G) conflict with one another? Do you take the more restrictive rule?

Subsections (A) through (G) within section 240 may conflict with one-another, but these are mostly exceptions (permissions) to the parent language. Whenever there is a conflict between mandatory rules in (A) through (G), the the most restrictive rule must apply.
On the other hand, if the permissions in (A) through (G) allow different settings/ratings, we are free to choose whichever one we want.

Do I have that right?
 
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