small neutral service entrance conductors

mnicholet · July 28, 2010, 5:06pm

This is a 200 AMP service. The 120V hot conductors look appropriate but the neutral is smaller. Problem with this? Thanks.

PICT0014 (Small).JPG

mlarson · July 28, 2010, 5:07pm

Neutral(grounded conductor) can be one size smaller.

mlarson · July 28, 2010, 5:12pm

Size the Neutral Conductor: 220.22

310-15(B)(6) states that the neutral service and/or feeder conductor can be smaller than the ungrounded (hot) conductors, provided the requirements of 215.2, 220.22 and 230.42 are met. 250.24(B)(1) states that the neutral cannot be smaller than the required grounding electrode conductor specified in Table 250.66

rmeier2 · July 28, 2010, 8:04pm

Although it may work out to be that way, one size smaller is not part of the NEC. The neutral conductor is sized according to the calculated maximum unbalanced load. As Michael said it can’t be smaller than the size permitted for the GEC.

250.24© Grounded Conductor Brought to Service Equipment. Where an ac system operating at less than 1000 volts is grounded at any point, the grounded conductor(s) shall be run to each service disconnecting means and shall be connected to each disconnecting means grounded conductor(s) terminal or bus. A main bonding jumper shall connect the grounded conductor(s) to each service disconnecting means enclosure. The grounded conductor(s) shall be installed in accordance with 250.24©(1) through ©(3).
Exception: Where more than one service disconnecting means are located in a single assembly listed for use as service equipment, it shall be permitted to run the grounded conductor(s) to the assembly common grounded conductor(s) terminal or bus. The assembly shall include a main bonding jumper for connecting the grounded conductor(s) to the assembly enclosure.
(1) Routing and Sizing. This conductor shall be routed with the phase conductors and shall not be smaller than the required grounding electrode conductor specified in Table 250.66 but shall not be required to be larger than the largest ungrounded service-entrance phase conductor. In addition, for service-entrance phase conductors larger than 1100 kcmil copper or 1750 kcmil aluminum, the grounded conductor shall not be smaller than 12½ percent of the area of the largest service-entrance phase conductor. The grounded conductor of a 3-phase, 3-wire delta service shall have an ampacity not less than that of the ungrounded conductors.
(2) Parallel Conductors. Where the service-entrance phase conductors are installed in parallel, the size of the grounded conductor shall be based on the total circular mil area of the parallel conductors as indicated in this section. Where installed in two or more raceways, the size of the grounded conductor in each raceway shall be based on the size of the ungrounded service-entrance conductor in the raceway but not smaller than 1/0 AWG.
FPN: See 310.4 for grounded conductors connected in parallel.

mnicholet · July 28, 2010, 8:28pm

Would you write up FI?

rmeier2 · July 28, 2010, 9:35pm

Mark do you see an issue with this installation?

mlarson · July 28, 2010, 10:36pm

It’s fairly common but I should have said just smaller.