Service-Entrance Conductor Size
A set of service-entrance conductors is installed from the termination box to each service disconnecting means. The minimum size of the service entrance conductors is determined by performing a load calculation in accordance with NEC Article 220.

On reviewing the load calculation form for any of the occupancies, you will find the service disconnecting
means and overcurrent protection is sized not smaller than 125% of the continuous load and 100% of the noncontinuous loads. In addition, the minimum size of the neutral or grounded conductor is determined.

Finally, the minimum size is determined for the raceway that encloses the service-entrance conductors
and feeders.

The following table shows the switch rating, the rating of the fuse in the switch, and the sizes of the ungrounded (hot) and grounded (neutral) as well as the size of the EMT to be installed to enclose the conductors.

Sizing the Neutral Conductors
Several factors come into play when sizing the neutral conductors for the service as well as for the feeders. Requirements include these:

• NEC 215.2(A)(1) requires that the grounded conductor be not smaller than an equipment grounding conductor determined from NEC Table 250.122. We made adjustments in the size of some neutral conductors as shown in the load calculation forms.

• NEC 220.61 provides procedures for calculating the feeder or service neutral load. We used these
requirements in calculating the neutral load for each feeder and service disconnecting means.

• NEC 250.24(C)(1) requires that the grounded conductor, that is, the neutral conductor, in a service
shall not be smaller than the required grounding electrode conductor. Grounding electrode conductor sizes are given in NEC Table 250.66.

• In NEC 250.24(C)(2) the grounded conductor is not permitted to be smaller than 1/0 AWG
when part of a parallel set if the conductors are installed in separate raceways.

This rule applies to the underground service conductors as they are installed in parallel but does not apply to
any of the service disconnecting means as none of these have parallel service conductors.

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