Reducing Neutral on Service

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Nom Deplume

Senior Member
Location
USA
Is it permissible to reduce the service neutral on a 200a 120/240v 1? service for site lighting at a commercial parking lot?
I would like to use URD 4/0-4/0-2/0 cable in my 2-1/2" PVC from the pole to the meter socket.

Most all of my loads are at 240v. The only 120v load is a 1500w heater in the control cabinet, the control power and a convenience receptacle.

What code article allows the reduction in size of a service neutral?
 

MasterTheNEC

CEO and President of Electrical Code Academy, Inc.
Location
McKinney, Texas
Occupation
CEO
Is it permissible to reduce the service neutral on a 200a 120/240v 1? service for site lighting at a commercial parking lot?
I would like to use URD 4/0-4/0-2/0 cable in my 2-1/2" PVC from the pole to the meter socket.

Most all of my loads are at 240v. The only 120v load is a 1500w heater in the control cabinet, the control power and a convenience receptacle.

What code article allows the reduction in size of a service neutral?

Well the minimum size of your grounded (neutral) would be in accordance with 250.102(C)(1), 230.23(B) and (C) if overhead components exist or 230.31(C) as well for underground components since you stated URD [2014 NEC] and then of course your calculation in accordance with 220.61 and the greater (larger) of the two would be the minimum size required. If you are looking for your starting points for your basic calculation requirement then look at 220.61(A).
 
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tom baker

First Chief Moderator
Staff member
Here is an easier way to understand the size of the neutral.
From the service to the utility transformer, the neutral is for both neutral current (white wire) or ground fault current (green wire).
You have to size it to the larger of the two.
White wire is the maximum unbalanced current per Art 220
Green wire is fault current, per section 250.66
If there is no neutral current use section 250.66 which bases it on the size of the ungrounded conductors.

Many code cycles ago, the minimum size of the neutral was two trade sizes smaller than the ungrounded conductors, or typically 4/0 4/0 2/0 for 200 ampere residential service, and 4/0 4/0 2/0 is the way it comes when you buy it. Some electricians don't want to do a load calculation or understand how to size the neutral.
 
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