Neutral Sizing

[102 Inspector]

Given a 200 amp residential service, typically as an inspector I find 2/0 CU conductors between the meter and the main disconnect. Just had an electrician call me and say he found a service with a #6 CU neutral conductor being provided. The home is approximately 40 years old with total electric baseboard, range and dryer. If proper load calculations were completed on the home, would this size neutral possible been adequate in 1975. I think I know the company that did the original and they were known for pushing the limits on certain items. (No longer in business).

 

[infinity]

250.24(C)(1) requires the neutral to be minimal size according to 250.102(C) which would be a #4 for #2/0 SEC's. Older versions of the code used T250.66 which is basically the same as the modernT250.102(C)(1).

250.24(C)(1) Sizing for a Single Raceway. The grounded conductor
shall not be smaller than specified in Table 250.102(C)(1).

 

[102 Inspector]

As I read more in the 1981 NEC, I am guessing that Table 250-94 was the applicable requirements for the conductor sizing which would have been #4 copper. Looking further back at Table 250-95, it states that the minimum size for grounding raceway and equipment was #6 copper for a 200 amp overcurrent device. Not sure if this is what was being applied at the time of installation or how it ended up at #6. Thanks for the response.

 

[iwire]

As I read more in the 1981 NEC, I am guessing that Table 250-94 was the applicable requirements for the conductor sizing which would have been #4 copper. Looking further back at Table 250-95, it states that the minimum size for grounding raceway and equipment was #6 copper for a 200 amp overcurrent device. Not sure if this is what was being applied at the time of installation or how it ended up at #6. Thanks for the response.

The minimum size neutral matches the minimum size of the EGC.