I had a conversation with another local contractor regarding the use of 4/0 4/0 2/0 AL USE.(3 Conductor Cable) for 200A residential services. Seems that he has been installing this cable for some time even in dwellings where there are no 240V appliances except for central air. I told him that to my understanding it was a code violation and that the grounded conductor had to be the same size as the ungrounded ones. He said that as long as there was any 240V load it could be derated 30%. He claims that it has never once been questioned.The whole conversation started when he stopped by a new house I was roughing in and noticed I use CU THHN and asked why I was doing my services the "expensive" way. I have used AL cable in the past but it was always 4/0 4/0 4/0. Am I wrong on this one?
Reuced Neutral Conductor
- Thread starter nizak
- Start date
- Status
- Location
- New Jersey
- Occupation
- Journeyman Electrician
He might be thinking about 220.61(B).
- Occupation
- Licensed Electrician
You can always reduce the neutral if it is carrying the imbalance between phases. For a feeder or service this is the case even if all the loads are 120V.
Volta
Senior Member
- Location
- Columbus, Ohio
So, the way I read it we can derate the portion of the range load, not the entire dwelling unit load.
NEC 220.61(B) said:
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
That section allows an additional reduction for a range or dryer. You can use the basic calculation in 220.61(A) for the neutral load then are permiited the additional demand in (B).
Volta
Senior Member
- Location
- Columbus, Ohio
Agreed.
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
I think you need to do what you feel most comfortable with, and what you think fits with the reputation of your company.
Yes, Contracting is competitive, but the NEC is also minimum safety, not necessarily good engineering design.
Yes, Contracting is competitive, but the NEC is also minimum safety, not necessarily good engineering design.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
The grounded conductor can not be any smaller than the required grounding electrode conductor for a service or no smaller than the required equipment grounding conductor for other than services.
How your AHJ wants you to prove the load on the grounded conductor could be a different story. Many will allow you to reduce a size or two without showing any calculations, others may not.
How your AHJ wants you to prove the load on the grounded conductor could be a different story. Many will allow you to reduce a size or two without showing any calculations, others may not.
- Status