frank_n
Senior Member
- Location
- Central NJ
I am doing a 200A Service Upgrade. What should I consider when sizing the neutral conductor. Is there a I don't want to run 2/0 unless I have to.
Frank
Frank
Sizing Neutral Conductor for 200A Service
- Thread starter frank_n
- Start date
- Status
Jim W in Tampa
Senior Member
- Location
- Tampa Florida
Assuming residential i would use 4/0,4/0,2/0 alumimum.Thinking there is a 70 % rule
jeff43222
Senior Member
- Location
- Minneapolis, Minnesota
I wondered about that when I did a 150A upgrade recently. The inspector called me and asked if I undersized the neutral in the mast (he couldn't see the markings on the jacket). I told him I was certain I used #1 copper for that part of the job, both for the two hots and the neutral. I double-checked the scrap white-taped wire I had, and it was indeed #1 copper.
That got me thinking, though. He wouldn't have called me unless undersizing was a problem. I always size my neutrals to be the same size as the hots. I looked through the code book and found the 70% rule, but I wasn't convinced it applied to services. Then again, they make 4/0-4/0-2/0 SER for a reason.
That got me thinking, though. He wouldn't have called me unless undersizing was a problem. I always size my neutrals to be the same size as the hots. I looked through the code book and found the 70% rule, but I wasn't convinced it applied to services. Then again, they make 4/0-4/0-2/0 SER for a reason.
- Location
- Illinois
- Occupation
- retired electrician
Is the 70% rule still in the code?
Don
Don
radiopet
Senior Member
- Location
- Spotsylvania, VA
2005 NEC -
220.61 Feeder or Service Neutral Load.
(A) Basic Calculation. The feeder or service neutral load
shall be the maximum unbalance of the load determined by
this article. The maximum unbalanced load shall be the
maximum net calculated load between the neutral and any
one ungrounded conductor.
Exception: For 3-wire, 2-phase or 5-wire, 2-phase systems,
the maximum unbalanced load shall be the maximum
net calculated load between the neutral and any one ungrounded
conductor multiplied by 140 percent.
(B) Permitted Reductions. A service or feeder supplying
the following loads shall be permitted to have an additional
demand factor of 70 percent applied to the amount in
220.61(B)(1) or portion of the amount in 220.61(B)(2) determined
by the basic calculation:
(1) A feeder or service supplying household electric
ranges, wall-mounted ovens, counter-mounted cooking
units, and electric dryers, where the maximum unbalanced
load has been determined in accordance with
Table 220.55 for ranges and Table 220.54 for dryers
(2) That portion of the unbalanced load in excess of 200 amperes
where the feeder or service is supplied from a
3-wire dc or single-phase ac system, or a 4-wire, 3-phase;
3-wire, 2-phase system, or a 5-wire, 2-phase system
220.61 Feeder or Service Neutral Load.
(A) Basic Calculation. The feeder or service neutral load
shall be the maximum unbalance of the load determined by
this article. The maximum unbalanced load shall be the
maximum net calculated load between the neutral and any
one ungrounded conductor.
Exception: For 3-wire, 2-phase or 5-wire, 2-phase systems,
the maximum unbalanced load shall be the maximum
net calculated load between the neutral and any one ungrounded
conductor multiplied by 140 percent.
(B) Permitted Reductions. A service or feeder supplying
the following loads shall be permitted to have an additional
demand factor of 70 percent applied to the amount in
220.61(B)(1) or portion of the amount in 220.61(B)(2) determined
by the basic calculation:
(1) A feeder or service supplying household electric
ranges, wall-mounted ovens, counter-mounted cooking
units, and electric dryers, where the maximum unbalanced
load has been determined in accordance with
Table 220.55 for ranges and Table 220.54 for dryers
(2) That portion of the unbalanced load in excess of 200 amperes
where the feeder or service is supplied from a
3-wire dc or single-phase ac system, or a 4-wire, 3-phase;
3-wire, 2-phase system, or a 5-wire, 2-phase system
Cavie
Senior Member
- Location
- SW Florida
Also, 310.15 (b) (6)
radiopet
Senior Member
- Location
- Spotsylvania, VA
310.15(B)(6)
(6) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services
and Feeders. For individual dwelling units of one
family, two-family, and multifamily dwellings, conductors,
as listed in Table 310.15(B)(6), shall be permitted as
120/240-volt, 3-wire, single-phase service-entrance conductors,
service lateral conductors, and feeder conductors
that serve as the main power feeder to each dwelling unit
and are installed in raceway or cable with or without an
equipment grounding conductor. For application of this section,
the main power feeder shall be the feeder(s) between
the main disconnect and the lighting and appliance branchcircuit
panelboards(s). The feeder conductors to a dwelling
unit shall not be required to have an allowable ampacity
rating greater than their service-entrance conductors. The
grounded conductor shall be permitted to be smaller than
the ungrounded conductors, provided the requirements of
215.2, 220.61, and 230.42 are met.
(6) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services
and Feeders. For individual dwelling units of one
family, two-family, and multifamily dwellings, conductors,
as listed in Table 310.15(B)(6), shall be permitted as
120/240-volt, 3-wire, single-phase service-entrance conductors,
service lateral conductors, and feeder conductors
that serve as the main power feeder to each dwelling unit
and are installed in raceway or cable with or without an
equipment grounding conductor. For application of this section,
the main power feeder shall be the feeder(s) between
the main disconnect and the lighting and appliance branchcircuit
panelboards(s). The feeder conductors to a dwelling
unit shall not be required to have an allowable ampacity
rating greater than their service-entrance conductors. The
grounded conductor shall be permitted to be smaller than
the ungrounded conductors, provided the requirements of
215.2, 220.61, and 230.42 are met.
- Status