Current Carrying??

tdecontrols

Member
Location
Florida
Occupation
EC
I have always counted the grounded conductor of a 120v 2wire circuit of a 120-208 3ph wye service as current carrying, is this correct? More and more I am seeing contractors using 2" pipes over 24in up to main pull boxes above the ceiling. Here is an example, a job I am doing a build-out on has a 42crt panel with two 2" conduits each of those have 20- 20a 120v 2wire gfci circuits in them. That is a total of 40 #10 Thhn wires, that would cause the derating to drop to 40% of the conductor. #10 is good for 40amps x 40% gives you 16amps. Which you could go to a 20a breaker for unless it is feeding multiple outlets... So back to the beginning of the question, Am I wrong in counting the grounded conductor as current carrying? And am I correct in not being able to go up on multi outlet branch circuits?
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
You are correct in both cases, on a 3 phase circuit you can only derate when all 3 phase conductors are involved and derating is required over 24"
'
Here's an guide provided by a Forum member:
208Y/120 volt system-different circuit types:

A)- 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
B)- 3 wire circuit w/ 2 ungrounded, 1 neutral = 3 CCC's
C)- 4 wire circuit w/ 3 ungrounded, 1 neutral = 3 CCC's*

Notes:
A)- A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
B)- In this circuit the neutral current will be nearly equal to the current in the ungrounded conductors so the neutral counts as a CCC
C)- In this circuit the neutral will only carry the imbalance of the current between the three ungrounded conductors so it is not counted as a CCC, with one exception, *if the current is more than 50% nonlinear then the neutral would count as a CCC.

 

tdecontrols

Member
Location
Florida
Occupation
EC
You are correct in both cases, on a 3 phase circuit you can only derate when all 3 phase conductors are involved and derating is required over 24"
'
Here's an guide provided by a Forum member:
208Y/120 volt system-different circuit types:

A)- 2 wire circuit w/ 1 ungrounded, 1 neutral = 2 CCC's
B)- 3 wire circuit w/ 2 ungrounded, 1 neutral = 3 CCC's
C)- 4 wire circuit w/ 3 ungrounded, 1 neutral = 3 CCC's*

Notes:
A)- A normal 2 wire circuit has equal current flowing in each of the circuit conductors so they both count as CCC's.
B)- In this circuit the neutral current will be nearly equal to the current in the ungrounded conductors so the neutral counts as a CCC
C)- In this circuit the neutral will only carry the imbalance of the current between the three ungrounded conductors so it is not counted as a CCC, with one exception, *if the current is more than 50% nonlinear then the neutral would count as a CCC.
In that case they should be dropping the multi outlet branch circuits to 15a breakers when they are at 40% or go up in wire size to #8. I am more than anything, just trying to be sure I am not missing some loop hole that is letting these guys do this. I was on another project that had 50 #10s in it. all on 20a breakers.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
In that case they should be dropping the multi outlet branch circuits to 15a breakers when they are at 40% or go up in wire size to #8. I am more than anything, just trying to be sure I am not missing some loop hole that is letting these guys do this. I was on another project that had 50 #10s in it. all on 20a breakers.


Why would they do that. A multiwire branch circuit in a 3 phase panel will be at most 3 conductors.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Here is what you de-rate by

Table 310.15(B)(3)(a) Adjustment Factors for More Than

Three Current-Carrying Conductors

Number of Conductors

Percent of Values in Table 310.15(B)(16) Through Table 310.15(B)(19) as Adjusted for Ambient Temperature if Necessary
4–6 80

7–9 70

10–20 50

21–30 45

31–40 40

41 and above 35

1Number of conductors is the total number of conductors in the

raceway or cable, including spare conductors. The count shall be

adjusted in accordance with 310.15(B)(5) and (6). The count shall not

include conductors that are connected to electrical components that

cannot be simultaneously energized.
 

tdecontrols

Member
Location
Florida
Occupation
EC
Why would they do that. A multiwire branch circuit in a 3 phase panel will be at most 3 conductors.
they are not multi wire. read what I first posted, this has to do with using long 2" stub ups out of a panel and filling it with #10 20a 2wire branch circuits with multiple recptacles on them. The job I am on they have 20crts that makes 40 current carrying condutors. which drops you to 40% of the #10, and that comes out to 16a. 210.19(2) would prevent you from putting this on a 20a breaker
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Gotcha-- I didn't read your first post. I saw Gus' response and ... and then I read multi outlet as multi wire... bad evening...lol

Couldn't you use 240.4(B) and still use a 20 amp breaker if the calculated loads were 16 amps or less?

The install in post 1 is also a violation of 312.5(C) assuming these panels are not surface mounted
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I have always counted the grounded conductor of a 120v 2wire circuit of a 120-208 3ph wye service as current carrying, is this correct? More and more I am seeing contractors using 2" pipes over 24in up to main pull boxes above the ceiling. Here is an example, a job I am doing a build-out on has a 42crt panel with two 2" conduits each of those have 20- 20a 120v 2wire gfci circuits in them. That is a total of 40 #10 Thhn wires, that would cause the derating to drop to 40% of the conductor. #10 is good for 40amps x 40% gives you 16amps. Which you could go to a 20a breaker for unless it is feeding multiple outlets... So back to the beginning of the question, Am I wrong in counting the grounded conductor as current carrying? And am I correct in not being able to go up on multi outlet branch circuits?
You are correct, and with any system (not just 208Y/120) a 2 wire circuit will always count as 2 CCC's. But quite often for an installation like the one that you've described you can ignore the derating because you can apply 310.15(A)(2)Exception.


310.15(A)(2) Selection of Ampacity. Where more than one ampacity
applies for a given circuit length, the lowest value shall be used.
Exception: Where different ampacities apply to portions of a circuit, the
higher ampacity shall be permitted to be used if the total portion(s) of
the circuit with lower ampacity does not exceed the lesser of 3.0 m
(10 ft) or 10 percent of the total circuit.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I agree with Trevor but if you re required to seal the conduit going from an area of different temperatures the the exception does not apply

Where more than two NM cables containing two or more
current-carrying conductors are installed, without maintaining
spacing between the cables, through the same opening in wood
framing that is to be sealed with thermal insulation, caulk, or
sealing foam, the allowable ampacity of each conductor shall
be adjusted in accordance with Table 310.15(B)(3)(a) and the
provisions of 310.15(A)(2), Exception, shall not apply.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I don't think I will ever get this rule when there is no pipe involved. I can put 6 nm cables thru a hole and fire caulk 1/2" of the cable and the exception is no longer usable yet I can have the same 6 cables run thru 3' of holes across studs and then the exception may come into play.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Dennis how would that section apply to a conduit run?

I am assuming there is nm in the conduit and that it is in an attic. In some areas they are requiring some caulk or something at the end of the conduit when the conduit goes from one unconditioned space to another conditioned space. Also, the section in 312.5 makes it non compliant if nm is in the conduit.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I am assuming there is nm in the conduit and that it is in an attic. In some areas they are requiring some caulk or something at the end of the conduit when the conduit goes from one unconditioned space to another conditioned space. Also, the section in 312.5 makes it non compliant if nm is in the conduit.

OK didn't sound like there was an attic involved to me more like a panel stubbed up with 2" conduits above a hung ceiling. Also I don't see anything in 334.80 that would apply to NM cables in a raceway with draft stop material installed at the ends.
 

kwired

Electron manager
Location
NE Nebraska
I have always counted the grounded conductor of a 120v 2wire circuit of a 120-208 3ph wye service as current carrying, is this correct? More and more I am seeing contractors using 2" pipes over 24in up to main pull boxes above the ceiling. Here is an example, a job I am doing a build-out on has a 42crt panel with two 2" conduits each of those have 20- 20a 120v 2wire gfci circuits in them. That is a total of 40 #10 Thhn wires, that would cause the derating to drop to 40% of the conductor. #10 is good for 40amps x 40% gives you 16amps. Which you could go to a 20a breaker for unless it is feeding multiple outlets... So back to the beginning of the question, Am I wrong in counting the grounded conductor as current carrying? And am I correct in not being able to go up on multi outlet branch circuits?
I am assuming there is nm in the conduit and that it is in an attic. In some areas they are requiring some caulk or something at the end of the conduit when the conduit goes from one unconditioned space to another conditioned space. Also, the section in 312.5 makes it non compliant if nm is in the conduit.
OP has raceway to a pull box above the ceiling then likely has smaller raceways with lesser derating requirements leaving that pull box. 10 ft or 10% of circuit length that was mentioned could apply, but you basically need a 100 foot long circuit before you can apply this allowance
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I need to shut the hell up--- I am reading everything with assumptions that are not written. I was working with nm cables-- why, IDK, I guess because that is the issue we see around here so I assumed that was what was going on... Obviously I am out of it these last two days....mea cupa
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I need to shut the hell up--- I am reading everything with assumptions that are not written. I was working with nm cables-- why, IDK, I guess because that is the issue we see around here so I assumed that was what was going on... Obviously I am out of it these last two days....mea cupa

LOL, no problem. I just wanted to make sure that I wasn't missing something and giving the OP the wrong information.
 
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