sokkerdude
Member
- Location
- Arkansas
Could someone please explain to me what, "a neutral conductor that carries only the unbalanced current from other conductors of the same circuit" is? What situtation this may be found in. Thank you
article 310-15(b)(4)(a) neutrals
- Thread starter sokkerdude
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- Location
- Massachusetts
Re: article 310-15(b)(4)(a) neutrals
The most common place you see that is the Neutral conductor in a service, no matter what combination of load you put on the service the neutral only carries the imbalance.
30 amps on phase A
50 amps on phase B
Neutral will have 20 amps, the imbalance between A and B
In commercial work we run a 12/4 cable and run 3 separate circuits off the 4 conductors most times the Neutral in this also just carries the imbalance of the 3 phase conductors, but there are some types of loads that this will not be the case.
[ March 23, 2003, 03:47 PM: Message edited by: iwire ]
The most common place you see that is the Neutral conductor in a service, no matter what combination of load you put on the service the neutral only carries the imbalance.
30 amps on phase A
50 amps on phase B
Neutral will have 20 amps, the imbalance between A and B
In commercial work we run a 12/4 cable and run 3 separate circuits off the 4 conductors most times the Neutral in this also just carries the imbalance of the 3 phase conductors, but there are some types of loads that this will not be the case.
[ March 23, 2003, 03:47 PM: Message edited by: iwire ]
stamcon
Senior Member
- Location
- South San Francisco CA
Re: article 310-15(b)(4)(a) neutrals
An electric dryer might use 240v for the heating element, but 120v for the motor and timer. The 120v is taken off of one of the hot legs and the nuetral.
An electric dryer might use 240v for the heating element, but 120v for the motor and timer. The 120v is taken off of one of the hot legs and the nuetral.
sparkmantoo
Member
- Location
- Virginia
Re: article 310-15(b)(4)(a) neutrals
what about non-linear loads that are encountered in electronic ballasts and other electronic equipment. should the neutral conductor be sized to compensate for these "harmonics" that are encountered?
what about non-linear loads that are encountered in electronic ballasts and other electronic equipment. should the neutral conductor be sized to compensate for these "harmonics" that are encountered?
bphgravity
Senior Member
- Location
- Florida
Re: article 310-15(b)(4)(a) neutrals
sparkmantoo, the code does not specifically require non-linear loads on neutrals to be sized larger. This is considered a design issue and a suggestion for this is at 220.22(FPN #2). As far as 310.15 is concerned, these conductors are required to be counted as current carrying conductors, and adjustments factors must be applied per 310.15(A)(4)(c).
sparkmantoo, the code does not specifically require non-linear loads on neutrals to be sized larger. This is considered a design issue and a suggestion for this is at 220.22(FPN #2). As far as 310.15 is concerned, these conductors are required to be counted as current carrying conductors, and adjustments factors must be applied per 310.15(A)(4)(c).
jtb
Senior Member
- Location
- Pennsylvania
Re: article 310-15(b)(4)(a) neutrals
Theoretically, the neutral current should never exceed 1.73 times the phase conductor ampacity.
For non-linear or harmonic loads, most just double the neutral size.
Theoretically, the neutral current should never exceed 1.73 times the phase conductor ampacity.
For non-linear or harmonic loads, most just double the neutral size.
bphgravity
Senior Member
- Location
- Florida
Re: article 310-15(b)(4)(a) neutrals
JTB, where do you get this value from (1.73)? Please explain.
JTB, where do you get this value from (1.73)? Please explain.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: article 310-15(b)(4)(a) neutrals
That "1.73" looks suspiciously like that "square root of 3" thingy that keeps popping up in 3-phase systems. You know, the one that you multiply by 120 to get 208, or the one that you multiply by 277 to get 480. I believe that JTB is right, but I do not recall the mathematics from which it is derived.
That "1.73" looks suspiciously like that "square root of 3" thingy that keeps popping up in 3-phase systems. You know, the one that you multiply by 120 to get 208, or the one that you multiply by 277 to get 480. I believe that JTB is right, but I do not recall the mathematics from which it is derived.
- Location
- Massachusetts
Re: article 310-15(b)(4)(a) neutrals
I do not know about the 1.73, but many times the job specs require us to run "Super Neutral" MC to feed the office cubes.
This can take many forms,
One form is 8 conductor #10 MC Black, White with Black stripe, Red, White with Red stripe, Blue, White with Blue stripe, Green and Green with yellow stripe. We would use this to feed office cubes that are wired with 3 circuits with separate Neutrals.
Another more common form is, 2 #10 Whites one with a stripe then 8 #12s Black, Red, Blue, and Black , Red, Blue with stripes, Green and Green with Yellow stripe We use this to feed office cubes that have 6 multi wire circuits.
I do not know about the 1.73, but many times the job specs require us to run "Super Neutral" MC to feed the office cubes.
This can take many forms,
One form is 8 conductor #10 MC Black, White with Black stripe, Red, White with Red stripe, Blue, White with Blue stripe, Green and Green with yellow stripe. We would use this to feed office cubes that are wired with 3 circuits with separate Neutrals.
Another more common form is, 2 #10 Whites one with a stripe then 8 #12s Black, Red, Blue, and Black , Red, Blue with stripes, Green and Green with Yellow stripe We use this to feed office cubes that have 6 multi wire circuits.
Ed MacLaren
Senior Member
Re: article 310-15(b)(4)(a) neutrals
Just happened to have a picture of Super Neutral MC.
Ed
Just happened to have a picture of Super Neutral MC.
Ed
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