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Discussion Starter #1
Debate came up about downsizing a neutral. Was going to run #10s after doing a voltage drop calculation, boss said run #12 for neutral. To my knowledge the neutral is counted in the calculation.
 

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Discussion Starter #3
Vintage Sounds said:
Is it an actual neutral, as in shared by all the other phases in the system ? What's the load?
Feeding Unit Heaters, 120v, 220ft, 9Amps, multiple CCTs sharing the neutral on a 3 phase system
 

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Not sure, but you could maybe get away with it because of this rule if you didn't have to factor in the VD.

4-024 Size of neutral conductor
(1) The neutral conductor shall have sufficient ampacity to carry the unbalanced load.
 

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Follow along to the next sub-rule...
4-024 Size of neutral conductor (see Appendix B)
(1) The neutral conductor shall have sufficient ampacity to carry the unbalanced load.
(2) The maximum unbalanced load shall be the maximum connected load between the neutral and any one
ungrounded conductor as determined by Section 8 but subject to the following:
(a) there shall be no reduction in the size of the neutral for that portion of the load that consists of
(i) electric-discharge lighting; or
(ii) non-linear loads supplied froma 3-phase, 4-wire system; and
(b) except as required otherwise by Item (a), a demand factor of 70% shall bepermitted to be applied
to that portion of the unbalanced load in excess of 200 A.
 

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No! Can't reduce that size wire.
If the circuit OCD is 20-amps and the load is 9, why couldn't you install a 20-amp rated neutral? (US install, I think the OP is Canadian and I think VD calculations are mandatory there where recommended here).

I would most likely install the #10, but I believe you would be allowed to install the #12 in the USA.
 

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Discussion Starter #9
I'm in Canada yes :)

Basically where it says in the code 'non linear' is what I'm going by. So if everything was perfectly balanced then the 3 phase set (RED, BLACK, BLUE and WHITE) would have nothing on the neutral returning. Since we'll never know when and if certain phases will be turned on its non linear. 4-024 (2) (a) (ii)
 

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Debate came up about downsizing a neutral. Was going to run #10s after doing a voltage drop calculation, boss said run #12 for neutral. To my knowledge the neutral is counted in the calculation.
If your code restricts you to a 3% or less VD, you will need to install #8 conductors.


#8 = 2.6% VD
#10 = 4.9% VD
 

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It means that you can start to derate the neutral after the 200A mark, and then only 70% of it.

So no, you can't run a #12 neutral with #10 hots.
Even if you have 20-amp overcurrent protection?

What if he was to install 15-amp overcurrent protection for that 9-amp load?
 

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Tom Henry has an excellent video on Sizing the Neutral. Basically if you have 1800 watts/120 volts on phases A, B and C there will no load on the neutral as it uses the other phases to return to source. This is a balanced load. If the load on A changes to say 2400 watts you will still have the same 1800 watts as a balanced load, but the extra 600 watts that is unbalanced will return to source on the neutral.
 

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Scared to post because it's a the great white north thread.

In the end the physic's don't lie.

For #12 about 120'

For #10 about 180'

For #8 about 230'

Before one has to remember VD if appliable.

I don't know what to say it's Canada! Eh!
 

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Feeding Unit Heaters, 120v, 220ft, 9Amps, multiple CCTs sharing the neutral on a 3 phase system

I would think that if they all came on the same time it is no big deal.

But, if they cycle then it is possible that one circuit could be on and the others off.

Then, you would have 9 amps on the #10 and the #12.

Im not sure how that would affect the VD tho.
 

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Discussion Starter #16
CADPoint said:
Scared to post because it's a the great white north thread.

In the end the physic's don't lie.

For #12 about 120'

For #10 about 180'

For #8 about 230'

Before one has to remember VD if appliable.

I don't know what to say it's Canada! Eh!
We have tables in our code up here for voltage drop. I'm wondering if in those calculations for table D3 they've included the return path. We're supposed to enter in the distance from the panel to the load into the formula, but in that formula have they calculated the return path? I guess I'm searching for two answers. Can I do it code wise? The answer is no because its a non-linear (unbalanced load).

The 2nd question has to do with the theory, what will happen to the cct if the neutral is downsized? How does Voltage drop effect the cct once it's gone through its load and done it job?
 

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The answer is no because its a non-linear (unbalanced load).
I guess I have a different understanding of a linear load than you. I was of the impression that resistance heaters (I think that's what is being wired) are always linear loads.
 

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I'm in Canada yes :)

Basically where it says in the code 'non linear' is what I'm going by. So if everything was perfectly balanced then the 3 phase set (RED, BLACK, BLUE and WHITE) would have nothing on the neutral returning. Since we'll never know when and if certain phases will be turned on its non linear. 4-024 (2) (a) (ii)
No resistive heat is linear, nonlinear would be any types of electronic loads
 

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Discussion Starter #19
hardworkingstiff said:
I guess I have a different understanding of a linear load than you. I was of the impression that resistance heaters (I think that's what is being wired) are always linear loads.
brian john said:
No resistive heat is linear, nonlinear would be any types of electronic loads
Good point. These are gas unit heaters in a large warehouse, they do have small motors in them to dissipate the heat outwards. I was thinking its none linear but its not (not non-linear? Lol) Thanks now I'm back to square one.
 

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Good point. These are gas unit heaters in a large warehouse, they do have small motors in them to dissipate the heat outwards. I was thinking its none linear but its not (not non-linear? Lol) Thanks now I'm back to square one.
I'm of the understanding that motors are non linear loads. So the motors in the gas heaters would be non linear. :laughing:

Communication, the hardest thing in the world to get correct.
 
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