Downsize neutral to sub panel? (need to fit in existing conduit)

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whackit

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Happy New Year!

I'm a contractor getting several different answers from my electricians so as usual--coming here for a tie breaker. I have a situation where a customer decided they want to add some outdoor heaters to an existing pool sub panel. The panel cable is currently undersized for the heaters and we will need to re-pull (panel is fine will obviously replace breaker). There are only small 120v loads on this panel. One 15amp lighting circuit and a 20amp outlet. Everything else will be 240. One electrician is telling me I can downsize my neutral to the same size as the ground as a minimum. The other is telling me I need to upsize the neutral to match the new hot legs. I would normally just go with all the same size but I am stuck with a 1" conduit that there is no getting around (under finished decking etc) being able to reduce the neutral would be helpful so I don't have to pack the conduit and can potentially get some larger wires in there. Thanks in advance.
 
Im being told we need a minimum 3awg feeder for minimum 100amp sub panel. Currently it's 70amp 4awg.

Loads are -

Heaters 65 amps (240v)
Pool Pump - 20amp (240v)
Lighting - 15amp (120v)
Outlets - 20amp (120v)
 
After removing the 4 awg , could he remove the conduit from the area not under the deck (except for the stubs) making the conduit under the deck a “sleeve”, then pull some sort of a direct burial cable, bypassing the 40% (and making the pull easier)?
Assuming:
1) if not terminating at boxes it is a sleeve and not a conduit or raceway run
2) sleeves do not have a max length
Those assumptions may be incorrect.
 
Other than the Heaters it appears you are giving us the size of the OC protection ahead of the loads. That will make the minimum feeder requirements excessive. Using those numbers I see a minimum of 119 amp feeder. #1 Cu THWN @ 75C. Minimum EQ is #6 cu. You need at least a 125 amp rated panel. I see a minimum of 1 1/4" conduit.
 
To directly answer your question... yes you can under-size the neutral based on your calculated load so long as it is sized no smaller than the appropriate equipment grounding conductor. With a 100 amp feeder, a #8.
It looks like you are providing breaker sizes and not actual loads. From what you show a#8 would obviously be large enough but you may be undersized with a 100 amp panel.
What are the actual loads (heater kw, motor hp, etc)
 
(2017 NEC) 215.2(A)(2) reference sizing based on 250.122, and amperage of grounded conductor "neutral" would be based on unbalanced load and can be sized accordingly allowing a smaller neutral than the current carrying conductors on your feeder, but not smaller than the EGC required for entire load. Also per 215.1(A)(1) ex#3 the grounded conductor "neutral" is permitted to be sized to 100% of the continuous plus noncontinous loads, not the 125% otherwise required. Also if you selectively choose to upsize your "neutral" the EGC must also be upsized in proportion to the increase in "neutral" size according to 250.122(B)
So overall a true load calculation would need to be done inorder to 1. Determine minimum conductor size, 2. to determine minimum "neutral" size, 3. that also will dictate the minimum EGC size. All this to determine minimum conduit size required.
Most just opt to go with whatever current carrying conductor size is what they'll use for the "neutral". But in your case trying to fit it into an existing conduit run the additional calculations would be warranted. Also be careful with the calculations as you can oversize yourself as @ptonsparky made reference to.
One other additional consideration, you never mention the type of conductors you are using. Most use Aluminum (its cheaper) but in your case trying to make it fit, copper while more expensive may end up being cheaper if it will fit, if you have to re-pipe the whole thing.
Bottom line which ever electrician did all this is probably the one that came closer to the truth for size and fit. Likely your neutral is going to be some are in between the 2 statements depending on the true load calculation.
 
As stated, the neutral only needs to be sized for the maximum unbalanced load and if present must be at least as large as the EGC.

If you only had 240V loads, you would not be required to have a neutral at all (unless there is a specific requirement for an outbuilding).

The loads as described were a 15A and a 20A 120V circuit plus a bunch of 240V loading, which means that the maximum unbalanced load on the neutral will be less than 20A. Since a 100A feeder requires a #8 EGC, a #8 neutral would be sufficient for this.

(Note: above is assuming Cu conductors.)

If you can find a supplier and are willing to pay the $$, something called compact stranded copper conductors will let you squeeze just a bit more into the conduit.

-Jon
 
I agree with the others. As long as the load can handle it then the neutral can be as small as the equipment grounding conductor. A 100 amp feeder can have a neutral as small as a #8 which appears to be more than adequate for your neutral loads.

Show the other electrician this section. T250.122 mentioned below is the table for sizing the equipment grounding conductor.

215.2(A)(2) Grounded Conductor. The size of the feeder circuit
grounded conductor shall not be smaller than that required by
250.122, except that 250.122(F) shall not apply where grounded
conductors are run in parallel.
Additional minimum sizes shall be as specified in
215.2(A)(3) under the conditions stipulated.
Click to expand...
 
Thanks for all the great replies...

Assuming I will use THHN copper conductors. Not a commercial job so costs need to be somewhat reasonable. We looked into bursting a new conduit and there would be too much collateral damage for owner (long story trust me here).

Actual loads are...

Heaters. 12000 W. 50 amps. I believe I must calculate this to 125% which would be 62.5amps. 240v
Pool Pump 3hp (max) Label lists maximum current as 16 amps.
Pool Heater 8amps (120)
Lighting circuit.. LED only. Minimal load 120v
20amp outlet. Rarely used.
 
You are pushing the 100 amps but likely OK due to the "safety" factor on the heater.
#3 THHN Cu Phases, "8 Neutral and a #8 Equipment Ground.
What size and type conduit ?
 
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augie47 said:
You are pushing the 100 amps but likely OK due to the "safety" factor on the heater.
#3 THHN Cu Phases, "8 Neutral and a #8 Equipment Ground.
What size and type conduit ?
Click to expand...
OP mentioned 1" conduit but didn't say whether it was PVC sch 40, sch 80, or some type metallic conduit.
 
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It looks like I can get 2-2-6-8 in there. Will be tight but allowable. Longish run so prefer to oversize if possible. About 40' with 2 90s. Lots of lube and fingers crossed!
 
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