Neutral Calculation No reduction

[brother]

Its been a while since I had to do a calculation lately

Checking this neutral calculation for a feeder. These guys are putting in an expresso stand with some extra cooking equipment.

They have

2 120v 7.5a grinders 1800va
1 120v 2000watt water heater
2 120v duplex receptacles 360va

208v 25a espresso 5200va
208v 25a protein machine 5200va
208v and 3744va other machine (do not know what its called LoL)

I got about 55amps total just for the feed, neutral amps I guess can be about 35 amps from the 120v loads. Haven't checked the other 'unknown machine' to see if it had any other neutral loads

Their pulling a smaller neutral for the length about 105 to 110 feet. It was my understanding that their are no neutral reductions allowed for this feeder?

Did I miss something?

 

[GoldDigger]

You say you have up to 35A neutral current from the 120V loads and 55A total.
Unless the 208V loads are really combined 208/120 they will not contribute any neutral load at all.

Tapatalk!

 

[charlie b]

I agree with the 55 amp calculation (I actually got closer to 56, but that's close enough). I come up with the same 35 amps for the neutral only if I make the design choice of putting all of the 120 volt loads on the same phase (not that I would do such a thing). But that allows me to conclude that 35 amps would be the maximum unbalanced current. 220.61(A) tells me that I can size the neutral for that value. This is not a situation of a ?permitted reduction,? in the context of 220.61(B). This is a simple calculation of the load. So if the wire size they chose for the neutral can handle 35 amps, I would call that acceptable.

 

[GoldDigger]

OK, that was 55A "for the feed, neutral amps ...." not "for the feed neutral amps....". My mistake.

Tapatalk!

 

[kwired]

Neutral of a wye secondary will cancel one another if balanced across all thee phases.

If you only have two phases and a neutral then the neutral will carry about the same current as the highest loaded phase conductor.

If you have significant non linear load the neutral could see more current then the phase conductors

Loads in the OP shouldn't have much contributions from non linear loads, and the neutral conductor in worst case shouldn't need to be any larger then the total load of all 120 volt equipment which is what you would have it all 120 volt equipment were connected to the same phase conductor, but in no case can it be smaller then the required equipment grounding conductor size.

 

[brother]

I agree with the 55 amp calculation (I actually got closer to 56, but that's close enough). I come up with the same 35 amps for the neutral only if I make the design choice of putting all of the 120 volt loads on the same phase (not that I would do such a thing). But that allows me to conclude that 35 amps would be the maximum unbalanced current. 220.61(A) tells me that I can size the neutral for that value. This is not a situation of a ?permitted reduction,? in the context of 220.61(B). This is a simple calculation of the load. So if the wire size they chose for the neutral can handle 35 amps, I would call that acceptable.

Ok. Since this is from a 4 wire 3phase system i guess the single phase for this feeder will be ok. I still would pull a same size neutral in case of add ons. i thought prohibition on the reduction dealt with only 3wire circuits from these 4wire 3phase systems.

 

[kwired]

Ok. Since this is from a 4 wire 3phase system i guess the single phase for this feeder will be ok. I still would pull a same size neutral in case of add ons. i thought prohibition on the reduction dealt with only 3wire circuits from these 4wire 3phase systems.

It does, but only in relation to the loads that utilize the neutral conductor. Your straight 208 volt loads do not add to the neutral current, so if you only had 208 volt loads you wouldn't even need a neutral conductor.

 

[texie]

One comment I might add for the benefit of the OP. While in his case the required neutral size for the load served also met the minimum size required by 215.2(A)(2), that is not always the case. In other words, any minimum neutral size calculation needs to be verified that it complies with 250.122.