Nec 220.61 B 2, a 70 % neutral & harmonic currents

[Jpflex]

I askwd a similar question a while back but i wanted to ecxpand


First, in 220.61 (C) point 2, makes no sence when NEC mentions NON LINEAR LOADS on a Y neutral system as being a determining factor to dissallow a 70% neutral reduction because point 1 already said ALL 3 phase Y systems with a neutral cannot have its neutral reduced

Second, the 2023 handbook explains that the neutral is considered as a current carrying conductor if the load of the electric discharge lighting, data process lighting or similar equipment on the neutral consist of more than half the total load.

I used to think nec did not allow a 70% reduction of neutral feeder to the anount in excess of 200 amperes, if NON LINEAR LOADS were served or to the portion of non linear loads.

It seems we can apply a 70% reduction to the neutral service or feeder wire in excess of 200 amperes regardless if non linear loads were served and as long as the transformer is not from a 3 phase Y system with ground. Is this correct?

 

[Jpflex]

3 phase system with a neutral* i meant to say

 

[Jpflex]

Or another example is having a single phase 120/240 VAC system where all lighting is non linear flouresent and loads are computers ( data processing).

I believe from why i read. The neutral in excess of 200 amperes can be reduced to 70% here. Is this also correct

 

[augie47]

First, in 220.61 (C) point 2, makes no sence when NEC mentions NON LINEAR LOADS on a Y neutral system as being a determining factor to dissallow a 70% neutral reduction because point 1 already said ALL 3 phase Y systems with a neutral cannot have its neutral reduced

Where, other than 220.61(C) does is mention that non linear loads on a wye system are not allowed ??

 

[Jpflex]

First, in 220.61 (C) point 2, makes no sence when NEC mentions NON LINEAR LOADS on a Y neutral system as being a determining factor to dissallow a 70% neutral reduction because point 1 already said ALL 3 phase Y systems with a neutral cannot have its neutral reduced

Where, other than 220.61(C) does is mention that non linear loads on a wye system are not allowed ??

I do knot know on top of my head of another code section not allowing non linear loads on a y system if a neutral is to be reduced in size and total load exceeds 200 amperes

But i do know it makes no sence to list 2 stipulations SECTION 1 AND 2 OF 220.61 C since they both are determined if the system is Y

Why not simply say no wye stems are allowed to have their neutral reduced, regardless of load type, etc etc

 

[augie47]

(C)(1) discusses a 3 wire circuit consisting of 2 ungrounded conductors of a 4 wire system and (C)(2) discusses non-linear loads.
Two separate conditions to take into consideration when looking at calculating the neutral and, to my knowledge, that's the only mention in the NEC

 

[tortuga]

In practice can't think of any time I have ever seen (or noticed) a neutral reduced in size on a 208Y/120 or a 480Y/277. I think I have seen it reduced in higher voltages like 4160Y/2400. Back in the 90's I recall some EE's specifying neutrals that were larger than the phase conductors but have not see that in a long time.

 

[Jpflex]

(C)(1) discusses a 3 wire circuit consisting of 2 ungrounded conductors of a 4 wire system and (C)(2) discusses non-linear loads.
Two separate conditions to take into consideration when looking at calculating the neutral and, to my knowledge, that's the only mention in the NEC

Ok ill look at it again but i believe they both involved Wye transformers