Neutral sizing

[OrlandoCB]

Good morning folks!
Was reviewing 250.24 (c) (1), regarding the sizing of the ungrounded conductor, and it came to my mind, when is this rule used?
Please correct me if wrong, but isn't the neutral sized according to the maximum possible unbalanced load on the neutral?

For example in a house using 240/120 I should directly use the maximum unbalanced load and multiply it by 140% (Based on 220.61 exception) and just ignore 250.24(c)(1)?

Thanks for your help not sure if my question is clear enough

 

[kwired]

It is saying in no case the grounded conductor can be smaller than the SSBJ.

If you have 3/0 ungrounded conductors and a maximum unbalanced neutral load of only 30 amps - you still need minimum of #4 AWG grounded conductor brought to the service.

If you have more than 85 amps neutral load then you will need more than 4 AWG. Many people run same size neutral as ungrounded conductors even though they often don't have to.

 

[OrlandoCB]

Thank you so much kwire !!
perfect explanation,

What about the exception on 220.61, this means that almost all houses that use 240/120 must have the neutral (grounded) actually bigger than the ungrounded ?

 

[kwired]

Thank you so much kwire !!
perfect explanation,

What about the exception on 220.61, this means that almost all houses that use 240/120 must have the neutral (grounded) actually bigger than the ungrounded ?

That exception only applies to two phase systems. You possibly never ever see one of those systems they were common in Philly area and still are a few around there from what I understand. So you can sort of forget that exception is there unless you ever are working on such a system.

Use of two phases and neutral of a three phase system doesn't give same current results on the neutral and for linear loads never will need more than the same ampacity on the neutral as for the phase conductors.

 

[OrlandoCB]

That exception only applies to two phase systems. You possibly never ever see one of those systems they were common in Philly area and still are a few around there from what I understand. So you can sort of forget that exception is there unless you ever are working on such a system.

Use of two phases and neutral of a three phase system doesn't give same current results on the neutral and for linear loads never will need more than the same ampacity on the neutral as for the phase conductors.

Totally my bad was confusing them with 1 phase 3 wire systems , thanks sir !!!

Now that we are talking about that, is there a phase shift on the two phases that enter a residential unit ( For 240 v appliances like AC units ) ?
For what i think they should be in phase in order to be added together

 

[kwired]

Totally my bad was confusing them with 1 phase 3 wire systems , thanks sir !!!

Now that we are talking about that, is there a phase shift on the two phases that enter a residential unit ( For 240 v appliances like AC units ) ?
For what i think they should be in phase in order to be added together

To make a single phase induction motor turn we must create a phase shift by using capacitors or difference in inductive reactance, or combinations of both in multiple windings. Each winding must reach magnetic peaks at different points in time or you have no rotating magnetic field to cause rotation in the rotor.

That single phase motor is essentially a two phase motor, but we create the second phase within the motor and supply it with a single phase voltage source.

A true two phase motor needs two out of phase two wire inputs supplied to it in order to function as designed. Those two inputs can have different configurations on how they may have a common system point - which is usually considered a neutral point, but to draw those systems out you typically have two lines at 90 degree angle to one another (because the phase angle is 90 degrees). A two phase three wire will result in an L shape with the corner of the L being the neutral. A two phase 5 wire will result in a + shape with the center point being the neutral.

 

[OrlandoCB]

To make a single phase induction motor turn we must create a phase shift by using capacitors or difference in inductive reactance, or combinations of both in multiple windings. Each winding must reach magnetic peaks at different points in time or you have no rotating magnetic field to cause rotation in the rotor.

That single phase motor is essentially a two phase motor, but we create the second phase within the motor and supply it with a single phase voltage source.

A true two phase motor needs two out of phase two wire inputs supplied to it in order to function as designed. Those two inputs can have different configurations on how they may have a common system point - which is usually considered a neutral point, but to draw those systems out you typically have two lines at 90 degree angle to one another (because the phase angle is 90 degrees). A two phase three wire will result in an L shape with the corner of the L being the neutral. A two phase 5 wire will result in a + shape with the center point being the neutral.

Thanks Kwired, totally makes sense that the ask for the 140% considering the 90 deg shift