basic circuits

[jpuljic]

In 3 wire single phase, We know that 2 hots share a neutral. The other day, I saw 3 hots sharing a single neutral, I know it is wrong, but I could'nt quite explain. Please help out. Thanks

 

[iwire]

If the supply is 3 phase it could be fine.

 

[mcclary's electrical]

In 3 wire single phase, We know that 2 hots share a neutral. The other day, I saw 3 hots sharing a single neutral, I know it is wrong, but I could'nt quite explain. Please help out. Thanks

If the neutral is sized properly, you could have all the hots you desire sharing one neutral.

But if all wires are the same size, that would be wrong

 

[LEO2854]

In 3 wire single phase, We know that 2 hots share a neutral. The other day, I saw 3 hots sharing a single neutral, I know it is wrong, but I could'nt quite explain. Please help out. Thanks

Welcome to the forum
3 hots sharing a single neutral is 3phase 4 wire

 

[brian john]

He said:

In 3 wire single phase

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[Dennis Alwon]

In 3 wire single phase, We know that 2 hots share a neutral. The other day, I saw 3 hots sharing a single neutral, I know it is wrong, but I could'nt quite explain. Please help out. Thanks

I would say it is wrong unless as stated the neutral was oversized. In the 2011 that will not be allowed any more.

 

[iwire]

He said:

......................

Yeah I read what he said, and it does not change my answer.

 

[LEO2854]

He said:

......................

He said//I saw 3 hots sharing a single neutral .
Which tells me it is posible he has a three phase system.maby he can verfie that for us .If it is single phase 4 wire circuit with 3 hots 1 neutral and all 4 wires are the same size then the neutral is over loaded.

 

[Barndog]

if it is a 3 phase system and all wires are the same size. and the 3 "hots" are A,B,C. the neutral shouldnt be over loaded because the neutral wire would just be carrying the inbalance of the 3 hots. in that case it should never be over the rating of the conductor.

 

[dicklaxt]

if it is a 3 phase system and all wires are the same size. and the 3 "hots" are A,B,C. the neutral shouldnt be over loaded because the neutral wire would just be carrying the inbalance of the 3 hots. in that case it should never be over the rating of the conductor.

Right on mate,you got it,,,,

dick

 

[TNGuy81]

If its 120/240 its wrong, wrong, and wrong because you will have 2 of the same phase returning on the neutral which in return will burn it up. You can only have A and B and thats it for residential service. a 3 phase service you can have 3 circuits sharing a neutral only if they are all seperate phases/legs ABC/1,3,5/2,4,6 etc. 2008 code on MWBC requires a 2 pole breaker now for this application and is only for (2) circuits on a 120/240 service.

 

[Barndog]

true i was talking 3 phase. yes in single phase you can only have 2 wires sharing a neutral of the same wire size and they would also have to be A,B in single and A,B,C in three pahse or you Might have overloading of your neutral conductor depending on the total current of the "hots" being supplied.

 

[brian john]

if it is a 3 phase system and all wires are the same size. and the 3 "hots" are A,B,C. the neutral shouldnt be over loaded because the neutral wire would just be carrying the inbalance of the 3 hots. in that case it should never be over the rating of the conductor.

To throw a curve in the mix, there are times when utilzing the correct Phases A, B and C you could overload the neutral or load it more than you would expect. This would be when the loads supplied have high harmonic currents.

 

[TNGuy81]

im not sure on the code part on a 3 phase but I have never put more than 3 circuits on a neutral. Its easier to just pull another neutral and its a lot safer. I was not disputing what you quoted either I was replying to the OP. I think we are on the same page here.

 

[Barndog]

i agree with you. i also perfer to use single neutrals when ever possiable. you either must use extreame caution or shut off up to 3 breakers when working on a 3 phase neutral. or you have the chance to get shocked off the wire if you break the return.

 

[LarryFine]

you either must use extreame caution or shut off up to 3 breakers when working on a 3 phase neutral.

Thus the pigtailing and handle-tie requirements.

... or you have the chance to get shocked off the wire if you break the return.

Or damage equipment still energized.

 

[Barndog]

Larry

when did the pigtail/ handle tie req. come into the NEC. i work at a facility that has a Building in the early 70's and almost all of the lighting and recpt. that are orinigal are three phase neutrals. with no handle tieing.