3 PHASE / 4 WIRE , COMMON NEUTRAL

[JEFF MILLAR]

With computers and harmonics in our circuits. Is it time to stop using the common neutral ?
It makes sense that circuits 2, 4 and 6 with a common neutral is still valid for lighting circuits.
For general purpose convenience do you think the common neutral is still valid or obsolete ?
I will learn from you all.

 

[xptpcrewx]

With computers and harmonics in our circuits. Is it time to stop using the common neutral ?
It makes sense that circuits 2, 4 and 6 with a common neutral is still valid for lighting circuits.
For general purpose convenience do you think the common neutral is still valid or obsolete ?
I will learn from you all.

The question is would you prefer to run 6 wires or only 4 wires to achieve the exact same thing?


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[electrofelon]

Didn't like what you heard in the other thread?

Receptacle circuits common neutral

It may become more an issue if they start pushing AFCI into non residential applications. I dont know of or haven't seen any 2 pole let alone 3 pole AFCI breakers yet. (Just to throw a wrench into it). Some Amazon entries

forums.mikeholt.com

I can throw out the opposite answer I gave in that thread if that is what you want to hear. Here goes: it's definitely time to stop using common neutrals. I see problems with MWBC's all the time. These harmonics are out of control and burning up neutrals and the wire and conduit savings are insignificant.

 

[mbrooke]

From my understanding there is no evidence of overheating from code complaint MWBC powering office equipment.

 

[ptonsparky]

Didn't like what you heard in the other thread?

Receptacle circuits common neutral

It may become more an issue if they start pushing AFCI into non residential applications. I dont know of or haven't seen any 2 pole let alone 3 pole AFCI breakers yet. (Just to throw a wrench into it). Some Amazon entries

forums.mikeholt.com

I can throw out the opposite answer I gave in that thread if that is what you want to hear. Here goes: it's definitely time to stop using common neutrals. I see problems with MWBC's all the time. These harmonics are out of control and burning up neutrals and the wire and conduit savings are insignificant.

Thank you. Just what I wanted to hear!

 

[electrofelon]

From my understanding there is no evidence of overheating from code complaint MWBC powering office equipment.

Yeah I have never personally seen it, and been on this forum for 15 years and only recall one instance of someone mentioning a problem with a burned-up neutral, and I think it was a feeder not a branch.

 

[zbang]

Same, only one burned neutral in years, and that was to a stage lighting rig with 80+ KW of lights all running at under 50% for hours.

 

[xptpcrewx]

With computers and harmonics in our circuits. Is it time to stop using the common neutral ?
It makes sense that circuits 2, 4 and 6 with a common neutral is still valid for lighting circuits.
For general purpose convenience do you think the common neutral is still valid or obsolete ?
I will learn from you all.

Just wondering why you might think the MWBC or feeder with common neutral is obsolete? Do you have any sound technical reasons to not do it? Claiming computers and harmonics is not a good reason (note: harmonics can be additive or subtractive)


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[LarryFine]

It seems the biggest objection to MWBCs has been having to use handle ties.

 

[electrofelon]

It seems the biggest objection to MWBCs has been having to use handle ties.

Yeah there are considerations for using or not using MWBC's, but harmonics/overloaded neuters is not one of them (99.99% of the time)

 

[LarryFine]

Yeah there are considerations for using or not using MWBC's, but harmonics/overloaded neuters is not one of them (99.99% of the time)

Haven't you heard that 78% of statistics are inaccurate?

 

[ptonsparky]

Haven't you heard that 78% of statistics are inaccurate?

That means 32% of them are.

 

[electrofelon]

Haven't you heard that 78% of statistics are inaccurate?

You can't generalize

 

[LarryFine]

You can't generalize

I always lie.

 

[electrofelon]

I always lie.

Do I exist?

 

[zbang]

that all was quick.

Harmonics? Hardly ever a problem on MWBCs or feeders.

 

[JEFF MILLAR]

I SEE NO COMMON ANSWER. It has been reported that a large current was found to be in the neutral.
Commercial building with lots of computers.

 

[xptpcrewx]

I SEE NO COMMON ANSWER. It has been reported that a large current was found to be in the neutral.
Commercial building with lots of computers.

The common answer is it’s not a problem enough to render MWBC’s obsolete. Yes harmonics can add up in the neutral when triplen harmonics are involved, just size the neutral appropriately and be done with it.


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[electrofelon]

I SEE NO COMMON ANSWER. It has been reported that a large current was found to be in the neutral.
Commercial building with lots of computers.

Also I think what you are missing is most all power supplies these days are power factor corrected and quite "clean". Just because something is "electronic" doesn't mean it has "lots of harmonics"

 

[JEFF MILLAR]

Thank you.