The Neutral

[stgeorge]

I had a classmate ask a question yesterday at school.

"If you install a 3-phase (with a neutral) disconnect do you need to disconnect the neutral with the hot-legs.? Or can the Neutral go straight to the Load bypassing the disconnect." ??

 

[roger]

I had a classmate ask a question yesterday at school.

"If you install a 3-phase (with a neutral) disconnect do you need to disconnect the neutral with the hot-legs.? Or can the Neutral go straight to the Load bypassing the disconnect." ??

A solid neutral is the norm.

Roger

 

[C3PO]

I had a classmate ask a question yesterday at school.

"If you install a 3-phase (with a neutral) disconnect do you need to disconnect the neutral with the hot-legs.? Or can the Neutral go straight to the Load bypassing the disconnect." ??

Roger is correct the Nuetral does not have to be disconnected but it does have to run with the ungrounded conductors(hot-legs).

 

[stgeorge]

Thats what i originally thought but then started to second guess myself.
Thank you for the infomation.

 

[ultramegabob]

I had a classmate ask a question yesterday at school.

"If you install a 3-phase (with a neutral) disconnect do you need to disconnect the neutral with the hot-legs.? Or can the Neutral go straight to the Load bypassing the disconnect." ??

where would you buy a 4 pole disconnect?

 

[Dennis Alwon]

where would you buy a 4 pole disconnect?

They make 4 pole discos.

 

[C3PO]

where would you buy a 4 pole disconnect?

Square D makes them.

 

[ultramegabob]

I have seen alot of 4 pole contactors, but never a 4 pole disconnect that I can recall, what is an application that would require that?

 

[haskindm]

Any "seperately derived 3-phase system" requires a 4-pole disconnect. They are readily available.

 

[walkerj]

A transfer switch for a genny could require one

 

[C3PO]

I have seen alot of 4 pole contactors, but never a 4 pole disconnect that I can recall, what is an application that would require that?

I guess if you need to switch the nuetral for some reason. Square D also makes a 6 pole but only in NEMA 4X or NEMA 12/3R enclosures. Not sure of an application for it though.

 

[Buck Parrish]

I had a classmate ask a question yesterday at school.

"If you install a 3-phase (with a neutral) disconnect do you need to disconnect the neutral with the hot-legs.? Or can the Neutral go straight to the Load bypassing the disconnect." ??

If it is a three phase Service you have to bond the neutral to the can. Terminated, then run through to the load.

 

[ultramegabob]

Any "seperately derived 3-phase system" requires a 4-pole disconnect. They are readily available.

that makes sense, thanks...

 

[haskindm]

Any "separately derived 3-phase system" requires a 4-pole disconnect. They are readily available.

I guess maybe that would be more correctly called a 4-pole transfer switch.

 

[ultramegabob]

I guess I was just picturing a 4 pole blade disconnect, didnt really think about a transfer switch.

 

[nakulak]

Any "seperately derived 3-phase system" requires a 4-pole disconnect. They are readily available.

would you happen to know the code section for this please ?

 

[POWER_PIG]

would you happen to know the code section for this please ?

Hmmm I know a genny is not considered a seperatly derived system unless the utility neutral is opened during transfer, 250.20 d1..... maybe thats what hes refering to,,,,,,,,I dunno, Im gonna go look again.

 

[haskindm]

would you happen to know the code section for this please ?

Article 100 - definition of "separately Derived System" states that a separately derived system shall "have no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system." This would require a 4-pole transfer switch in a 3-phase system. Also 514.11 motor fuel pumps require that the grounded conductor be disconnected along with the "hot" conductors. This would require a 4-pole switch on a 3-phase pump.

 

[wasasparky]

...This would require a 4-pole transfer switch in a 3-phase system.

Only IF you wanted the genny to be a separately derived system.