277volt nuetral used in 120v system

[Toros]

Hi,
can I use the neutral of 480/277v system
in 120v circuit feeding 120v loads????
tanx

 

[JFletcher]

Hi,
can I use the neutral of 480/277v system
in 120v circuit feeding 120v loads????
tanx

No. 200.6, 300.3, and all conductors must originate from the same panel.

eta: not to mention creating a MWBC with 277 on one phase and 120V on another would definitely fry all your 120V equipment should you lose the neutral, perhaps even upon connection. You cant group those conductors in the panel nor install handle ties b/c 120 and 277 would be coming from 2 different panels. Safety wise, what you ask would be extremely dangerous to servicing personnel as well.

 

[iwire]

No and it would be hazardous to do so.

It would be using grounding and grounding electrode conductors as circuit conductors

 

[kwired]

NEC won't allow it, but POCO's do that all the time with a common neutral for primary and secondary distribution.

 

[iwire]

NEC won't allow it, but POCO's do that all the time with a common neutral for primary and secondary distribution.

Not a just a common neutral, a multigrounded neutral.

I don't see that as the same thing as having using EGCs and GECs as circuit conductors.

 

[dionysius]

I will assume you have a need for 120V and 240V. I will also assume you have a good ufer CEC ground.

This is a good question...... What if the 480/277 neutral is bonded to a great ufer ground?? Technically it should be ok but code wise is different.

Normally the 120V trafo is a separately derived entity. The primary, if single phase, will be 2 wire only 480V (with no neutral). The secondary will be 240/120 split phase and the ufer ground will be the neutral. It will also be the ground.

If a 3 phase is used the trafo primary will be a delta (so 3 wires, no neut) and the secondary will be 3 phases of 240/120 split phase delta. The ufer ground will be the neutral. It will also be the ground for all the metal.

I say ufer ground since I do not trust most other grounds. If you want 208v you will use a Y secondary.

 

[iwire]

This is a good question...... What if the 480/277 neutral is bonded to a great ufer ground?? Technically it should be ok but code wise is different.

Normally the 120V trafo is a separately derived entity. The primary, if single phase, will be 2 wire only 480V (with no neutral). The secondary will be 240/120 split phase and the ufer ground will be the neutral. It will also be the ground.

If a 3 phase is used the trafo primary will be a delta (so 3 wires, no neut) and the secondary will be 3 phases of 240/120 split phase The ufer ground will be the neutral. It will also be the ground for all the metal.

I say ufer ground since I do not trust most other grounds.

Most likely the OP has a 480 delta 208Y/120 transformer supplied from a 480Y/277 service.

NEC rules being what they are both these systems require grounding electrodes and those electrodes will be bonded together. It would still be dangerous to use these grounding electrode conductors as circuit conductors.

 

[electrofelon]

This is a good question...... What if the 480/277 neutral is bonded to a great ufer ground?? Technically it should be ok but code wise is different.

Normally the 120V trafo is a separately derived entity. The primary, if single phase, will be 2 wire only 480V (with no neutral). The secondary will be 240/120 split phase and the ufer ground will be the neutral. It will also be the ground.

If a 3 phase is used the trafo primary will be a delta (so 3 wires, no neut) and the secondary will be 3 phases of 240/120 split phase The ufer ground will be the neutral. It will also be the ground for all the metal.

I say ufer ground since I do not trust most other grounds.

Lets get a few things straight:

1. Very few buildings have an UFER ground and the electrical system works fine. What do you think the grounding electrode is doing that is so important anyway?

2. "The UFER ground would be the neutral " no the neutral comes from the transformer windings. There is a gec connected to it, but note the neutral is STILL bonded to the GES even without the sds gec (by the transformer equipment grounds).

3. Current must return to its source. A neutral from another source won't even function in a different system unless there is a path back to its source (most nec systems would have this system interconnnection.).

 

[ggunn]

If a 3 phase is used the trafo primary will be a delta (so 3 wires, no neut) and the secondary will be 3 phases of 240/120 split phase delta.

What does that mean? You can't have three 240/120 split phase from a single three phase transformer with center tapped secondary coils, can you? The center taps would all be at different potentials from each other; you can't tie them together.

 

[electrofelon]

What does that mean? You can't have three 240/120 split phase from a single three phase transformer with center tapped secondary coils, can you? The center taps would all be at different potentials from each other; you can't tie them together.

I guess u could have each delta coil center tapped (but not all connected) It would be really ridiculous! You would need 3 isolated neutral bars in the panel. Maybe next time I'm ordering gear I'll ask for that with a straight face

 

[kwired]

Not a just a common neutral, a multigrounded neutral.

I don't see that as the same thing as having using EGCs and GECs as circuit conductors.

That is true, and with the MGN system they have they don't use EGC's but there is a GEC to every electrode used and some current does pass through those electrodes, most of it likely being current associated with the meduim voltage system more so then low voltage systems.