Zig Zag Neutral for new equipment

[Joe Hans]

I'm installing a new production line that was manufactured in Italy. The electrical requirements of the new line are;
400 VAC, 3 Phase, 50Hz, 2500A. They also require a neutral (230VAC) for mostly heating (resistive loads). The total connected load to the neutral is about 1200A but much of this is well balance between all three phases. The actual demand on the neutral should be quite low.
The existing electrical system at our facility consists of a 2000KVA transformer with 34.5 KV (primary delta) and 480 / 277 wye on the secondary. The new equipment can handle the higher voltage on the phases and the frequency should not be a problem either. I am worried about the 277 VAC for the neutral. When our system was installed back in 1985 the neutral from the transformer was never run to the switchgear inside of the building. Unfortunately this is about a 200 foot run underground in 6 - 6"rigid conduits encased in concrete. Getting an additional conductor through the conduits could be quite difficult. I was wondering if a zig zag configuration could be used on a 480/277 system and provide a 230 VAC neutral? I'm a little worried of the 20% increase in voltage for the resistive loads. I would like to drop that by at least 10% or more and get a little closer to the 230V recommended.

 

[sparkyrick]

I'm installing a new production line that was manufactured in Italy. The electrical requirements of the new line are;
400 VAC, 3 Phase, 50Hz, 2500A. They also require a neutral (230VAC) for mostly heating (resistive loads). The total connected load to the neutral is about 1200A but much of this is well balance between all three phases. The actual demand on the neutral should be quite low.
The existing electrical system at our facility consists of a 2000KVA transformer with 34.5 KV (primary delta) and 480 / 277 wye on the secondary. The new equipment can handle the higher voltage on the phases and the frequency should not be a problem either. I am worried about the 277 VAC for the neutral. When our system was installed back in 1985 the neutral from the transformer was never run to the switchgear inside of the building. Unfortunately this is about a 200 foot run underground in 6 - 6"rigid conduits encased in concrete. Getting an additional conductor through the conduits could be quite difficult. I was wondering if a zig zag configuration could be used on a 480/277 system and provide a 230 VAC neutral? I'm a little worried of the 20% increase in voltage for the resistive loads. I would like to drop that by at least 10% or more and get a little closer to the 230V recommended.

Off the topic, but if your service is 480V only, what lighting do you have? Since most facilities have 277V lighting. Just curious.

 

[iwire]

Off the topic, but if your service is 480V only, what lighting do you have? Since most facilities have 277V lighting. Just curious.

He has 277 volt.

The existing electrical system at our facility consists of a 2000KVA transformer with 34.5 KV (primary delta) and 480 / 277 wye on the secondary.

 

[GoldDigger]

He has 277 volt.

:thumbsup: But the existing neutral was not wired to the place the OP needs it.
In another thread the consensus was that recreating the neutral in a system with an existing neutral will be a code problem *unless* it is done inside the utilization equipment instead of in the building wiring.

It (zig-zag to get a neutral) can be done as part of an SDS though.

 

[sparkyrick]

I'm installing a new production line that was manufactured in Italy. The electrical requirements of the new line are;
400 VAC, 3 Phase, 50Hz, 2500A. They also require a neutral (230VAC) for mostly heating (resistive loads). The total connected load to the neutral is about 1200A but much of this is well balance between all three phases. The actual demand on the neutral should be quite low.
The existing electrical system at our facility consists of a 2000KVA transformer with 34.5 KV (primary delta) and 480 / 277 wye on the secondary. The new equipment can handle the higher voltage on the phases and the frequency should not be a problem either. I am worried about the 277 VAC for the neutral. When our system was installed back in 1985 the neutral from the transformer was never run to the switchgear inside of the building. Unfortunately this is about a 200 foot run underground in 6 - 6"rigid conduits encased in concrete. Getting an additional conductor through the conduits could be quite difficult. I was wondering if a zig zag configuration could be used on a 480/277 system and provide a 230 VAC neutral? I'm a little worried of the 20% increase in voltage for the resistive loads. I would like to drop that by at least 10% or more and get a little closer to the 230V recommended.

He has 277 volt.

Are you sure about that

 

[GoldDigger]

One of the problems of an SDS solution to get the right voltage is that it would remove the need to pull a neutral 200', but needs both an EGC and GEC instead, where only an EGC exists right now.
Again, if the equipment manufacturer did the needful inside using a transformer the NEC problems might not come up.
In the other thread, the line to missing neutral load was just low power controls. Here it is major power.

 

[Smart $]

I always love to hear about U.S. manufacturing facilities that buy these expensive production lines made in Europe and fail to anticipate the electrical requirements in doing so.

:rotflmao:

 

[Phil Corso]

Joe...

1) The present phase-neutral load at 230V is 1,200A! At 277V it will increase to 1,450A! Is the Load Temp-Controlled so that the Demand at 277V won't be greater than its demand at 230V!

2) If Demand can be kept at the 230V level, then the Zig-Zag Xfmr's 3-ph capacity needs to about 830kVA!

In short, the you have to compare the cost of the Zig-Zag to the cost of installing an adequate neutral conductor!

Regards, Phil Corso

 

[iwire]

But the existing neutral was not wired to the place the OP needs it.

Are you sure about that

Apparently not.

 

[Smart $]

...

In short, the you have to compare the cost of the Zig-Zag to the cost of installing an adequate neutral conductor!

I believe Code compliance, as was already mentioned, is at issue before any financial concerns. 450.5 says in part, "shall not be installed on the load side of any system grounding connection". Refer to the section for full requirement text.

 

[Phil Corso]

Smart A,

Just gave Joe additional CON-argument against Z-Z Connection!

Phil

 

[Phil Corso]

Gentlepeople,

FYI, the Z-Z Xfmr's size can be materially reduced to, say 'X', if one can guarantee that 'Expected' neutral-load imbalance will never exceed 'X' !

Phil

 

[Phil Corso]

Smart A, Reur 450-5 comment:

As long as Neutral-load's neutral-conductors are insulated and connected to a equivalent "neutral block" and not directly connected to 'Ground' then cited Art will not be compomised!

Phil

 

[Joe Hans]

Off the topic, but if your service is 480V only, what lighting do you have? Since most facilities have 277V lighting. Just curious.

Most of our overhead lighting is 480. Office areas have there own local lighting panels.

 

[Joe Hans]

I always love to hear about U.S. manufacturing facilities that buy these expensive production lines made in Europe and fail to anticipate the electrical requirements in doing so.

:rotflmao:

The new equipment was originally to be installed in Brazil or Europe. Fortunately for us the new company chose our location to start a new North American based division. Yes the equipment was expensive and yes we knew the electrical was going to be an issue.

Thanks for all of the other comments concerning the issue. My guess is that we will try to pull new neutral conductors from the transformer to the switchgear and abandon the zig zag option. Since the single phase heaters tied to the neutral are controlled with the PLC we can anticipate faster heat up times for the extrusion equipment, once the extruders are running most of the heat is generated from the mechanical work from the screws. I will also try changing the taps on the primary side of the transformer to reduce the voltage level some.

Thanks,
Joe

 

[Smart $]

Smart A, Reur 450-5 comment:

As long as Neutral-load's neutral-conductors are insulated and connected to a equivalent "neutral block" and not directly connected to 'Ground' then cited Art will not be compomised!

Phil

That's not how I see it it...

450.5 Grounding Autotransformers. Grounding autotransformers
covered in this section are zigzag or T-connected
transformers connected to 3-phase, 3-wire ungrounded systems
for the purpose of creating a 3-phase, 4-wire distribution
system or providing a neutral point for grounding purposes.
Such transformers shall have a continuous per-phase current
rating and a continuous neutral current rating. Zigzag-
connected transformers shall not be installed on the load
side of any system grounding connection, including those
made in accordance with 250.24(B), 250.30(A)(1), or
250.32(B), Exception No. 1.

Perhaps you can explain another interpretation which would permit the zigzag on the load side of the system disconnecting means...

Please note there is an exception to 450.5 which I did not include in the quote because it did seem to be relevant.

 

[winnie]

Hmm. You are installing a 1700KVA load on an existing system with a 2000KVA transformer.

IMHO with a grounded supply the zig-zag transformer is not an option. 450.5 prohibits it being used as a grounding autotransformer, and 210.9 and 215.11 require that you bring a neutral to autotransformer circuits (with some exceptions that don't apply).

What would happen if you changed the supply transformer to an ungrounded configuration, and then used a zig-zag transformer to create the neutral/grounding point inside the facility?

IMHO this is an out-there idea, and you are better off simply getting the neutral pulled somehow.

-Jon

 

[winnie]

Perhaps you can explain another interpretation which would permit the zigzag on the load side of the system disconnecting means...

Please note there is an exception to 450.5 which I did not include in the quote because it did seem to be relevant.

I think that Phil is saying that if you use a zig-zag transformer to derive a neutral that you _don't_ ground, then it isn't a grounding autotransformer and that 450.5 doesn't apply. I agree with him on this point.

However the other autotransformer rules prohibit this use, rendering my agreement moot.

-Jon

 

[Phil Corso]

Smart A,

I apologize! You are correctI I missed the point about the existing supply Xfmr supplying 480/277! Hence, its neutral is already grounded. But, it's not extended into the area where the new equipment is to be installed!

Good... nay, excellent, P-U!

Sincerely, Phil

 

[Smart $]

I think that Phil is saying that if you use a zig-zag transformer to derive a neutral that you _don't_ ground, then it isn't a grounding autotransformer and that 450.5 doesn't apply. I agree with him on this point.

...

I presumed y'all would realize the derived neutral is be required to be grounded [250.26(3)], thus making it a grounding transformer.