Zig Zag Neutral for new equipment

Status
Not open for further replies.
winnie said:
...
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?
Click to expand...
Probably better off getting a 480V PRI - 400Y/230V SEC isolation transformer.
 
Smart $ said:
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:
Click to expand...

I live in the UK (a part of the EU) where the voltage is still 433/250V. We bought a plant from Belgium (also a part of the EU) that required 380/220V. The manufacturers wouldn?t change their voltage specification so I had to install a 1500KVA 11/.38KV transformer and switchboard to feed the new plant.
Running a dual voltage plant isn?t ideal, in fact it?s a pain in the **** but needs must.

With the loading given by the OP I can?t see any other option other than a new transformer and the associated switchgear.

The argument about importing equipment can go two ways, we get equipment from the US that is supposedly compatible with our voltage. Except for a minor problem. Our supply isn?t centre grounded.

While ever stuff is sold outside it place of origin this will always be a problem. Learn to live with it.
 
Joe Hans said:
When our system was installed back in 1985 the neutral from the transformer was never run to the switchgear inside of the building.
Click to expand...

Please clarify what you do have.

Is this service conductors or feeders to another building or structure?

If service conductors you need (and did in 1985 as well) a grounded conductor brought to service equipment. If there are only three conductors - maybe at one time was a corner grounded delta?

If a feeder supplying a separate building or structure you didn't need a grounded conductor but did at least need an equipment grounding conductor. It also was permissible to run a grounded conductor only and bond it at the separate building up until either 2005 or 2008 (can't quite recall which).
 
kwired said:
Please clarify what you do have.

Is this service conductors or feeders to another building or structure?

If service conductors you need (and did in 1985 as well) a grounded conductor brought to service equipment. If there are only three conductors - maybe at one time was a corner grounded delta?

If a feeder supplying a separate building or structure you didn't need a grounded conductor but did at least need an equipment grounding conductor. It also was permissible to run a grounded conductor only and bond it at the separate building up until either 2005 or 2008 (can't quite recall which).
Click to expand...

We have a 2000KVA (34.5KV delta pri / 480/277 sec wye) transformer located on a vault about 200' from our switchgear. The feed from the transformer to the switchgear consists of 6 - 6" GRC encased in concrete. Each 6" pipe has 3 - 1000 kcmil phase conductors and 1 - 2/0 ground conductor. My options as I know it are listed below from the least expensive up...

1.) Re-purpose the 6 - 2/0 ground conductors as neutrals and land them on a new isolated neutral bar in the switchgear. Bond all 6 - 6" conduits and use them as the ground. (Not sure if NEC would approve)

2.) Use the 2/0 ground conductor as a pull wire and pull in 2 new 2/0 conductors. Use one as the ground and one for the neutral. Each pipe would then have 3 - 1000 kcmil and 2 - 2/0 conductors. I'm a little nervous with this method. If the phase conductors are damaged then I'm **** out of luck. The new 1000 kcmil is about $18.50 per foot.

3.) Re purpose the existing ground wire as the neutral (same as item #1). Run an external ground from our switchgear to the transformer. I'm not sure this would be approved by the NEC. I think article 310.4?? requires parallel feeds to contain all conductors to eliminate induction issues.

4.) Zig zag setup.......

5.) Replace the transformer with a 2000-2500Kva 400/230 system.
 
Joe Hans said:
... When our system was installed back in 1985 the neutral from the transformer was never run to the switchgear inside of the building. ...
Click to expand...

Joe Hans said:
We have a 2000KVA (34.5KV delta pri / 480/277 sec wye) transformer located on a vault about 200' from our switchgear. The feed from the transformer to the switchgear consists of 6 - 6" GRC encased in concrete. Each 6" pipe has 3 - 1000 kcmil phase conductors and 1 - 2/0 ground conductor. ...
Click to expand...
By the way you say it, that is a supply-side bonding jumper using today's terminology. Are you certain it is a grounding conductor? The reason I ask is because back in 1985 it was commonplace to run a grounded conductor and compliant to not run a wire-type bonding jumper. Given that EGC and grounded conductors are bonded at service (or sometimes first if SDS) disconnecting means, it was and still is commonplace to not have a neutral bus in switchgear and simply use an equipment grounding bus for both.

The point here is that you may have a then Code-compliant neutral conductor.

You still have not clarified whether this a service or an SDS.
 
Last edited:
This is a service to this particular building. The transformer is owned by American Electric Power and we own everything from the bushings in. I am going to have AEP open the secondary side of the transformer to have a good look and take pictures next week.
 
Joe Hans said:
This is a service to this particular building. The transformer is owned by American Electric Power and we own everything from the bushings in. I am going to have AEP open the secondary side of the transformer to have a good look and take pictures next week.
Click to expand...
To me that means the conductors entering the building are service conductors, only one grounded conductor (or set when paralled) is needed, install bonding jumper at service equipment and separate neutrals from equipment grounding conductors anywhere beyond that point.
 
kwired said:
To me that means the conductors entering the building are service conductors, only one grounded conductor (or set when paralled) is needed, install bonding jumper at service equipment and separate neutrals from equipment grounding conductors anywhere beyond that point.
Click to expand...
Probably used 'combined' grounded-grounding bus. Commonplace in industrial service switchgear. The entire bus serves as the MBJ too (let's not get into compliance issues that we discussed in another thread ;)).

Though most make no considerations for parallel neutral current path on supply side of service equipment, we can cover GRC bonding at both gear and transformer.
 
I'm still trying to figure out how the OP thinks the 50Hz is not a problem. Not sure what kind of production equipment this is but, there may be devices (motors, xfmrs, contactors, etc.) on there that will not like 60Hz.
 
Status
Not open for further replies.
Top