480 VOLT 4 wire circuit

[jimbo123]

When installing a 3 phase 60 amp 480 circuit from a mcc bucket is the fourth wire that is usually located at the bottom of the mcc attached to ground buss a neutral or a ground wire ? I see some lighting panels using this conductor as a neutral wire, and then someone else using it as egc for something else.
The mcc's come from the service gear.

 

[augie47]

It being a MCC, playing the odds I'd say an equipment grounding buss.
Can you tell if it's insulated (isolated) from the bucket ?
The majority of the MCCs I see have no grounded (neutral) buss, but, some do.

 

[iwire]

I agree with Gus.

 

[jimbo123]

At this time I don't know if it is insulated from the bucket. There is a main cb at the mcc coming from the service panel I have to check to see if it is ID green or gray plus test it to mcc. Thanks

 

[Barndog]

It being a MCC, playing the odds I'd say an equipment grounding buss.
Can you tell if it's insulated (isolated) from the bucket ?
The majority of the MCCs I see have no grounded (neutral) buss, but, some do.

I would also agree. We have about 25 MCC's in the plant i work at and none of them have a Neutral connection.

 

[jimbo123]

Where would the 277v neutral come from for the lighting panels ?

 

[cadpoint]

Where would the 277v neutral come from for the lighting panels ?

After a transformer!

 

[jim dungar]

The majority of the MCCs I see have no grounded (neutral) buss, but, some do.

It would be extremely odd to see an MCC that has a neutral bus that spans across multiple sections, like the phase and ground ones do. Typically when an MCC is built as a 4 w (i.e. 480Y/277) the neutral is simply a multi-terminal bus in a compartment, just like it is in a panelboard.

According to the OP this MCC is not the service but it has both neutrals and grounds connected to the same bus bar.

 

[Cow]

It definitely sounds like someone has been cheating by using the ground bar as a neutral buss.:roll:

Since curiosity would get the best of me, I'd probably put an amp clamp around the ground wire feeding the MCC just to see how much current was traveling back on it...

 

[walton]

You can't run a 4 wire circuit off a 480v 3 phase MCC. There is no neutral available so the 4th wire would be a ground. A neutral would have to be established at a 480/277 wye transformer.

 

[jimbo123]

There is no 480/277 transformer to pickup a neutral anywhere i look. The fourth conductor in my pvc conduit [coming from service panel] taped gray which would indicate a neutral. Does this mean they used wrong color tape and are cheating at the Mcc as stated in a previous post ? The lighting panel [277v] is feed from Mcc

 

[augie47]

If it's a 3 phase circuit with 4 wires coming from your service panel and it's in PVC, the 4th wire should be an equipment ground and so identified.
It sure sounds like someone using the EGC as a neutral for your 277 panel.

 

[Cow]

Is the MCC in the same building as the service panel that feeds it?

If you see where I'm going with this, I'm wondering if they're treating the MCC like service equipment?

 

[jimbo123]

No service and Mcc are in seperate building. Will recheck everything tonight again . but 99% sure everything is the way i discribe.

 

[Cow]

It sounds like they're treating this MCC as the service disconnect for the building. If it's listed suitable for use as a service disconnect and there's a grounding electrode system installed I don't really see the problem.

There aren't supposed to be any other metallic paths between this MCC building and the one that feeds it since this is only a 4 wire feed and not a 5 wire.

 

[puckman]

I am told this was done over 30 years ago and they only used 4 wire then. The forth wire is a neutral and the mcc 's are connected to the building steel . THE neutral connection block has continuity to the mcc buckets and mcc cabinets.
If there is contact between phase wire and mcc or neutral do you think breaker back at switchgear will clear.