4.16kV MV MCC neutral bus

[mull982]

I'm looking at an application with a new 4.16kV MCC where the customer wishes to serve L-N loads. I've never been involved with a MV MCC that required a neutral as most of the 4.16kV systems have either been LRG systems or just 3-Wire systems.

Based on the requirements of 250.30 I'm trying to determine if we need to have a neutral bus in the MV MCC and bring the neutral to this bus with bonding to ground or if we can just bring the neutral directly from the transformer to the load since only one load requires this neutral. I've always had situations with LV switchgear where the neutral was brought into the first disconnecting means with the system bonding jumper being either at the transformer or the first disconnecting means.

If the system bonding jumper is provided at the transformer secondary is there a requirement to bring the neutral into the first disconnecting means as opposed to routing it directly to the load or another location outside of the switchgear? The only potential functional issue that I'd see would be with ground fault settings with the CT's/relay not seeing the neutral current but am not sure from an NEC standpoint if this would be compliant.

 

[jim dungar]

I know that at 480V the neutral bus is not required. You can bring the load neutral directly to the incoming termination.

 

[Ainsley Whyte]

I'm looking at an application with a new 4.16kV MCC where the customer wishes to serve L-N loads. I've never been involved with a MV MCC that required a neutral as most of the 4.16kV systems have either been LRG systems or just 3-Wire systems.

Based on the requirements of 250.30 I'm trying to determine if we need to have a neutral bus in the MV MCC and bring the neutral to this bus with bonding to ground or if we can just bring the neutral directly from the transformer to the load since only one load requires this neutral. I've always had situations with LV switchgear where the neutral was brought into the first disconnecting means with the system bonding jumper being either at the transformer or the first disconnecting means.

If the system bonding jumper is provided at the transformer secondary is there a requirement to bring the neutral into the first disconnecting means as opposed to routing it directly to the load or another location outside of the switchgear? The only potential functional issue that I'd see would be with ground fault settings with the CT's/relay not seeing the neutral current but am not sure from an NEC standpoint if this would be compliant.

What voltage for those L-N Loads ? and also is it three phase loads ?

 

[Jraef]

L-N on 4160V is 2400V.
I have never heard of anything that would use 2400V single phase power L-N, but then again I have not heard of everything.

Typically an MV MCC is not the Service Entrance gear so you would not bond the N to ground there, it would be done ahead of the MCC. I have never seen it in an MV MCC, but in LV MCCs you can usually get what's called a "Neutral landing pad", basically a short piece of bus in just one section, so that you can make one or two neutral connections for loads rather than run a N bus through the entire thing.

Looking at an MV MCC design book I have from A-B however, they don't offer that for MV MCCs, in fact they don't offer 4 wire as a source option at all. I also looked at an Eaton MV MCCs and switchgear guides I have, they don't offer 4 wire for metal clad or metal enclosed switchgear either.

So bottom line you are likely going to have to get something custom made, so you can probably get what you want at that point.

 

[masterinbama]

L-N on 4160V is 2400V.
I have never heard of anything that would use 2400V single phase power L-N, but then again I have not heard of everything.

Typically an MV MCC is not the Service Entrance gear so you would not bond the N to ground there, it would be done ahead of the MCC. I have never seen it in an MV MCC, but in LV MCCs you can usually get what's called a "Neutral landing pad", basically a short piece of bus in just one section, so that you can make one or two neutral connections for loads rather than run a N bus through the entire thing.

Looking at an MV MCC design book I have from A-B however, they don't offer that for MV MCCs, in fact they don't offer 4 wire as a source option at all. I also looked at an Eaton MV MCCs and switchgear guides I have, they don't offer 4 wire for metal clad or metal enclosed switchgear either.

So bottom line you are likely going to have to get something custom made, so you can probably get what you want at that point.

I have seen it once in my 40 years.
Engineer speced 2400v to 120v control transformers at an outdoor booster pump station.

Sent from my LML211BL using Tapatalk
Same utility also had 2400v phase to phase systems.

 

[mull982]

L-N on 4160V is 2400V.
I have never heard of anything that would use 2400V single phase power L-N, but then again I have not heard of everything.

It is feeding a test station for an R&D facility that will be testing protypes of large power supplies and want 3-PH as well as L-N power avalaible.

Typically an MV MCC is not the Service Entrance gear so you would not bond the N to ground there, it would be done ahead of the MCC. I have never seen it in an MV MCC, but in LV MCCs you can usually get what's called a "Neutral landing pad", basically a short piece of bus in just one section, so that you can make one or two neutral connections for loads rather than run a N bus through the entire thing.

You are correct this will not be SE. NEC 250.30 gives 2 options for system bonding jumper locations on a SDS with one of those options being in the switchgear. If it is in the switchgear then you would need a neutral bus/pad to install you system bonding jumper to ground. I agree that it would not be needed here if bonding jumper was done at the transformer itself.

Looking at an MV MCC design book I have from A-B however, they don't offer that for MV MCCs, in fact they don't offer 4 wire as a source option at all. I also looked at an Eaton MV MCCs and switchgear guides I have, they don't offer 4 wire for metal clad or metal enclosed switchgear either.

So bottom line you are likely going to have to get something custom made, so you can probably get what you want at that point.

Yes I have had manufacturers tell me that this will be a custom build but can be done. I'm just trying to determine if it meets code requirements. I'd also expect there to be an issue with GF sensing on relay without being able to sense neutral current if not brought through switchgear.