Connecting neutrals in a CT cabinet.

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conmgt

Senior Member
Location
2 Phase Philly
I opened up a CT cabinet recently and noticed that the neutrals (4 - 250MCM) from the utility landed in a 4 hole lug that was bolted to the inside bottom of the cabinet.
The neutrals that led from the cabinet to the service panel landed in a lug bolted to the inside back of the cabinet.
The continuity between the base of the cabinet and the back wall of the cabinet was several 2 inch strips of welding between the two parts of the cabinet. This seemed less than ideal to me.
All neutral current was passing via those welds.

Does this seem to be bad practice?
Would it not be "better" to have both of those 4 hole lugs on the same sheet of metal...either the bottom panel or the back panel?
Better yet, one lug that contained all of those neutrals or is the steel between the lugs sufficient?
 

kwired

Electron manager
Location
NE Nebraska
I opened up a CT cabinet recently and noticed that the neutrals (4 - 250MCM) from the utility landed in a 4 hole lug that was bolted to the inside bottom of the cabinet.
The neutrals that led from the cabinet to the service panel landed in a lug bolted to the inside back of the cabinet.
The continuity between the base of the cabinet and the back wall of the cabinet was several 2 inch strips of welding between the two parts of the cabinet. This seemed less than ideal to me.
All neutral current was passing via those welds.

Does this seem to be bad practice?
Would it not be "better" to have both of those 4 hole lugs on the same sheet of metal...either the bottom panel or the back panel?
Better yet, one lug that contained all of those neutrals or is the steel between the lugs sufficient?

You are saying part of the current path from incoming neutral to outgoing neutral is the CT cabinet itself?

If so, I would say this is not that great of an idea and should be considered a violation of 250.6(A)

I was thinking there was a code section that was more obvious of a violation, but am not finding anything other than 250.6(A) so far. Will post if I find what I think I am looking for.
 

conmgt

Senior Member
Location
2 Phase Philly
You are saying part of the current path from incoming neutral to outgoing neutral is the CT cabinet itself?

Yes. That is exactly how it is wired.

Found what I was looking for, 200.2(B):

That's the answer.

So what is the solution? As in what product could be used to connect the two? Will not the cabinet and neutrals need to be bonded together? I can't seem to find an 8 port mechanical lug. I could bolt that to the cabinet for bonding and land all 8 conductors to it. Or a power distribution block with 4 ports on each side.
 

eHunter

Senior Member
Yes. That is exactly how it is wired.



That's the answer.

So what is the solution? As in what product could be used to connect the two? Will not the cabinet and neutrals need to be bonded together? I can't seem to find an 8 port mechanical lug. I could bolt that to the cabinet for bonding and land all 8 conductors to it. Or a power distribution block with 4 ports on each side.

Would an Ilsco connector work for you?
http://www.ilsco.com/e2wShoppingCat...k=2100001183:3100012208:3100012606:3100012940
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
what would be wrong with stacking two 4 port connectors right to the sheet metal. No need for a bonding jumper then as the bolt can serve for that, and no concern about neutral current flowing through the sheet metal.

It seems likely to me though that the welding you are describing might well be there specifically for the purpose of being a neutral current path.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
It seems likely to me though that the welding you are describing might well be there specifically for the purpose of being a neutral current path.
Possibly.
But even then, 200.2(B) would be violated even if the two connections were to the same continuous piece of the metal cabinet. Having it be to two well-connected pieces does not make that less of a concern.
Now if the CT cabinet really is governed by NESC rather than NEC, then it depends what if anything NESC says about the situation.
 
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conmgt

Senior Member
Location
2 Phase Philly
what would be wrong with stacking two 4 port connectors right to the sheet metal. No need for a bonding jumper then as the bolt can serve for that, and no concern about neutral current flowing through the sheet metal.

It seems likely to me though that the welding you are describing might well be there specifically for the purpose of being a neutral current path.

I'll check to see if the bolts holes line up. Stacking one on top of the other was one of my first thoughts but spinning one around to sit it on top of the other didn't appear to let the bolt holes line up.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Possibly.
But even then, 200.2(B) would be violated even if the two connections were to the same continuous piece of the metal cabinet. Having it be to two well-connected pieces does not make that less of a concern.
Now if the CT cabinet really is governed by NESC rather than NEC, then it depends what if anything NESC says about the situation.

B) Continuity. The continuity of a grounded conductor
shall not depend on a connection to a metallic enclosure,
raceway, or cable armor.

It appears to me that the connection is not to the box but to the welded piece, especially since they went to all that trouble to put it there. How is this any different than landing multiple grounded connectors to a neutral bar? The only thing different is how the neutral bar is connected to the box, and what material the neutral bar is made of.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
It appears to me that the connection is not to the box but to the welded piece, especially since they went to all that trouble to put it there. How is this any different than landing multiple grounded connectors to a neutral bar? The only thing different is how the neutral bar is connected to the box, and what material the neutral bar is made of.
As I read the OP's description, there is not a "welded piece" joining the two attachment bolts, just that the two separate pieces of the cabinet are joined by a heavy weld (2" of welding = 2" long weld bead). Maybe the OP can clarify that.

PS: There is, IMHO, a big difference between a ground-ground or ground-neutral bond and the continuity of a current carrying neutral, and the code seems to be recognizing that.
 
Last edited:

conmgt

Senior Member
Location
2 Phase Philly
It appears to me that the connection is not to the box but to the welded piece, especially since they went to all that trouble to put it there. How is this any different than landing multiple grounded connectors to a neutral bar? The only thing different is how the neutral bar is connected to the box, and what material the neutral bar is made of.

To be clear:
The welded piece is bottom of the cabinet, not a separate piece within the cabinet. The back and sides are all one piece formed from one sheet of steel but the top and bottom of the CT cabinet is made of separate sheets spot welded in place.
The one lug is bolted to the bottom sheet and the other is bolted to the back sheet.
 

meternerd

Senior Member
Location
Athol, ID
Occupation
retired water & electric utility electrician, meter/relay tech
I opened up a CT cabinet recently and noticed that the neutrals (4 - 250MCM) from the utility landed in a 4 hole lug that was bolted to the inside bottom of the cabinet.
The neutrals that led from the cabinet to the service panel landed in a lug bolted to the inside back of the cabinet.
The continuity between the base of the cabinet and the back wall of the cabinet was several 2 inch strips of welding between the two parts of the cabinet. This seemed less than ideal to me.
All neutral current was passing via those welds.

Does this seem to be bad practice?
Would it not be "better" to have both of those 4 hole lugs on the same sheet of metal...either the bottom panel or the back panel?
Better yet, one lug that contained all of those neutrals or is the steel between the lugs sufficient?

Most of the CT cans we use have a neutral bus inside which is isolated from the enclosure. Some utilities choose to ground the neutral at that location and some do not. Code does not limit the number of neutral grounds ahead of the service disconnect, so it's OK to have it grounded, but why it isn't terminated on a neutral bus or equivalent is a mystery. What exactly IS the fault current rating of a "welded strip"?
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Code does not limit the number of neutral grounds ahead of the service disconnect, so it's OK to have it grounded, but why it isn't terminated on a neutral bus or equivalent is a mystery.

Ahead of the service disconnect the NEC requirement that the grounded conductor continuity must not depend on connection to an enclosure is not applicable either, but like you I do not see why the two neutrals do not either come to a common point or be interconnected by something other than the enclosure.

I can imagine the neutral being interrupted because part of the enclosure rusts out, for example.
 

kwired

Electron manager
Location
NE Nebraska
To be clear:
The welded piece is bottom of the cabinet, not a separate piece within the cabinet. The back and sides are all one piece formed from one sheet of steel but the top and bottom of the CT cabinet is made of separate sheets spot welded in place.
The one lug is bolted to the bottom sheet and the other is bolted to the back sheet.

I can imagine the neutral being interrupted because part of the enclosure rusts out, for example.

Kind of beat me to posting what I was thinking. Lug bolted to bottom of what is likely an outdoor enclosure. Where will condensation accumulate and corrosion maybe begins? Right where that lug is mounted on the bottom.:(
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Kind of beat me to posting what I was thinking. Lug bolted to bottom of what is likely an outdoor enclosure. Where will condensation accumulate and corrosion maybe begins? Right where that lug is mounted on the bottom.:(

Be not afraid, NESC will protect it! (or, perhaps it does not follow NESC either?)
 

david

Senior Member
Location
Pennsylvania
I do not think that just because a utility provides a piece of equipment to a customer that it is under the utilities control. Here the utility provided meter cans for all services for years. They have since stop that practice. They have a list of cans they will accept.

If a non-utility employee provides the conductors and lands them in the CT cabinet I feel it is under the control of the NEC.

Anyhow all the utilities in this area require that the installation be inspected before they will energize. If the same is true in your area then the install is approved under the provisions of the NEC.

Most of the time it?s a combination of both however any work not done by the utility falls under the NEC.

I recognize things are done differently in different areas
 
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