480/277 3 phase

[Jpflex]

On a 480/277 400 amp 3 phase service.
Do you need to bond the neutral to ground inside the current transformer box?
The neutral bar only has space for one wire.

Assuming a separately derived system transformer I would actually say the answer could potentially be a NO because NEC typically allows the system bonding jumper (connection between transformer secondary windings mid/ neutral point and ground only at ONE location to avoid objectionable current or a parallel neutral current path.

This bond could technically be in the transformer if located outdoors away from the first point of disconnect for a YES to your question and not bond the neutral grounded conductor to the first point of disconnect neutral and ground buss as traditionally done

Or a NO if the transformer is located indoors adjacent to the first point of disconnect panel, where you would bond the neutral bus and ground buss but according to code not at two locations if objectionable current can result


In older systems pre 1996 where a neutral servers also as the supply side bonding jumper I think it’s allowed to have this bonding at both the first point of disconnect and transformer

 

[augie47]

If it's service conductors, follow post #5 (skip post 21, irrelevant on services).
Mostly I see bonding via the neutral in the CT.
On smaller services, often by use of a stud kerney

 

[kwired]

Assuming a separately derived system transformer I would actually say the answer could potentially be a NO because NEC typically allows the system bonding jumper (connection between transformer secondary windings mid/ neutral point and ground only at ONE location to avoid objectionable current or a parallel neutral current path.

This bond could technically be in the transformer if located outdoors away from the first point of disconnect for a YES to your question and not bond the neutral grounded conductor to the first point of disconnect neutral and ground buss as traditionally done

Or a NO if the transformer is located indoors adjacent to the first point of disconnect panel, where you would bond the neutral bus and ground buss but according to code not at two locations if objectionable current can result


In older systems pre 1996 where a neutral servers also as the supply side bonding jumper I think it’s allowed to have this bonding at both the first point of disconnect and transformer

OP was asking about services not separately derived systems.

Everything ahead of service disconnecting means is bonded to the grounded conductor and does lead to parallel paths on objects not intended to carry current, good design practices can help minimize this to some extent though.

 

[Jpflex]

OP was asking about services not separately derived systems.

Everything ahead of service disconnecting means is bonded to the grounded conductor and does lead to parallel paths on objects not intended to carry current, good design practices can help minimize this to some extent though.

Ok yes but I believe the concept is the same except the grounded electrode conductor for bonding ends at the first point of disconnect.

Still what I was saying in regards to the transformer (seevice) main bonding jumper being at the transformer or first point of disconnect typically being only at one location is the same. At least that’s how code outed it with some exemptions

 

[kwired]

Ok yes but I believe the concept is the same except the grounded electrode conductor for bonding ends at the first point of disconnect.

Still what I was saying in regards to the transformer (seevice) main bonding jumper being at the transformer or first point of disconnect typically being only at one location is the same. At least that’s how code outed it with some exemptions

OP is asking about bonding the CT enclosure of a service supply. Outside of multi tenant or other multi-meter situations this is usually on the supply side of the service disconnecting means. Often can be POCO equipment as well and not subject to NEC or the cabinet is provided by POCO, the EC maybe mounts it, but POCO still terminates things inside to their methods.

 

[garbo]

When we installed 600 & 800 amp three phase services would always perform the bonding inside of the 8 by 8 or 12 by 12" through that came off the CT cabinet. Would cut the cover 1' long and tap a few screws for that portion that covered section and either have an engraved plate or P touch label stating that bonding point was behind that 1' section.