GEC termination at CT cabinet

[electrofelon]

Code says that the grounded (usually neutral) conductor must be bonded to a supply side CT enclosure,

Not quite. Here are the actual code sections. I am nitpicking your statement a bit because, to me, your wording makes it sound like the grounded conductor in the CT cabinet must be bonded to the CT cabinet, when in fact there are other options:


250.142 Use of Grounded Circuit Conductor for Grounding Equipment. (A) Supply-Side Equipment. A grounded circuit conductor shall be permitted to ground non–current-carrying metal parts of equipment, raceways, and other enclosures at any of the following locations:

250.92 Services.
(A) Bonding of Equipment for Services. The normally non– current-carrying metal parts of equipment indicated in 250.92(A)(1) and (A)(2) shall be bonded together.
(1) All raceways, cable trays, cablebus framework, auxiliary gutters, or service cable armor or sheath that enclose, contain, or support service conductors, except as permit‐ ted in 250.80
(2) All enclosures containing service conductors, including meter fittings, boxes, or the like, interposed in the service raceway or armor

(B) Method of Bonding at the Service. Bonding jumpers meeting the requirements of this article shall be used around impaired connections, such as reducing washers or oversized, concentric, or eccentric knockouts. Standard locknuts or bush‐ ings shall not be the only means for the bonding required by this section but shall be permitted to be installed to make a mechanical connection of the raceway(s). Electrical continuity at service equipment, service raceways, and service conductor enclosures shall be ensured by one of the following methods:
(1) Bonding equipment to the grounded service conductor in a manner provided in 250.8
(2) Connections utilizing threaded couplings or threaded hubs on enclosures if made up wrenchtight
(3) Threadless couplings and connectors if made up tight for metal raceways and metal-clad cables
(4) Other listed devices, such as bonding-type locknuts, bush‐ ings, or bushings with bonding jumpers

 

[ggunn]

Not quite. Here are the actual code sections. I am nitpicking your statement a bit because, to me, your wording makes it sound like the grounded conductor in the CT cabinet must be bonded to the CT cabinet, when in fact there are other options:


250.142 Use of Grounded Circuit Conductor for Grounding Equipment. (A) Supply-Side Equipment. A grounded circuit conductor shall be permitted to ground non–current-carrying metal parts of equipment, raceways, and other enclosures at any of the following locations:

250.92 Services.
(A) Bonding of Equipment for Services. The normally non– current-carrying metal parts of equipment indicated in 250.92(A)(1) and (A)(2) shall be bonded together.
(1) All raceways, cable trays, cablebus framework, auxiliary gutters, or service cable armor or sheath that enclose, contain, or support service conductors, except as permit‐ ted in 250.80
(2) All enclosures containing service conductors, including meter fittings, boxes, or the like, interposed in the service raceway or armor

(B) Method of Bonding at the Service. Bonding jumpers meeting the requirements of this article shall be used around impaired connections, such as reducing washers or oversized, concentric, or eccentric knockouts. Standard locknuts or bush‐ ings shall not be the only means for the bonding required by this section but shall be permitted to be installed to make a mechanical connection of the raceway(s). Electrical continuity at service equipment, service raceways, and service conductor enclosures shall be ensured by one of the following methods:
(1) Bonding equipment to the grounded service conductor in a manner provided in 250.8
(2) Connections utilizing threaded couplings or threaded hubs on enclosures if made up wrenchtight
(3) Threadless couplings and connectors if made up tight for metal raceways and metal-clad cables
(4) Other listed devices, such as bonding-type locknuts, bush‐ ings, or bushings with bonding jumpers

Fair enough. FWIW I almost never see the inside of a POCO CT enclosure and I don't remember a grounding conductor coming out of one.

 

[ggunn]

How is this handled when the service is ungrounded delta?

 

[electrofelon]

How is this handled when the service is ungrounded delta?

That would be covered by 250.24(E):

(E) Ungrounded System Grounding Connections. A premises wiring system that is supplied by an ac service that is ungroun‐ ded shall have, at each service, a grounding electrode conduc‐ tor connected to the grounding electrode(s) required by Part III of this article. The grounding electrode conductor shall be connected to a metal enclosure of the service conductors at any accessible point from the load end of the overhead service conductors, service drop, underground service conductors, or service lateral to the service disconnecting means.

Looks like what the OP originally asked would be totally fine for an ungrounded system.

 

[jaggedben]

Not quite. Here are the actual code sections. ...

Plus the definition of a supply-side bonding jumper, which includes on the supply side of service equipment.

 

[ggunn]

It's much easier for me to remember the what if I understand the why; is there an overarching philosophy or physics principle that governs how grounding conductors must be run, sized, and connected? I get it that one must not intentionally run current through a grounding conductor, but otherwise it just looks to me like a confusing maze of rules.

 

[electrofelon]

It's much easier for me to remember the what if I understand the why; is there an overarching philosophy or physics principle that governs how grounding conductors must be run, sized, and connected? I get it that one must not intentionally run current through a grounding conductor, but otherwise it just looks to me like a confusing maze of rules.

Yeah I hear ya. I find parts of article 250 to be quite unorganized and illogical. The most frustrating thing is, the GEC is by far the least important conductor yet it has the most rules.

 

[wwhitney]

It's much easier for me to remember the what if I understand the why; is there an overarching philosophy or physics principle that governs how grounding conductors must be run, sized, and connected?

My attempt at an answer, not sure it's a coherent philosophy:

- Current is to remain on the circuit conductors.

- All other metal gets bonded together to avoid potential difference between two things you can touch.
-- Downstream of the service/SDS disconnect, the EGC is used to do this bonding and is sized based on the upstream OCPD.
-- Upstream you use continuity of the metal enclosures/conduits, supply side bonding jumpers, or on grounded supply systems, the grounded service conductor (and on SDSs? not sure). And there is no upstream OCPD, so the sizing is different.

- You can also touch the earth, so the bonded metal gets earthed as well.
-- On an ungrounded system, the GEC goes directly to the bonded metal.
-- When one of the circuit conductors is grounded, that earthing takes priority (not sure why), so the GEC go directly to the circuit conductor. Then the bonded metal gets connected to that circuit conductor and to earth by the Main (service) or System (SDS) Bonding Jumper.

Cheers, Wayne

 

[electrofelon]

My opinions of the way it should be are:

1. Dump all the special GEC stuff (irreversible splice, bonded at both ends of metal raceway), and it should not be required to be larger than #6 regardless of the electrode type.

2. SDS's can be system grounded by the EGC run with the primary

3. instead of bonding bushings and bonding locknuts, have UL actual enforce/require quality fittings with proper threads and a good locknut that you can hammer nice and tight. I swear locknuts get thinner and thinner every year.......

4. Except on maybe resi loadcenters, stop with the concentric/eccentric KO's on everything.

5. I am a proponent of splitting up 250 into two separate articles, bonding and earthing.

There are a bunch more, but Ive got to tell these kids to get off my lawn..........

 

[letgomywago]

My opinions of the way it should be are:

1. Dump all the special GEC stuff (irreversible splice, bonded at both ends of metal raceway), and it should not be required to be larger than #6 regardless of the electrode type.

2. SDS's can be system grounded by the EGC run with the primary

3. instead of bonding bushings and bonding locknuts, have UL actual enforce/require quality fittings with proper threads and a good locknut that you can hammer nice and tight. I swear locknuts get thinner and thinner every year.......

4. Except on maybe resi loadcenters, stop with the concentric/eccentric KO's on everything.

5. I am a proponent of splitting up 250 into two separate articles, bonding and earthing.

There are a bunch more, but Ive got to tell these kids to get off my lawn..........

I'm ok with splitting up 250 that'd make people unfamiliar with US terminology able to see how things are done here. It would also help end some of the mis applying that goes on between GEC and EGC.