System Bonding at First Point of Disconnect

[ccarr7]

All,

I'm reviewing a new service that will have a 600A main breaker at the main distribution panel. On the line side of this panel will be a CT cabinet with a 600A disconnect that is manually operated in case the service ever needs to be dumped from outside of the building (i.e. fire department in an emergency situation). I believe that this disconnect and CT cabinet will be two separate enclosures adjacent to each other.

I typically have electricians install the ground electrode conductors to the first point of disconnect and bond the neutral to ground for the system there. However, in the past the first point of disconnect has always been a breaker in the meter socket or at the main panel.

My question is, should I treat this manually operated disconnect as the location for the neutral-ground bond and the landing point for the ground electrode conductors or should this action take place at the main distribution panel where the first breaker (600A) resides, with an equipment ground conductor run back to the manually operated disconnect?

I'm leaning towards the latter.

Thanks,
Creig

 

[augie47]

It might be treated differently in other jurisdiction, but locally the grounding would originate at the disconnect. Here, if the metercenter is adjacent to the 600 amp disconnect, and the disconnect has no overcurrent protection, a separate equipment ground is normally not required, (if your distribution has meters, the meters do not normally have isolated neutrals anyway).

 

[RUWired]

My question is, should I treat this manually operated disconnect as the location for the neutral-ground bond and the landing point for the ground electrode conductors or should this action take place at the main distribution panel where the first breaker (600A) resides, with an equipment ground conductor run back to the manually operated disconnect?

I'm leaning towards the latter.

Thanks,
Creig

It sounds as if the outdoor service disconnect does not have overcurrent protection. That would be a violation of 230.91.

article 250.24(D) requires the grounding electrode conductor to be connected to the service enclosure. I would consider the outdoor disconnect the service disconnect enclosure, but IMO it would need to be changd out to a fused unit.

Rick

 

[augie47]

Rick, not know the particulars hurts but 230.91 does allow overcurrent to be "immediately adjacent thereto". If his distribution meets that criteria, would it not be acceptable ?
Sounds like a AHJ call possibly !
At 600 amp, I would have concern about the AIC with the non-fuse standard rating of 10k. To address this, it may become fusible anyway.

 

[RUWired]

I doubt that he would be putting a disconnect outside for emergency purposes if the main breaker was also outside.

 

[cripple]

System Bonding at First Point of Disconnect

Section 230.82(2) permits the installation of the meter disconnect, which by the NEC is consider to be located on the supply side of the service disconnect. The meter disconnect is required that all metal housings and service enclosures to be grounded in accordance with Part VII and bonded in accordance with Part V of Article 250. Article 250 Part VII and Part V are the requirements for bonding of electrical the methods of equipment grounding which has none to do with the grounding of the service. The AHJ could interpret that it is the service disconnect, then section 250.24 would apply.

 

[art82]

you should not consider that pnl as a new service even though its going to a ct it becomes a sub meter the service its coming out of already is a main so anything out of that is a sub

 

[George Stolz]

Is it a meter disconnect? I haven't built a lot of 600A services, but it seems big for a meter disconnect - and is a meter disconnect a moot point on a CT metering system?

 

[iwire]

Is it a meter disconnect? I haven't built a lot of 600A services, but it seems big for a meter disconnect -

It could be.

and is a meter disconnect a moot point on a CT metering system?

No not at all, sometimes the CTs need to be serviced.

 

[Goroon]

...and bond the neutral to ground for the system there..

...and bond the neutral to ground for the system there..

600 a service.. this may apply ?
You instal the CT's the same as a seperatly derived system, and the connection needs to be at the CT's or the first point of disconnect. We use dual ended Sections with CT at both service points. Should one of the CT bucket sections (or circuits) be removed, the Bonding Jumper for that CT system is also removed. Only ONE Connection point from Neutral To Ground.

The finial connection to the grounding system is permited to be a common point in the SW Gear for Dual Feed SWGR.

See also:

IX. Instruments, Meters, and Relays
250.170 Instrument Transformer Circuits.
[HTML]110.23 Current Transformers.

Unused current transformers associated with potentially energized circuits shall be short-circuited.[/HTML]

230.82 Equipment Connected to the Supply Side of Service Disconnect.

230.94 Relative Location of Overcurrent Device and Other Service Equipment.

"Bonding Jumper, Main". The connection between the grounded circuit
conductor and the equipment grounding conductor at the service.

 

[iwire]

600 a service.. this may apply ?
You install the CT's the same as a seperatly derived system, and the connection needs to be at the CT's or the first point of disconnect. We use dual ended Sections with CT at both service points. Should one of the CT bucket sections (or circuits) be removed, the Bonding Jumper for that CT system is also removed. Only ONE Connection point from Neutral To Ground.

Thats great but does not universally apply.

In this area we often have a separate CT cabinet that is bonded and there is a bond in the service disconnect enclosure. The NEC allows this 'double bonding'

 

[Cavie]

It sounds as if the outdoor service disconnect does not have overcurrent protection. That would be a violation of 230.91.

article 250.24(D) requires the grounding electrode conductor to be connected to the service enclosure. I would consider the outdoor disconnect the service disconnect enclosure, but IMO it would need to be changd out to a fused unit.

Rick

If the wires from the outside disconect are under the concrete slab of the building and turn up and into the interior fused disconect, they are concidered "outside the structure" and outside fusing is not required.

 

[nakulak]

personally I would make the disco fused, make it the main, and go on down the road. (just did a service like that with CT - util disco - ats - gen disco). I don't see any advantage of not having the first disco as main, and I don't see any advantage of not having it fused ?

 

[iwire]

personally I would make the disco fused, make it the main, and go on down the road. (just did a service like that with CT - util disco - ats - gen disco). I don't see any advantage of not having the first disco as main, and I don't see any advantage of not having it fused ?

Some power companies would require that they lock up the enclosures ahead of the meter, in an installation as you describe this would deny access to the over current protection by the occupants. But some power companies also require a disconnecting means ahead of the metering.

It is for those reasons that the NEC allows 'meter disconnects' ........ at least that is my understanding.

 

[nakulak]

around here, they might lock up the case, but locking the handle in the closed position would not generally be done (except by mistake). So the tenants would still have access to close or open the switch.

(I missed where he said ahead of CT. here we would just put it after CT - no issue)

 

[iwire]

the tenants would still have access to close or open the switch.

240.24 requires the overcurrent devices to be 'readily accessible'. Some areas interpret that differently.

 

[nakulak]

240.24 requires the overcurrent devices to be 'readily accessible'. Some areas interpret that differently.

a fuse does carry and control electrical energy, but at the point that the fuse operates it also uses energy. This would mean that the fuse is, by NEC definition, not a device.

However, I can see where some would disagree with this (even if they are wrong in that assertion)

 

[RUWired]

If the wires from the outside disconect are under the concrete slab of the building and turn up and into the interior fused disconect, they are concidered "outside the structure" and outside fusing is not required.

Cavie i agree that article 230.6 considers conductors outside if they are under 2" of concrete, but where does it say that the service disconnect or any disconnect serving the building is exemt from over current protection other than 230.94. Even then the OCP is required to be adjacent to.

Rick

 

[iwire]

a fuse does carry and control electrical energy, but at the point that the fuse operates it also uses energy. This would mean that the fuse is, by NEC definition, not a device.

You will have to take that up with the CMP,:grin: IMO fuses and circuit breakers must remain readily accessible to satisfy 240.24.