600 amp feeders protected bu 800 amp service disconnect

[DaveBowden]

I'm bidding a job for a church. They have 2 buildings with a common roof (outdoor area between the buildings is under the roof but you have to go outside to get from 1 section to the other) with an existing 400 amp service. One bulding is being torn down and replaced with a new building. The existing 400 amp main fused service disconnect has 2 risers going through the roof with a ct can at the top of the risers for the metering.
In the existing electrical equipment room (which is in the building that is staying) the feeders leave the 400 amp main and go into a trough which feeds a 200 amp main breaker enclosure, a 125 amp main breaker panel, and 3 200 amp fused disconnects. The main breaker enclosure feeds an existing subpanel in the kitchen (staying) and the 125 amp main breaker panel feeds the remainder of the load on the building that is staying. The 3 200 amp disconnects feed MLO panels in the section that is being torn down.
The engineer has drawn the new service with an 800 amp main disconnect feeding the trough in the equipment room. The 2 panels that feed the building they're in are re-fed in the trough. I don't have any problem with that part. The part I have to question is where he calls for 2 paralleld sets of 350kcmil CU to be fed in the trough and then run underground outside over 300 feet and then back into a new 600 amp main breaker distribution panel in the new building.
I don't like the idea of having 600 amp wire run that far with only an 800 amp breaker protecting it.
Does this sound like a code compliant install?

 

[GoldDigger]

With the conductors good for 3/4 of the upstream OCPD rating and run outside the building, it looks code compliant.
But if the load is anywhere close to 600A, I would make sure that a voltage drop calculation was done for the 300+ foot run.

 

[Sierrasparky]

With the conductors good for 3/4 of the upstream OCPD rating and run outside the building, it looks code compliant.
But if the load is anywhere close to 600A, I would make sure that a voltage drop calculation was done for the 300+ foot run.

what code would this 3/4 rule be?

 

[augie47]

I do not see that being Code compliant !
IF you located the new 800 amp main on the outside of the building and routed the new
conductors (remaining totally outside) to the new panel and complied with the other rules in 240.21(B)(5) the install could be Code compliant.

 

[DaveBowden]

The only place the feeders will be inside the building on the end they're fed from is just in the trough. We'll come up the outside of the existing building and LB into the back of the trough through the block wall.
On The downstream side they'll come in underground into the bottom of the MDP panel.

 

[charlie b]

The only place the feeders will be inside the building on the end they're fed from is just in the trough.

240.21(B)(5) starts with the requirement that the feeder be outside the building except at the point of termination. You are talking about being inside at the point of origin and inside again at the point of termination. I agree with Gus: not compliant.

 

[charlie b]

The 2 panels that feed the building they're in are re-fed in the trough. I don't have any problem with that part.

I am not convinced. But then, there is some missing information, and I might not have the proposed installation clearly in mind. Let me summarize what I think you said:

• There is an 800 amp breaker.
• It connects to two parallel 350?s (combined ampacity 620 amps).
• The pair of 350?s is run to the trough.
• Inside the trough, you have one tap, using a wire size you did not name, serving an existing 200 amp main breaker enclosure at a distance from the tap point that you did not name.
• Inside the trough, you have a second tap, using a wire size you did not name, serving an existing 125 amp main breaker panel at a distance from the tap point that you did not name.
• Inside the trough, you have a third tap, using two parallel 350?s a total distance of 300 feet to a 600 amp main breaker distribution panel.

Is that right? If so, then depending on the wire sizes and distances for the first two taps, you may or may not have been given a compliant design.

 

[DaveBowden]

the tap to the 200 amp enclosure is 3/0 THHN cu.
The tap to the 125 amp main breaker is #1 THHN CU.
The enclosure and the mb panel are directoy above the trough fed through close nipples.
The feeder from the 800 amp main is 3 sets of 350kmcil - not 2 sets.

 

[augie47]

Looks good to a point, but as charlieb and I have noted, you are feeding two sets of 350kcmil with an amapcity of 620amps and protecting them by an 800 amp overcurrent device. When the overcurrent device exceeds the conductor ampacity, the conductor must be installed according to one of the tap rules (other than as allowed by "next size up" rule).The only tap rule you could use is 240.21(B)(5) which does not allow your conductors to be inside the building except at the point of load termination.

(If the load allows you to use 700 amp fuses in the 800 amp service disconnect the situation would be different)

 

[GoldDigger]

Which means that you can use larger conductors to a junction box just outside and then change to smaller wire.

 

[augie47]

Which means that you can use larger conductors to a junction box just outside and then change to smaller wire.

Just have to be cautious that you don' "tap a tap". The conductors to your outside box would need to be full size.

 

[GoldDigger]

Just have to be cautious that you don' "tap a tap". The conductors to your outside box would need to be full size.

I hoped that would be inferred from "larger", but that is open to misinterpretation and your wording is much safer.

 

[DaveBowden]

I got an update on the service. Now they tell me the 800 Amp service disconnect if non-fused so there will be no overcurrent protection for any of the taps. Just the main breakers in each panel. 1 -200 amp 1 - 125 amp in the existing building and 1 - 600 amp in the new building. The service disconnect is rated to be used as service equipment.

 

[GoldDigger]

I got an update on the service. Now they tell me the 800 Amp service disconnect if non-fused so there will be no overcurrent protection for any of the taps. Just the main breakers in each panel. 1 -200 amp 1 - 125 amp in the existing building and 1 - 600 amp in the new building. The service disconnect is rated to be used as service equipment.

The NEC requires that any service disconnect incorporate or have in the immediate vicinity an OCPD or multiple OCPDs to protect the service wiring.
If it has no OCPD in the vicinity, it can be a disconnect, but not a service disconnect and the wires downstream are still service wires, with all of the accompanying restrictions (like not coming inside very far and not occupying the same raceway with protected conductors (e.g. feeders or branches).)
Just the marking that it is service rated does not make it, by itself, a service disconnect!

 

[Smart $]

The NEC requires that any service disconnect incorporate or have in the immediate vicinity an OCPD or multiple OCPDs to protect the service wiring.
If it has no OCPD in the vicinity, it can be a disconnect, but not a service disconnect and the wires downstream are still service wires, with all of the accompanying restrictions (like not coming inside very far and not occupying the same raceway with protected conductors (e.g. feeders or branches).)
Just the marking that it is service rated does not make it, by itself, a service disconnect!

Agree. 230.82 is the section which restricts what can be on the supply side of the service disconnecting means. No disconnect switches other than meter disconnect switches are permitted... and with CT metering, that cannot apply.