Parallel Service feeders w/ parallel wireways?

N

Npstewart

Senior Member
Good afternoon!

I have a job where im being asked to change a meter center for an apartment complex to a wireway / disconnect arrangement due to lead times. Unfortunately, im having to do this with most jobs these days. However, the EC drew a sketch with this request based on field conditions, and the request was one I haven't came across before in the past. Generally, when I haven't something before, I always like to question it.

The service is 1200A single phase fed via 4 sets #500 kcmil Al. For whatever reason, the EC wants to feed the 1200A disconnect, and then come out of the 1200A with 4 sets, BUT, wants to feed two different wireways with 2 sets of #500 kcmil Al (ie. two parallel sets to each respective wireway).

My immediate thought was that this would not be code compliant because Parallel conductors need to be identical in length and routing, etc. However, they sort of are (respectively, per set). Next, I thought this would be sort of like a tap, but im not sure thats the case because the conductors are full size. However, perhaps it is a tap because (2) Sets of #500 kcmil is good for 620A, which is far less than the 1200A OCP.

Obviously, the respective phases would be out of balance but other than that, I can't think of why this wouldn't be compliant other than the reasons I mentioned.

Putting load calculations aside, has anyone seen or done this before? Or, have a relevant code section?

BASIC DIAGRAM ATTACHED
 

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  • PARALLEL SERVICE WIREWAY.pdf
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There is no reasonable code compliant way to feed the 5 meters on each side. The two sets of 500 kcmil are tap conductors, and must terminate in an OCPD with rating not greater than the ampacity of the conductors.

Note, if you took two sets of 500 to each meter and two sets out of the meter to the disconnect, it would be code complaint, but don't think that would be physically possible.

If the length of the wire between the 1200 amp disconnect and the small disconnects would be 10' or less, you could run individual sets of conductors from the 1200 amp disconnect to the meters. These conductors would have to be rated greater of 120 amps or the rating of the disconnect below the meter. One issue would be getting enough termination lugs on the load side of the 1200 amp disconnect to connect 10 sets of conductors.
 
don_resqcapt19 said:
There is no reasonable code compliant way to feed the 5 meters on each side. The two sets of 500 kcmil are tap conductors, and must terminate in an OCPD with rating not greater than the ampacity of the conductors.

Note, if you took two sets of 500 to each meter and two sets out of the meter to the disconnect, it would be code complaint, but don't think that would be physically possible.

If the length of the wire between the 1200 amp disconnect and the small disconnects would be 10' or less, you could run individual sets of conductors from the 1200 amp disconnect to the meters. These conductors would have to be rated greater of 120 amps or the rating of the disconnect below the meter. One issue would be getting enough termination lugs on the load side of the 1200 amp disconnect to connect 10 sets of conductors.
Click to expand...

Right, kind of what I was figuring.

So if it remained 4 sets of conductors then they’re no longer tap conductors. Then, those conductors would be tapped to feed each individual disconnect - in which case only the small conductors feeding the meter would need to comply with the respective tap rules.


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Npstewart said:
Right, kind of what I was figuring.

So if it remained 4 sets of conductors then they’re no longer tap conductors. Then, those conductors would be tapped to feed each individual disconnect - in which case only the small conductors feeding the meter would need to comply with the respective tap rules.


Sent from my iPhone using Tapatalk
Click to expand...
If all four sets are connected to a power distribution block that has room for 10 tap conductors, the installation would be compliant as long as you keep the tap conductor wire length to less than 10'. You could go to 25', but then the tap conductor would have to be much larger and probably not work.
 
What I had in mind was distribution block in wire way from the 600. Then tap to each of five. Then you could use a 200 amp conductor to each meter and disconnect. Then we would have a feeder tap. The feeder being full sized to the 600 or twin 350 taped by a 200 amp (1/3) conductor.
Using 240.21 (B) (2)
Do once to left and once to right.
As long as connected load for the set of five was under 600 amps.
Then you have service disc 1 and service disc 2 in separate enclosures.

Would this not work?
 
don_resqcapt19 said:
Still have the issue of connecting 5 sets of conductors to the load side of the disconnects.
Click to expand...
Tulsa Electrician said:
What I had in mind was distribution block in wire way from the 600. Then tap to each of five. Then you could use a 200 amp conductor to each meter and disconnect. Then we would have a feeder tap. The feeder being full sized to the 600 or twin 350 taped by a 200 amp (1/3) conductor.
Using 240.21 (B) (2)
Do once to left and once to right.
As long as connected load for the set of five was under 600 amps.
Then you have service disc 1 and service disc 2 in separate enclosures.

Would this not work?
Click to expand...
I think I like the 2 x 600A setup. Seems a little nicer only having 5 taps per feeder, and easier to comply with 10' tap rule (if you want less than 200A to each meter) . Although you lose some diversity and demand factors which could be a deal breaker.

For the single 1200 approach, I would consider a bussed gutter for easy convenient tapping and if long enough, should allow for 10 foot tap rule no problem.

 
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