Most cost effective wiring distribution in a condo building

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classicaldg

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San Luis Obispo, CA
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Architect
Hello,
My architecture firm has in-house electrical designers, and we are currently working on a condo building electrical system replacement. The building has two wings of condos and was built in 1924. The electrical system will be entirely new.

From the main electrical meter panel, a 3" conduit that carries the electrical panel feeds to each condo unit goes underground to each of the wings, then up the exterior wall to the attic of each wing. From there, the electrical feeds go to each condo unit.

From where the 3" conduit enters the attic space, what is the most cost effective way to run the electrical panel feeds to each condo unit. Is it a gutter that attaches to the 3" conduit and that runs the length of the attic, then above each condo unit, a conduit will be attached to the gutter and run down to each condo unit electrical panel?

Or is there another way to distribute the electrical feeds from the 3" conduit to each condo unit.

Thank you - classicaldg
 
I'm reading it like there are multiple feeders (one for each unit) in the 3" conduit. How many condo units are in each wing? You cannot run a lot of feeders in a single 3" conduit without derating. Once you are past the meter (and I assume a unit disconnect) you will want a separate conduit to each unit.
 
From what I gather from the op, is all of the feeders to the units are in the three inch conduit, then enter a wire way that runs the entire length of the attic, where each is distributed. A problem I see, is this wire way passing through firewalls? Probably wasn’t any when the building was built in 1924, but I would guess codes would require them now.
 
Maybe the “In-House Electrical Designers” should be posting regarding this project instead of architect...?
 
Sounds like a fire claims nightmare. Why not keep it separated, let each condo have its own UG feed, just buy some saddles for the trench, that keeps the potential legal issues at bay, not sure how many units your talking but I'd stay clear of the 1 jumbo conduit to save a little money, what if a sub feed needs replacing for some unknown reason you'll have to pull past all the other shared area feeders.
 
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Followup after re reading your post closer ... I presume you have an existing 3" which lets say feed 8 units, that's 32 splices in a roughly 3x3 pull box,
from there if legal in your state run individual SER cable to each condo. That's a less labor extensive approach I'd think.
 
petersonra said:
Why in the world would you need a 3-in conduit to feed a single condo unit in the first place?
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Coppersmith said:
I'm reading it like there are multiple feeders (one for each unit) in the 3" conduit. How many condo units are in each wing? You cannot run a lot of feeders in a single 3" conduit without derating. Once you are past the meter (and I assume a unit disconnect) you will want a separate conduit to each unit.
Click to expand...
Yes, there are 7 units in one wing and 6 units in the other wing.
Another C10 said:
Followup after re reading your post closer ... I presume you have an existing 3" which lets say feed 8 units, that's 32 splices in a roughly 3x3 pull box,
from there if legal in your state run individual SER cable to each condo. That's a less labor extensive approach I'd think.
Click to expand...
Would the SER cables be in lieu of the gutter? It is possible to upload the riser for the project so you can see what I referring to?
 
classicaldg said:
Yes, there are 7 units in one wing and 6 units in the other wing.
Click to expand...

If you run the feeders for seven units through one conduit you will have to derate the wires to 45% of capacity due to heat. This means you will have to make the wires much larger to get the capacity you need.

7 x 3 current carrying conductors = 21 ccc. 21 requires a 45% derating. Further derating may be required due to ambient temp in attic.
 
The question is whether using a gutter for the length of the attic is the most cost effective way to run the electric feeds to each of the condo units. If not, is there a less expensive method to run the electric feeds through the attic. Thank you for looking at this.
 
infinity said:
I agree need more information. Starting after the meter what is in the 3" conduit?
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Rob, please see below for the riser diagram. In the 3" conduit are electric feeders to each condo unit. Once the 3" conduit gets to the attic, what is the most cost effective method to run the feeds through the attic to each of the condo units? My riser shows a gutter. Is a gutter more expensive or less expensive than using, for example, an armor cable to each condo unit. How would you run the feeders? Thanks for reading this post.
 
I am curious as to where POCO considers the service point to be. Does the 600A main belong to POCO or count only as a safety disconnect with the service point to each unit being in the neighborhood of the breaker at the individual meter? Or are both sides of the individual meters "customer wiring" downstream of a single service point?
Either way the conductors downstream of the meters are definitely not service wiring, escaping any limits on length inside the building.
Even though broken up by firewalls, are all of the attic spaces part of the common area outside the individual condo boundaries? Is there a rated fire barrier between each condo and the attic space, requiring care with the feeder penetration into the condo?
How would the choice of a gutter instead of conduit affect that?
This may all be very standard stuff, but I am not familiar with it and curious.
 
GoldDigger said:
I am curious as to where POCO considers the service point to be
Click to expand...
In Calif. The Utility is responsible for only servicing their lines into the Pull section upstream from meter period , as usual they own the meter but the line lug connections,hardware and load lugs are the responsibility of the field electrician. When a switch gear or typical panel is installed as a complete unit with pull section, The meter section and distributions all the bussing, torques, connections thermal protections involved within that equipment is a field electricians problem.
 
You're 3" (and likely the 2.5") is much too small. I didn't perform a calculation but I'm guessing that with derating your conductors are also too small.
 
By looking at this spec, the allowed number of #1 in a SC80 Pvc is 13 using THHW or 16 using THWN2 ... you have 18 + ground/s
Table C:10 page 784 - 785 NEC 2020

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