What size service conductors do commercial buildings use

[rockwithjason]

once you start getting into the 2000a range bus duct becomes more of an option. we have several 2000a bus ducts and several 4000a bus ducts here at the plant. we installed a 4000a generator connection box here and used 9 parallel runs of 750 mcm at a cost of $18 per foot. the total job cost was around $70k

[Rob_b]

Originally Posted by awdblazer

i have pulled parallel 5000kcm with a jacket rated for 13.8kV
generator leads to a step up transformer

Why would they even bother with such large cable? I've seen where bussbars are used for things like that. A site I worked with in Honolulu used bussbars from their transformers to the MCC gear. They had 4 - 5000amp step down 13400/480V that had a 200' + run to the MCC gear.

[foolishpride]

Originally Posted by awdblazer

i have pulled parallel 5000kcm with a jacket rated for 13.8kV
generator leads to a step up transformer

5000 KCM? I think you put one too many zeros in that.

[awdblazer]

definitely 5000
i believe the generator was 100MW

[Gooch]

Originally Posted by awdblazer

definitely 5000
i believe the generator was 100MW

so the wire was about the size of 4" pipe?

[PRH44]

Originally Posted by awdblazer

definitely 5000
i believe the generator was 100MW

Maybe you may have used 500KCMIL this is sometimes referred to as
"500,000" (circular mils).
100MW at 13800 volts would be roughly 4188 amps.
I am assuming you used MV90 or MV105 cable in a ductbank or above ground conduit.
It would take (9) 500,000 circular mil (or 500KCMIL) cables for each phase to accomplish this primary.
However most unlikely one would use a single 4500 or 5000 KCMIL cable. If this is in fact true I would love to see a picture of this cable or at least the specifications on the wire and the connectors to terminate such cable.

[PRH44]

Originally Posted by Gooch

so the wire was about the size of 4" pipe?

The copper mass of a 5000KCMIL would be roughly 2.25 inch diameter. If insulated the following would be present
1. Copper conductor
2. Inner semi-conducting layer
3. XLPE insulation
4. Outer semi-conducting layer
5. Semi-conducting tape
6. Copper wire screen
7. Separator tape
8. PE outer sheath

You could be really close to a 4inch diameter !!!



The cable below is 15000 volt 750KCMIL it has copper mass .9 inch diameter over all structure is 1.75 inch diameter. I cannot imagine handling cable over twice that size I would love to see it. I am sure somewhere in the world something like that would exist.

[Gooch]

Also, take a look in the NEC at the ampacity table. the ampacity difference between a 1750KCM and 2000KCM is 15 AMPS. the size difference is 250KCM, which in itself is good for 255amps. This is part of the reason you don't see much over 750 kcm as it's cheaper to add additional parallel runs rather than a larger size wire. I've done numerous jobs with 500 KCM, a few with 600 and even less with 750, I've never done anything larger than that. not to mention none of the supply houses stock it so you'd have to order a 500' minimum.

[fast one]

Prh44, Imagine pulling 750 triplex copper in a substation. Not fun at all

[rlitman]

Originally Posted by Gooch

Also, take a look in the NEC at the ampacity table. the ampacity difference between a 1750KCM and 2000KCM is 15 AMPS. the size difference is 250KCM, which in itself is good for 255amps. This is part of the reason you don't see much over 750 kcm as it's cheaper to add additional parallel runs rather than a larger size wire. I've done numerous jobs with 500 KCM, a few with 600 and even less with 750, I've never done anything larger than that. not to mention none of the supply houses stock it so you'd have to order a 500' minimum.

Yes. This is due to the skin effect. It's not something you'd notice with smaller cables at 60hz, but it does come into play with these kind of sizes.

[PRH44]

Originally Posted by rlitman

Yes. This is due to the skin effect. It's not something you'd notice with smaller cables at 60hz, but it does come into play with these kind of sizes.

I agree, you really waste copper mass when get into the larger sizes. For that reason alone smaller parallel runs make a more logical choice.

Originally Posted by fast one

Prh44, Imagine pulling 750 triplex copper in a substation. Not fun at all

sounds like you had the pleasure . Takes some rigging doesnt it!

[Roots]

The larger/largest industrial and commercial centers frequently have poco transformers and switching on site. With transformer secondary cables sized upwards of 2000, often paralleled, or large bus bars feeding the facility. It's not uncommon to also have a medusas nest of 1000, 750, & 500 cables as well.

[Alchymist]

Originally Posted by rlitman

Yes. This is due to the skin effect. It's not something you'd notice with smaller cables at 60hz, but it does come into play with these kind of sizes.

Originally Posted by PRH44

I agree, you really waste copper mass when get into the larger sizes. For that reason alone smaller parallel runs make a more logical choice.

Some of the high power RF stuff I worked with used tubing for conductors - all the current was carried in the tube, the hollow inside would have carried very little current even if present. The higher the frequency, the less the core carries. Noticeable at 400 Hz also.

[Roots]

Originally Posted by Alchymist

Some of the high power RF stuff I worked with used tubing for conductors - all the current was carried in the tube, the hollow inside would have carried very little current even if present. The higher the frequency, the less the core carries. Noticeable at 400 Hz also.

It that very reason, skin effect, that larger bus bars are often tubes or square - hollow inside.

[Zelatore]

Wow, that spool of 4/0 marine cable I have left over from my last inverter install now looks sorta puny! I was only dealing with about 500 amps at 12VDC... At least my stuff is very fine strand and more flexible (and expensive) than the typical on-shore stuff.

I can't think of any application in my situations where I'd ever need to go past 4/0. After that I start moving the voltage up. Heck, a lot of medium size boats are moving to 24 or 36 as their base voltage with DC/DC converters at the end to power the device just to get away from pulling huge cables. It ends up being cheaper and easier in the end.

[PRH44]

Originally Posted by Alchymist

Some of the high power RF stuff I worked with used tubing for conductors - all the current was carried in the tube, the hollow inside would have carried very little current even if present. The higher the frequency, the less the core carries. Noticeable at 400 Hz also.

Hollow tubing is commonly used in substation structures, on different voltage levels, from medium at 15000 to high at 136000 60 HZ.
I wired an induction furnace were the phase conductors were actually hollow and water cooled! The voltage and hertz were variable, its been a while I can not remember the upper limit for the Hertz. That was pretty cool to see. I have some photos somewhere I will try to find them.

[Stuart in MN]

Originally Posted by PRH44

I wired an induction furnace were the phase conductors were actually hollow and water cooled!

Water cooled conductors are pretty common for things like induction furnaces - I used some for a plasma arc torch design years ago, it was kind of hard to get used to the idea that you can run water through an electrical cable without getting shocked.

[The Frisco Kid]

In commercial installations, I always laugh at multiple runs of 500 when 750 would have been fine. Till I have to bend it into the generator MLCB, that is!!!!

[Delta74]

largest to date for me, 8 runs per phase of 1000 MCM for feeds from the 13.8 Kv gen's and 6 gen sets on site. no pics sorry they wont even let us take our cell phones on site.

[RPH]

Induction heating is the area of my job. We build heat treat, tube Welders, brazing units, bonding systems, and billet heaters. Anywhere from line frequency to 450 kHz. Water cooling of the "wires" is required. Without it copper melts. The systems I work on go from 6kW on the low end to 3 mW of power on the high end. All kinds of strange conductors utilized to insure efficient power transfer. But when it goes bang it's spectacular. Some of the neatest things on my desk are from the melted results.