generaldiddy
Member
after the main disconnect on a 2000 amp service, i am installing 6 sets of 4-500 mcm. instead of using 6 - 4 inch conduits, i was thinking of using a troff, does anybody know what size troff would be needed??
2ooo amp service
- Thread starter generaldiddy
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e57
Senior Member
- Location
- San Francisco, CA
see 386.22 - I'll let you do the math... But, I would suggest thinking about it some more. At that amperage I might think about over-sizing it substantially, ventilating it possibly, and think really hard about the cable lay in a gutter - I might even lean toward another method like - cable tray and MC at 750 to reduce the sets, or buss which may present a savings in copper and certainly perform better IMO.
- Location
- Massachusetts
I have 'done the math' and have found it is often cheaper to run more sets of smaller conductors then to go big. Of course they are many factors to consider.
I don't know the correct way to phrase it but you get less capacity per pound of copper as you increase the conductor size.
I have done similar to what the OP describes when I was a helper, we made Bakelite spacers to rack the conductors on in the trough to let air flow around them.
I don't know the correct way to phrase it but you get less capacity per pound of copper as you increase the conductor size.
I have done similar to what the OP describes when I was a helper, we made Bakelite spacers to rack the conductors on in the trough to let air flow around them.
e57
Senior Member
- Location
- San Francisco, CA
Wasn't the math I was thinking of. I wasn't into calculating the area of the conductors and gutter....
Anyway - 6 seems like a lot of sets to run, and space in a gutter. Even 6 runs of MC in a tray would be a wrestling match IMO. The weight 24 500's alone sounds difficult to handle. Even keeping 6 sets, - going to 750 AL sounds better to me... While you and I don't know the particulars like mounting method/location and length. One would assume it is a short run ceiling mounted from one cabinet to another. But anything more than that I think the mat/labor lines might cross sharply.
Anyway - what got me thinking in the first place is the racking and spacing of the conductors in a gutter - is there a code for such? If not it does seem like it should at least mimic cable tray spacing, 392.8(D), and or 300.20(A)....
generaldiddy
Member
thank you guys for the input. a little more information, not so typical setup, the main switch is 40 feet away from the switch gear, two rooms away. 750s sound a little harder to work with, and to put in a change order from 500s to 750s would be something when your dealing with the school construction authority.
e57
Senior Member
- Location
- San Francisco, CA
If they designed and spec'ed - how would you get the gutter in past them?
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I would rather install those 500's in 6 raceways rather than one 40' wireway any day of the week. 500's aren't so bad to work with. 
generaldiddy
Member
thanks again guys. i was trying to avoid the code book on this one because sometimes you can get lost in there,but... after all i still didnt get the troff size. a lot of opinions thanks for the input. im going to roll it around in my head and maybe call a couple of memorable guys i worked with thru the years and get there input also.thank you, love this forum!
- Location
- Massachusetts
- Location
- New Jersey
- Occupation
- Journeyman Electrician
The fill calculation requirments for metal wireways are in 376.22(A).
The sum of the cross sectional areas of all conductors at any cross section of the wireway cannot exceed 20%.
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