800 amp feeder in two 3" EMTs?

[iwire]

OK check my work if you don't mind.

I need to run a 208Y/120 volt 800 amp' feeder, the total connected load maxes out at 690 amps. Space is limited and the equipment is not set up to accept two 500 Kcmil copper per phase. The documents indicate four conductors per phase.

3/0 CU @ 90C 225 amps

4*225=900 amps.

However I have to run this in two conduits. The neutral is not a CCC so I have a total of six CCCs in each conduit.

900*.8=720 amps {80% derate per T310.15(B)(2)(a)}

I plan on running about 10' in 3" EMT eight THHN 3/0 and 1/0 EGC per tube.

3/0 THHN = 0.2679 sq in. (Table 5)

1/0 THHN = 0.1855 sq in (Table 5)

0.2679*8+0.1855= 2.3287 sq in.

3" EMT 40% fill = 3.538 sq in. (Table 4)

It looks like it will be a hot dog in a hallway.

 

[tkb]

You could use 2-1/2" EMT if you want to.

2-1/2" w 8-3/0 & 1-1/0g = 39.75% fill

Did you try the spread sheet that I sent you?
It makes this very easy.

 

[infinity]

Looks good to me. I have pulled 4-600 kcmil conductors in a 3" EMT so your 8-#3/0's +g should be a piece of cake.

 

[winnie]

Your math checks out to me.

It looks like you also have room for 8x4/0 + 1x2/0 in each pipe, which would mean your conductor ampacity would exceed the OCPD, which you might consider if that 690A connected load is ever going to go up, or if someone is going to decide that you have non-linear loading.

-Jon

 

[iwire]

Did you try the spread sheet that I sent you?
It makes this very easy.

No I did not, honestly I forgot about that.

Will it size wireways as well?

I have a 10" x 10" wireway 'nipple' that I have to fit nine 500s and nineteen 3/0s.

 

[augie47]

I know $$ is $$ but I sorta agree with Winnie. If I understand your post and it's only 10 ft, I'd be tempted to go to 4/0, same conduit and never have to worry about having to recalculate in the event of added load.

 

[iwire]

I know $$ is $$ but I sorta agree with Winnie. If I understand your post and it's only 10 ft, I'd be tempted to go to 4/0, same conduit and never have to worry about having to recalculate in the event of added load.

Money not as much as an issue as fitting, I would have to draw it out but this run will be in LFMC, EMT, wireway, EMT, wireway, switchgear, wireway, disconnects.

What I really have to do is run an 800 amp 3 phase four wire 'switch leg' through an overcrowded electric room and then back to where I started.

 

[augie47]

IN that case your math looks perfect

 

[tkb]

No I did not, honestly I forgot about that.

Will it size wireways as well?

I have a 10" x 10" wireway 'nipple' that I have to fit nine 500s and nineteen 3/0s.

Yes it does do wireways.

You allowed 20% & 30 CCC in any cros section.

10 x 10 would be filled 9.85%
8 x 8 would be filled 15.39%

 

[lauraj]

Why are you using the 90?C column to size your wire? Wouldn't you be limited to the 75?C column due to the temperature rating of the equipment?

 

[iwire]

Why are you using the 90?C column to size your wire? Wouldn't you be limited to the 75?C column due to the temperature rating of the equipment?

I can base my derating on the 90C rating but when it's all said and done I still have to be under the rating at 75C.