Voltage Drop Underground Feeder 800 feet

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Fordean

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New Jersey
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Electrical Contractor
I have to price out a project.

760 feet of 4 wire 208v 3phase Underground Exterior. 200 amp Service. Load at service is not calculable.
4 inch PVC

But I am guessing. Maybe 135 amps. For Large Block heaters for Generators. (Block Heat are supposedly 50 amp each 1phase) 4 units So far with 2 spares. Means center phase will be higher.

I used two different VD calcs. And two different answers. 1 said 3/0 still good to use. Which I feel hard to believe. Other said 250MCM should be used.. Which I feel is correct.

What size wire is correct. Just double checking.

Also How many handholds do I need and size. Planned on Using 48x48 x 36deep, Two separate areas. I plan on splicing somewhere (maybe once or twice). Would like to pull with none. But think its unlikely.
 
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Have you considered stepping up for the run and back down at the other end? The reduced cost of the smaller wires might be greater than the cost of the the transformers/parts. You can run 480v delta + EGC and avoid running a neutral.
 
zbang said:
Have you considered stepping up for the run and back down at the other end? The reduced cost of the smaller wires might be greater than the cost of the the transformers/parts. You can run 480v delta + EGC and avoid running a neutral.
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Was coming straight off utility pole. Its a 208 bank now. What happens is. Their is a 400 amp service in the building. To get to it would require same distance but more labor to pipe into building.

I did not want to attempt. Extracting a load like this from just a 400 amp. Trying to avoid this. Put a lot of work into stuff like this and not even get it.

Figure trying to take a 200 amp service off a 400 amp that's was precalculated. Wasn't practicle. Probably took much to take.
 
Fordean said:
...... I am guessing. Maybe 135 amps. For Large Block heaters for Generators. (Block Heat are supposedly 50 amp each 1phase) 4 units So far with 2 spares. Means center phase will be higher.

I used two different VD calcs. And two different answers. 1 said 3/0 still good to use. Which I feel hard to believe. Other said 250MCM should be used.. Which I feel is correct.

What size wire is correct. Just double checking.

Also How many handholds do I need and size. Planned on Using 48x48 x 36deep, Two separate areas. I plan on splicing somewhere (maybe once or twice). Would like to pull with none. But think its unlikely.
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I didn't run any numbers but given your info I would use 3\0. Block heaters aren't going to care a whit about voltage drop and I don't see them drawing max amps all night long.

As for pull boxes you don't need any unless you can't handle the wire without breaking the length into smaller reels.
 
ActionDave said:
I didn't run any numbers but given your info I would use 3\0. Block heaters aren't going to care a whit about voltage drop and I don't see them drawing max amps all night long.

As for pull boxes you don't need any unless you can't handle the wire without breaking the length into smaller reels.
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I just figured I go by the book on VD. Which is no more than 3 Percent. Just got two different answers.

South wire voltage drop, and another Calc forgot which site.
 
Fordean said:
I have to price out a project.

760 feet of 4 wire 208v 3phase Underground Exterior. 200 amp Service. Load at service is not calculable.
4 inch PVC

But I am guessing. Maybe 135 amps. For Large Block heaters for Generators. (Block Heat are supposedly 50 amp each 1phase) 4 units So far with 2 spares. Means center phase will be higher.

I used two different VD calcs. And two different answers. 1 said 3/0 still good to use. Which I feel hard to believe. Other said 250MCM should be used.. Which I feel is correct.

What size wire is correct. Just double checking.

Also How many handholds do I need and size. Planned on Using 48x48 x 36deep, Two separate areas. I plan on splicing somewhere (maybe once or twice). Would like to pull with none. But think its unlikely.
Click to expand...

With the information you have provided i came up with 350 MCM copper or 500 MCM Aluminium at 3%. I would go to 5% and use 4/0 copper or 300 MCM Aluminium. I would use Aluminium either way, its a lot cheaper on a run like this and a hell of a lot easier to pull on a run like this.
 
Fordean said:
I just figured I go by the book on VD. Which is no more than 3 Percent. Just got two different answers.

South wire voltage drop, and another Calc forgot which site.
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There is no "by the book" on VD...

But if you are referring to the NEC's FPN/INs on the matter, it's 5% total feeder and branch circuit, i.e. service to furthest load. You can, if you wish, include the service entrance conductors in that 5%.
 
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I wouldn't use vaults or step up/down transformers for this one. We do long pulls fairly often, I did a 1300' run of 4" pvc with 250 USE aluminum a few months back, nothing to it really and it's great not having to go back and splice through vaults. Just more possible points of failure when you do it that way.
 
Canton said:
With the information you have provided i came up with 350 MCM copper or 500 MCM Aluminium at 3%. I would go to 5% and use 4/0 copper or 300 MCM Aluminium. I would use Aluminium either way, its a lot cheaper on a run like this and a hell of a lot easier to pull on a run like this.
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Don't think a 200 amp panel will accept 500 MCM Not sure
 
Fordean said:
Don't think a 200 amp panel will accept 500 MCM Not sure
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I use a large j-box nippled to the panel with distribution blocks or insulated taps to size the wire down to the normal 200 amp size. 500mcm wouldn't leave much room for branch circuits if you went direct to the panel with it.
 
Another option that hasn't been mentioned is to get a 240/480V 1? 3W service. Of course, POCO would have to be willing to provide it. Then you'd only need a service rated 100A plus what ever future loads may be (VA?480V).

At load end, install a 240/480V 1? 3W MCB panelboard, install all 1-pole breakers and run 2-wire circuits (240V L-N) to loads.

This route saves you the transformer cost... but the panelboard and breaker prices may not make it the better deal. However, don't forget to include the extra labor, service/primary disconnect and all other not-so-obvious parts and pieces in with the transformer cost for the comparison. I'm not a planner/estimator so I have no idea how the two methods weigh out.
 
Fordean said:
I just figured I go by the book on VD. Which is no more than 3 Percent. Just got two different answers.

South wire voltage drop, and another Calc forgot which site.
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new code is 2% feeders, 3% branch circuits. are you calcing drop to a panel?

if the block heaters were 208 and you could use a 208 volt 3 wire panel, this would
work better for you. the 120 volts kills you.

aluminum simpull:

760 feet
100 amps highest leg
500 mcm
VD 2.69%

week before last, i pulled a 675' run of three 500mcm simplull with a ground unbroken.

the peak strain on the gauge was 1,000# going around the second 90, pulling without lube.
most of the run was between 500 and 750 lbs... just the last 5' was a spike.

use a steel 90 on the end where the puller is going to be.. it'll cut the load a bunch.
and use a swivel on the pull so the conductors don't spiral. cuts the pulling load a fair bit.

and if the voltage drop is higher, it'll just result in less power being consumed by the heaters.
 
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