Voltage Drop
- Thread starter jvan61
- Start date
- Status
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
electricman2
Senior Member
- Location
- North Carolina
- Occupation
- Retired Electrical Contractor
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: Voltage Drop
I am always amazed when people ask questions like this. This is 1/2 mile. just curious what it is you are running so far away.
It might be more cost effective to drop another service out by this load if that is an option.
I am always amazed when people ask questions like this. This is 1/2 mile. just curious what it is you are running so far away.
It might be more cost effective to drop another service out by this load if that is an option.
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: Voltage Drop
I once installed a 50 hp 480 motor in a well 1/4 mile from the controller. I used 4/0 quad al USE voltage drop was OK.
I once installed a 50 hp 480 motor in a well 1/4 mile from the controller. I used 4/0 quad al USE voltage drop was OK.
Re: Voltage Drop
1phase or 3phase?
1phase, resistive load:
3% Vd on 480V = 14.4V
R = E/I so R(total) = 14.4V/86A = .167 Ohms
Round trip is 5.6 X 1000 feet so your wire has to be
R(per 1000') = .167 Ohms/5.6 (1000s of feet)
or R(per 1000') = .0299 ohms/1000'
Look at Chapter 9, Table 8 - gives you resistance per 1000'
500Kcmil Cu (uncoated) = .0258 ohms/1000'
Table 9 doesn't exactly apply (it says 3phase). But if you wanted to use it, then per the AC resistance, steel conduit column:
500Kcmil Cu (uncoated) = .029 ohms/1000'
Not much difference for unity pf.
Three phase with an inductive load gets a little whinnier, but still all in your NEC. Look at Chapter 9, Table 9, Note 2. The default table values are for .85pf, which is likely good for general motor loads.
For balanced 3ph, look at the line to neutral (277) Vd. It doesn't matter if the loads are all 480V, or even if you don't have a neutral - answers come out the same. Don't forget the neutral isn't drawing any current, so the distance is just oneway.
3% of 277 = 8.4V
For 2800',
R(per 1000') = 8.4/(86 X 2.8)
= .035 ohms per 1000'
Using Table 9 and the default .85pf:
Steel conduit will require more than 1000Kcmil
750kcmil in PVC conduit is .036 ohms/1000'
1000kcmil in PVC is .032 ohms/1000'
Don't forget, in either case, the grounding conductor has to be upsized the same percentage as the supply conductors were.
Three phase, unbalanced, inductive load, I'll need more information - just send it along with a check and I'll get started. Could take me a while, don't think I've ever done one.
carl
1phase or 3phase?
1phase, resistive load:
3% Vd on 480V = 14.4V
R = E/I so R(total) = 14.4V/86A = .167 Ohms
Round trip is 5.6 X 1000 feet so your wire has to be
R(per 1000') = .167 Ohms/5.6 (1000s of feet)
or R(per 1000') = .0299 ohms/1000'
Look at Chapter 9, Table 8 - gives you resistance per 1000'
500Kcmil Cu (uncoated) = .0258 ohms/1000'
Table 9 doesn't exactly apply (it says 3phase). But if you wanted to use it, then per the AC resistance, steel conduit column:
500Kcmil Cu (uncoated) = .029 ohms/1000'
Not much difference for unity pf.
Three phase with an inductive load gets a little whinnier, but still all in your NEC. Look at Chapter 9, Table 9, Note 2. The default table values are for .85pf, which is likely good for general motor loads.
For balanced 3ph, look at the line to neutral (277) Vd. It doesn't matter if the loads are all 480V, or even if you don't have a neutral - answers come out the same. Don't forget the neutral isn't drawing any current, so the distance is just oneway.
3% of 277 = 8.4V
For 2800',
R(per 1000') = 8.4/(86 X 2.8)
= .035 ohms per 1000'
Using Table 9 and the default .85pf:
Steel conduit will require more than 1000Kcmil
750kcmil in PVC conduit is .036 ohms/1000'
1000kcmil in PVC is .032 ohms/1000'
Don't forget, in either case, the grounding conductor has to be upsized the same percentage as the supply conductors were.
Three phase, unbalanced, inductive load, I'll need more information - just send it along with a check and I'll get started. Could take me a while, don't think I've ever done one.
carl
Re: Voltage Drop
(snip)I am always amazed when people ask questions like this.(snip)
(snip)I'm with Peter. Why can't the utility provide a service at the site? (snip)
**************************************
Uhh guys and girls, I would say it's pretty apparent j doesn't understand the physics or science behind the proposed installation. Gee - do you suppose that's why he is asking?
It's been my experience it's usually the customer squawking at the up front install cost. Last one of these I looked at, the utility wanted $3,000 per pole and the customer needed 7 poles. For $21K she was looking for an alternate solution.
I can think of several reasons why I would put in something like that. The first one to mind is: If after much discussion, the customer pulled out his checkbook, looked me in the eye and said, "That's the way I want it." My response would be, "I'll need $25,000 up front to get the wire ordered and the backhoe on the way. We can be digging before dark if you want." And I'd be smiling when I said it.
carl
(snip)I am always amazed when people ask questions like this.(snip)
(snip)I'm with Peter. Why can't the utility provide a service at the site? (snip)
**************************************
Uhh guys and girls, I would say it's pretty apparent j doesn't understand the physics or science behind the proposed installation. Gee - do you suppose that's why he is asking?
It's been my experience it's usually the customer squawking at the up front install cost. Last one of these I looked at, the utility wanted $3,000 per pole and the customer needed 7 poles. For $21K she was looking for an alternate solution.
I can think of several reasons why I would put in something like that. The first one to mind is: If after much discussion, the customer pulled out his checkbook, looked me in the eye and said, "That's the way I want it." My response would be, "I'll need $25,000 up front to get the wire ordered and the backhoe on the way. We can be digging before dark if you want." And I'd be smiling when I said it.
carl
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