400 amp service
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hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: 400 amp service
Jersey
I came up with 1500kcmil@320amps to maintain a 2%VD but if these are feeders and not service conductors then for 3% your looking at 900kcmil
500kacmil will give you about a 5.5% drop if the service is ever loaded to the max of 320 amps (80%)
800' is a long run
Jersey
I came up with 1500kcmil@320amps to maintain a 2%VD but if these are feeders and not service conductors then for 3% your looking at 900kcmil
500kacmil will give you about a 5.5% drop if the service is ever loaded to the max of 320 amps (80%)
800' is a long run
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
Re: 400 amp service
hurk,
In reading your post, I see an interesting point. You used 320 amps for your voltage drop calculation. Why not 400 amps since it is a 400 amp service. At times 400 amps may indeed be used, do we only worry about an assumed continuous load?
I have a reason for asking this, I am always trying to decide what amperage to use in VD calculations at marinas when feeding power outlets for the boats.
hurk,
In reading your post, I see an interesting point. You used 320 amps for your voltage drop calculation. Why not 400 amps since it is a 400 amp service. At times 400 amps may indeed be used, do we only worry about an assumed continuous load?
I have a reason for asking this, I am always trying to decide what amperage to use in VD calculations at marinas when feeding power outlets for the boats.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: 400 amp service
because most 400 amp meter sockets are only rated 320 amps continous (80%) hence the trade "slang 320 can" But I doubt that the load one this service will ever come close to drawing that much unless there is alot of electric heating.
because most 400 amp meter sockets are only rated 320 amps continous (80%) hence the trade "slang 320 can" But I doubt that the load one this service will ever come close to drawing that much unless there is alot of electric heating.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: 400 amp service
heck, why not take it up to 550V and reduce the wire size even more?
I would guess that might well be true, but nobody seems to actually do this. I think there is some fear preventing doing something that seems like a perfectly safe and reasonable thing to do. maybe there is something I am missing.
heck, why not take it up to 550V and reduce the wire size even more?
tx2step
Senior Member
- Location
- North Texas, DFW area
Re: 400 amp service
I've used two transformers to do this, as well. It works just fine and you have the added advantage of having transformer taps to adjust voltage (usually in 2.5% steps). If you have a fairly steady load, it works even better.
If you turn off the power to the first (step-up) transformer until this panel is needed in the future, then you will avoid the core load of the 2 transformers.
There are some types of loads that you can have voltage regulation problems with, though, like some large X-Ray machines that go from zero load to 100% load almost instantly and are very sensitive to a dip in supply voltage.
I've used two transformers to do this, as well. It works just fine and you have the added advantage of having transformer taps to adjust voltage (usually in 2.5% steps). If you have a fairly steady load, it works even better.
If you turn off the power to the first (step-up) transformer until this panel is needed in the future, then you will avoid the core load of the 2 transformers.
There are some types of loads that you can have voltage regulation problems with, though, like some large X-Ray machines that go from zero load to 100% load almost instantly and are very sensitive to a dip in supply voltage.
physis
Senior Member
Re: 400 amp service
But using a transformer still puts very close to the same voltage drop on the conductors and when the load after the transformer changes, still, so does the voltage. As long as the current is relatively constant you can select the appropriate tap and it would be fine. But if the load changes much, so will the voltage.
But using a transformer still puts very close to the same voltage drop on the conductors and when the load after the transformer changes, still, so does the voltage. As long as the current is relatively constant you can select the appropriate tap and it would be fine. But if the load changes much, so will the voltage.
tx2step
Senior Member
- Location
- North Texas, DFW area
Re: 400 amp service
That's true, that's why I said that it works best with a fairly steady load. It doesn't work as well if the load varies widely from low to high. It also doesn't work well for a large motor with a high starting current. But for a fairly constant load, it works pretty well.
The cost of the transformers and the length, size and installation method of the feeder will usually determine whether it is a cost effective approach.
It is sometimes a lot less expensive to upsize a smaller feeder operating at a higher voltage to control voltage drop than it is to upsize a much heavier feeder operating at a lower voltage.
Sometimes it is a lot less expensive to upsize from, say, 3/0 to 4/0 (or maybe even #250) than it is to upsize from 500 to 750. You just have to run the numbers, considering all of the variables, to see. Plus, you may be equipped to pull #4/0 where you aren't able to pull #750. Big wire and pipe are expensive. Or you may want to do smaller parallel runs.
There is no magic bullet that makes the effect of distance go away -- either way, you'll have to deal with voltage drop to some degree. But with a steady load, using the transformer taps can help.
That's true, that's why I said that it works best with a fairly steady load. It doesn't work as well if the load varies widely from low to high. It also doesn't work well for a large motor with a high starting current. But for a fairly constant load, it works pretty well.
The cost of the transformers and the length, size and installation method of the feeder will usually determine whether it is a cost effective approach.
It is sometimes a lot less expensive to upsize a smaller feeder operating at a higher voltage to control voltage drop than it is to upsize a much heavier feeder operating at a lower voltage.
Sometimes it is a lot less expensive to upsize from, say, 3/0 to 4/0 (or maybe even #250) than it is to upsize from 500 to 750. You just have to run the numbers, considering all of the variables, to see. Plus, you may be equipped to pull #4/0 where you aren't able to pull #750. Big wire and pipe are expensive. Or you may want to do smaller parallel runs.
There is no magic bullet that makes the effect of distance go away -- either way, you'll have to deal with voltage drop to some degree. But with a steady load, using the transformer taps can help.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: 400 amp service
But The equivalent amount of power @ 240 volts (400 amps) would require 750kcmil wire to be ran. So which would be cheaper the 750 or the transformers?
Yes the voltage that drops across a resistance is always the same if the same current is applied, but @ 480 the current is cut in half and the voltage is doubled resulting in a much less % of VD and if there is a 4 volt drop on the primary side (480) of the transformer then the VD on the secondary (240) side will only be 2 volts. Big difference.
Sam the % of voltage drop is much less when your voltage is higher, A 200 amp load on 3/0 copper @ 480 volts a run of 500' is only 2.8%
But The equivalent amount of power @ 240 volts (400 amps) would require 750kcmil wire to be ran. So which would be cheaper the 750 or the transformers?
Yes the voltage that drops across a resistance is always the same if the same current is applied, but @ 480 the current is cut in half and the voltage is doubled resulting in a much less % of VD and if there is a 4 volt drop on the primary side (480) of the transformer then the VD on the secondary (240) side will only be 2 volts. Big difference.
physis
Senior Member
Re: 400 amp service
Well, what's happening Wayne is the voltage is only being changed the few volts that appear over the voltage drop.
You have a good handle on Ohm's law stuff. No matter how you slice it, you still have the same resistance in series that comes from the service conductors. The voltage adjustments made using the transformer really have a negligable impact on the effect of voltage drop across those conductors. It really can only work where the load is stable. And if that's the case it's fine.
But you can't remove the existance of voltage drop with a transformer. You can only use it to compensate for it, based on a given condition.
Edit: I have to make leaving a word out Error B.
[ July 06, 2005, 02:03 AM: Message edited by: physis ]
Well, what's happening Wayne is the voltage is only being changed the few volts that appear over the voltage drop.
You have a good handle on Ohm's law stuff. No matter how you slice it, you still have the same resistance in series that comes from the service conductors. The voltage adjustments made using the transformer really have a negligable impact on the effect of voltage drop across those conductors. It really can only work where the load is stable. And if that's the case it's fine.
But you can't remove the existance of voltage drop with a transformer. You can only use it to compensate for it, based on a given condition.
Edit: I have to make leaving a word out Error B.
[ July 06, 2005, 02:03 AM: Message edited by: physis ]
tx2step
Senior Member
- Location
- North Texas, DFW area
Re: 400 amp service
Wayne -- What voltage drop calculator are you using?
I've been using one on electrician.com but it doesn't have a voltage selection for 240V 3 phase. It has 208V 3P3W but not 240V.
I need to find a more versatile Vd calculator.
Wayne -- What voltage drop calculator are you using?
I've been using one on electrician.com but it doesn't have a voltage selection for 240V 3 phase. It has 208V 3P3W but not 240V.
I need to find a more versatile Vd calculator.
physis
Senior Member
Re: 400 amp service
Voltage drop is a function of current.
Voltage only matters if you step up the voltage, then send it over a conductor, and step it down again.
Oooooooooooooohhhhhhhhhhh, that's what hassaf's talking about. Well that'll work.
Sorry, I noticed the two transformers but the concept of raising the voltage across the conductors slipped by me. I didn't see it until I went to describe it.
Uhhh, carry on gentlemen.
Sorry.
Voltage drop is a function of current.
Voltage only matters if you step up the voltage, then send it over a conductor, and step it down again.
Oooooooooooooohhhhhhhhhhh, that's what hassaf's talking about. Well that'll work.
Sorry, I noticed the two transformers but the concept of raising the voltage across the conductors slipped by me. I didn't see it until I went to describe it.
Uhhh, carry on gentlemen.
Sorry.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: 400 amp service
tx2step Try this one:
www.elec-toolbox.com Voltage Drop Calculator
I have never noticed the missing 240 3? on electrician.com one? But your right and several other Java script ones on the net also are missing it?
H'mmmmm
tx2step Try this one:
www.elec-toolbox.com Voltage Drop Calculator
I have never noticed the missing 240 3? on electrician.com one?
But your right and several other Java script ones on the net also are missing it?H'mmmmm
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: 400 amp service
That's good I was starting to think you were loosing it?
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