Min requirement for Getting 277V/480V

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kalanjeya

kalanjeya

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Hello all,

I am a kid in this field and interested to learn a lot. Could you tell what is the minimun requirement for the project needs to get 277/480 V. (because I am familier in designing only 120/208V , I never crossed the voltage).
 
Keep in mind that 277/480 gear is 10 x the cost of 120/208. The decision to go with the higher voltage:
More dangerous, requires a higher standard of workman ship
Load
Voltage drop
Industrial or commerical
Cost of gear
Size of gear
For example a water pump station is, with 2 20 hp motors is better at 120/208 than 277/480. But above that size then it makes more sense to use 277/480.
 
There is no simple, all-encompassing answer. In general, 277/480 is better than 120/208 when there are large motors, when there are lots of motors, when the building is large, and when the building is far away from the point at which the utility provides power to the site. For example, a building with several floors and with corridors over 200 feet long would probably work best with a 277/480 distribution system, and with step down transformers and 120/208 panels in electrical closets at key locations within the building.
 
But my senior engineer said, it is utility service people choice .Even we have 75HP fire pump and no source of 277V/480V , we can not help it out .

If we tell the utility people about our requirement of higher voltage , will they arrange for higher voltage ?
 
Re: Min requirement for Getting 277V/480V

kalanjeya said:
Hello all,

I am a kid in this field and interested to learn a lot. Could you tell what is the minimun requirement for the project needs to get 277/480 V. (because I am familier in designing only 120/208V , I never crossed the voltage).
Click to expand...

This is one of those things that is almost unanswerable.

For reasons that I never understood, to get 480V service in this area is 5-10 times the cost of the same amount of power at 208V. Because of this, it is common to put in a 208V/120 service and add transformers inside the building to feed 480v loads.

One would be inclined to think that the utility company would save money on copper by using 480V services over 208V services, and the transformers should be about the same price.

I have always suspected it is some kind of political issue to shift cost from smaller users to larger users.

For equipment, most of the time, it seems like it is more cost effective to go 208V for things that are 20HP or less and 480V above 20Hp. Just a rough guide.
 
Re: Min requirement for Getting 277V/480V

petersonra said:
it is common to put in a 208V/120 service and add transformers inside the building to feed 480v loads.
Click to expand...

Will you step up the volts from 120/208V to 277/480V ?

I am working for a company in Virginia, When i design a apartment building which is includes some retail shops, would this 120/208V service used for commercial purpose comes under normal tarrif or commercial tarrif ?
 
Re: Min requirement for Getting 277V/480V

I don't know the answer to your question as I do not live in VA, and don't even know why it is this way here. I do know it is very common around here to either get 208/120 or 240/3ph service rather than 480v/3ph service. Transformers are indeed used to step up either the 208 or 240 to 480 for 480V loads.

I know almost nothing about the commercial side of electrical utilities.

kalanjeya said:
petersonra said:
it is common to put in a 208V/120 service and add transformers inside the building to feed 480v loads.
Click to expand...

Will you step up the volts from 120/208V to 277/480V ?

I am working for a company in Virginia, When i design a apartment building which is includes some retail shops, would this 120/208V service used for commercial purpose comes under normal tarrif or commercial tarrif ?
Click to expand...
 
I imagine the POCO would base the decision of delivery voltage on the total KVa load. Which would be more economical for them? Insulation is cheaper than conductor, although that's not important at these voltages.
 
480v

480v

In this area, POCO will pretty much give you whichever one you request if they are having to install the transformers.
As others have stated, there is a sizble cost increase for 480v gear. You must offset that by comparing wire sizes, starter sizes, voltage drop, losses from in-house trasformers, etc.
 
Re: 480v

Re: 480v

augie47 said:
As others have stated, there is a sizble cost increase for 480v gear. You must offset that by comparing wire sizes, starter sizes, voltage drop, losses from in-house trasformers, etc.
Click to expand...
Right. The higher-current, lower-voltage gear also has a cost differential. You have to compare the costs of doing it both ways, including POCO charges.

Remember, too, that transformers do not provide free power; it takes twice the current at 240v to provide a certain amount of current at 480v. Watts is watts.
 
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