480V or 120V

[mull982]

I have a load that requires about 10A at 230V. I have voltages avaliable of 120/208 and 480V to feed this load. The distance of this load however is about 1000V. For this particular case would it be better to run 120V out to a 120/230V step up transformer or run 480V to a 480/240 step down transformer. At 120V the load looks like it will be about 19A. What is the most economical solution?

In general what is the cut-off point for using 480V over 120V in a situation like this. Is it a certain amperage at 120V that will determine the cut-off range or will the wire size at 120V determine the cut-off range to switchint to 480V?

 

[winnie]

Keep in mind that 230V is likely a rating for a device intended to be connected to a 240V supply.

If your only choices were a 480V to 240V step down, or a 120V to 240V step up transformer, and you already have 480V or 120V available, then it is a no brainer: use the 480V to 240V step down transformer. In this situation, the transformers are essentially the same size, and the same cost; in fact this might be done with the _same_ off the shelf transformer, just with different connections. At 480V your load is 1/4 the current, and you can tolerate 4x the voltage drop, meaning much smaller conductors or less voltage drop for the same conductors.

However you do have a third choice: run 208V and use a buck/boost to get to 240V. The buck/boost transformer is an 'autotransformer', and the KVA rating of the transformer is much lower than the total load served. This means a much less expensive transformer. But at 240V you will need thicker, more expensive conductors than at 480V.

-Jon

 

[rootboy]

I'd go with 480 and step it down.

Does your equipment need to be isolated? If so, a buck-boost (autotransformer) won't do this for you.

 

[infinity]

I agree, go with the highest voltage possible and step it down at the point of use. This will save some large dollars on smaller conductor sizing.

 

[frenchelectrican]

I have a load that requires about 10A at 230V. I have voltages avaliable of 120/208 and 480V to feed this load. The distance of this load however is about 1000V. For this particular case would it be better to run 120V out to a 120/230V step up transformer or run 480V to a 480/240 step down transformer. At 120V the load looks like it will be about 19A. What is the most economical solution?

In general what is the cut-off point for using 480V over 120V in a situation like this. Is it a certain amperage at 120V that will determine the cut-off range or will the wire size at 120V determine the cut-off range to switchint to 480V?

i hope you mistype this " 1000V" instead of should be correctaly say 1000FT if so.

IMO it is no brainer to just yank the 480v and run to that location and use the transformer to down step to 120/240V

btw is this load is a single phase or tri phase ??

let set a example with the distance and wire size and voltage drop issue.

at the end you want 120/240 volt single phase appaction ok

10 amp @ 240 v 1000' run wire size is #4 CU , 6.2VD ,2.6% VD

now change this figures with 480 instead of 240 volts you will be suprised with this.

5 amp @ 480 V 1000' run wire size #10 CU 12.4 VD, 2.6% VD

keep in your mind why i say 5 amp @ 480 volts because i keep the KW [ kilowatts load ] the same just change the voltage and amprage.

you can see why it is no brainer to use smaller wire for same load on 480 volts instead of 240 volts which it will cost more for wiring matairls.

and can use just one transformer to downstep to proper voltage rating instead of buying 2 transformers one to up step and downstep at end of run on 208 side.

Merci, Marc