240V 150A to 480V ? A

[sparkylife92]

Hey guys I'm doing a little side gig for someone it would be good to be friends with. They want me to wire a compactor for them. They said they wanted 150 amps at 240 volt. After looking at the current situation involving the electrical capabilities I have decided the best thing to do is to wire the compactor at 480 volt and a switch on the controller makes this possible. I'm assuming that since I've increased the voltage I can lower the amperage. Can anyone tell me a formula to make sure I do a proper conversion to make this job done rite.

 

[infinity]

If the load is only inductive like a motor then doubling the voltage will cut the current in half. Example below:

Welcome to the Forum.

 

[Tulsa Electrician]

You can use ohms law as an example.
240 V x 150 A = 36,000 VA
36,000 VA / 480V= 75A


As mentioned be sure your load is capable of the change in voltage.

 

[Carultch]

If the load is only inductive like a motor then doubling the voltage will cut the current in half. Example below:

Welcome to the Forum.

Does this require user-configuration to select the voltage? Or is this the nature of a motor's winding in general, that it automatically draws a fixed steady state KVA that is independent of voltage, at any voltage within its rating range?

I would expect you'd have to change a tap on the motor windings, for it to work with a voltage that different.

 

[infinity]

Does this require user-configuration to select the voltage? Or is this the nature of a motor's winding in general, that it automatically draws a fixed steady state KVA that is independent of voltage, at any voltage within its rating range?

I would expect you'd have to change a tap on the motor windings, for it to work with a voltage that different.

Yes you would wire it based on the applied voltage.

 

[texie]

Hey guys I'm doing a little side gig for someone it would be good to be friends with. They want me to wire a compactor for them. They said they wanted 150 amps at 240 volt. After looking at the current situation involving the electrical capabilities I have decided the best thing to do is to wire the compactor at 480 volt and a switch on the controller makes this possible. I'm assuming that since I've increased the voltage I can lower the amperage. Can anyone tell me a formula to make sure I do a proper conversion to make this job done rite.

You need to be more clear on the specs for the equipment. How do they know they need 150 amps @ 240 volt? And do you have the required power available? The required power is not the same as amps and will not change regardless of amps.

 

[LarryFine]

Welcome to the forum.

Let's start with what is the available source voltage? It's likely not worth transformer-ing it.

Your source still has to supply the same Kva at its voltage. It doesn't make free power.

 

[sparkylife92]

Hey guys thank you all for the information. So currently I'm considering calculating the ampacity off of the motor horsepower. I wish I had better specs im doing this as a favor to a Chinese scrap yard that's doing me some favors if you know what I mean and they don't have the manual or specs for this. I have a nameplate for the motor and a hand drawn picture asking for 3 phase 240 with 150 amps. I dont know if you have been to a scrap yard but they tend to use equipment from items they received. The best panel I have found is a newer 480 mdp and considering my options its the one to come out of. This compactor is able to be switched between 230v and 460v. Crazy enough I never seen a switch that can do this I may have to rewire the peckerhead no big deal. I'm just wondering if I can possibly find a better way to calculate the ampacity to of the 480 volt 3 phase breaker and wire compared to a 240 volt 3 phase told to be 150 amp. Not exactly what im used to having to deal with but trying to make it correct.

 

[sparkylife92]

Welcome to the forum.

Let's start with what is the available source voltage? It's likely not worth transformer-ing it.

Your source still has to supply the same Kva at its voltage. It doesn't make free power.

Thank you. I have a 480v 3 phase feet that feeds a 3 phase 75kva transformer dropping down to 240 volt. Now this transformer dosnt feed a panel near it and has 2 different pipes coming out of it already. I dont want to mess with or fix current problems but feed a peice of equipment the correct way. Why im thinking come out of the decent 480v mdp.

 

[Carultch]

Hey guys thank you all for the information. So currently I'm considering calculating the ampacity off of the motor horsepower. I wish I had better specs im doing this as a favor to a Chinese scrap yard that's doing me some favors if you know what I mean and they don't have the manual or specs for this. I have a nameplate for the motor and a hand drawn picture asking for 3 phase 240 with 150 amps. I dont know if you have been to a scrap yard but they tend to use equipment from items they received. The best panel I have found is a newer 480 mdp and considering my options its the one to come out of. This compactor is able to be switched between 230v and 460v. Crazy enough I never seen a switch that can do this I may have to rewire the peckerhead no big deal. I'm just wondering if I can possibly find a better way to calculate the ampacity to of the 480 volt 3 phase breaker and wire compared to a 240 volt 3 phase told to be 150 amp. Not exactly what im used to having to deal with but trying to make it correct.

The NEC has tables for the FLC rating ("full load code" current, as opposed to FLA "full load actual" amperes), that index current to the nominal voltage and horsepower. Not having a motor nameplate to use for finding FLA, this is the best you can do.

You don't just translate horsepower to Watts, and then divide by voltage (and sqrt(3) if applicable), because there's power factor and efficiency to also account for. Plus, the breaker for a motor doesn't follow the same sizing method as breakers for loads in general, due to the fact that motors initially spike their current, and you don't want to nuisance trip the breaker on inrush current.

 

[LarryFine]

I have a 480v 3 phase . . .

Okay, now that we know this, yes, use the highest voltage available, all other things being equal.

 

[LarryFine]

. . . FLC rating ("full load code" current, as opposed to FLA "full load actual" amperes) . . .

So that's what they stand for.

 

[infinity]

Okay, now that we know this, yes, use the highest voltage available, all other things being equal.

I agree. If the unit is dual voltage why run a 150 amp circuit when you can run a 75 amp circuit (OP's numbers).

 

[Hv&Lv]

So that's what they stand for.

I always thought it was “Full Load Current” and “Full Load Amps”
Both are the same, used interchangibly.

 

[LarryFine]

I always thought it was “Full Load Current” and “Full Load Amps”
Both are the same, used interchangibly.

As did I.

 

[Carultch]

So that's what they stand for.

That was Eric's joke. Eric from Mike's video team.

It's a fortunate coincidence that his joke definitions can help you remember that difference between them.

 

[Hv&Lv]

That was Eric's joke. Eric from Mike's video team.

It's a fortunate coincidence that his joke definitions can help you remember that difference between them.

Ahhh.
I haven’t watched the videos.
I've been on here enough to “know” you and wondered why you typed that..

 

[Jpflex]

Does this require user-configuration to select the voltage? Or is this the nature of a motor's winding in general, that it automatically draws a fixed steady state KVA that is independent of voltage, at any voltage within its rating range?

I would expect you'd have to change a tap on the motor windings, for it to work with a voltage that different.

The motors KVA shouldn’t change much whether the voltage is 240 and ampere 32 or 480 volts and 16 ampere. Mathematically, all you are doing is switching the positions of the products, voltage and current to be multiplied which yields the same KVA, perhaps you’re already aware.

Second a motor usually has 9 leads and for running a higher voltage you will wire the motor in series since more volts will have to be impressed across a larger span of wire turns

A lower voltage supply yields the motor being wired in parallel.

What I don’t get is that once I had single phase motors used as a rock pulverizers that ran better with the higher voltage option with less current but equal KVA as explained above compared to a lower voltage supply but higher current. I’m aware of the heat involved in the second option but the motors were designed to run either way and I didn’t expect such a difference in performance when the overall power was the same?

 

[LarryFine]

The motors KVA shouldn’t change much whether the voltage is 240 and ampere 32 or 480 volts and 16 ampere.

The power should theoretically be identical, except:

What I don’t get is that once I had single phase motors used as a rock pulverizers that ran better with the higher voltage option with less current but equal KVA as explained above compared to a lower voltage supply but higher current. I’m aware of the heat involved in the second option but the motors were designed to run either way and I didn’t expect such a difference in performance when the overall power was the same?

Half the current also means half the voltage drop.

 

[ggunn]

Half the current also means half the voltage drop.

If the conductor size is the same, of course.