transformer

[DBack Elec]

I am installing a 120/240 volts 28 amps 1 phrase Hotsy spray washer. The supply power is 480 volts. I plan to use a transformer. My question is what size KVA do you suggest I use. I have an idea but would like conformation. Thanks

 

[LarryFine]

Well, let's see: 240v x 28a = 480v x 14a. = 6.72Kva.

If you're sure you'll never need to supply any additional 120/240v loads, I'd say a 7.5Kva; 10Kva would give you a bit of headroom.

If you want to plan for the future, go with 25Kva and a 100a panel.

 

[DBack Elec]

Well, let's see: 240v x 28a = 480v x 14a. = 6.72Kva.

If you're sure you'll never need to supply any additional 120/240v loads, I'd say a 7.5Kva; 10Kva would give you a bit of headroom.

If you want to plan for the future, go with 25Kva and a 100a panel.

No future load, just the Hotsy. The customer for the Hosty wanted me to put in a 15 KVA transformer. I have a 10 KVA in stock. I used your calculations to help prove my point. Thanks Larry Fine

 

[weressl]

No future load, just the Hotsy. The customer for the Hosty wanted me to put in a 15 KVA transformer. I have a 10 KVA in stock. I used your calculations to help prove my point. Thanks Larry Fine

You would want to take the inrush current into consideration if there is a pump motor associated with the pressure washer.

 

[DBack Elec]

You would want to take the inrush current into consideration if there is a pump motor associated with the pressure washer.

28 amps x 240 volts= 6720 watts
6720 X 125%= 8400 watts
Still under 10 Kva, I think I'm alright.
Thanks

 

[mayanees]

... agree with Laszlo's concern

... agree with Laszlo's concern

DBack,

The inrush of concern would be that of a motor, on the order of 5-6 times the running amps.

Not knowing the piece of equipment you're referring to, I'd be a little leary. Perhaps a call to the manufacturer would be in order.

Off hand, I'd say if it's a 3 HP motor, no problem. But if it's a 5 HP motor, which is what NEC 430.248 translates to for 28 amps at 230V, I'd call Hotsy and get their advice.

My first inclination would be for the 15kVA, and if the customer asked for that, you're hanging yourself out there with a 10.

JM

 

[LarryFine]

The customer for the Hosty wanted me to put in a 15 KVA transformer.

In that case, install it and charge what you should, and save the 10 KVA for another day.

 

[brian john]

If inrush is an issue check the manufactures web site or if necessary contact the manufacture for acceptable motor starting for specific HP and KVA.

 

[DBack Elec]

In that case, install it and charge what you should, and save the 10 KVA for another day.

Thanks guys, that is what I will do.