Choosing Isolator Rating for Dish Washer

vi ra; well your looking 200 AMPS, is your dish washer at the airport for food service? for the isolator, a transformer? 400 volt two 230 volt single phase 50 kva transformer. perry.

Is this a 3 phase supply?

Yes, 3 phase supply. Thank you for your intersting.

A 46 KW, in our standards above 2.2 KW equipment should be at 440~460V or 230V, 3 phase. I will assume if this is 230V this must be 3 phase.

You can size your isolator switch, basing on the LRA Lock Rotor Amps of the motor plus some factor.

There is nothing so special about isolator switch, its just a switch but sizing does matter. Picking the under size switches ' might get burn.

Whether its single or three phase,you calculate your active power,using your cosφ=0.8 or whatever is in the equipment data and you have your kw=46,your voltage=230,find your current from P=VIcosφ for single phase or P=√3VIcosφ for three phase.when you get your current value,multiply it by the factor k based on the size of cable used in running the dish washer.Check your tables of k value for different cable sizing and applications.The value you get after multiplying by the factor k is the the size or rating of isolator you need for the equipment.

Hi

As you are from Singapore, and that this is a 3 phase machine. Rule of thumb is that you multiply the kW Ratting by 2, this will give you the aproxmate current draw per phase. That is about 100 amps per phase.

So knowing the current ratting, and due to the fact that this is a dishwasher, I presume that most of the power is in heating. The other presumption that i have is that this Isolator Switch will only be used for Isolation, not for inter-rupting the wash cycle.

Conclusion: Isolator should have a minimum value of 100 amps per phase and have a minimum of AC-1 Rating

Hope this is of help

Cheers

Joe

46 KW = 46,000 W. Since it is 3-phase 230 volt, 46,000/(200 x √3) ≈ 133 A. The power factor for a heater is 1.00, but there may be a motor included in the total load, so 150 A is probably a good estimate. AC-1 is acceptable duty for heater contactors, but AC-3 is more usual for motors. You may need to see if the dishwasher has separate contactors (starters) for these functions.