Electric Heater Design

[MNIK]

Electric heater of around 18 KW is used in fan coil units for heating the air, supply voltage 380V/3PH/60 HZ

Now My Current is I= P/1.733XV=18000/1.733X380=27.3 A and my contactor is 30 Amps uptil here it is clear.

Now i want to caluculate the resistance of each wire and these wires are connected in star.

P= (VLXVL)/R= 3X (VPXVP)/R

R= 3 X (VPXVP)/P= 3X220X220/18000= 8.04 Ohms. Where VL&VP are the line and phase volatges respectively.

But when i measure the resistence using a multimeter the reading it is showing is 17 Ohms.

Pls can any one provide the answer for this.

[Spark e]

It looks to me that you have calculated the resistance of one element of your 18 kw heater at 8 ohms but when you measured the resistance you have measured across two elements phase to phase so the reading would be 16 or 17 ohms. I guess because it's a balanced load there is no neutral starpoint connection.

[MNIK]

Thank for info.

I have 3 elememts when measure for each elememt it is 8 ohms

[rebeccaasmit]

Thanks for posting this !!

In my case i also have 3 elements and when i measure for each element it gave me the same result 8 ohms.


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[spinlondon]

3 phase without a neutral works, by using one phase as feed, and another as return.
As such, the resistance betwen two phases when measured at the power intake, will include two elements and associated wiring.