Load Calculation

There is no calculation other then the standard one for a single phase load. If a load is across to phase conductors in a three phase 4 wire system, it is a "single phase" load and not a two phase load.

Guess,

Before answer your question. you hve to know what is phase voltage and wht is line voltage!

if you airconditioner is rate of 220v, you will distroy it when you connect it to two phase! no matter what yours is 3ph 4 wires or 3ph 5 wires.

First you have to know the power rating of your country. Is it 115V or 220V? These are just examples of the various avaialble to diffierent countries. If it is 115 then connecting on the two phases would give you something in the range of 230V and connecting a phase and the neutral would give you a 115V.

If it is a 220V system then connecting a phase and a neutral would give you the required 220V but if you connect across two phases then the voltage would be 390V.

Mind you there are also different arrangement of the 3 phase. It can be WYE or DELTA arranged and this would also have some impact on the individual phases you connect to.

So you need to further get some details on the properties of the power supply from your service provider.

The supply voltage here in Saudia are phase to phase 220V and phase to neutral 127V, as the airconditioners are mostly of 220V so here the airconditioners are being connected between two phases to get 220V.

Now My concern is that an airconditioner of 18000 BTUH while connecting on 220 V accros the two phases it is taking around 13 Amps, while 18000 BTUH is equal 5.25KW. where as by calculation of a single phase the ampare are quite different (high), that I want to know.

Ok For both instances the current is defined as follows;

Ib = P(Watts)/V (where V =127V) for single phase and

Ib = P(Watts)/(SQRT{3}*V where V = 220V for the three phase.

You may go ahead then and consider using the power factors and efficiencies if they are available.

SQRT is the Square Root.

Try this:

18,000 BTUH = 5.27KW

Line Current ==> 5.27kW/220V = 23.9A

Phase Current ==> 23.9A/1.73 = 13.9A

TAKE CARE!!!!! commonly when it is 220v it is between phase and neutral wire:There are 380v between two phases!!!!!!!!!!!!

USE 1.414 INSTEAD OF 1.732 TO CALCULATE THE LOAD

SORRY USE 1.414 INSTED OF 1.732 AND CALCULATE THE PHASE CURRENT BY DEVIDING THE ANSWER BY 1.732.

Hope that will answer your query

Hi Manzoor,

As north of 60 says you are just need single phase calculations for this airco, however look on the specification plate for the current draw of your unit. Does that agree with the calculated figure of 24A? I agree with the calculation that 18000btuh = 5.25kW thus you must draw 24Amps at 220V. If you draw less then you are not getting 18000 cooling. (or you are getting something for nothing!)

Is something wrong with the gassing of the unit for example?

regards

chas

It should be possible to look this up in the Operation and Maintenance Manual that came with the equipment.

If not, then there should be a rating plate somewhere on the equipment.

If not, then the manufacturer's telephone number must be easily accessible.

John 11:35.

If the air-conditioning is built for 3 phases of 220 V phase-to-phase and if the supply source is 3*220 V, then, for 18000 BTUH [5.274 kW] the current will be 5.274*1000/220/sqrt(3)=13.84 A per phase.

If the air-conditioning is built for single phase 220 V the current will be 5.274/220=23.97 A

In my opinion, a power factor of 0.85 usually can be employed so the actual current may be 23.97/0.85=28.2 A