3 Phase Electric Heat Strips

[wrangoth]

We have a auditorium with a split system. Two condensors on the roof twinned to one air handler in a mechanical off the auditorium.

The air handler is equipped with two 15 kw heat strips. The problem we are having is when the unit is running with the heat strips only we can check the supply temp just past the strips and we are only reading 75-76 degree heat.

The supply is reading 67-68. We have an amp draw of 11 amps each strip. We have outdoor dampers but they are closed with only a small amount of outside air slipping past.

Any suggestions?

[wrangoth]

Additional information.

I would like some information on how to electrically troubleshoot a 3 phase 460 volt heater.

[hyperion]

If you electriclly isolate the heaters and then measure the resistance of each heater element or group of elements. Once you have this reading, along with the current being draen by each element or group of elements, you should be able to apply Ohms Law from which you will be able to calculate the expected current. V/I=R and W=V*I. Where V=volts, I=current , R=resistance and W=watts. If this is not confirmed by the actual current drawn, then you possibly have a faulty element. If one of the elements has a different resistance, then this could be the faulty one. Proceed carefully and do not jump to a conclusion.

[qqjersey]

sounds like heaters are not 100% for 15kw, check overloads they may be weak and cutting out.

[chemi-cool]

You can also check the currant draw with clamp Ampere meter and get the state of the heating stripes strait away.

[frank]

The air handler is equipped with two 15 kw heat strips. The problem we are having is when the unit is running with the heat strips only we can check the supply temp just past the strips and we are only reading 75-76 degree heat.

The supply is reading 67-68. We have an amp draw of 11 amps each strip. We have outdoor dampers but they are closed with only a small amount of outside air slipping past.

11amps per strip doesn't mean anything unless we know the voltage.

The temperature rise across a heater battery is also dependant on the air volume passing over it.

Do you know the airflow?

[wrangoth]

I really need a good explanation for troubleshooting a 3 phase heater.

I have no problem with single phase but the 3 phase confuses me.

1. Should all legs of the heater have identical ohm readings? Is it a must to disconnect the wiring before ohming it? If ohms read different, is that a sure indicator that the heater is bad?

2. Should all legs have identical amp readings? On this unit each leg is getting the same voltage.

[chemi-cool]

I really need a good explanation for troubleshooting a 3 phase heater.

I have no problem with single phase but the 3 phase confuses me.

1. Should all legs of the heater have identical ohm readings? Is it a must to disconnect the wiring before ohming it? If ohms read different, is that a sure indicator that the heater is bad?

2. Should all legs have identical amp readings? On this unit each leg is getting the same voltage.

3 phase heaters are connected in Y arrangement.
From one side, all the legs are connected to 0 and the other 3 legs are connected to to the 3 phases.

As I've said before, switch it on and check with clamp ampere meter, on a faulty heater, you will get different reading.
If Ω's is what you are after, then disconnect each heater for accurate reading.

[wrangoth]

Thanks. I checked each leg with the amp meter and found one with no amperage. It is a 30 kw heater but it has 4 7.5 kws in the circuit. Two are piggy backed to make one heater.

One heater was not working. Thus the low temp rise. Thank you.

[qqjersey]

A basic 3 phase 15 kw heater at 240v should draw 40 amps

[Magoo]

If 460 VAC heaters try delta connection and really start heating, so long as supply and protection and air flow can handle load.
magoo