# How to verify if all 3 AC phases are in order? [closed]

We have 220V main lines where we currently live and we have a 3-Phase connection. We have an Air conditioning unit that requires 3 phase AC input with the correct phase sequence.

If the phase sequence is not right, it displays an error code for that. A while ago there was an electricity breakdown in our area and ever since that was resolved we are receiving that error. This happened a year ago as well but a quick phase load wire rotation by the electrician solved the problem.

This time, however, no matter what combination they try it does not seem to work. I have a sequence detector tool but that does not work now either.

The electricians from our maintenance company refuse to admit that the problem lies somewhere in the supply and claim that 380V - 396V are there the problem is with your unit. But if the unit had gone bad how come another device has also gone bad at the same time?

How can we verify their claim? The Air conditioning unit's electrician says that the main line is not supplying the 3 phases correctly and their electricians say that all our 390 volts are there between every 2 phases and the fault is indoors.

Please note: I do know that this is dangerous work, and I am not doing it myself. Only (so called) qualified electricians are working on this. I am just asking to learn so i can plead my case with their manager.

## closed as off-topic by Nick Alexeev♦Apr 9 at 3:14

• This question does not appear to be about electronics design within the scope defined in the help center.
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• Do you have anything that uses 3-phase other than the air-con unit and your sequence detector tool? – Charles Cowie Apr 8 at 17:16
• Can you put a scope on the mains lines? – Tyler Apr 8 at 17:16
• Nope sorry, only those 2 things. All other Aircon units work on single phase – Hanky Panky Apr 8 at 17:16
• @Tyler unfortunately I don't have a scope and these guys don't bring one. They act dumb and say here see on our multi-meter everything is 380 – Hanky Panky Apr 8 at 17:21
• In a brushless DC motor, if it's rotating backwards you just swap any two wires going to the motor. Wouldn't the same thing apply here? Could you not verify things just by conencting a 2 or 4 channel oscilloscope to the lines? I don't think you even need Y-connected resistors as a dummy load. You might be able to rent a handheld scope. – Toor Apr 8 at 17:30

You get a phase sequence indicator. There are two kinds, one uses a small 3-phase motor and it rotates in one direction or the other. The second kind does it electronically. They start at well under \$100.

You should not attempt to connect an oscilloscope or an electronic grade DMM to the mains, especially 3-phase mains, unless you have the proper equipment, including probes and you know exactly what you are doing, you could be injured, die or destroy your equipment. Not only are the voltages high, but the potential fault currents tend to be extraordinarily high (I've seen as much as approaching 10kA in a light industrial situation).

• I didn't realize they had little 3 phase motors just for that purpose. I was thinking that was one approach but thought that any available motor would be too big, heavy, and expensive – Toor Apr 8 at 21:40
• @Toor I would expect any industrial electrician to have one. – Spehro Pefhany Apr 8 at 23:24

There are only two possible connections to get the phase sequence correct; A-B-C or C-B-A. Swapping any TWO (and only two) wires changes the rotation. So if you have done that, that's all you can (or need to) do. Whether it is A-B-C, B-C-A or C-A-B is totally irrelevant, the rotation sequence is the same.

I'm more curious about the voltage levels you state. First you say you have 220V, then later you say they are feeding you 380V - 396V? If you meant that you have 220V line-to-neutral then that's OK, but if you meant that you had 220V line-to-line and now you have 380V line to line, that's likely your problem. The error code is likely a common code that just means something is wrong with your mains supply.

We have 220 V main lines where we currently live and we have a 3-Phase connection. We have an Air conditioning unit that requires 3 phase AC input with the correct phase sequence.

With 220 V phase to neutral you should have $$\ \sqrt 3\$$ 220 = 380 V phase to phase.

If the phase sequence is not right, it displays an error code for that.

Useful.

A while ago there was an electricity breakdown in our area and ever since that was resolved we are receiving that error.

So the unit has never run since.

This happened a year ago as well but a quick phase load wire rotation by the electrician solved the problem.

So it has run since. It appears that phase-sequence reversal solved the problem but the error message stayed on. (See previous paragraph.) And which electrician swapped the phases? Yours or the power company's?

This time, however, no matter what combination they try it does not seem to work.

There are only two 3-phase sequences possible: A-B-C or A-C-B.

I have a sequence detector tool but that does not work now either.

Why tell us that?

The electricians from our maintenance company refuse to admit that the problem lies somewhere in the supply and claim that 380 V - 396 V are there the problem is with your unit.

Refuse to admit? You haven't proved a phase-sequence reversal yet.

But if the unit had gone bad how come another device has also gone bad at the same time?

What other device?

How can we verify their claim?

A qualified person would use a phase-sequence meter to check for correct sequence and a voltmeter to measure the supply voltage.

The Air conditioning unit's electrician says that the main line is not supplying the 3 phases correctly and their electricians say that all our 390 volts are there between every 2 phases and the fault is indoors.

That would be easy for an electrician to check and for you to observe.

I don't think you have demonstrated that there is a supply problem. Your story above is not consistent or is confused. You need to straighten this out and get supporting measurements before you tackle the supply company. You may be simply missing one phase internally in your house but since there is no location in your post or user profile (that's what it's for) we have no idea what local electrical regulations are applicable or what faults are likely.