Connection of small 1 phase motor

[19tom56]

I have not worked a lot with 1 phase motors, but mainly 3 phase.

Today I had to replace a 1 phase 220 Volt Capasitor start extractor fan motor.

The extractor unit is a radial wheel mounted at the motor shaft.

Everything was connected accoding to the diagram in the lid of the connecting box. Full load is 6.5 Amp. The electromagnetic circuit breaker is a Telemecanic C6 ( 6 amp ) There is no thermal protection in this installation.

First a small test run before the motor and fan was connected to the ducting. It ran 10 seconds, then the breaker tripped.

An investigation showed that the motor wireing coming to the therminal block on motor had been slightly overheated.

A new motor was ordered and a Motorstarter with thermal protection. However thermal motorprotection in a 2 pole version seem to be nonexisting.

Waiting for new parts we decided to install everything again and connect the ventilation duction. Also I reversed the 220 volt Line and Neutral line. The installation drawing states U1 and U2 AC, but not if any are required Line and the other Neutral.

Motor now ran fine, no signs of overheat. Current draw 3 Amp.

The questions are
1. Why did fuse trip and motor wireing overheat.

2. Is it safe to install this motor without a dedicated over current protection. ( There is only a 6 Amp short circuit protection )

3.If electrical diagram is marker U1 and U2, is any supposed to be 220V and the other 0V ( 220 V single phase system )

4. Is there any way you can use a 3 pole 3 phase motorstarter with thermal overload on a 2 pole 1 phase installation.

Regards Torben

 

[itsmoked]

1. Why did fuse trip and motor wiring overheat.

You can actually overload some fans when you run them with no air resistance. A lot of blowers and fans do become overloaded in that situation. It is usually a pretty big overload but not big enough to immediately trip the protection - just enough to get things simmering hot first.

2. Is it safe to install this motor without a dedicated over current protection. ( There is only a 6 Amp short circuit protection )

You need some sort of overload protection. For a smaller 1ph motor it can be a delay fuse or just a thermal circuit breaker that is accurately sized.

3.If electrical diagram is marker U1 and U2, is any supposed to be 220V and the other 0V ( 220 V single phase system )

I don't believe it should matter but maybe someone else will chime in with case where it does.

4. Is there any way you can use a 3 pole 3 phase motor starter with thermal overload on a 2 pole 1 phase installation.

It should work fine but would generally be overkill as a fuse or breaker alone can do the job.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

Answers:

1. Could be anything. Faulty motor. Highly loaded. Anything.
2. Some would say, yes. This is because the fuse rated amps are so close to the motor's. I would say no. Fuses are not usually thermally adapted to motor windings.
3. You can connect either way. The motor doesn't mind. If the markings had said U1 and N (or something like that), then you should connect N to neutral. But, in this case no bother.
4. Yes. It is done all the time. Make sure that all thermal elements are in series with the motor (connect all three breaker elements in series). This is so that the heat in the motor starter case corresponds to a three-phase connection. Some (very many) motor straters also have a phase loss protection and that would operate if you do not make all elements carry the same current.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[19tom56]

Thank you very much for the very quick response
Torben

 

[waross]

FUSE?? BREAKER?? You stated that the motor was protected by a 6 amp breaker. For a motor rated at 6.5 amps Full-Load-Current that draws 3 amps loaded that should be adequate protection.
I agree with itsmoked.If you were running the fan open with no ducting the motor will often overheat,.
Most single phase motor protection switches that i see break both lines but have protection on only one line. That is adequate for single phase protection.
I think that Gunnar's finger slipped and he wrote phase loss protection when he meant differential or unbalance protection.
But yes; many three phase motor protectors will trip on differential or unbalance if the motor current does not go through all three poles. itsmoked's information concerning internal heat generation is also valid.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Skogsgurra]

Bill, phase loss is the severest form of unbalance I can imagine. Connecting two elements (or one) is equal to phase loss from the protection's point of view.
We have a slightly different thinking in Euroland and Dollarland. We put protection on all induction motors (either in the starter or a 'Klixon' in the winding) while there seems to be more discussions about it on your side of the water.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[waross]

Hi Skogs.
Phase loss to a motor will certainly cause a current unbalance and that will cause an unbalance trip.
However I know phase loss protection as a device that checks phase angles to prove the presence of all three phases. True phase loss protection will not be fooled by single phase applied to three terminals.
I sometimes use solid state monitors on refrigeration compressors that have both phase loss and unbalance protection. Either condition will shut down the motor and the monitor reprts the condition that caused the shut down.
However I'm just nit-picking over one word. Your advice was excellent no matter what word was used.
Respectfully
Bill

Bill
--------------------
"Why not the best?"
Jimmy Carter