230V motor fed from a 480V source

[kharris]

While performing service on a shaker at a tile manufacturing plant, the operator asked me why shaker#1 was so loud. He said it started about 4 months ago. I looked at the motor and from what I could make out on the nameplate, the motor is only rated for 230V. When I checked voltage at the starter, the meter read 480V. How can a 230V rated motor run on 480V for four months without burning up? From what I have observed so far, this machine runs for what seems to be 10-30 minutes at a time, and not all that often. The nameplate was hard to read, but I did not notice a dual rating.

 

[shamsdebout]

Interesting, I am not an expert with motors but as you mentioned the intermittent use is allowing the motor to die slowly.

 

[mcclary's electrical]

Since you said it was hard to read, is there any possibility the motor is dual voltage? How many wires in the motor junction box?

 

[kwired]

You are probably missing something here. I only give that motor a few minutes at the most at two times voltage.

If the other way around 480 volt motor operating at 240 it could possibly operate for a long time especially if not loaded very heavily.

When I checked voltage at the starter, the meter read 480V.

what is voltage at motor? if there is a voltage tranformation someplace between starter and motor the voltage may be ok at the motor.

 

[frenchelectrican]

I have a feeling there is something is missing along the way due the OP did not stated what conferaton the motor is hooked up in delta or wye format.

Now if you have 480 volt supply to the motour that is wired for 240 volts a good chance you will burn up the windings pretty fast no question asked.

there is one way but it will be a long shot I think someone did change from delta to wye connection on the motor if that the case you will see T4-T5-T6 is connected together that based on 9 lead motour if other types then the bet is off.

Merci,Marc

 

[broadgage]

Could it be UK spec motor intended for use on 240/415 volt supply.
240 volt in delta, or 415 volt in Y (or star as it is known here)
If wired in Y such a unit should be fine on 480 volts 60 cycles.

UK type motors normaly have 6 terminals, not 6 wires. these terminals are supplied with brass links whereby they may be connected in Y or delta.
No change of principle is involved, compared to USA practice, but if the terminals are hidden under the wires, it can look like a 3 wire single voltage motor.
There are normaly 3 terminals in each of two rows, one row above the other.
For delta service, each terminal is linked to the one above it, and the 3 phase supply is connected one wire to each pair of terminals.
For Y service, the top row of 3 terminals are connected to each other, but not to anything else. The 3 phase supply is then connected one wire to each of the bottom row of terminals.

 

[PowerQualityDoctor]

As said before, this must be 230/400v motor connected at Wye, so each winding received 277v.

I assume the 480v is 60Hz and the rated 230v is 50Hz. If my assumptions are correct, there is no problem with the flux of the motor as 480/60 equals to 400/50. On the other hand, the motor rotates 20% faster than rated. Usually, there should be no problem with this, but maybe this is the source of noise?

The 20% higher voltage is normally not a problem for motors. If the loading on the motor is 100%, it will make the motor more efficient. If the loading is low, it will reduce the motor efficiency.

Another source for noise can be harmonics. What is the harmonic levels? Do you use VSDs?

 

[Besoeker]

How can a 230V rated motor run on 480V for four months without burning up? From what I have observed so far, this machine runs for what seems to be 10-30 minutes at a time, and not all that often. The nameplate was hard to read, but I did not notice a dual rating.

At twice rated voltage the motor would saturate (magnetic flux).
It would take many times its rated current - more than locked rotor. This should result in the protection tripping. If it didn't, the motor, the cabling from the starter to the motor and, depending on how it is fed, possibly the cabling to the starter, not to mention the isolator and contactor would cook rather quickly.
And you would notice that distinctive once sniffed, never forgotten smell of overheating windings.
So I really don't think your motor can be rated at just 230V.

 

[mcclary's electrical]

At twice rated voltage the motor would saturate (magnetic flux).
It would take many times its rated current - more than locked rotor. This should result in the protection tripping. If it didn't, the motor, the cabling from the starter to the motor and, depending on how it is fed, possibly the cabling to the starter, not to mention the isolator and contactor would cook rather quickly.
And you would notice that distinctive once sniffed, never forgotten smell of overheating windings.
So I really don't think your motor can be rated at just 230V.

YOur post got me to thinking about a service call I had a few years back. The owner told me her water quit working, she had a "handyman"look at it several months before. Her tank and pressure switch were in the house wired to 240 volt. The wiring between the house and the well had failed underground somewhere. Out by the well,there was another outbuilding. I see a piece of UF coming out of the ground and into the building. Inside,he had cut the UF and put a normal cord in on it and plugged it in to a 120 volt outlet!! It ran for 5 months straight before she called me saying her electric bill was 500 a month ever since ihe did that.It was not cutting off by the pressure switch. He had it running all the time.She had awesome pressure, but it was costing her bigtime! I unplugged it straight out of the wall, rewired it to new wires I installed in a trench, hooked it right back up to the 240 volt pressure switch and it ran fine.Toughest pump I've ever seen.