Motor strapping HV-LV

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Open Neutral

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Got a phone query re: installing a replacement Dayton 2NKX7 3ph 208-230/480V 1.5 HP motor.

They are running it on 208, and when wired for "low voltage" it hums, period. They restrapped it for "high voltage" and it runs. I can't see a diagram at the URL so am taking their word for it. The dead motor it replaced was strapped exactly as this one's "high voltage"....

The obvious answer is the sheet with strappings is wrong, but I find that dubious. I told them to measure each leg's current and compare to the spec. Other than that, it will take some eyes-on.... and it's 36 ft in the air on an exhaust fan.

Suggestions?
 
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GoldDigger

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Open Neutral said:
Got a phone query re: installing a replacement Dayton 2NKX7 3ph 208-230/480V 1.5 HP motor.

They are running it on 208, and when wired for "low voltage" it hums, period. They restrapped it for "high voltage" and it runs. I can't see a diagram at the URL so am taking their word for it. The dead motor it replaced was strapped exactly as this one's "high voltage"....

The obvious answer is the sheet with strappings is wrong, but I find that dubious. I told them to measure each leg's current and compare to the spec. Other than that, it will take some eyes-on.... and it's 36 ft in the air on an exhaust fan.

Suggestions?
Click to expand...
Possibly there is a problem with one phase of the three phase supply connection? The low voltage strapping appears to be wye internally, with no line connection to the center point, while the high voltage connection is delta internally. The wye connection might fail completely with a missing phase while the delta connection might act as an open delta and let the motor run, although at reduced power because of the low voltage. This could also have something to do with why the original motor failed. :)
If the motor is sitting there humming and something is done to start it turning, does it continue to turn?


There is an online picture of what may be a comparable motor nameplate here. There does not appear to be any room for error in the wiring as long as the supply phasing and connections are correct.


003800x600.jpg
 
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gar

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130427-1716 EDT

Open Neutral:

Measure the input line to line voltage. The implication is 6 coils. These are connected in parallel for low voltage, and series for high voltage. See the wire numbering and circuit at http://www.google.com/search?q=thre...pI8SoqQHi9IHABA&ved=0CDQQsAQ&biw=1001&bih=507

You can make sure that internally it is a wye by unconnecting 7, 8, and 9. If there is continuity between any two of these wires, and for all combinations, then the motor is internally a wye circuit.

.
 
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hurk27

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Double check the 6 and 9 wires, easy to mix them up for low voltage but since for high voltage they get connected together it always seems to work. they should have a line under the number to indicate which is which. continuity between 9,7,8 will tell you it a wye as well as tell you which one is #9, 6,3,8 will tell you its a delta as well as tell you which one is 6
 
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Open Neutral

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I was thinking 6 coils as well. Is there a NEMA or other standard of the numbering of same?

One early thought {...while they described the sitrep to me..} was one of the coils was wired bassackwards, leading to no net flux. But they insisted they'd checked twice.....
 
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GoldDigger

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Open Neutral said:
I was thinking 6 coils as well. Is there a NEMA or other standard of the numbering of same?

One early thought {...while they described the sitrep to me..} was one of the coils was wired bassackwards, leading to no net flux. But they insisted they'd checked twice.....
Click to expand...

This would not explain why the original motor was also found wired in the 480 configuration. The only thing that I think could have caused that to be the only configuration that worked for both motors would be some kind of problem with the 3-phase supply.
Measure both the line to neutral and line to line voltages at an accessible location on the ground, but be prepared to have to measure that at the motor too. Be sure to use a low impedance meter so that you are not seeing capacitive voltages.
Just measuring the line currents from somewhere on the ground will give you a good clue though!

PS: A three phase motor with only two phases driven (possible only with a wye?) should be able to start and rotate as long as it is not under load while starting. And if the third phase line is open on the supply side, you would then see a real voltage, with current available, on the third line coming from the motor, since the motor would be acting as a rotary phase convertor.
 
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don_resqcapt19

don_resqcapt19

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GoldDigger said:
Possibly there is a problem with one phase of the three phase supply connection? The low voltage strapping appears to be wye internally, with no line connection to the center point, while the high voltage connection is delta internally. The wye connection might fail completely with a missing phase while the delta connection might act as an open delta and let the motor run, although at reduced power because of the low voltage. This could also have something to do with why the original motor failed. :)
If the motor is sitting there humming and something is done to start it turning, does it continue to turn?


There is an online picture of what may be a comparable motor nameplate here. There does not appear to be any room for error in the wiring as long as the supply phasing and connections are correct.


View attachment 8450
Click to expand...
That is a standard NEMA 9 lead motor connection. (there are actually 12 leads to get the 6 coils but 3 of the leads are internally connected) The coils are 1 and 4, 2 and 5, 3 and 6, 7 and 10, 8 and 11, 9 and 12. 10, 11, and 12 are internally connected. It is connected in a double wye for low voltage and a single wye for high voltage. There are 6 coils all rated for 240 volts. The double wye is coils in parallel and the single wye is coils in series.
 
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hurk27

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Portage, Indiana NEC: 2008
GoldDigger said:
PS: A three phase motor with only two phases driven (possible only with a wye?) should be able to start and rotate as long as it is not under load while starting. And if the third phase line is open on the supply side, you would then see a real voltage, with current available, on the third line coming from the motor, since the motor would be acting as a rotary phase converter.
Click to expand...

I don't think that is so, without phase rotation the motor will just sit there and hum until it is turned, it can be started in either direction similar to a single phase cap start motor when the start winding is gone, many times when a three phase motor is connected to a load that might move the motor to spin such as a fan or blower with air flowing over it, even water pumps, the motor will take off and run in what ever direction the air movement pushes it.

We had a very large water pump (300hp) a couple weeks ago that had a bad check valve and we found it running backward, the other pumps feeding the same manifolds was causing it to start in reverse because it had a blown fuse.
 
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kwired

kwired

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Location
NE Nebraska
hurk27 said:
Double check the 6 and 9 wires, easy to mix them up for low voltage but since for high voltage they get connected together it always seems to work. they should have a line under the number to indicate which is which. continuity between 9,7,8 will tell you it a wye as well as tell you which one is #9, 6,3,8 will tell you its a delta as well as tell you which one is 6
Click to expand...

I like this suggestion - especially if both high and low voltage sources prove to be good. If you accidentally swap six and nine leads, at the low voltage connection - the 3-6 coil is shorted across and not connected to anything outside of itself and one input conductor, but this input goes nowhere so the rest of the motor is only seeing two phases and those two are not quite connected in usual fashion either. But the loss of one phase is enough to make it unusable.

If you confuse 6 and 9 when connecting to high voltage it is not a problem because they connect together in this configuration anyway.
 
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GoldDigger

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hurk27 said:
I don't think that is so, without phase rotation the motor will just sit there and hum until it is turned, it can be started in either direction similar to a single phase cap start motor when the start winding is gone, many times when a three phase motor is connected to a load that might move the motor to spin such as a fan or blower with air flowing over it, even water pumps, the motor will take off and run in what ever direction the air movement pushes it.

We had a very large water pump (300hp) a couple weeks ago that had a bad check valve and we found it running backward, the other pumps feeding the same manifolds was causing it to start in reverse because it had a blown fuse.
Click to expand...

A wye wound motor with two phase lines driven would still have a rotating (partly oscillating) magnetic field. It just would not have much torque, and would need some flywheel effect to carry it through the full revolution. A delta wound motor with only two lines hot will have only one winding driven and so no rotation at all.
 
kwired

kwired

Electron manager
Location
NE Nebraska
GoldDigger said:
A wye wound motor with two phase lines driven would still have a rotating (partly oscillating) magnetic field. It just would not have much torque, and would need some flywheel effect to carry it through the full revolution. A delta wound motor with only two lines hot will have only one winding driven and so no rotation at all.
Click to expand...
Are you sure about that?

If a delta wound motor is missing an incoming line, then yes only one winding has full voltage applied to it, but the others still are connected and current will flow through them, but it should be half of rated voltage across each winding as they are in series connected between the two good input leads. This motor probably will have rotation also but not much torque.

I could be wrong, but that is my best guess at what would happen.
 
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