Two speed 3 phase motor wiring question

[RexV24]

Hi Guys,

I have a motor here that is 460V / 3ph and it is a two speed. At high speed, the motor is running at 15HP and at low speed, the motor is running at 3.8 HP. It is a Baldor M1211T if it helps. My question comes in that pins 1,2,3 are L1,L2,L3 for low speed while pins 4,5,6 are not connected. I have 14 gauge running to pins 1,2,3. For high speed, pins 4,5,6 are L1,L2,L3 (which i have 8 gauge running to the motor), but pins 1,2,3 are now jumped. I can achieve this with a few contactors so that we can switch them from low to high. My question is that when running at high speed, would it be ok to have pins 1,2,3 jumped with 14 gauge? Thanks,

 

[Smart $]

Yes, #14 is okay.

Per documentation:

Line draw when in LOW mode is 8.7A.
Line draw when in HIGH mode is 20A.

Worst case scenario is 10A on #14. Likely scenario is just 8.7A.

When you have a chance, measure both and report back. :happyyes:

https://www.baldorvip.com/servlet/productInfoPacket/M1211T.pdf

 

[RexV24]

Will Do,

I don't think it is a problem, but what was a little confusing for me is that i have the Line portion covered, but in high speed, would there be 20A going through pins 1,2,3? or is that just like a switch where a 14 gauge would be sufficient. Thanks,

 

[Smart $]

Will Do,

I don't think it is a problem, but what was a little confusing for me is that i have the Line portion covered, but in high speed, would there be 20A going through pins 1,2,3? or is that just like a switch where a 14 gauge would be sufficient. Thanks,

Refer to the last page of the linked pdf. The 20A gets divided between the two windings per leg in HIGH speed. The windings are connected in series for LOW speed. The 8.7A in series versus 20A in parallel suggests the windings are not equal, but for a motor circuit, #14 is good for 20A anyway (16A motor FLA factored 125%).

 

[Jraef]

Will Do,

I don't think it is a problem, but what was a little confusing for me is that i have the Line portion covered, but in high speed, would there be 20A going through pins 1,2,3? or is that just like a switch where a 14 gauge would be sufficient. Thanks,

Don't over think this.

430.22
(B) Multispeed Motor. For a multispeed motor, the selection
of branch-circuit conductors on the line side of the
controller shall be based on the highest of the full-load
current ratings shown on the motor nameplate. The ampacity
of the branch-circuit conductors between the controller and
the motor shall not be less than 125 percent of the current
rating of the winding(s) that the conductors energize

 

[Smart $]

Don't over think this.

430.22
(B) Multispeed Motor. For a multispeed motor, the selection
of branch-circuit conductors on the line side of the
controller shall be based on the highest of the full-load
current ratings shown on the motor nameplate. The ampacity
of the branch-circuit conductors between the controller and
the motor shall not be less than 125 percent of the current
rating of the winding(s) that the conductors energize

That doesn't help. :happyno:

There is no current rating for the jumpered-in-HIGH windings.

 

[Jraef]

That doesn't help. :happyno:

There is no current rating for the jumpered-in-HIGH windings.

Sure there is, it has to be right on the nameplate.

Since the HP is so much different, this is a Variable Torque 2 speed 1 winding motor, meaning it is a Y - YY connection. 1, 2, 3 are the connections for low speed, 4, 5, 6 are left open, so the motor is only one Y winding that is twice as long. At high speed, the line is connected to 4,5,6 and 1,2,3 are shorted, creating 2 parallel Y windings. The current flowing through 1,2,3 at that point is the same as is flowing through 4,5,6 as part of the total circuit for High speed, so must be rated for that current. The "jumper" is done at the contactor in the starter and is usually a piece of bus bar shorting across all three contacts. If you use wire, why get cheap on a couple of 2" pieces of wire?



Link to the image for a better view.
http://www.pdhonline.com/courses/e106/image004.gif

 

[Smart $]

Sure there is, it has to be right on the nameplate.

Don't know specifically what is on the nameplate but the specs correlate FLA (20/8.7) to HP (15/3.8). There is no spec for rated current across T123-connected windings.

Since the HP is so much different, this is a Variable Torque 2 speed 1 winding motor, meaning it is a Y - YY connection. 1, 2, 3 are the connections for low speed, 4, 5, 6 are left open, so the motor is only one Y winding that is twice as long. At high speed, the line is connected to 4,5,6 and 1,2,3 are shorted, creating 2 parallel Y windings.

I am aware of how it is connected.

The current flowing through 1,2,3 at that point is the same as is flowing through 4,5,6 as part of the total circuit for High speed, so must be rated for that current. The "jumper" is done at the contactor in the starter and is usually a piece of bus bar shorting across all three contacts. If you use wire, why get cheap on a couple of 2" pieces of wire

It is an assumption the same amount of current is flowing through 123 as 456. The difference in HP between series (LOW) and parallel (HIGH) connection implies otherwise.

He's using #14 between starter contactor and motor 123. Using a larger wire size for jumpers at the contact makes no difference. The wires between contactor and motor 123 must also be sized for the proper winding current. We could say with a 20A draw in HIGH, the rated current through 123 is 10A each, so #14 is good... but 10A is an assumption. I have not explored a mathematical solution.