Forward/Reverse motor with one contactor

[SFportTECH]

Is there any drawback to creating a forward/reverse pump control circuit using only one contactor, and using a relay that switches two phases back and forth.
I have a pump control panel with two pumps, two contactors, and not enough space in the cabinet to add two more contactors for the traditional way of setting up a forward/reverse circuit using two motor starters for each pump.

 

[TwoBlocked]

The relay is probable not rated for the hp of the pump and may not last long. Depending on the size of the cabinet and the money available, you might be able to replace the contactors with VFDs. Another possibility is to install manual reversing switches after the pumps. But are these centrifugal pumps? If so, reversing the motor will not reverse the flow, just make things less efficient.

 

[hillbilly1]

Is there any drawback to creating a forward/reverse pump control circuit using only one contactor, and using a relay that switches two phases back and forth.
I have a pump control panel with two pumps, two contactors, and not enough space in the cabinet to add two more contactors for the traditional way of setting up a forward/reverse circuit using two motor starters for each pump.

If it is for unjamming the pump, @TwoBlocked suggestion would be the best way to go about it.(the manual drum conntroller)

 

[SFportTECH]

If it is for unjamming the pump, @TwoBlocked suggestion would be the best way to go about it.(the manual drum conntroller)

Yes, simply for unjamming.

 

[LarryFine]

Just to add, reversing a 3ph motor by swapping two lines can be done with a DPDT switch (such as a 4-way switch (but with an adequate rating, of course)) or contactor.

 

[SFportTECH]

Just to add, reversing a 3ph motor by swapping two lines can be done with a DPDT switch (such as a 4-way switch (but with an adequate rating, of course)) or contactor.

My problem so far has been finding a DPDT switch with the correct rating. I need 2 HP rated switch.

 

[LarryFine]

My problem so far has been finding a DPDT switch with the correct rating. I need 2 HP rated switch.

A drum switch like that shown in post #2 is probably your best bet, unless you can find a DPDT contactor.

 

[GoldDigger]

My problem so far has been finding a DPDT switch with the correct rating. I need 2 HP rated switch.

The HP rating for the switch (in addition to the Amp rating) is based on the need to make the connection with full starting transient current for the motor across the closing or opening contacts. This rating is not as important when the reversing switch will only be operated while the contactor is open, with the switching of the starting current always being done by the contactor.

 

[SFportTECH]

The HP rating for the switch (in addition to the Amp rating) is based on the need to make the connection with full starting transient current for the motor across the closing or opening contacts. This rating is not as important when the reversing switch will only be operated while the contactor is open, with the switching of the starting current always being done by the contactor.

Good point, but it still needs to be rated for the current, and I'm having a hard time finding DPDT with anything over 10 amps. Am I not looking in the correct places?

 

[synchro]

Good point, but it still needs to be rated for the current, and I'm having a hard time finding DPDT with anything over 10 amps. Am I not looking in the correct places?

I don't know if meets your requirements for voltage and current, but there is this:
https://www.gordonelectricsupply.co...-30A-120-277V-Dpdt-Maintained-Contact/5628989

If the need for unjamming the pumps is infrequent and you have room external to the pump control panel, DPDT safety switches could be used and are available for higher voltages and currents. They can of course also be used as a transfer switch.

An issue with using a manual switch is that it should be flipped when the contactor is open or it will have to handle high starting currents, as GoldDigger mentioned.

 

[hillbilly1]

A four way switch might work, you would have to label it “not a disconnecting means”, and the motor would have to be off before switching.

 

[sparkie1]

Use your normal motor-starter circuit and use a cam switch like this to change directions. They aren't bad to mount, fit in a 6" deep box and tend to be pretty reliable.

Motor Reversing Cam Switches - ASI

Motor Reversing Cam Switches / Motor Controls are available at ASI. ASI offers inventory, pricing, & datasheets for Motor Reversing Cam Switches.

www.sourceasi.com

 

[hillbilly1]

Use your normal motor-starter circuit and use a cam switch like this to change directions. They aren't bad to mount, fit in a 6" deep box and tend to be pretty reliable.

Motor Reversing Cam Switches - ASI

Motor Reversing Cam Switches / Motor Controls are available at ASI. ASI offers inventory, pricing, & datasheets for Motor Reversing Cam Switches.

www.sourceasi.com

Probably could even fit it on the control panel door.

 

[sparkie1]

Probably could even fit it on the control panel door.

It does. They typically have a mounting flange that threads and screws into the front of the door, then you lock the cam in place and set it. But they are a good 3" deep, sometimes more, so it takes a bit of a deeper box for them.

 

[SFportTECH]

It does. They typically have a mounting flange that threads and screws into the front of the door, then you lock the cam in place and set it. But they are a good 3" deep, sometimes more, so it takes a bit of a deeper box for them.

My reluctance to using such a switch is there is no protection from an operator mistakenly leaving it in reverse allowing the pump to run in reverse while in auto.

 

[SFportTECH]

My reluctance to using such a switch is there is no protection from an operator mistakenly leaving it in reverse allowing the pump to run in reverse while in auto.

It does. They typically have a mounting flange that threads and screws into the front of the door, then you lock the cam in place and set it. But they are a good 3" deep, sometimes more, so it takes a bit of a deeper box for them.

I think I'm going to make it work by changing out the starters for a for/rev starter. I want to reduce the chance of the pumps being left in reverse and in auto or the excessive reversing of the motor while in operation, such as a momentary barrel switch, which could be abused and damage the motors.

 

[sparkie1]

I think I'm going to make it work by changing out the starters for a for/rev starter. I want to reduce the chance of the pumps being left in reverse and in auto or the excessive reversing of the motor while in operation, such as a momentary barrel switch, which could be abused and damage the motors.

That's a wise call given what you need. You can't really do it with just a switch and have it run forward in auto. You could certainly add contacts and disable the circuit when in reverse if you want to use a job button or something. But I feel like just using contactors would be an easier choice.

 

[Jraef]

Good point, but it still needs to be rated for the current, and I'm having a hard time finding DPDT with anything over 10 amps. Am I not looking in the correct places?

That’s because when you need something rated for 2Hp, it’s called a “contactor”.

I don’t understand the need to reverse with a relay instead of a 2nd contactor. It’s still two devices, likely the same size. What the point?

 

[garbo]

Years ago I installed maybe a dozen drum switches for purpose of unjamming pumps & screw conveyors. Always used the pole that only opened & closed ( not the reversing poles ) in series with the stop button so operator could not attempt an instant reverse. Operator had to hit the start button every time handle was thrown.Think it was terminal 5 & 6. Back then most models could be secured to large panels and only have the drum handle outside of panel.

 

[garbo]

That’s because when you need something rated for 2Hp, it’s called a “contactor”.

I don’t understand the need to reverse with a relay instead of a 2nd contactor. It’s still two devices, likely the same size. What the point?

Retired but in my 50 enjoyable years as an industrial electrician we never used a relay to reverse any motors over 1/8 HP. Reversing contactors provide a second safety condition is that they are mechanically interlocked so both sets of contacts can not be closed at the same time.. I was taught back in the 1960's to electrically interlock every reversing contactor by two methods . Would go thru the NC contact of the down button to feed the NO up button and same with other button and use the NO & NC contacts that are pre wired on reversing contactors. Worst Arc that I ever almost got blinded on was as an apprentice and the electrician was in a hurry to get a piece of equipment back on line. He had me remove one cover on a size 3 reversing starter to inspect contacts then told me to hold a jumper to supply 120 volts to contactor. When I started to reinstall cover he told me to leave it off. At the same time that I was installing jumper he turned on the 3 phase safety switch and boom. Here the contactor that still had cover on had contacts welded closed and mechanically interlock was broken. If I had a hammer or wrench in my hand would have thrown it out him. Took awhile to see clearly.Back then nobody had PPE except for rubber gloves for switching 13.2 KV switchgear.