How does this switch work?

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sw_ross

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A customer has a 10hp fan motor for a grain bin that he was having a hard time getting started so he took it upon himself to rearrange the connection leads to this switch just to "see if it would help"!

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I'm trying to understand how this switch is supposed to work, compared to the wiring diagram, to see if I can get the leads back to their proper location.
I don't think anything is wrong with the motor. He was trying to get the motor to run off a generator. I think the problem was related to the generator.
I just got a service panel installed at the bin site, so generator is not necessary.

When I manually push in the contactor button the motor get up to speed but doesn't stay engaged. The coil seems good (ohmed it out). I think it's related to the farmer messing with the start switch.

I'm trying to understand how the switch works. When you push to start does it engage start capacitors? And then when it gets up to speed and it spring returns back to the run position it dis-engages the start capacitors? I need to understand how the switch is designed to work so I can test out the function of the switch to make sure it's good and to get the leads back to the proper locations.

The wiring diagram shows a "circuit 1" and a "circuit 2". On the diagram it shows an angled blade and a straight blade, but doesn't show what's going on internally to the switch...

Also, the diagram shows 2 of the leads from the switch going to T1, but that not evident, unless it's the leads going through the start capacitors?

Also, is there any way he could have burned out the switch? He tried feeding it with a generator that was set on 3-phase 120/240? It was being fed by a 2-pole breaker, so theoretically it should have still been getting 240 volts.

Thanks for any input!
 
sw_ross said:
A customer has a 10hp fan motor for a grain bin that he was having a hard time getting started so he took it upon himself to rearrange the connection leads to this switch just to "see if it would help"!

View attachment 19183
View attachment 19184
View attachment 19185

I'm trying to understand how this switch is supposed to work, compared to the wiring diagram, to see if I can get the leads back to their proper location.
I don't think anything is wrong with the motor. He was trying to get the motor to run off a generator. I think the problem was related to the generator.
I just got a service panel installed at the bin site, so generator is not necessary.

When I manually push in the contactor button the motor get up to speed but doesn't stay engaged. The coil seems good (ohmed it out). I think it's related to the farmer messing with the start switch.

I'm trying to understand how the switch works. When you push to start does it engage start capacitors? And then when it gets up to speed and it spring returns back to the run position it dis-engages the start capacitors? I need to understand how the switch is designed to work so I can test out the function of the switch to make sure it's good and to get the leads back to the proper locations.

The wiring diagram shows a "circuit 1" and a "circuit 2". On the diagram it shows an angled blade and a straight blade, but doesn't show what's going on internally to the switch...

Also, the diagram shows 2 of the leads from the switch going to T1, but that not evident, unless it's the leads going through the start capacitors?

Also, is there any way he could have burned out the switch? He tried feeding it with a generator that was set on 3-phase 120/240? It was being fed by a 2-pole breaker, so theoretically it should have still been getting 240 volts.

Thanks for any input!
Click to expand...
That is just about the only place you see that switch is on these grain aeration fans. It is basically the equivalent of having a three wire start-stop station. I can't recall which "circuit" is which, but when the switch is in the center position one will be closed and one will be open. Wire the closed one in as you would a stop pushbutton and the open circuit as you would a start pushbutton.

Spring return position of the switch closes the start contact. Stop contact is opened when the handle is in the other direction from center.

Add: his problem with using this on the generator may be too much voltage drop during starting and that is dropping out the holding contact on the starter. Holding the switch in start position until it reaches higher speed and voltage rises again may be what is necessary for a successful start.
 
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The voltage to the two wires on the side of the contactor closes the contactor. I'd suggest measuring this voltage and pressing the start button (after changing the wiring back to the way it was supposed to be).

If you don't get a voltage there, either the switch is bad, or the thermostat is open. If you have a high voltage across the thermostat, it may be bad, or the connection may be bad.

If the thermostat looks good, and you don't get voltage at the contactor coil, of if the switch doesn't maintain voltage at the coil, the switch is probably bad.

If you get voltage across the contactor coil, and the motor still doesn't start, then the contactor or motor may be bad.
 
Start caps

Start caps

So, related to the switch, when I identify which "circuit" closes when the switch is pressed to the "start" position I'm assuming that would engage the start caps?

If I open up the motor wiring box I should be able to identify which lead go through the start caps (typically black cases?), vs which leads feed the run caps (typically silver?)?

At the same time I'll probably check the caps.

Then when it spring returns to the "run" position it disengages the start caps?

I don't know what kindve voltage he got out of the generator on startup, I wasn't there when he attempted to use the generator.

On the wiring diagram, the 2 leads drawn on the left side of the contactor I assume are the coil connections.
 
I never looked at the picture of the schematic before my first post, have seen many units with the type of switch used here though - but sure looks like they are using L1 to T1 contact as both a motor circuit contact and as the control circuit holding contact. Never seen that done before, not a good idea, unless I am not seeing it correctly.
 
sw_ross said:
So, related to the switch, when I identify which "circuit" closes when the switch is pressed to the "start" position I'm assuming that would engage the start caps?

If I open up the motor wiring box I should be able to identify which lead go through the start caps (typically black cases?), vs which leads feed the run caps (typically silver?)?

At the same time I'll probably check the caps.

Then when it spring returns to the "run" position it disengages the start caps?

I don't know what kindve voltage he got out of the generator on startup, I wasn't there when he attempted to use the generator.

On the wiring diagram, the 2 leads drawn on the left side of the contactor I assume are the coil connections.
Click to expand...
The Start position should have nothing to do with the starting caps, those should be switched internally on the motor. It sounds like you are not maintaining voltage to the coil.

You are correct about the caps, run caps are usually silver, metallic case and starting caps are black plastic case.
 
Thanks for input!

Thanks for input!

Thanks for giving feedback on my initial query!

I think I've got it figured out now. it does make sense now that it is more like a 3-wire start/stop station.

Thanks for giving me some confidence to go back to this jobsite next week and troubleshoot this motor!
 
the start position puts power to the coil from L1
it picks up and puts power to the load side T1
upon release to run power from the load side is put to the coil from T1 (latching it)
stop interrupts power to the coil

the flat/angle symbols mimic the actual plug blades on the switch
the 2 wires from T1 go to the flat/horizontal blades, does not matter which one
on the switch the upper/top angled blade goes to L1
the lower/bottom angled spade on the swtch goes to the contactor
this should work
if not test temp switch
the temp sw goes from L2 to the other side of the contactor coil (you can test to see if is bad just jumper L2 to the coil and try to start)

if that does not work just swap the two angled blades on the switch

MAKE SURE POWER IS OFF!!!!!!
CHECK WITH A METER ON L1 and L2, between each and each to gnd
 
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