Motor overload tripping

[retirede]

Oh btw, make sure nobody did away with the relief valve, and if the one that is there pops off below the working pressure of the tank. It will be made of brass and have a number stamped on it. It will look something like this View attachment 2565945

There is also an adjustable type, You probably want it to pop off at like 185 if you are setting the high limit on the pressure switch to 175

The relief valve is usually based on the ASME rating of the pressure tank (presuming there’s a tank). It could be possible to raise the pressure control and overload the motor without popping the relief valve.

Field-adjustable safety relief valves are not allowed any more. If it’s the adjustable type, it will have a wire and lead seal to make it evident if it was tampered with.

If somebody removed the relief valve, they should be hanged, drawn, and quartered!

 

[electro7]

So can somebody explain to me how this works?

I am assuming the contactor opens, which disconnects the voltage to the motor, when the overload heaters get to hot from overload current. The red reset button engages the contactor to allow for a closed circuit again and for the motor to turn back on. Is that correct?

I am going to head there and turn the overload heaters around but not understanding how they would trip if they are backwards. He said it happens 3 or 4 times a day they have to go reset the red button.

I'm going to turn off the circuit and switch the overload heaters around, then turn the circuit back on and press the red reset button to reset it. Does that sound right/okay?

Sent from my SM-G998U using Tapatalk

 

[Joethemechanic]

ASME rating of the pressure tank

Yeah the ASME plate on the tank will have a WP listed relief should pop off a good bit below that pressure. Relief should also have a cfm rating above the compressor's cfm. And yeah I have seen ones too small put in tanks with a reducing bushing.

If somebody removed the relief valve, they should be hanged, drawn, and quartered!

I agree, but I've seen compressed air butchery out in the field that made me want to run out of the building

 

[don_resqcapt19]

So can somebody explain to me how this works?

I am assuming the contactor opens, which disconnects the voltage to the motor, when the overload heaters get to hot from overload current. The red reset button engages the contactor to allow for a closed circuit again and for the motor to turn back on. Is that correct?

I am going to head there and turn the overload heaters around but not understanding how they would trip if they are backwards. He said it happens 3 or 4 times a day they have to go reset the red button.

I'm going to turn off the circuit and switch the overload heaters around, then turn the circuit back on and press the red reset button to reset it. Does that sound right/okay?

Sent from my SM-G998U using Tapatalk

I don't understand how the motor could run with the heaters installed the wrong way unless something has been modified.
If it runs, I have no idea of how it could trip and be reset.

With that design of overload protection, when you push the reset button, the levers move down, close the NO overload relay contact, and the levers push against the gear keeping the switch closed. When the motor is running the motor current flows through the heater element. When there is too much current, the eutectic alloy metal around the gear shaft melts, permitting the gear to spin. When the gear spins, the lever moves out, and opens the overload relay contact causing the starter to drop out.

 

[Joethemechanic]

I am assuming the contactor opens, which disconnects the voltage to the motor, when the overload heaters get to hot from overload current. The red reset button engages the contactor to allow for a closed circuit again and for the motor to turn back on. Is that correct?

When the heaters get hot from overcurrent they allow a set of contacts to open. The contacts are in series with the magnetic coil that closes the contactor when it is energized. That causes the motor contactor to open.

 

[jim dungar]

There should be a set of contacts behind the lug on the lower left of the overload block. You can find it by following the red wire which are visible just below the nameplate. The overload open will be closed when the relay is tripped and closed when the relay is reset.

It is possible that someone removed or bypassed this contact in the starter control circuit. They then installed the thermal units upside down to complete the current path to the motor.

I would be suspect of the entire motor control circuit.

 

[Joethemechanic]

I would be suspect of the entire motor control circuit.

Yeah 100%

 

[retirede]

Yeah the ASME plate on the tank will have a WP listed relief should pop off a good bit below that pressure. Relief should also have a cfm rating above the compressor's cfm. And yeah I have seen ones too small put in tanks with a reducing bushing.


I agree, but I've seen compressed air butchery out in the field that made me want to run out of the building

Just to add some detail…
ASME section VIII states that the relief valve must begin to open at not more than 90% of the Maximum Allowable Working Pressure (MAWP) which is stamped on the nameplate. MAWP is not the same as “Working Pressure” (also called “Design Pressure”).

OK, I think we’re far enough off topic now!

 

[Tulsa Electrician]

Do you have an uglys book.
This basic circuit is in the book.
If not, I get ya a pic

 

[Tulsa Electrician]

Found a little better pic

 

[Joethemechanic]

OK, I think we’re far enough off topic now!

Well it is very important chit if you are messing with things that have pressure vessels. I've seen the aftermath of those kinds of explosions

 

[hillbilly1]

So can somebody explain to me how this works?

I am assuming the contactor opens, which disconnects the voltage to the motor, when the overload heaters get to hot from overload current. The red reset button engages the contactor to allow for a closed circuit again and for the motor to turn back on. Is that correct?

I am going to head there and turn the overload heaters around but not understanding how they would trip if they are backwards. He said it happens 3 or 4 times a day they have to go reset the red button.

I'm going to turn off the circuit and switch the overload heaters around, then turn the circuit back on and press the red reset button to reset it. Does that sound right/okay?

Sent from my SM-G998U using Tapatalk

The cog will spin either way, but the lever may not be long enough to catch the cog, but apparently yours is. I’m betting the pressure relief valve (also known as an unloaded valve) for the cylinders is not working. You should easily hear a release of air pressure as soon as the compressor shuts off. It’s usually a small tube that runs from the cylinder to the bottom of pressure switch. If it is not working, the compressor is starting under high head pressure, and will overload the motor. With the tank pressurized, then drops to cut-in pressure, does the motor struggle starting back up?

 

[hillbilly1]

Here is a better explanation.

Unloader Valve: Its Purpose | Quincy Compressor

A reciprocating air compressor is a positive displacement mechanical device that relies on a cylinder and crankshaft-driven piston to produce compressed air. An unloader valve is one of the many small but essential parts and components that ensure the effective, efficient operation of a...

www.quincycompressor.com

 

[Joethemechanic]

Be sure to check dirrection of rotation, Most likely marked on the compressor flywheel with an arrow. If it's turning backwards the intercooler pressures will do wacky stuff.

 

[Jraef]

They didn't. They allowed current to flow while the motor was in an overload condition. Guessing. Do a smell test of the motor.

My thoughts exactly. By the heaters not being installed right all along, the motor was allowed to run in an overload condition repeatedly and has now fried the winding insulation.

Here is what they are supposed to look like installed correctly.

 

[Tulsa Electrician]

One item to point out is the trip levers position on the wheel,up. It's important to lift the lever up when installing the heater.

 

[kwired]

Resetting these prior to a cool down can also destroy them. Particularly if done multiple times.

Solder pot just needs to be heated up and allowed to cool properly and it will be fine again. This works on all brands of this style of element if they are reset before cooling down.

 

[kwired]

Screenshot_20230623-070213.png
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One item to point out is the trip levers position on the wheel,up. It's important to lift the lever up when installing the heater
One item to point out is the trip levers position on the wheel,up. It's important to lift the lever up when installing the heater.

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  Screenshot_20230623-070213.png
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I am very familiar with these Square D overloads. Have a facility I have done work in for years and they are all over that place. I didn't know it was possible to install them backwards and actually work. But giving it some thought, if they are backwards I could see them fitting and even letting you "reset" the overload mechanism. But if you do so that ratchet wheel is farther forward than it is in the position it was designed for, this possibly could let the contact mechanism sit closer to the point where it does switch states and it may not be reliable even if the ratchet wheel never turned.

OP says pressing the reset does let it run again. I also imagine having the elements installed backwards changes how heat is distributed compared to what it was designed for, and this could do a couple things. It could cause trip at lower level than intended or it could cause trip at higher level than intended. Lower level would be kind of a nuisance, higher level would allow overloading of the motor. The "heater" of these units is right behind the plate with the number stamped on it. Heat management is critical in selecting the proper units. You use different selection tables based on size of enclosure it is installed in, whether there is other heat producing items within that enclosure, as well as number of thermal units your controller has. Enclosed starters already have the proper table included with them. Open starters will have more than one table and you choose which one you need, or if you have different conditions than they give you tables for the catalog does have all the tables and instructions on how to select the right table. Other manufacturers have similar methods and multiple tables as well.

 

[ptonsparky]

Solder pot just needs to be heated up and allowed to cool properly and it will be fine again. This works on all brands of this style of element if they are reset before cooling down.

I've done this with ABs. Doesn't work consistently. I've had to replace the pots.

 

[Joethemechanic]

One item to point out is the trip levers position on the wheel,up. It's important to lift the lever up when installing the heater.

I have a #3 out on the shelf, and I wanted to get a picture of the heaters installed correctly ,,,,BUT,,,,,,,