Importance of Phase Rotation on Chain Hoists

dvsDave

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Explain the importance of correct phase rotation when powering 3 phase chain motors.

As usual, please let students answer for the first week, then everyone else can chime in.
 
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RonHebbard

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(Well, since it's past a week . . .) Could it be ABC (or equal) = up, ACB (or equal) = down?
OK. Anyone with knowledge of your typical 3 phase motors knows reversing any two phases causes them to rotate in the opposite direction.
The REAL query is: Why is this of paramount importance in the operation of the great majority of 3 phase chain hoists??
Toodleoo!
Ron Hebbard
 

RonHebbard

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So that after plugging it in, somebody marks the "UP" and "DOWN" buttons properly? And then makes sure to check it every time it's reconnected?
Nothing wrong with that but what's the paramount reason why it matters, c'mon lads n' lasses, you can parse this??
Toodleoo!
Ron Hebbard
 

YesItWillWork

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My suspicion would be the limit switches. If you hit the upper limit you want the hoist to disable going up but still want to be able to go down.
If the phase rotation is backwards so that up is down and down is up then those limit switches won't engage and stop the travel, but it would stop you when you try to come back down?
 

RonHebbard

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My suspicion would be the limit switches. If you hit the upper limit you want the hoist to disable going up but still want to be able to go down.
If the phase rotation is backwards so that up is down and down is up then those limit switches won't engage and stop the travel, but it would stop you when you try to come back down?
Calling @dvsDave and / or @egilson1 and / or @What Rigger? [B] @derekleffew [/B] [B] @RonaldBeal [/B] and /or @ all other REAL riggers; I suspect we have a WINNER personally, I'dve settled for the chain hoists would've ignored their limits, the limits you were counting / depending upon for too, too, many reasons and would be more than STARTLED when the hoist, or all the hoists in your rig, were missing their limits when they'd been operating FLAWLESSLY during your out only a few sleep deprived hours earlier.
Give the lad from down under a PRIZE!
Toodleoo!
Ron Hebbard
 
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egilson1

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My suspicion would be the limit switches. If you hit the upper limit you want the hoist to disable going up but still want to be able to go down.
If the phase rotation is backwards so that up is down and down is up then those limit switches won't engage and stop the travel, but it would stop you when you try to come back down?
Congratulations!
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A few notes:
1. Technically the entire assembly is called a hoist. The electrical widget that receives the three phase power and spins is called a motor.
2. If you need to, use the search function here on controlbooth to look up what three phase power is and how it works so the next statements make sense. The motor in the hoist is the exact opposite of the generator. When Phase A is at peak, the rotar (shaft) spins to align with the phase A coil. Then when phase B is at peak it spins to allign with phase B. And then phase C. Around and around we go. this is of course over simplafied as there are other components between the source of powrt and the motor, like contactors.
3. So if the generator is outputting ABC and the motor receives ABC, the hoist will run as intended. BUT if the motor gets anything but ABC (ACB for instance) then it is going to spin in the opposite direction than was intended.
4. There are two issues with this. Obviously when running reverse phase you can suck the chain out of the hoist, or run the hook attachment into the chain guide. Both are bad. But as mentioned the limit switches won't work properly, as when you are pressing the UP button, the hoist is moving down, and the limit switch for down will be activated at some point. But you're pressing UP. So the hoist keeps on running. Depending on the limit switch design, you can very quickly damage the switch by crushing parts. Then when the phase issue is corrected your down limit won't work because its broken, and you'll run the chain out of your not paying attention.

The moral of the story is to ALWAYS check the phase of your hoists. Even if your working in your own venue where you "KNOW" the power. That transformer that blew last week? what if Mr./Ms./Mrs. utility worker changed the phase order when they installed the new transformer? Or maybe it was the electrician who was installing a few new circuits for FOH. And we all know that every vendor has had their hoists wired the exact same way right (sarcasm alert!)?

As I mentioned this is a "CliffsNotes" version written a half hour before I leave for a trip.
 
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JonCarter

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OK, guys, educate me. Don't "limit switches" activate and disconnect the motor when specific physical events occur? E.g., when either end of the chain reaches the point where it's about to run out of the mechanism? Why does the direction of motion when the event occurs matter whether it's going up or down?
 

Mac Hosehead

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As I understand it, there are two limit switches. One for DOWN and one for UP. The UP limit switch will interrupt the UP control line when activated and the DOWN switch will interrupt the DOWN control line. If the motor is wired wrong you will use the DOWN control line to go up and when the UP switch is activated at the limit you will keep going.

Other motorized gear used onstage will usually have limit switches. Bad things will happen if they don't work correctly.
 
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RonHebbard

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OK, guys, educate me. Don't "limit switches" activate and disconnect the motor when specific physical events occur? E.g., when either end of the chain reaches the point where it's about to run out of the mechanism? Why does the direction of motion when the event occurs matter whether it's going up or down?
@JonCarter I'll try and explain it, others will likely post wile I'm doing my slow-typing best. I'll attempt to oversimplify and use a more familiar electric garage door opener for illustration purposes, the same situation applies to (within) electric chain hoists.

If your typical (3 phase) electric door opener is wired and phased correctly, you momentarily actuate the Up button and the door begins travelling up.
The door continues upwards until its upper end of travel (EOT) is reached. The upper EOT intentionally DOES NOT inhibit all power, if it did you wouldn't be able to close the door; instead the upper travel EOT opens the holding circuit for the up bound travel and your door stops.

Similarly, when you momentarily actuate the Down button the door begins closing and stops when its downward EOT switch is reached (actuated).

The important point is: The upper EOT switch is wired in the upper EOT circuit ONLY.
Similarly the downward EOT switch is wired in the downward EOT circuit ONLY.
WHEN THE PHASES ARE INCORRECTLY CONNECTED:
You actuate your DOWN switch, your door travels UP, when it reaches its UP EOT it keeps right on running BECAUSE the up EOT is connected to interrupt the upward power. As far as your (Dumb) door knows it doesn't know its moving Up, it (thinks) it's already running DOWN so why should it bother stopping when its Up EOT is reached?

The same situation applies when you actuate your UP switch and your door travels DOWN.

A few differences between typical electrically actuated door openers and electrically powered chain hoists:

Door openers often utilize momentary push buttons and associated electromagnetically actuated contactors with associated holding contacts.
Electrically powered chain motors often utilize momentarily actuated push buttons sans holding circuits and cease motion immediately upon release of their actuating buttons.
Door openers are often fitted with switches to cease downward motion upon hitting an object (your car, child's bike, your baby's carriage, any object not expected to be impeding its downward travel prior to reaching your driveway).
Some STOP; others STOP and immediately REVERSE.

Many / most electrically operated door openers are equipped with light beams and photo cells (or proximity sensors) to interrupt motion if / when the light beam is interrupted, regardless of direction: You could be under the light beam or you could be standing clear with one arm extended above the light beam, in either situation, whether the door is going to hit you moving down, or maim you on its way up, interrupting the light beam normally ceases all travel.
I'll click Post and see how many others have posted while I've been pecking away.
Toodleoo!
Ron Hebbard
 

DrewE

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What Ron says is true (well, at least to the extent of my knowledge).

Just to be perfectly clear, the basic reason why the limit switches do not interrupt both controls is that you'd still like to be able to move the hoist or door or whatever in the opposite direction of travel once you've reached maximum travel in a given direction. Once the door is all the way open, it's handy to be able to close it under power control; but if the limit switch affected both direction controls, you could only move it manually (until clear of the limit switch). It's rather obvious once you think it through all the way, but not necessarily before then.
 

RonHebbard

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What Ron says is true (well, at least to the extent of my knowledge).

Just to be perfectly clear, the basic reason why the limit switches do not interrupt both controls is that you'd still like to be able to move the hoist or door or whatever in the opposite direction of travel once you've reached maximum travel in a given direction. Once the door is all the way open, it's handy to be able to close it under power control; but if the limit switch affected both direction controls, you could only move it manually (until clear of the limit switch). It's rather obvious once you think it through all the way, but not necessarily before then.
@DrewE Excerpted from my Post #15: "The upper EOT intentionally DOES NOT inhibit all power, if it did you wouldn't be able to close the door "
Toodleoo!
Ron Hebbard
 
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Ancient Engineer

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Every single time I have rented gear that was "checked" before it went out, I check all motor cables with a meter.

More than half of the time there are issues.

Mostly NC situations. But there are still some "special" phasing things too.

I suspect the end got pulled off somehow and when the "technician" reapplied the connector they made their best guesses and kept on going.

I check my own cables periodically, just in case somebody has decided to "help" me with a spot repair.

Ten minutes with a meter will eliminate, or prove out a major source of motor mayhem... IMHO
 

BillConnerFASTC

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Most motorized lifts and hoists I specify rely on encoder for limits. They all have normal end of travel and ultimate end of travel hard struck switches. If any of those are struck, something went wrong, so all travel is stopped and it requires some level of intervention to drive back into normal travel range and reset all. Of course that's not chain motors, without all the built in redundancy and safety of theatrical hosts.
 
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