# Crane Hoist overloads



## Wirenuting (Sep 12, 2010)

There are exceptions to the O/L requirement. 
One example is a motor that is limited in its travel. 
The example given is an elevator. 

Can a hoist lift father then all the way?
Can it lover further then all the way?

If the answer is no then IMO it is covered by the exception.

edit: a crane is designed under engineering supervision. They can design anything they want. 
It is up to the user to not alter the design.


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## mutabi (Jun 2, 2009)

I understand that "engineers" design the system....It would be nice to know why regular overloads were not used, and why the thermals only work when the hoist is travelling up....curious


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## Wirenuting (Sep 12, 2010)

mutabi said:


> I understand that "engineers" design the system....It would be nice to know why regular overloads were not used, and why the thermals only work when the hoist is travelling up....curious


The thermals only work while lifting because this is the only time a limited duty motor might be expected to become over loaded. 
Since you've already lifted a load fully you have not exceeded the cranes capacity. While lowering it you no longer have the overload condition to worry about. 

Besides, IMO it's better to over tax the motor on the lower cycle then have an o/l trip and leave a load suspended. 

Keep in mind that I haven't worked on a crane in 25 years. I'm just trying to pull cobwebs off what I remember.


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## varmit (Apr 19, 2009)

While I don't agree with the practice, most cranes have no overloads on the starters. The theory is that the duty cycle is so short, that the O/L will not have time to react. There is an exception permitting the motor mounted temperature sensor, but it would seem to me that this would react more slowly than a standard, class 10 O/L.

As for the O/L not being in the circuit on a "down" function, this is a safety consideration to allow a load to be lowered instead of being stuck in a hazardous position.

I have worked on a lot of cranes and I hate the hack ways that they are designed. I have seen "Class I, div. 2 cranes with control pendants, from the factory, with standard 22 mm pushbuttons in a plastic enclosure with a 120 volt control circuit. I called the OEM and complained. I was told " That there was no problem with this." I quit doing there work due to liability concerns..


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## saurabh jain (Feb 28, 2013)

I think , earlier the Demag design this type of proection system in hoist oeration. But they use signle phase preventor in incoming supply.


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## sparkywannabee (Jan 29, 2013)

"I have worked on a lot of cranes and I hate the hack ways that they are designed. I have seen "Class I, div. 2 cranes with control pendants, from the factory, with standard 22 mm pushbuttons in a plastic enclosure with a 120 volt control circuit. I called the OEM and complained. I was told " That there was no problem with this." I quit doing there work due to liability concerns"

Why is that unsafe.


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## JRaef (Mar 23, 2009)

The NEC allows for the motor to have "other means" of thermal overload protection. Embedded motor winding thermal detectors is actually a BETTER method than a standard external TOL relay, it's just more expensive for the motor suppliers. In the case of specialty motorized equipment like cranes, they are likely more inclined to put it in the motor, because then it doesn't leave the proper TOL setting or heater element selection up to the skill of the installer. Remember, many hoists are installed by crane technicians, not trained electricians.


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## varmit (Apr 19, 2009)

sparkywannabee said:


> "I have worked on a lot of cranes and I hate the hack ways that they are designed. I have seen "Class I, div. 2 cranes with control pendants, from the factory, with standard 22 mm pushbuttons in a plastic enclosure with a 120 volt control circuit. I called the OEM and complained. I was told " That there was no problem with this." I quit doing there work due to liability concerns"
> 
> Why is that unsafe.


Please read NEC article 501. Think about it: You have a push button that will arc when used. Install this in an area that can possibly have an explosive atmosphere. THIS IS A REALLY BAD IDEA!


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## JRaef (Mar 23, 2009)

varmit said:


> Please read NEC article 501. Think about it: You have a push button that will arc when used. Install this in an area that can possibly have an explosive atmosphere. THIS IS A REALLY BAD IDEA!


A lot of PB mfrs offer Cl1 Div2 contact block assemblies for their buttons. The contacts are in hermetically sealed tubes, called "reed switches" operated by magnets so that there is no arc or spark to to atmosphere.

http://www.ab.com/industrialcontrols/products/push_buttons/hazardous_location/pdf/hazard.pdf


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## varmit (Apr 19, 2009)

JRaef said:


> A lot of PB mfrs offer Cl1 Div2 contact block assemblies for their buttons. The contacts are in hermetically sealed tubes, called "reed switches" operated by magnets so that there is no arc or spark to to atmosphere.
> 
> http://www.ab.com/industrialcontrols/products/push_buttons/hazardous_location/pdf/hazard.pdf


These were the standard contact blocks.


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