Overloads needed for jib crane?

[AutoXer]

We're installing a rotating jib crane. On the crane is a 3 ton hoist that utilizes a 2hp, 3ph, 230VAC motor. The hoist is on a motorized trolly that has a 1/4hp, 3ph, 230VAC motor. The crane uses an pendant control with 4 buttons(up, down, left and right). The crane was manufactured by Coffing. The crane was shipped to us as an "assemble on site" package. It has only one place to supply power and one nameplate.

Does the feed to this crane need motor overloads? I can't see any overload devices on the equipment or in the manufacturers prints. Am I being too careful? Should the crane be considered "industrial equipment" that has to meet NFPA 79 at it's place of origin?

Here's what I'm thinking I need: disconnect, short circuit and overcurrent protection for the branch circuit that will feed the crane. Size the circuit slightly larger than that of the required nameplate current data. Am I right? ...or do I need overloads.

 

[itsmoked]

Does it have a VFD built in somewhere?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

Yes, I'd venture to say that the "Overloads" are there, but maybe not in a form you are used to looking for. If there is a VFD, the OL function is typically provided by that VFD. Same is usually true if it is a soft starter.

But to speak to your question directly, no you cannot just put in an OL relay to feed a circuit like this. You will need separate OL relays for each motor. No exception.

 

[AutoXer]

There is no VFD. Only reversing contactors that are mounted on the hoist itself.

It's one of these:

http://www.coffinghoists.com/ecpage.html

Model ECMT-6010-15

You really think I have to put seperate(hoist/trolley) external overloads on that thing?

 

[bklauba]

I cannot think of a situation where a 3 phase motor powered DOL (Direct Off Line) does not deserve overload protection. Surely the cost of a few overload relays (~ $40 - 70 each) preventing toasting a motor is a good investment. Each motor would need its own O/L. Neither fuses or CB's protect motors effectively, since their current and time delay charactersitics simulate cable over-current, not motor over-current conditions. That job is best done by an overload relay. Check out the solid state overload relays; several brands are available, ABB, Sprecher & Schuh, A-B.

BK

 

[dpc]

If this is in the US, the individual overloads are a legal requirement. Any possibility there is a thermistor or temp sw in the motors?

 

[itsmoked]

Most people do not use overloads on these things as they are typically under 1HP and only run for seconds at a time, (~1% duty cycles), and only when somone's finger is on the button. Either the motor runs or someone stops and deals with it. It cannot be subtly overloaded and run until it melts down or turns into a smoking fireball.

The factory will not say, "you don't need overloads", but I've never seen them used on these. Logically you don't need them, code wise, I believe you do unless sub 1hp motors don't, I don't recall off-hand.

Now that I look back and see you have a 2HP unit I would probably include overload protection.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[BJC]

One option is to rewire the overload relay so that tow contacts trip the motor and the third triggers an alarm circuit. Use a heater one or two sizes smaller in the alarm circuit.
I would do this in a hoist because you don't want the motor to cut out with a load hanging on the jib.
The more modern option would be to use a solid state OL relay, The last one I used had alarm contacts but I can't remember if they could be set at say 95% of full load.

 

[AutoXer]

"AutoXer(name changed for reprinting purposes),

Per our interpretation of the specifications we are not required to install thermal protection on the hoist, this is optional equipment that has to be specified by the users depending upon local codes in the area of the hoist installation and use. If you need such devices we can provide them, with an additional charge. If you have any questions please let me know.


Joe Schmoe(name changed for reprinting purposes)
Applications Engineer
Coffing Hoists
PH# 800-694-****
Fax# 800-374-****"

 

[jraef]

I think that fits with Keith's (itsmoked) assessment. They sell them without OLs, then if you get nailed on inspection, they tell you they could have put them in if you asked. Otherwise, it appears they are assuming the duty cycle is so limited that they don't need them.

Here is the wiring diagram; no OL shown.

 

[roydm]

This post got me thinking, safety wise, is it better to risk overloading the hoist or have it trip with a suspended load. Quite often the hoist may be non-accessible e.g. over a loading area. Perhaps an isolation switch with overload in the supply would be better.
Another motor application that doesn't have overloads is a fire water pump.
Roy

 

[eeinpa]

I'm no expect on hoists, but we do have a lot of them in our shop. Some of them do incorporate a thermal switch in the motor windings. I think that is the manufacturers' "weasel-way" of providing overload protection.

While it may not be technically "right", there are millions of hoists being used this way every day. *I* wouldn't sweat it, but I have many more serious legacy problems to deal with.

IMHO, if you get nailed by an inspector on this fine a point, you are damn lucky to have such a clean facility!

 

[davidbeach]

Motors with built in thermal overload protection are not required by the NEC to have external overload protection.

 

[AutoXer]

Otherwise, it appears they are assuming the duty cycle is so limited that they don't need them.

Is duty cycle a determining factor for need? Is this in the NEC?

 

[jraef]

Is duty cycle a determining factor for need? Is this in the NEC?

No, and I'm not saying I agree with that philosophy, I was just trying to second guess someone else's.

I also would think that if the motor had built-in thermal protection, it would be shown on the wiring diagram or at least stated in the manual. But then again, that may be a ploy to get people to call their service department and incur fees.