Traveling Bridge Crane Blown Fuse

[Saturn_Europa]

I thought everyone might get a kick out of this. We had a "service tech" come out for a warranty request about 18 months ago on out bridge crane. If I remember right he came out on a Friday afternoon.




Anyway, the hoist was not working and after verifying there was no short circuit or open windings I replaced all three fuses and the hoist now works. The motor starters are three pole IEC contactors without motor overloads. I am assuming they are using the fuses as OCPD and motor overload. It is in a very inconvenient spot and I hate working on ladders around electrical devices so I am considering installing automatically resetting motor overloads.

Has anyone had seen fuses used as OCPD and motor overloads on a 2hp 480v 3 phase motor? I am assuming there are no built in motor loads in the motor itself.

 

[Tony S]

I thought everyone might get a kick out of this. We had a "service tech" come out for a warranty request about 18 months ago on out bridge crane. If I remember right he came out on a Friday afternoon.


View attachment 14971

Anyway, the hoist was not working and after verifying there was no short circuit or open windings I replaced all three fuses and the hoist now works. The motor starters are three pole IEC contactors without motor overloads. I am assuming they are using the fuses as OCPD and motor overload. It is in a very inconvenient spot and I hate working on ladders around electrical devices so I am considering installing automatically resetting motor overloads.

Has anyone had seen fuses used as OCPD and motor overloads on a 2hp 480v 3 phase motor? I am assuming there are no built in motor loads in the motor itself.

Fuses are often the only protection for crane motors.

Before making any alteration, speak to the crane manufacturers and your insurance company first. Alterations could invalidate your insurance.

 

[iwire]

I am considering installing automatically resetting motor overloads.

I would really hesitate to do that with a machine like a crane.

I agree with Tony, check with the manufacturer.

 

[drcampbell]

It's a good thing Class R (rejection) fuseholders were used to prevent an inappropriately-rated fuse from being installed.

 

[Saturn_Europa]

Fuses are often the only protection for crane motors.

Before making any alteration, speak to the crane manufacturers and your insurance company first. Alterations could invalidate your insurance.

Thanks for the comments guys. I'll call the crane company and ask about adding overloads.

Why are fuses usually the only protection for crane motors?

 

[ActionDave]

Thanks for the comments guys. I'll call the crane company and ask about adding overloads.

Why are fuses usually the only protection for crane motors?

430.33 allows it for intermittent duty motors.

 

[Tony S]

Thanks for the comments guys. I'll call the crane company and ask about adding overloads.

Why are fuses usually the only protection for crane motors?

I don’t know about US crane motors but usually they are designed to handle heavy overloads, way above normally accepted levels.

I don’t know about you, I’d rather the motor keeps going during a lift rather than give up.

 

[GoldDigger]

I don’t know about US crane motors but usually they are designed to handle heavy overloads, way above normally accepted levels.

I don’t know about you, I’d rather the motor keeps going during a lift rather than give up.

And you certainly do not want to lose braking action!

 

[jumper]

It's a good thing Class R (rejection) fuseholders were used to prevent an inappropriately-rated fuse from being installed.

Douglas Adams "a common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools."

 

[Tony S]

Sorry to resurrect this thread, what was the outcome, what did the manufacturers/insurance say?

The same problem has just reared its ugly head this side of the water which is why I’m asking.

 

[Saturn_Europa]

Sorry to resurrect this thread, what was the outcome, what did the manufacturers/insurance say?

The same problem has just reared its ugly head this side of the water which is why I’m asking.

I put the jumper wire back in!

J/k


As far as I know it hasn't blown the fuses since.

Probably an unrelated issue but I asked everyone to leave the disconnect up/ energized to make sure the heaters in the control panel stay on to keep the condensation down.

Also cleaned up the switch contacts on the hand held controller. The up button didn't work that well.

Never called the manufacturer.

Good luck!

 

[Besoeker]

And you certainly do not want to lose braking action!

I have not a lot of experience with cranse/hoists. But the control circuit was always designed to ensure that the brake was automatically engaged if the main contactor was out.
In fact the brake was always on until energised to be disengaged.

 

[GoldDigger]

I have not a lot of experience with cranse/hoists. But the control circuit was always designed to ensure that the brake was automatically engaged if the main contactor was out.
In fact the brake was always on until energised to be disengaged.

It seems possible that with fuses you could lose one or two hot leads, single or zero phasing the motor and still leaving the lead that supplies the brake control hot and commanding the brake to disengage.
I am not aware of anybody using three phase transformers with phase loss protection to power a control circuit. Might be common, I guess?

 

[Besoeker]

It seems possible that with fuses you could lose one or two hot leads, single or zero phasing the motor and still leaving the lead that supplies the brake control hot and commanding the brake to disengage.
I am not aware of anybody using three phase transformers with phase loss protection to power a control circuit. Might be common, I guess?

It's simpler. The main contactor has to be closed for the brake to be released and their coils both come from the same supply. At least that's how I did it.

 

[GoldDigger]

It's simpler. The main contactor has to be closed for the brake to be released and their coils both come from the same supply. At least that's how I did it.

The main contactor has a three phase coil?

 

[Tony S]

Most of the brakes I’ve worked on were DC with a few 3Ph electro/hydraulic thrown in to add interest.

The problem that’s reared its head is similar to the OP, what I’m going to suggest is overloads operated by CT’s. Fortunately the manufacturers are old friends so I’ll call them tomorrow.

 

[Besoeker]

The main contactor has a three phase coil?

Um, no.

 

[GoldDigger]

Um, no.

So one fuse opening could cause the motor to stop working without opening the contactor and automatically applying the brake, right?

mobile

 

[Besoeker]

So one fuse opening could cause the motor to stop working without opening the contactor and automatically applying the brake, right?

mobile

That's what phase failure relays are for.

Many of the cranes we did had six pulse variable speed DC drives.
The firing circuit for the SCRs was designed with a phase loss circuit on it.
The semiconductor fuses were fitted with trip indicators which operated microswitches.

 

[Jraef]

So one fuse opening could cause the motor to stop working without opening the contactor and automatically applying the brake, right?

mobile

No. How it's typically done is that the two phases feeding the brake rectifier are the same two phases feeding the control circuit. So if one fuse blows, the control circuit drops out and the brake coil drops out, no matter what.