Wiring a safety Warning alarm bell for a crane.

[Logan2112]

Hello, Okay, so, we have a 20 ton Overhead Bridge crane that has a Bridge, Trolley, Hoist. I am installing a remote control pendant but I will also need to add a warning light and an audible warning device when the bridge is traveling. I am not too familiar with relays but am wanting to get it in my skill set. I need the bell to only go off when you are either traveling (FWD) or (REV) In order to do that I am sure I need at least one relay in-line with the contactor (motor starter). For anyone unfamiliar, if I don't have a way to close the circuit from the direction not being used, it will back feed and most likely blow a fuse or an overload. If I had reversing contactors with a physical interlock, I could make that work, but I do not. This is a very old crane. Using Nema 1 -- 3 phase starters. The coil is 120v
Anyone who can draw me a schematic gets a cookie. I have looked around other websites and can't find a forum with Overhead Crane installation or maintenance experience. Thank you.... Logan

 

[GoldDigger]

I am guessing that you want to drive it directly from the output of the Contactor rather than from the control wiring side?
You can drive two relays, one from each travel direction, and parallel their output contacts to control the alarm circuit.
Do you have separate FWD and REV starters or one starter and a reversing contactor? If the latter, just drive the relay from the starter and ignore whether it is set to FWD or REV.

 

[petersonra]

Is there a light that comes on when the bridge is moving forward and reverse? If so, wire a relay coil across each light and use the relay contacts to turn on the bell.

 

[Logan2112]

I am guessing that you want to drive it directly from the output of the Contactor rather than from the control wiring side?
You can drive two relays, one from each travel direction, and parallel their output contacts to control the alarm circuit.
Do you have separate FWD and REV starters or one starter and a reversing contactor? If the latter, just drive the relay from the starter and ignore whether it is set to FWD or REV.

It is set up with a FWD and a REV contactor. I don't have any relays to look at at the moment so I don't remember how they get wired I just remember that both contactors go through each relay only the output is either NO or NC depending on which button is pushed. I think I see what you are saying. I can use one contactor per relay and use the 120 volt from one of the phases to drive the coil in the relay. and wire the outputs on the normally open sides so that one will always be open preventing back feed?.. is that about right?

 

[Logan2112]

Is there a light that comes on when the bridge is moving forward and reverse? If so, wire a relay coil across each light and use the relay contacts to turn on the bell.

The light has to come on when you turn on the remote and stay on until you turn off the remote no matter what button you push.

 

[LarryFine]

If there is a single contactor or something else that has power in both directions, wire a relay to trigger the warning devices.

If there are two separate contactors, wire a relay to each one. Parallel NO contacts from each one, so either will trigger them.

 

[Logan2112]

If there is a single contactor or something else that has power in both directions, wire a relay to trigger the warning devices.

If there are two separate contactors, wire a relay to each one. Parallel NO contacts from each one, so either will trigger them.

Yes sir.. I was making it more difficult than it needed to be. lol thanks for the input. I honestly was trying to wire in a fail safe if someone was to accidentally press both buttons at the same time.

 

[LarryFine]

I honestly was trying to wire in a fail safe if someone was to accidentally press both buttons at the same time.

That interlock action should be part of the existing circuitry.

 

[retirede]

Yes sir.. I was making it more difficult than it needed to be. lol thanks for the input. I honestly was trying to wire in a fail safe if someone was to accidentally press both buttons at the same time.

It possible that additional aux contacts can be added to the existing contactors and no relays would be required.

 

[hillbilly1]

Yes sir.. I was making it more difficult than it needed to be. lol thanks for the input. I honestly was trying to wire in a fail safe if someone was to accidentally press both buttons at the same time.

If it is a reversing contactor, it will usually have mechanical and electrical interlocks built in, so whichever button is pushed first, it will only go that way until released.

 

[Logan2112]

If it is a reversing contactor, it will usually have mechanical and electrical interlocks built in, so whichever button is pushed first, it will only go that way until released.

Unfortunately, these are motor starters and not connected so no mechanical interlock. I will have to go inspect to see if there is an electrical interlock.

 

[Logan2112]

The relays came in. After looking over them, I was wondering if I could just use one to do the trick. If I wire the forward contactor through the relay using the (Normally Closed) and then wire the Reverse using a (Normally Open) and jump it to (A2) to power it, wouldn't that work the same way?

That interlock action should be part of the existing circuitry.

 

[retirede]

Can you post a sketch of your idea?

 

[Logan2112]

Can you post a sketch of your idea?

 

[retirede]

It looks like one wire from the bell should should go to both sets of contacts, the other to the common line?

 

[Logan2112]

It looks like one wire from the bell should should go to both sets of contacts, the other to the common line?

I didn't draw in the Neutral (common) wire, but it goes to the pendant, the relay and the bell.

 

[Russs57]

"It possible that additional aux contacts can be added to the existing contactors and no relays would be required."

And that would also allow him to add an electrical interlock on the starters if there isn't one now.

 

[Logan2112]

"It possible that additional aux contacts can be added to the existing contactors and no relays would be required."

And that would also allow him to add an electrical interlock on the starters if there isn't one now.

Its a very old crane. The motor starters are Square D Nema 1 type. Not the Schneider type. I could install aux contactors, yes, but I could also install one relay to do the same job. It's all a matter of cost in the company's eyes and space. I personally like the AUX con. route, then there is also the mounting. I haven't had a chance to go up and physically look at it in some time. This is a very busy season and it has been in use, since I haven't installed the remote yet, there's no need for the bell. Anyway, I'm very grateful for all the input here. It has really been helpful.

 

[Russs57]

I don't think I have ever seen a Square D NEMA starter that didn't have a "4th pole" auxiliary contact. Look at the top left all the way in the back. Easy to overlook.

 

[paulengr]

I don't think I have ever seen a Square D NEMA starter that didn't have a "4th pole" auxiliary contact. Look at the top left all the way in the back. Easy to overlook.

Aux contacts are not extra poles. The current capacity is lousy. They are strictly for controls. A true 4 pole contactor is used to break neutrals such as in automatic transfer switches. Five pole contactors are used in single coil two speed starters. Six or more contacts are common in lighting contactors where you are switching banks of lighting circuits, or operating a separate motor like an auxiliary oil circulation pump. But for controls aux contacts are fine. Agreed that the layout on older SqD contactors can be a little obscure. Look up the “Schneider Wiring Diagrams Book”. It is nicely illustrated in there along with a ton of sample starter wiring schemes.

Hands down this is a huge hint to OP. You need this book. Download and study it. You will quickly come to understand just about every starter wiring scheme and motor control circuit in existence.