Help with 20 HP motor starter in NEMA4 Enclosure

[leitmotif]

Matt,

I don't know if you have read my last post in your recent thread about safety design for your SEW drives project?

http://www.plctalk.net/qanda/showthread.php?t=79059&page=2

It all boils down to the Risk Assessment.

There is no point in you or others trying to design a safety system without knowing the hazards you are safe guarding against.

As TConnolly said, there is not enough information here yet for anyone to decide what is or is not needed.

Having said that, the fact that someone has selected a safety rope switch and emergency stop for this conveyor would suggest there are certain hazards involved. Both of these are emergency stop protection measures. You do not wire these up any old way. In most cases a dual channel safety relay would be used here, but perhaps single channel would do? leaving a second contact free for a PLC or whatever.
What needs to be driven to a safe, or dead stop when an emergency stop is activated? Just the conveyor? Maybe pneumatics or hydraulics as well?
What controls need to be isolated, if any?
You don't just do it as good practice, it has to be required to prevent known hazards. Maybe doing so might create another hazard?

But yet again we are working without a Risk Assessment, so we cannot make these decisions for you.

There most certainly is no "one size fits all" with safety. Every situation is unique and must be assessed individually.

Proceed with caution Matt.G.

Safety assessment - fooey - all we know is conveyer 20HP motor and some kind of mining and outdoors. No where enough info to even think of risk assessment.

Some kind of mining - rock quarry vs coal? Just might make a differance.

Outdoors how far away from nearest person??, remotely operated??,

Conveyer speed? What happens if someone falls in?

Belt screw bucket vibrating??

 

[Bit_Bucket_07]

I need to quote a NEMA 4 enclosure, Motor Controls for a 20HP conveyor feeder.

My problem is this needs a safety cable switch as well. So what am I going to have to do here?
The safety cable switch a Bulkpro SS-2 safety rated pull switch. Can I use that alone to open the control voltage for the starter? Or must it go through a sfety relay?

Your customer specified a safety pullcord switch. Did your customer specify a light curtain or safety relay? No?

The micro switches in your specified pullcord switch are rated for 15 Amps at 120 VAC. The Guardmaster safety relay contacts are rated for 3 Amps. Either switch should handle the inrush current of 2 to 3 amps for a typical NEMA Size 2 starter.

If you feel better about installing a safety relay, then let's just hope that Bubba and Cletus don't decide to tweak the rotary switch one fine day and convert it into a timer. "More complex" isn't always "safer".

 

[TConnolly]

Milmat1,

Ultimately the responsibility for a safe system design falls upon you. The customer has specified that he wants to interface with the control system with a pull cord. He hasn't specified how the pull cord works the controls. You need to do a risk assessment and determine what will be the safest design. An internet bulletin board is a place to solicit options and ideas and learn what options may be available, but don't let the egos and opinions of the board members override your best judgement. Remember that the men and women operating the conveyor have spouses and children at home that depend on them for their livelihood. Don't take shortcuts.

 

[milmat1]

Your customer specified a safety pullcord switch. Did your customer specify a light curtain or safety relay? No?

The micro switches in your specified pullcord switch are rated for 15 Amps at 120 VAC. The Guardmaster safety relay contacts are rated for 3 Amps. Either switch should handle the inrush current of 2 to 3 amps for a typical NEMA Size 2 starter.

If you feel better about installing a safety relay, then let's just hope that Bubba and Cletus don't decide to tweak the rotary switch one fine day and convert it into a timer. "More complex" isn't always "safer".

Actually our wonderful salesman presented it to me. They specified a remote panel (at the conveyor site) With start/stop switches, a safety cable and estop button.
My concern was that as soon as we say ESTOP BUTTON I think safety relay. Because a button itself is just a button.
I rarely ever deal with ACL motors and I really don't like them because of the "fire and forget" type of operation.
In the quote I included an MSR126 single channel safety relay. And I will feel much better knowing it is there if we do this. I would always rather go overkill on such things..

Milmat1,

Ultimately the responsibility for a safe system design falls upon you. The customer has specified that he wants to interface with the control system with a pull cord. He hasn't specified how the pull cord works the controls. You need to do a risk assessment and determine what will be the safest design. An internet bulletin board is a place to solicit options and ideas and learn what options may be available, but don't let the egos and opinions of the board members override your best judgement. Remember that the men and women operating the conveyor have spouses and children at home that depend on them for their livelihood. Don't take shortcuts.

WELL SAID !!
And exactly correct !!
I bet you guys can guess what my next thread is going to be about.....

THANK YOU !!