Help with determine safety circuit on machine...

[JoseM]

Guys,

I'm trying to determine what components I need to purchase to do the safety monitoring for the E-stops on a machine that I'm working to automate.

I need good assistance from you guys since I've never done this but I'm very excited for the challenge.

When an E-stop is pressed what exactly is suppose to happen? Do the 120V ac that is energizing the coils for the motor contact needs to dropped? Could that be a potential hazard if we are talking about an elevator that is half way up and all of the sudden looses power?

Do I need to have a "Safety Relay" for every motor I have on this machine? Do I need "Safety Relays" and "Safety Contacts"? any other thing that you guys think I need please let me know.

 

[OkiePC]

Elevator of what? I am sure that there are explicit regulations for any people mover.And What does the vertical transfer of work? Screw? Hydraulic? Chain? Cables?

Anything you do needs to start with a risk assessment. Search the forum for safety risk assessment and you are sure to get many links to give you guidelines for performing a risk analysis first.

If you find the existing circuit is adequate, and you only need to monitor it for display purposes, then post the specifics of the hardware already in use. If you intend for the monitoring contacts to affect the operation of the machine, then even more care is required...you can make a machine behave safe with a welded power contactor if you mimick safety with monitoring contacts but you may be allowed to that if you take extra steps like testing procedures. All of this is also heavily dependent on country and local codes where the machine will operate.

Whether you need to interrupt motor power with more than one contactor also depends on the risk.

In my experience (mostly with older rules) any risk that can lacerate skin or break bones calls for safety devices rated to category 4 or 3 which means, yes, real safety switches, relays, and contactors as well as specific circuit designs emphasizing manual reset and contactor monitoring (can't be reset if any main power pole sticks).

For suspended loads, failsafe mechanical braking is almost always a necessity but if the lift mechanism is a screw or hydraulic cylinder it's different. If you yank the power the heavy thingy needs to freeze with a legally regulated "drop" distance limit, if people can get under it without removing guards.

 

[Clay B.]

Risk assement

As Okie said any safety design start with a Risk Assessment.

Figure out how the machine device whatever can do damage. That decides what safety device is required. It will vary depending on where your machine is located.

Here is a good place to find info on Risk Assessment>

http://search.usa.gov/search?affiliate=usdoloshapublicwebsite&query=risk+assessment+form

This is the place to find OSHA Risk Assessment forms. In most locals this is a good place to start. Some go above this level but in most locals don't. Once you get this doen you are ready to figure out what devices you need.

 

[OkiePC]

Thanks, Clay. I need to read the latest stuff. I drilled into this nice overview from your link.
http://www.osha.gov/Publications/OSHA3170/3170-02R-2007-English.html#Recognizing4