Guard Switches

[daxtojeiro]

Hi all, can someone tell me if I need 1 or 2 guard switches per guard on machines or does it depend on a risk assesment? Is there anywhere someone can point me to find out this info for sure as Ive only added 1 switch per guard on a machine Ive just finished and I need to ensure this is Ok many thanks Phil

[ianbuckley]

It depends upon what the guards are protecting (thus the safety rating). To meet traditional category 3 or 4, you will need redundant contacts. For category 1 or 2, you can use other methods.

[BobLfoot]

I second Ian on it depends on what youa re guarding. Robots have their own spec in ANSI which OSHA references, as do Presses. The best way to protect yourself is to have a full risk assesment done and make sure your guard is adequate to the risks.

[daxtojeiro]

Hi all, thanks for the replies. I did a PILZ safety course last year but can't recall if they ever mentioned needing 2 switches. We have risk assessed it and decided the catagory, but I thought that was for the safety relay selection. The switches are the correct standard (Allen Bradley Guard Master) but Im just not sure when 2 are needed Cheers Phil

[Veganic]

What category have you decided upon?

[panic mode]

it's because some of the sensors are Cat3/Cat4 rated (with proper controller). you need to do risk assessment, determine category and then start picking hardware.

[daxtojeiro]

Hi all, we have done a risk assesment and decided on cat2. So a Cat 3 and above would need 2 switches? Phil

[paulengr]

It depends on what you are referring to as a "category" rating....different codes use different definitions. And you don't "decide" on a rating. The risk assessment DEFINES the rating. To make it easy, the term to look for is "control redundant". If control redundancy is required, then you need the redundancy. Even then, depending on the design of the sensor it may have that level of redundancy internally (light curtains are known for this).