Safety Category for Attached Circuit

dYoast

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A gentleman I work with has come up with the attached circuit for safety doors. He is arguing that it is safety category 4, and I am in disagreement. I think at best it would be safety category 3.

Please give an opinion one way or another and your reasons for your opinion.

One of us is wrong and must be convinced.

Thanks in Advance.
 
hummm if i had to take a guess i would have to aggree with you and say that cat 3 is the best this circuit can do- - -ive always been told that for a circuit to be Cat 4 every E-stop button or switch must be wired into its own safty relay - that once you start placeing Safty devices in SERIES on the input circuit - you lose Cat 4 rateing - at least thats how it was explained to me by the PILZ people when i was working on my last project.

i always prefer to err on the side of caution
 
Are there two doors with a switch each or one door with two switches?
What is function of the 31/32 contact in the switch. Is it monitoring the solenoid?
Ask yourself this question: Will the system detect if the 21/22 contact welds in one of the two switches?
 
AJZ said:
Are there two doors with a switch each or one door with two switches?
What is function of the 31/32 contact in the switch. Is it monitoring the solenoid?
Ask yourself this question: Will the system detect if the 21/22 contact welds in one of the two switches?
Click to expand...

There are two doors with a switch each.
31/32 is monitoring the solenoid.
No detection for a welded 21/22, but what does that imply?
 
Ultimately, the entire system might not even be cat 3. The Estop relays are connected to an air cylinder (valve?) and the inhibit input of a motor controller. Those elements will define how safe the system really is.
 
I would say it is Cateqory 1.

Is the switch diagram correct? Does it really have two NC switching contacts?
 
Alaric said:
Ultimately, the entire system might not even be cat 3. The Estop relays are connected to an air cylinder (valve?) and the inhibit input of a motor controller. Those elements will define how safe the system really is.
Click to expand...

They control the main air valve for the machine.
Can you explain further?

AJZ said:
I would say it is Cateqory 1.

Is the switch diagram correct? Does it really have two NC switching contacts?
Click to expand...

Why do you rate it Category 1?

Yes, there are two NC switching contacts for the key.
 
I see no hazard evaluation of the doors. What is their risk potential for hurting someone?

Getting a little simplistic maybe - what if these are for a linen closet or the bathroom door in your house?

As an aside - I just started evaluation of relocating from Seattle to Aberdeen. Need to evaluate risk of flooding in low land areas. Once I have an idea of the risk I guess I can assign a Cat number to it??
Dan Bentler
 
leitmotif said:
I see no hazard evaluation of the doors. What is their risk potential for hurting someone?

Getting a little simplistic maybe - what if these are for a linen closet or the bathroom door in your house?
Dan Bentler
Click to expand...

The risk potential started with the machine designer. They wanted to build a machine that was Category 3 and didn't think the Banner switches were capable of that level. My company wanted to continue to use the Banner switches.


kiwi sparky said:
Even If wiring and attached devices were wired to category 4 (which they are not) The safety monitoring device ES-FA-6G is only Cat2.
http://www.sensor.co.kr/PDS/E-Stop%20Decision%20Tree.pdf Page 2
Click to expand...

What if the Banner ES-FA-9AA were used instead in a single channel configuration? My guess is that I would still have the same result.


Can somebody quote a standard that absolutely states you have to be redundant for a certain category?
 

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