Is this Circuit Correct? Safe?

[TimGanz28]

In the attached document is the circuit safe that is the floor door switch and the hopper door switch as it's single channel on hardwire and the other channel is input to the plc to let the HMI know which switch is open.

The switches are Allen Bradley tongue switches red and safety rated but I thought both channels had to go to a safety controller or safety relay?

Also the way it's wired it breaks common power to the output card. Is that a safe design? I normally see a red safety contactor in front of motor loads and these are normal contactors and would not remove power if contactor is welded.

This is OEM equipment and only about 6 years old.

 

[itsmoked]

I'm not following you.. The two switches are in series which is correct. They are interrupting the HOT to all the PLC outputs thereby barring them from controlling anything. It's unclear what AC/2.03 does.

I'm not seeing the problem.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

If it was a medium-integrity system in Europe then it almost certainly would use both channels connected to (e.g.) a Pilz relay or similar. What you've got there is an old-fashioned way of doing it, but whether it meets US code requirements or not I'll defer to others. It doesn't meet the requirements of the higher categories of EN 954 in that format, nor the newer replacements for EN 954.

 

[TimGanz28]

That is what I am trying to determine if it meets current standards as my company is about to buy a new machine just like it from the same OEM and the circuit is the same per their drawings in 2014.

 

[waross]

The only thing that I see is that from the part of the drawing you have shown us;
When the doors close, the controlled equipment may start. This may be OK or may be covered in part of the drawing that we don't see.
On the other hand that may be the preferred mode of operation.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

Tim - the members here are scattered across the globe. If you need help with code problems it helps if we know which code you're working to. I know some of the European stuff reasonably well, but my ANSI / NFPA / FM / CSA knowledge is far weaker. The drawing looks North American in style, but I'm guessing.

 

[controlsdude]

The "risk assessment" that they should do for this style machine would tell you whether single channel or dual channel is required. If your questioning the safety then I would ask for this assessment then go from there. Otherwise your just guessing on what is the safety level required.