Safety contactors in front of VFDs

[Ken Moore]

Is this a machine safety or process safety application. In most cases, the VFD, STO is not rated correctly for use in process safety. In machine safety, the device is always in demand, and the safety rating is based upon mean time between failures, and that it fails safe. In process safety the safety rating is based upon probability of failure on demand, or how likely is it to work, when I needed it.

Some large chemical companies and refineries have been doing safety systems before there was SIL ratings. I worked for one, and we used "industrial" rated relays and contactors for safety. We had our own in house approved devices, derived from historical service. This may be one of those legacy type situations.

 

[Tinine]

Right, but he said that the customer has specified contactors that aren't safety rated, so there's no guarantee that the NC aux contacts are following the main contacts.

Greetings Joseph.
Fond memories of Harrisonburg VA. I supplied a lot of machinery to the Tenneco-Walker plant there.
Love the place.


Rgds,


Craig

 

[joseph_e2]

Greetings Joseph.
Fond memories of Harrisonburg VA. I supplied a lot of machinery to the Tenneco-Walker plant there.
Love the place.


Rgds,


Craig

Small world! What all did you supply? That's where I'm working now.

 

[Tinine]

Adaptive Motion CNC Tube Benders?


I was the founder/owner of the company.


We also did the electric bend-head conversion on one of the Pipelines (got into trouble over that )


Started dealing with that plant back in 1984 when Randy Meadows was my contact.


Rgds,


Craig