Safety interlock switch without a relay


Thread Starter


Can I use a safety rated interlock switch in series with a VFD/motor to isolate power without a relay and meet CE safety standards? The switch contacts are rated for the motor amperage (10A contacts ithe 2.06FLA. I need this to be OK for US and European markets (CE).

Application is commercial food prep equipment. I have one severe pinch point that I want to insure that has no power to it for cleaning. Currently the cleaner has to remove two covers to access the pinch point. One is labeled as "hazzardous voltage" and one is label "pinch point". Still stupid people are getting fingers cut off because they do not unplug the equipment.


Mark R. Hron

I need a lot more info about your machine and its use. The simple answer is yes, but it may not be the right answer.

1) Does this machine have a lockout tag-out procedure written and is always used before entering the pinch zone? Are all workers trained on it?
if yes, yes, then use any kind of switch that is right for the application or even use no switch.
if no:

2) Is this switch intended to protect workers instead of lockout tag-out? If the answer to that is yes, and the severity of injury is high, then you must have a monitored safety circuit (install the safety relay that monitors the contacts of the switch intended to make the machine safe).

There are no stupid people causing accidents. There are only unsafe environments that must be made safe by properly enforced policies and procedures and or equipment designs.

My thought process is this: Only use as much technology as you need, no more.

So in this case, if I can make it easy and preferable to do the lockout, the enforced safety policy would be my choice. If not, then go double redundant with a safety rated relay for monitoring.

- Mark R. Hron
NO. the switch needs to be monitored on reset you really need to read the machine safety directive, En-954, and a few of the others.

My recommendation would be to make it a category 4 circuit, the cost of adding a safety relay is cheap $400 or so, such as a pilz PMOZ8P, would be pretty close to the requirements for your application.

Worse case is you would have to add 2 contactors if the PILZ does not meet the power requirements of the drive.
There is no easy answer for you as this becomes an exercise that sometimes is very lengthy and exhaustive in nature.

First you must do a "risk assessment" of your machine. Both the US and EC have guidelines for performing this task. The outcome of the risk assessment establishes a risk category that in turn defines the level of ciruit performance required of your application. If the category turns out to be of the "simple" or "single channel" level then your safety switch would work. However, if the category turns out to be of the "control reliable" level then you must use safety relay with your safety switch for automatic monitoring of the system.

Michael Griffin

A safety relay is normally used to monitor the safety interlock switch(es) to ensure it hasn't malfunctioned, that there are no shorts in the wiring, etc. For many applications involving serious hazards (e.g. those which can cause permanent injury), you may need redundant switches. The safety relay would monitor both switches simultaneously to ensure they switch together (much like a two hand control system). If one switch sticks or fails, then the safety relay will detect the discrepancy and shut down. If you look at microwave ovens, you will notice they have redundant interlock switches on the door.