Control relays with lockable test button

We've started using these relays from Magnecraft as general purpose control relays in our panels. Interposing relays on PLC outputs, small single phase motor control, etc. One of the nice features is a momentary test button that can be locked on by lifting up a small lever on the face of the relay. This is a great troubleshooting aid, but some safety concerns have been raised about the locking capability of the button. It essentially acts as a bypass function; what happens if someone inadvertently leaves it in the "on" position?

The simple answer is to just not use them in cases where the bypass could cause a safety hazard. But someone pointed out that since relays have common bases, a plain-type relay that goes bad could mistakenly be swapped out with a lockable-button-type. The same logic applies if we remove the locking lever. This possibility suggests that we should completely eliminate our stock of these relays to prevent them from being used improperly.

I'm curious if anyone here uses this type of relay and if you've encountered similar issues?

I've used Turck Releco relays for years which have a similar feature.

If you have a situation where you don't want the relay bypassed then use a relay with a different base, perhaps a terminal style relay.

I'd suggest that if the only thing keeping a system safe is a single relay the design is flawed anyway. There should be a lockable disconnect, or a latching E-Stop, or a H-O-A switch, or something.

I've used similar relays for years, and like you found them tremendously useful for troubleshooting.

As far as the socket question, I don't think it works. You can take a standard octal socket, for example, and insert a standard relay, a relay with override, a relay with the wrong coil voltage, a time delay, and even an analog signal conditioner. If you try to make it idiot proof, they just build a bigger idiot!

TConnolly said:

I've used Turck Releco relays for years which have a similar feature.

If you have a situation where you don't want the relay bypassed then use a relay with a different base, perhaps a terminal style relay.

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We also use these relays. They are really good for troubleshooting like people have said.

Tom Jenkins said:

If you try to make it idiot proof, they just build a bigger idiot!

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Heh!

That's a good one!

If the relay is controlled by a PLC, you could wire a NO contact from it to a PLC input. If the input is on but the output is not, it means the relay is in bypass and the PLC logic can do whatever it needs to do in response.

Steve Bailey said:

If the relay is controlled by a PLC, you could wire a NO contact from it to a PLC input. If the input is on but the output is not, it means the relay is in bypass and the PLC logic can do whatever it needs to do in response.

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That's an astute observation.