ABB Safety relay's Reset/Test inputs

[unsaint32]

My questions are about ABB's safety relay JSBT5. A1 and A2 of course energize its coil. X1 and X2 are for stop reset. For this posting, let's assume that all coils and loads use 24V, and PB1 to A1-A2, and PB2 to x1 and x2. And let's assume that there is only one NO contact although this particular relay has 3 NO and 1 NC contacts. I am uploading a pic.

Question #1) What happens to the contacts if I press PB2 (the reset PB) while the A1-A2 coil is already energized? My guess is nothing happens.

Question #2) The manual of this relay says the X1-X2 can be used as test inputs that test that contactor positions have returned/dropped before a new start can be permitted. I just don't see how. Can you explain please.

Thanks.

 

[antsrealm]

I'm not an expert by an means and have occasionally used the ABB safety products previously know as jokab safety over here in Australia.


If the outputs are off then you would need the safety signals to be high to indicate it's safe, estop / light curtain etc. Then finally the X1 and X2 needs to be momentarily closed to reset the relay and close the internal safety contacts.

Normally when using safety contactors we would wire x1 through the NC auxiliary contacts of the safety contactors in series and then through the NO reset button then back to X2. This ensures both safety contactors have infact opened before allowing the reset. This way if a contactor has welded shut you cannot reset the system and forces you to replace the welded contactor.

Tony.

 

[Timbert]

In your circuit, PB2 should be connected between X1 and X2 only. X1 and X2 should not be connected directly to +24 and/or 0V.

Question #1) What happens to the contacts if I press PB2 (the reset PB) while the A1-A2 coil is already energized? My guess is nothing happens.

I can't answer authoritatively as I don't have one to actually test but it shouldn't do anything.

Question #2) The manual of this relay says the X1-X2 can be used as test inputs that test that contactor positions have returned/dropped before a new start can be permitted. I just don't see how. Can you explain please.

These relays are typically used with external safety (positively-guided) contactors as the safety relay can only handle 1.5 KVA. As Ant says, the auxiliary contact of which is wired in series with PB2 between X1-X2. This way a failure of the external safety contactor can be detected.

A failure internal to the safety relay will also be detected without the need for external connections. In either case you will be unable to reset the safety relay.

 

[unsaint32]

In your circuit, PB2 should be connected between X1 and X2 only. X1 and X2 should not be connected directly to +24 and/or 0V.

Thank you. I didn't understand Antsrealm until now. Thank you guys.

I can't answer authoritatively as I don't have one to actually test but it shouldn't do anything.

At my work, we have a start and stop PB for a VFD driven motor, and the stop PB is used as a reset of a safety relay that energizes a contactor that energizes the VFD. So, restarting the circuit from a shutdown requires a reset by pressing the stop PB. But if the safety relay was already energized (therefore the VFD was already energized), pressing the reset PB (stop PB) would only send a proper input signal to a PLC but not shut down the VFD.

So, like you, I could not test it, but it makes sense that the reset button was design not to change the contact status if the relay was already energized.

 

[unsaint32]

Normally when using safety contactors we would wire x1 through the NC auxiliary contacts of the safety contactors in series and then through the NO reset button then back to X2. This ensures both safety contactors have infact opened before allowing the reset. This way if a contactor has welded shut you cannot reset the system and forces you to replace the welded contactor.

So, that is a way of adding a prerequisite condition for a reset, such as deactivation of any movement-causing load. Brilliant. But, I still don't know why the x1x2 is called a "test" input. Thanks Antsrealm.

 

[antsrealm]

So, that is a way of adding a prerequisite condition for a reset, such as deactivation of any movement-causing load. Brilliant. But, I still don't know why the x1x2 is called a "test" input. Thanks Antsrealm.

I just had a quick look at the manuals. This is an extract from the JSBT5 manual.

The test input is intended to supervise that contactors or valves
have dropped/returned before a new start can be permitted. The
test input can also be used for starting and the start button can be
supervised (see connection example on next page).

On the drawing for this one it shows the contactor auxiliaries in series with the start button as I described.

Seems that some of there products call it a reset input and others call it test but there descriptions in the manuals seem similar. Might be worth contacting the ABB rep and finding out what the differences are.



Thanks.