ndzied said:
...Note that this is a simplified circuit. We almost always use dual channel e-stop circuits and safety relays now but the idea is to talk about if you would use a lighted pushbutton to reset the safety circuit and if so, how would it function.
Hi Norm,
I'm going to take your advice here and, for the most part, ignore the traditional wiring diagrams you provided, as they are not Safety circuits, at all, and in my opinion we really should not be referencing them when going to discuss resetting a Safety circuit.
Anyway, that's just my two cents on that...
There are indeed IEC (International Electrotechnical Commission) Standards out there for these colour codes, for both push button actuators and indicators, resets and whatnot. These International Standards are usually disseminated to the various Regional and National Standards. It just seems like most folk don't know of them or are not too inclined to follow them?
A bit of light reading here from a previous thread in which I "get into" the colour coding on an illuminated Emergency Stop reset push button, among other things...
E-Stop manual reset button
However, I will say, as I did somewhere in the other thread, that these Standards are not solely applicable to Safety circuits. In fact, they are not called out as Safety related at all. We can actually apply these Standards to the example non-Safety MCR circuit here, or any other standard control circuits, if we wish. They just advise us as to what is acceptable in general and we must interpret these Standards ourselves when applying them to circuits that happen to be Safety related.
Example: non-illuminated reset push button
Colour: BLUE
Meaning: Mandatory action
Description: Actuate in a situation which requires a mandatory action
Examples of application: Resetting function
A reset of a Safety circuit is a "Mandatory action". As such, the IEC Standards dictate that BLUE is the preferable colour to use here. Not because it is for a Safety reset, but because it is for a "Mandatory action". A standard reset function may also be classed as a "Mandatory Action". Therefore, we cannot say that BLUE is reserved for Safety resets. Any Mandatory action may use the colour BLUE.
Illuminated reset push button
Colour: BLUE
Meaning: Mandatory action
Description: Indication of a condition requiring operator intervention
Operator action: Mandatory action
Again, BLUE is the preferred colour to use for the indication of a Mandatory action. Note how the wording suggests that the ON state of the BLUE indicator is required to signify the Mandatory action (reset) is required, and not the OFF state.
Typically, for Safety resets, an illuminated BLUE reset push button will normally be turned OFF when the Emergency Stop Safety function is reset. When the Safety function is tripped, the BLUE indicator will turn ON to signify that the Mandatory action reset is required. Another method used is to make the indicator flash to signify the reset is required. The method I "broke down" at the end of the linked thread is also OK, by my interpretation of the Standards. That is, normally OFF when healthy, flashing when tripped and E-Stop still latched, solid ON when E-Stop unlatched but still not reset, and OFF again when reset. I have also gone through the flashing indicator frequencies set out in the Standards.
I'll let you read the linked thread, if you wish, and if any questions, fire away.
Regards,
George
