Should protective relays be door or din-rail mounted

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If you are faced with designing switchboards, you have undoubtedly been faced with the choice of mounting a protective relay either on the door or on inside the panel on a din-rail.  The viability is key, to allow your user to easily determine a fault, and address it, and so a door mounted relay can be advantageous.  Example KPM161 Insulation Monitor.  Now on the other hand you may want to keep the door clean for clutter to not overwhelm the user, with information will not be in use daily, so you decide to din-rail mount the protective relay.  Example KCM161 Insulation Monitor.  If the relay activates then give the user a light to alert of the faulty situation.  So what may be the best choice?

#1 Evaluate the capability of the potential user of your panel.  If this is a manned machine room, there will be some education required of the personal, prior to taking duty.  They will have been to school for a few years to learn the craft, and thus it is likely that staff will know what the meter mounted on the door means.  The overwhelming will not happen.  If the engine room is not manned, the crew member may not know what it all means, and it becomes important to keeping it simple, and thus din-rail mount many protective devices.

#2 Is the door real estate already crowded with other functions, putting some protective devises inside the panel, and give a simple light if a fault is detected, that way many protective functions can be shown on a few lights.  Neat and simple.

#3 Is the voltage too high for door mounted protection, greater than 250VAC, the relay must be din-rail mounted, unless there are possibilities in reducing the voltage, and still keep the protection level.

These are just some of the choices that a designer must make, and they can be a challenge to pinpoint is some switch boards.  Example on a Yacht – who will be at the switch board in the dead of night when the chief engineer is sleeping.  Will it be a deck hand that have anchor watch?

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