Control Panel Fault Finding

mfearnon

Hi,

Can anyone give me a few pointers or is their a system or routine when fault finding in a control panel. I'm working with 3ph panels running motors etc, I'm new to this sort of thing but looking to get a bit of info to make me more confident with panels.

Thanks

Bull76

Hi,

Fault finding and the experience of fault finding is a time earned skill.

Observation is useful, Look for what is different. Touch and verify connections whilst the panel is locked out. Know the system, if you know the system then you can fault find what is wrong easier.

Then it is a case of confirmation of voltages and tracing signals. Components can be verified whilst the panel is Locked out. Continuity of relays, contactors, switches and fuses etc when panel is Locked out.

Take note of what is wrong and when it is happening, at least then you have a sequence of when. Then ask questions of what, why, when, where, How.

Sorry can't be more help.

brightspark

Have you just started your apprenticeship?

If working without drawings...
I usually check overloads/fuses/safety relays first, then check coils, stop and start buttons.

When working with drawings, it will depend on what is and isn't working, fully dead and I will be checking the main control circuitry, randomly picking midpoints in the circuit to try and narrow down where the fault is. If the machine is stopping at a certain point in its sequence I will check relevant limit switches etc.

A lot comes with experience, smelling or spotting burnt connections, knowing what typically fails on that particular machine, knowing a motor making a humming noise is probably single phasing but might be physically stuck.

You will never stop learning and some of it becomes instinctive after a while making it hard to describe to others exactly why you checked one component and not another.

You need to be able to fully understand the various styles of electrical drawings, recognising the various components by their symbols etc., and be able to follow the circuit from one page to another.

With PLCs etc without access to the program I basically just check to see if the relevant output has come on, if it has I check the circuit after the plc, if it hasn't I make an educated guess as to what inputs are needed to make that input come on (limit switches made or not made, button pressed etc)

Mr Magnolia

Check the obvious stuff first, e-stops, pull-cords, H/O/A's and the scada too to make sure none of these are holding the motor out. Most of the time this will be what's wrong.

Next, if it's direct on line (DOL) check the overload hasn't tripped and everything is on at the MCC. Check the relays to make sure they switch when you bypass, sometimes they burn out and get stuck. Then, I'd try and start the motor, keep an eye on the ammeter if there is one or stick a grip amp on it. If it goes over the overload setting or the rating for the motor then it might be jammed or the windings could be burnt out. You'll need to megar the windings to verify spent this really.

After that, start with the drawing/schematic. This is where the valuable info is. You'll need to set your meter to the control voltage and check where in the control circuit the voltage is lost. Start at the last contact in the circuit and work your way back. When I was trouble shooting control circuits I did it live but I knew what I was at. BTW, I'd never open the terminal block of a motor with it live, too easy for stuff to fall onto the terminals and cause a dangerous short. I can't think of any reason why you'd ever have to open it live so don't. Check the voltage at the MCC out-going terminals for phase-loss not at the motor.

Check if there's a thermistor/PT100 in the windings holding it out. If I can think of anything else I'll post it up. There's loads of stuff, just comes with experience as said above but you've a few things to think about. Belt away with any specific questions.