Testing Motor Control Panels

[Walden]

I recently went to witness the testing of a small electrical control panel on behalf of one of my clients. The control panel contained a small electronic temperature controller, two MCBs, a contactor and thermal overload relay and 4 plug-in relays. The specification called for the insulation to be Meggered at 500 volts. The controller and the neon indicators in the control panel door were isolated since the manufacturers’ of these items stated that they were not suitable for a high voltage test. This left the MCBs, the contactor and its overload and the four plug-in relays which were duly tested and passed. How can this be called a test when 80% of the equipment is removed from the procedure? How do you test modern control panels and other installations that contain electronic components, which cannot be tested in the conventional way?

 

[jbartos]

Comment: The specifications for the panel testing was not specific enough to call for testing of those items that were omitted.

 

[Sanditech]

I am not sure of the UK spec No (poss IEC439), but any circuit protected by a 16A SCPD, when proved by functional testing does not require a Megger / Hi Pot test. This rule is used within the UK panel manufacturing industry to negate the need for protracted testing on multi cubicle switchboard control and metering circuits.

 

[jbartos]

Comment: Often, transient voltage suppressors are applied on the power supply input to protect the control panel from overvoltages. Then, the hi-pot test tests for something what will actually not materialize if TVSSs function properly. However, any reasonable insulation test is good to see how good the insulation is. The removed devices are usually tested by their manufacturer in order to pass QA/QC.