Trip Testing for MCBs

[Knobhead]

not in to this sort of thing guys, could someone explain primary and secondary injection?
Many thanks.
Danny

Large ACB’s, OCB’s, VCB’s, Etc have CT’s to give a ratio of the current to the protection instruments. So a 200/5 CT will give 5A to the instrument when 200A is flowing through the main circuit. They also isolate the HV from the instrument.

So to set 200A O/L's at 125% with primary injection a current of 250A would be passed through the primary and the trip time measured. With secondary injection only 6.25A is needed. Further tests would be carried out at higher currents to check the current/time curve.
Now imagine primary testing a 1600A breaker, 125% = 2000A. I don’t even want to think of testing a 6000A breaker.

The primary injection equipment is hefty to say the least hence my reference to ordering a Dr. Scrotes surgical support. An absolute pain to connect up as Engineer said!

 

[1ManRiot]

MCB = mechanical circuit breaker? What is the difference to a regular 230V RCD?(new in the game)I presume testing them is a bigger deal than testing RCDs? We test RCDs on the random 230V supplies in trackside cabinets using a Megger IR/RCD tester.

 

[IQ Electrical]

MCB = mechanical circuit breaker? What is the difference to a regular 230V RCD?(new in the game)I presume testing them is a bigger deal than testing RCDs? We test RCDs on the random 230V supplies in trackside cabinets using a Megger IR/RCD tester.

MCB = Miniature Circuit Breaker.

The MCB is an overcurrent protective device whereas an RCD (Residual Current Device) only protects against earth leakage and must normally be used in conjunction with an overcurrent protective device or can be combined with an overcurrent protective device, known as an RCBO.

The test currents for RCD testing are typically much smaller (mA) than for MCB testing so the testing is much simpler and the cost of the equipment much less.