Fault current vs. Time

Hi guys,

Interesting question popped up from an electrical engineer with whom we're doing a project.

What is the maximum fault current that a C-bus dimmer can handle and for what time. The MCB's spec'd apparently has a 50 ms reaction time.
Will it trip before the dimmer fry?

Thanks
Brodsky

 

The first thing is the MCB will be rated relevant to the CCT eg 10, 16,20 amps depending on cable etc. You have to consider the dimmer channel probably a 1 or 2 amp channel (if using din). For this typical scenario your dimmer circuit (triac output stage) will be looooooooong gone before the MCB trips out.

If you are using Pro Dimmers say 10amps per channel with a 10 amp MCB if you had a load of say 12-13 amps you might get the MCB to trip without damaging the dimmer output stage. For a short circuit fault say goodbye to your channel. This scenario has nothing to do with C-Bus in particular and everything to do with the electronics involved in leading edge dimmers (all manufacturers)

Surely your electrical engineer could have told you this?????

 

It depends a lot on the dimmer.
Most 'leading edge' dimmers made by Clipsal use a very robust 40 A triac which has an I-squared-T rating of 500A-sq-sec.
If your electrical engineer knows about coordination of overcurrent protection, this is enough information to find a suitable protection device.
The Universal dimmers are a different story.. not sure the best answer for that case.