Miniature Circuit Breakers, that is. Like what you find in your consumer unit/fusebox as they used to be called.

 

I googled it this morning 'cos I only had a vague idea that there was something electromagnetic inside, and found this page(s):

http://www.engineersgarage.com/insight/how-mcb-works

 

You click in the Table of Contents box at the top right to move from one page to the next; 12 in all.

 

Brilliantly clear explanation with excellent photos.

Never realised how fast they are; 2.5 milliseconds for an overcurrent trip, they say. That explains why something as fleeting as a bulb failure can trip one.

 

Looks like a handy site too. :clap:

 

Is there a thread anywhere with links to 'interesting engineeringy stuff to read on the internet when you have a spare half-hour'?

If there isn't, maybe I'll encourage others to post their links in here and modify the title to suit?

 

Cheers, enjoy. If it's your sort of thing.

Edited 14 December, 201510 yr by Wino

Thats interesting!

The wire doesnt even need to be live does it.. I cut a dead cable the other day and it clicked it off. Must be the earth?

That would have been an rcd that tripped, not an mcb. It would have sensed an imbalance due to the neutral and earth being connected briefly and a few milli amps flowed back down the neutral from the neutral bar, down the earth,causing it to trip.

That would have been an rcd that tripped, not an mcb. It would have sensed an imbalance due to the neutral and earth being connected briefly and a few milli amps flowed back down the neutral from the neutral bar, down the earth,causing it to trip.

ooh okay. im learning, im learning.. haha

 

so, it was the bigger one at the end of he row of the smaller ones. is that the RCD? residual current device, right? i thought they were all the same.. obviously not... 

 

ive only basic understandings of electrics. I am Gas Safe and can tell you many many things about boilers, heating and plumbing.. i wire in motorised valves, wire plugs, check boiler controls and use a continuity test to check switches and what not, but when it comes to the consumer unit, ive never been educated on that.. but i am keen to learn.. its magic though, right?  

It would have been an RCD. Saved many a life in equipment repair places in the older days after they were fitted. And for the BT jointer's in here- possibly a few more than burnt /singed bits in the days of older power feeding on Coax cables( amplifiers on equipment in remote places were fed by HV,USUALLY 1000 VAC), using the coax cable. We were supposed to test them on a regular basis, but where I worked, getting traffic cleared off one of the routes to Uncle Sam's war room was difficult.

But coax cables even dead still hold charge- many's the arc I've seen on discharging a dead coax,with looot of volts on it when working.

Modern jointer's have no worries. Since the days of transistorised kit, power feeding is via current limited low voltage equipment.

Don't think they are used on Rail kit, as we've had reports of 22/7 Key folks getting decent belts when trying to "liberate" cable carrying 650V AC.

Edited 5 January, 201610 yr by VWD