Power breaker - solve an argument please!

[bopdude]

Originally Posted by homealone

I raised this point with an electrician doing some wiring in our kitchen, he said we were protected by the RCD switches in the consumer unit - that they were the primary circuit breakers, & thus plugging in 'extra' ones was not necessary, whether wall plate or garden ???

- that is assuming they are properly fitted & earth bonded, of course

You can never be too safe, I have worked on R.C.D's that were faulty and wouldn't trip under fault, of any kind

Better safe than sorry And if in doubt, ask, get somebody suitable.

[homealone]

Originally Posted by bopdude

You can never be too safe, I have worked on R.C.D's that were faulty and wouldn't trip under fault, of any kind

Better safe than sorry And if in doubt, ask, get somebody suitable.

Absolutely, hence my caveat about 'properly installed'

[bopdude]

Originally Posted by homealone

Absolutely, hence my caveat about 'properly installed'

Indeed, what some folks aren't aware of is the test button on an R.C.D. this, when pressed should trip the breaker telling the owner that it is fully functional, just because it's there doesn't mean it's working, TEST them people


Just like you would a fire / smoke alarm.

[homealone]

Originally Posted by bopdude

Indeed, what some folks aren't aware of is the tst button on an R.C.D. this, when pressed should trip the breaker telling the owner that it is fully functional, just because it's there doesn't mean it's working, TEST them people


Just like you would a fire / smoke alarm.

Good advice

[SMHarman]

Originally Posted by greencreeper

Me as a teenager, happily cutting my grandad's hedge when the hedge trimmers just stopped. Completely dead. Odd. Checked the plug - still firmly in. Consumer unit - no tripped switch. Hmmm. Changed the fuse in the plug - still nothing. Resigned myself to a new pair of hedge trimmers. Started to tidy away the cable when I found these bare wires - as if someone had caught the cable in a pair of hedge trimmers and not realised

So - safety starts with the individual. I never touch hedge trimmers now.

These things are additional protection, not a failsafe. I cut through the hedgetrimmer cable once. Slice sufficiently clean and quick that it did not trip the the house RCD or the one on the wall socket. Be careful.

[altis]

Perhaps it is helpful to understand how these devices work.

Residual Current Devices or RCDs sense any difference between the currents in the live and neutral conductors. If things are working properly, all the current entering an appliance through the live conductor will return through the neutral. If something conducting, such as a human, provides another route from live to earth then these currents will not balance. Commonly, these devices look for a difference of more than 30mA. As little as 60mA across the chest can overwhelm the human body's muscle control and prevent the heart from operating properly. Above about 200mA, it will stop completely.

Note that RCDs cannot detect faults, such as fire, that do not involve another current path. You should also use a fuse or circuit breaker with a current rating lower than the cable as well.

More details:
http://en.wikipedia.org/wiki/Residual-current_device

[SMHarman]

Exactly, so when the cable was cut the power did not go elsewhere and subsequently there was no power through the cable - no differential.

[Rob]

It's worth remembering that RCDs, since they can only work by detecting a current differential, i.e. leak to earth, requires that current to flow. Thus they won't stop you getting a shock, if you touch a live cable. However they should respond sufficiently quickly that the shock won't be fatal.

That's where the test thing comes in, but how many of us do that with RCD's hidden in inaccessible cupboards. In a way, even with a RCD protected consumer unit (fuseboard) the plug in device is good belt and braces. As that plug in is usually accessed to connect your device, it's much more likely you'll press the test button too.