why didn't fuse blow?

[charles]

I prefer the in-line RCDs since some sockets are mounted so that you can't get an RCD plug into them

[stuart noble]

Good advice. Thanks

[Bob Eager]

I put an RCD socket by the back door.

[ARWadsworth]

Mounted too low to the skirting/worktop etc?

[charles]

correct. You win a prize.

[dennis]

Turn them upside down.

[ARWadsworth]

That's a bad installation then:-(

And where do you charge all the electrical appliances with the transformer plugs that suffer the same proplem?

I always thought that 2 double sockets on the landing would be enough for recharging purposes. It's not.

[Andy Dingley]

Fuses take time to respond, and this time is (roughly) inversely proportion= al to the square of the current. If you cut the cable quickly, you can beat= the fuse - although this is really rare for small fuses. If you cut the ca= ble by tearing it, so that the "short circuit" through the blade either doe= sn't happen, or only happens briefly, then the energy in the fuse is insuff= icient to break it.

[Mark Evans]

And thus able to learn the lesson that it's a bad assumption that cutting the cable will ensure that it is no longer live.

[John Rumm]

Well to be fair, your would probably learn that lesson even without the RCD, it would just hurt a whole lot more, and the amount of time you have available to benefit from what you have learnt might be considerably shorter! ;-)

[dennis]

There appears to be a fair few people here that think an RCD stops all people getting killed. Its not that simple.

The current/time limit is set so most people will not be killed. There is still a small group of people that can be killed before the RCD trips.

Those people won't know who they are so never treat a cable as off even if you have an RCD.

It will protect the majority of people most of the time but there will still be deaths.

[Martin Brown]

It is a good working approximation in most cases it works. Far better than being fried to a crisp or seriously burned which is what happens if you grab live and neutral in the same hand. Most people that have never had a shock assume that you can let go - you can't.

A hapless friend fell for exactly that scenario in a physics lab where someone had wired a mains cable with a plug on each end!

That is good advice.

You would have to be incredibly unlucky and have the current across your heart to get a fatality inside the proper RCD profile. I would be interested to see any credible evidence of a fatality where a working RCD had failed to protect a vulnerable adult. Defective RCDs may sometimes fail to trigger leading to death but that is a different matter (you should always test them first).

I don't count any articles in magazines that also cover UFOs, alien abductions, spontaneous combustion, Elvis is alive etc.

[dennis]

How about this from

>The current is the controlling factor for Electrocution and Electrical Shock. The threshold for perception is about 100 microamps (0.0001 Amps). Also See Microshock Electrocution Hazards for currents less than 100 microamps. The National Electrical Code (NEC) considers 5 milliamps (0.005 Amps) to be a safe upper limit for children and adults hence the 5 milliamps GFI circuit breaker requirement for wet locations. The normal nervous system reaction to any perceptible electrical shock may cause a person to injure themselves or others, therefore the so called safe limit does not assure freedom from injury.

The more serious electrocution and shock hazards occur above the let go limits. 99% of the female population have an let go limit above 6 milliamps, with an average of 10.5 milliamps. 99% of the male population have an let go limit above 9 milliamps, with an average of 15.5 milliamps. Prolonged exposure to 60 Hz. currents greater than 18 milliamps, across the chest causes the diaphragm to contract which prevents breathing and causes the victim to suffocate. No data is available for females or children but suffocation is presumed to occur at a lower current level.

[John Rumm]

Potentially nasty - but not as bad as a hand to hand shock...

As with most cases in this area, its hard to be certain about things since the actual numbers are so low.

With the possible exception of the toddler playing with the unterminated flex and plug, I don't recall reading of any deaths that happened in spite of an RCD operating (and in that particular case I don't know if there was a RCD at all, and if there was, if it operated - I suspect the answer to both those is no)

You actually need a confluence of a greater set of circumstances than just someone being particularly sensitive. The points of contact make a huge difference, as does the quality of the independent earth connection through the person getting the shock.

In (the far more rare) cases where one has made direct contact to both line and neutral, then a low impedance connection to earth would be beneficial since it would maximise detectable leakage. However the current profile of the shock could potentially be way above the trip threshold of the RCD since it can only limit the duration, not the current. In the more common case of direct or indirect contact to only a live, a high impedance connection to earth will serve to limit the shock current, which along with the RCD imposed time limit is usually adequate to protect even sensitive individuals.