do you think the 17th edition has gone too far with RCDs

[NoHounds]

YES
NO

this was supposed to be a poll but i just released i can only make one on general discussion

 

[RF Lighting]

No. I think they have got it about right.

 

[martinxxxxxx]

No

And don't ban chocolate either, otherwise I would be in the sh1t for a few days each month

 

[conny]

No,
and don't ban chocolate because I would be a crazy barsteward permanently!

 

[NoHounds]

thanks MOD 11

 

[streetlighter]

I think RCBOs are the way forward for circuit protection in most situations

 

[Paul_C]

Voted yes. It's gone completely overboard.

At this rate the 18th edition will be demanding RCD protection for every circuit at origin, no exceptions.

 

[RF Lighting]

I bet there were loads of people refusing to RCD protect sockets likely to supply equipment for use outdoors back in 1992, as it was pointless and overkill.

 

[Gees]

I am NOT an electrician but have a background of 40 years in the electrical/electronics industry.
A 30 ma RCD is designed to protect people from death by elecrocution?
To trip a 30ma RCD would take in theory 8K oms from 240 volts to a perfect earth?
If I measure the resistance of my body ( or any other person for that matter), NOT with a 500 volt megger of course, I have a hard time getting it to read less than 800K ( using a fluke 32 Multimeter )
that would give by calculation only .3 ma .. Am I missing something ?

 

[kai]

The best thing in the 17th, was the compulsion to fit an RCD on the shower circuit - sanity has prevailed here, compared with the 16th edition!

 

[RF Lighting]

I am NOT an electrician but have a background of 40 years in the electrical/electronics industry.
A 30 ma RCD is designed to protect people from death by elecrocution?
To trip a 30ma RCD would take in theory 8K oms from 240 volts to a perfect earth?
If I measure the resistance of my body ( or any other person for that matter), NOT with a 500 volt megger of course, I have a hard time getting it to read less than 800K ( using a fluke 32 Multimeter )
that would give by calculation only .3 ma .. Am I missing something ?

Body resistance changes depending on circumstances. Imagine a wet hand on an earthed metallic thing. Touching a live wire with the other hand would result in a severe shock across the chest.

Now imagine the same person touching the same wire, but stood on a wooden floor wearing rubber soled shoes. Not only does the electricity have a longer path through the body to earth, but also the increased resistance of his footwear and the flooring.

That example shows how you could receive a falat shock in some circumstances.

If the person receiving the shock is sufficiently well insulated from earth, then the current flow will be limited by the resistance of the body and the path to earth, as ohms law states. Whilst unplesant the shock would normally not be fatal.

Now back to person one. He has a much lower resistance to earth, so by ohms law again, a higher current will flow through him. This current may easilly exceed 30mA, and a shock of any duration could well prove fatal to the poor chap.

If the circuit includes an RCD, once the amount of current flowing to earth via the poor chap exceeds 30mA, the RCD will very quickly trip, automatically disconnecting the supply. This will greatly increase the chances of the man surviving the electric shock.

 

[securespark]

 

[Paul_C]

There's also the factor to consider that by far the largest portion of the body's resistance is in the epidermis. Higher voltages tend to break down the resistance of the outer skin layers, and the resistance of the tissues beneath can be surprisingly low, which is why medical apparatus has to be manufactured to keep leakage currents to an absolute minimum.

Obviously this is an extreme example, but the table about a third of the way down this page shows just how low the internal resistance of the body can be:

http://www.dc.state.fl.us/oth/deathrow/drorder.html

However, this brings up several points about the way the RCD has been promoted to the general public, with its ability to protect being grossly exaggerated. I find a lot of people seem to have been left with the idea that if you have an RCD in use there's no way you could sustain a fatal, or even serious, electric shock, which is nonsense.

A sustained current of less than 30mA through vital areas of the body could quite easily prove fatal to some people, and of course if you get yourself across L & N without there being 30mA flowing to earth simultaneously, the RCD will do nothing to protect you directly.



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[securespark]

At this rate the 18th edition will be demanding RCD protection for every circuit at origin

Sounds good to me.

More RCBO's and fewer RCD's.

In fact, I was in Ricky Tomlinson's house last week explaining the importance of RCD protection and he said "RCD my arse!".

So I gave him a quote.

 

[Paul_C]

More RCBO's and fewer RCD's.

For those circuits requiring protection, I would much rather see individual branch-circuit RCBO's than a single RCD.