Saftey before RCDs

[marcuswareham]

I understand the importance of RCDs, what they do & how they can save lives. I agree with there requirements. I also understand you can meet ADS disconnection times with high enough Zs values for relevant fuses or MCBs, etc

In the 18th edition the use of RCDs is much more widespread

The question is RCDs are not new and have been around for some time, In the 15th edition in 1981 RCD use was not so widespread and as far as I can tell (I don’t have a copy and was not alive when they came out) it was only required for a socket which could maybe be used outside to be RCD protected, however the risks were much the same in 1981 we still use a lot of the same appliances used then (more computers now) but things like power tools which could cut there own power cable was used for example , etc

So what changed why was it safe then but not now?

I guess this argument could be taken back to the 1st edition of the wiring regs which now look like a joke, although our usage and power requirements have changed dramatically since then hence the need for updates

Maybe this is a silly question, like why do we now need smartphones but didn’t 20 years ago, but would be interested in peoples views

Thanks Marcus

 

[pc1966]

The idea of monitoring the actual earth conductor current has its places, for example the likes of the Zappi charger that has various PME fault protection steps as there it is the CPC itself presenting a shock risk if it becomes elevated in voltage.

But like many other issues of safely measuring potentially high currents in power circuits it is best to use a current transformer arrangement so the through-path is unlikely to fail or be damaged by high fault currents, then use some electronics to trigger on the smaller CT output.

 

[derek]

America has a big thing about arc-flash, there are a lot of injuries and deaths (comparatively speaking) related to that compared to here. I don't know why, maybe more high power machinery, maybe differences in electrical system design, etc.

It has been alleged that the USA has a very casual approach to the importance of thoroughly testing electrical installations and that if the circuit breaker holds all is good, meaning that AFDDs are far more important there to prevent fires caused by poor terminations. That's not to say they wouldn't help in this country as well especially if they can disconnect the supply to appliances that are dangerous.

 

[Mike Johnson]

I don't know the requirements for testing in the USA, but have seen advertisements on e-bay for second hand MFT's in the USA so assume they do have a regime for testing?

 

[marcuswareham]

It has been alleged that the USA has a very casual approach to the importance of thoroughly testing electrical installations and that if the circuit breaker holds all is good, meaning that AFDDs are far more important there to prevent fires caused by poor terminations. That's not to say they wouldn't help in this country as well especially if they can disconnect the supply to appliances that are dangerous.

Have you seen JWs video on the AFDDs, it would appear as if a few of them will allow enough arching to cause a fire before they trip :- S
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Ok thanks, there probably more trouble than there worth then - I did think the principle seemed really good actually checking the Voltage of the Earth.
Thanks.

JW also does a very good video on pointing out the flaws behind the VOELCBs

View: https://www.youtube.com/watch?v=JMh684HniF0

 

[pc1966]

I also remember reading this on how the USA breakers (of the time, it is 1990 here, might have improved now) let through a lot more fault energy that our MCBs:

https://paceforensic.com/pdfs/Circuit_Breakers_The_Myth_of_Safety.pdf