RCD test button

[Michal]

What was the reasons for changing intervals time between,from quarterly to every 6 months?.

 

[pc1966]

I take it from that you'd never install a TT system then? Is a TT system a poor design?

Well for TT I personally would have both a 100mA delay RCD up-front and the 30mA RCD/RCBO for the additional protection for this very reason - you become reliant on the (usually untested) electronics for protection. With two of them you don't have a single point of failure.

But in the TT case there is a good enough reason to rely on a RCD in that you usually don't have any other option. In the TN cases it is usually possible to meet disconnection on the OCPD if well designed, and only some difficult cases (e.g. high current circuit) where the supply Ze is not going to allow it to be met.

 

[radiohead]

Well for TT I personally would have both a 100mA delay RCD up-front and the 30mA RCD/RCBO for the additional protection for this very reason - you become reliant on the (usually untested) electronics for protection. With two of them you don't have a single point of failure.

But in the TT case there is a good enough reason to rely on a RCD in that you usually don't have any other option. In the TN cases it is usually possible to meet disconnection on the OCPD if well designed, and only some difficult cases (e.g. high current circuit) where the supply Ze is not going to allow it to be met.

Completely agree.
But I take issue with the statement
It is one of the reasons that I don't approve of ignoring the Zs or R1+R2 values and assuming the RCD side will cover their asses on any fault,
No competent electrician is going to ignore clear problems with an existing install or install a circuit with such a poor design input that the design Zs way exceeds the max for the chosen OCPD.
As I have stated on here before, where an existing circuit needs to have (say) a type B device changed for a type C device because of a change of use, but the max measured Zs slightly exceeds that permitted for a type C I see no reason why an RCD cannot be an acceptable means of meeting the disconnection time. After all only a fraction of an ohm over the permitted max for the OCPD will still see it trip almost instantaneously even if the RCD fails.
Ive seen EICR's code 2 a circuit because the measured reading for the OCPD is slightly exceeded even though an RCD is in place. Wrong and ridiculous. Easy for these guys to spend other peoples money on unnecessary remedials.
And if RCD's are so unreliable why are we using them for additional protection? Now considered essential.
The highlighted statement assumes that any use of an RCD for earth fault protection, which is permitted by Bs7671, is a dangerous 'cowboy' botch. Absolute rubbish. Any device incorrectly used is going to be potentially dangerous, an RCD correctly used for earth fault protection is perfectly safe and compliant. It is the installer that makes an installation unsafe, Not the device.

 

[pc1966]

Completely agree.
But I take issue with the statement
It is one of the reasons that I don't approve of ignoring the Zs or R1+R2 values and assuming the RCD side will cover their asses on any fault,
No competent electrician is going to ignore clear problems with an existing install or install a circuit with such a poor design input that the design Zs way exceeds the max for the chosen OCPD.

My apologies if that bothered you but I was not referring to competent electricians here, more the "drive by" EICR sort that take one look at the RCD and pass it without checking Zs, etc.

As I have stated on here before, where an existing circuit needs to have (say) a type B device changed for a type C device because of a change of use, but the max measured Zs slightly exceeds that permitted for a type C I see no reason why an RCD cannot be an acceptable means of meeting the disconnection time. After all only a fraction of an ohm over the permitted max for the OCPD will still see it trip almost instantaneously even if the RCD fails.
Ive seen EICR's code 2 a circuit because the measured reading for the OCPD is slightly exceeded even though an RCD is in place. Wrong and ridiculous. Easy for these guys to spend other peoples money on unnecessary remedials.

I would agree with you there when it is only just over the tabulated Zs you still have some margin in real life as the UK Zs values allow for simultaneously minimum supply voltage, max operating temperature, and worst-case MCB magnetic trip tolerance.

And if RCD's are so unreliable why are we using them for additional protection? Now considered essential.

For additional protection it is always better to have one. Even if it has a few percent chance of failing and not being spotted, the remaining time it is going to help save lives.

The highlighted statement assumes that any use of an RCD for earth fault protection, which is permitted by Bs7671, is a dangerous 'cowboy' botch. Absolute rubbish. Any device incorrectly used is going to be potentially dangerous, an RCD correctly used for earth fault protection is perfectly safe and compliant. It is the installer that makes an installation unsafe, Not the device.

The use of RCD protection is allowed, and it is always better than not having it. My point is simply it is not something I would be happy with as the primary means of disconnection without any additional means.

The subject was brought up by the point about testing them, and that in most cases they will go untested for 5-10 years, any my own feeling is I would not want to depend on electronics with a single point of failure over that sort of a time-scale.

So I'm sorry if you feel it was an attack in some way, that was not what I meant.

 

[loz2754]

So we only have to forget to do it twice a year instead forgetting to do it four times a year!

 

[telectrix]

So we only have to forget to do it twice a year instead forgetting to do it four times a year!

forget what? ?

 

[Mike Johnson]

As FatAlan posted earlier, just put a sticker on the DB "saying do not touch this button"

 

[Dustydazzler]

Perhaps rcd test buttons should glow red ...

 

[Mike Johnson]

Or Green, or be capable of colour change according to how much is flowing through them or how many circuits are switched on, entertainment for the children, Oh can we get it to Violet?