Lowest n/e Ir value for a rcd to trip does anyone know?

[dannyv]

Can anyone tell me how low the Ir value would be n/e for a rcd not to hold in! Would like to know as I always get problems prior to changing fuseboards

 

[Deleted member 9648]

Irrelevant really.....if it's under 1mohm you will have to sort it.

 

[johnboy6083]

ohms law. 7.6kohms or 0.0076Mohms.

this is assuming that the voltage is 230v and that the RCD will trip at exactly 30ma.

Both of the above statements cannot be guaranteed

Edit: i totally agree with wirepuller, if i gets anywhere near 1Mohm, then invesitgate further.

 

[Deleted member 9648]

The voltage on the Neutral will be around 0v I think you will find

 

[johnboy6083]

smartarse! lol

 

[Sparky Ninja]

It would depend completely on the sensitivity of the device.

As wirepuller says, it is irrelevant as BS7671 2008 states >1Mohm, although (in the words of Tony Cable) that is simply an exam question and anything near that would require investigation. The answer would definately not be an IR value, and would be more of a low reading ohmeter value.

 

[dannyv]

What's the best quickest test to do on a fuseboard change survey to see if you ll get rcd trip problems neutral to earth across the whole install ?

 

[tony mc]

Stick a earth leakage clamp meter around the tails and this will give you a start.

High leakage try taking the fuses out one at a time but this only gives you live earth leakage as the neutrals are all in one bar. So if high leakage still there taking neutrals out one at a time to find cct but this if hassel on a tight 3036 board or any board crammed with cable.

Make sure loads are disconnected unplugg in case of faulty appliance.

 

[Sintra]

What's the best quickest test to do on a fuseboard change survey to see if you ll get rcd trip problems neutral to earth across the whole install ?

Method 2 IR test.

 

[Deleted member 9648]

There's only one way...do an IR test.... anything under 1mohm will need investigation.
Also check for borrowed neutrals...most likely on the landing light of a 60's built house.

 

[Deleted member 9648]

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