Shower shock in TT systems

[LastManOnline]

Do you encounter many issues with homeowners experiencing "tingling" from electric showers in homes with a TT supply system?
Reason I ask is because everytime we respond to this issue it always turns out to be a result of a plumber replacing copper with Qualpex or the service provider replacing metallic with plastic. This results in the "TT" system having a much higher fault loop impedence and creates issues, regarding the functional earthing in the shower. Bearing in mind the much more common use of TT in the UK, is this a widespread problem for you?

 

[pc1966]

I'm not sure TT is that common in the UK, mostly it is TN-S and TN-C-S as far as I know, some of the sparks on here ought to know better than me.

But you are right that non-conductive plumbing replacements is a serious issue if there no adequate earth rod, or if the water and gas supplies are not properly bonded at the incoming point.

Also the issue of a "functional" earth is a bit misleading, it really is there for fault protection (class I appliance). The "functional" aspect if simply it has a mA or two of leakage due to capacitors in the mains filter (added these days due to electronic controls and their switching power supplies). If the shower CPC goes back to the MET properly, as it should, and the system earth impedance is below the 200 ohms (UK spec, no idea if ROI is different there) then you won't have much volts to worry anyway.

Even if the shower was not "functionally" earthed you would see several mA of leakage in a house due to the wiring capacitance anyway, not to mention other electronics with filters all adding to the total CPC current (from memory my own flat was in the 6mA region last time I clamped the tails with a low current ammeter). So really it is an issue of inadequate earthing.

 

[davidanthony41]

Do you encounter many issues with homeowners experiencing "tingling" from electric showers in homes with a TT supply system?
Reason I ask is because everytime we respond to this issue it always turns out to be a result of a plumber replacing copper with Qualpex or the service provider replacing metallic with plastic. This results in the "TT" system having a much higher fault loop impedence and creates issues, regarding the functional earthing in the shower. Bearing in mind the much more common use of TT in the UK, is this a widespread problem for you?

Yeah what pc 1966 said

 

[pc1966]

If the shower CPC goes back to the MET properly, as it should, and the system earth impedance is below the 200 ohms (UK spec, no idea if ROI is different there) then you won't have much volts to worry anyway.

Just to note I was talking about domestic TT here, with a 100mA delay incomer (or less) so an earth rod below 200 ohms is good enough.

For a TT farm or light industrial place on 300mA or higher RCD then the rod would need to be less, and obviously for TN system you would expect under an ohm or so.

 

[LastManOnline]

Just to note I was talking about domestic TT here, with a 100mA delay incomer (or less) so an earth rod below 200 ohms is good enough.

For a TT farm or light industrial place on 300mA or higher RCD then the rod would need to be less, and obviously for TN system you would expect under an ohm or so.

Good to know. Thanks for that. I had thought (wrongly) that TT was more common in UK

 

[pc1966]

Good to know. Thanks for that. I had thought (wrongly) that TT was more common in UK

I think TT is the norm in many European countries, but in the UK it is more likely in rural regions.

Having said that, it still makes an occasional appearance in terraced blocks in cities, etc, that you would imagine should be easily earthed to the DNO supply. But probably for historic reasons was not.

As mentioned above, other folk on here with more experiance will know better. I wonder if there are official stats on this somewhere?