Touch voltage to earth

[Jako13!]

Can somebody explain if you had a 230v to earth fault the variables that determine touch voltage of a person to earth and is this voltage less the closer you get to the MET of an installation.

Thanks guys

 

[Jako13!]

During a fault you will get the supply volts times R2/(R1+R2) relative to true Earth where R1 includes the supply phase impedance, and R2 includes the supply ground.

But it is complicated by the other aspects such as any water/gas bonding to metallic pipes that might raise the local earth where you are standing up a bit relative to true Earth.

So you can see voltages from around 1/2 supply (on long supply cable with R1 around R2) to close to the supply (if R2 is very high on TT system). But the danger of serious impact also depends on the exposure time, hence the values of 0.4s (typical LV TN-S) and 0.2s (TT) for max disconnection to try and keep the likely current-time exposure down.

If you are unfortnuate enough to be in good contact, say a swimming pool , then the current can be much higher even though a similar disconnection time is likely. Hence the requirement for SELV in that sort of high risk area as an RCD limits the exposure time, not the actual current, you might get.

So basically it’s the difference between the raised voltage of the installation when the fault occurs the the true earth we may be standing on that determines the voltage?

 

[LastManOnline]

See this attachment for the long answer...

Can anyone give me the name on this link. Can't download it for some reason so hoping to just Google it?

 

[loz2754]

Can anyone give me the name on this link. Can't download it for some reason so hoping to just Google it?

https://onlinelibrary.wiley.com/doi/pdf/10.1002/9781444324273.app01

 

[LastManOnline]

https://onlinelibrary.wiley.com/doi/pdf/10.1002/9781444324273.app01

?. Much appreciated

 

[Vortigern]

Any advice very welcome.

My advice is leave it at that! Reading it will give you a headache )

 

[LastManOnline]

My advice is leave it at that! Reading it will give you a headache )

The advance warning is much appreciated?

 

[LastManOnline]

The advance warning is much appreciated?

By the way, one of your comments sometime ago about "Earthing and bonding been one of the most confusing topics" you have experienced came to my mind last night in relation to several electrical forums I, ve been dipping in to. Its seems to be an ongoing issue within the industry