Main Earth Bonding in a Commercial

[DSpark1]

Hi,

need abit of help in regards to earth bonding.

I'm working on a building with 10 studio flats and all the plumbing is done in plastic pips apart from the terminations of the shower and the water heater.

the main incoming water supply is via a blue plastic pipe, which goes into a manifold and is then spit to the 10 studio flats via plastic pipes. i have ran a 10mm earth cable from my MET to the manifold, however havent taken an earth to the individual studio's as all the pipe work is plastic.

do i need to take a 10mm from the manifold to each studio? and if not then how can i prove i dont have to, as when i was speaking to the NICEIC they said you need to check the discconnection time using 230v/0.03A (being an 30mA rcd protection on the circuits at the board), which gives an aswer of 7666 ohms. But what does that mean? between what do i need to be gettin 7666 ohms?

also i am planing to use this building for my niceic assessment so i will have to no reason's for my doings and he will ask :S

thanks in advance

 

[Guest123]

What the NICEIC are trying to say in their own way is that you need to test the pipework to see wether or not it is an extraneous conductive part.

They have their own take on the figure being 7667 ohms, based on a 30mA fault current. All other bodies recommend using 10mA in the calculation which gives a value of 23,000 ohms.

http://www.electriciansforums.net/e...ical-regulations/16558-extraneous-yes-no.html


The test to see if a service pipe or exposed structural steelwork is an extraneous conductive part is - using an insulation resistance tester set at 500V, test between the installation MET and the pipework or steelwork in question. If the value is greater than 23,000 ohms (7667 ohms according to NICEIC) then the part is considered not to extraneous and therefore does not require bonding.

If you have access to GN 8, you will find usefull info in there.

 

[DSpark1]

Hi Lenny, thanks for your earlier answer. I checked the resistance and it is 15000 ohms however this is with no water in the system. Surely water in the system will make a difference. Do I have to take a reading with the water in the system and then it has to be over 7666 ohms?


If the reading is less than 7666 ohms can I link the pipe with the earths from the water heater and the shower?

 

[telectrix]

think you'll find that water in the pipes will make as much difference as a fart in a thunderstorm. your 15K reading is below what most sparks recommend but above the niceic recommended 7667, so as far as niceic are concerned, they are not extraneous and don't require bonding..

 

[Inteificio]

water is not very conductive at all, if de-ionised it is a surprisingly good insulator.

The more ions you get in there the lower the resistance gets. Humans are basically salt water and conduct electricity. Tap water rarely does.

The reason tap water is so dangerous is the conductivity is similar to a person, but higher resistance so the human in the water becomes the lowest resistance path.

So water is not dangerous due to being conductive, quite the opposite, it is due to being a lousy conductor.