TT Ze >200 ohms Advice Needed

[Wattsy]

Hi, what would you guys do if your doing some work on someones TT installation and the Ze is 320ohms?

I know its recomended that it doesn't exceed 200 ohms but rcds will operate at 1667 ohms

I will investigate it and advise the customer if it needs a new electrode etc but is it still acceptable to continue work ie. extending a circuit?

Many Thanks

 

[paul b b]

i would not extend circuit untill ze was down to below 200, if its easy to fit a new rod (or 2) do so asap

 

[sparkytim]

Its your call but can you find the regulation that says it HAS to be less then 200ohms?

I have many times come across this situation and tried to reduce the Ra by various means and still NOT been able to get below the 200.

At 320ohms you still have a HUGE way to go before you hit the Regulation minimum for a 30 m A RCD.

I have a Mobile home park I look after which has a certain section it has proved IMPOSSIBLE to reduce below 300 or so, I am confident that no one is at risk.

The only problem I have had is with BG "Testing" the earth with a Plug in Zs indicator which has Max Range of 200ohms, and refusing to install a new boiler until it was "made safe".

 

[Wattsy]

Thanks for the replies i think i'll investigate the earth rod and put in the minor works certificate that a new earth electrode is advised etc.

Because if you go by Reg 411.5.3

Ra x delta n equal to/less than50v

then 320 x 0.03 = 9.6v

So that equation is satisfied

Has anyone else got any views on this situation?

Sparkytim how did you get over the situation with BG?

 

[Andy™]

you should find out why its so high - i.e gorund conditions or dodgy connection.

 

[sparkytim]

Hi

Despite trying to educate them, they insisted that they would NOT instal boiler untill "made safe".

Fortunatly that side of the site had better ground conditions and I was able to reduce to below 200 by installing a 2nd stake.

 

[batty]

It may be a bad connection at rod which needs investigating as it may get worse. I would try a new rod if that doesn't work at least you tried. In my area we have clay which gives a very good earth or chalk which is a nightmare and sometimes you cannot get a good reading let alone knock another rod in.