Max Ze for TT system

[Deleted member 9648]

Sorry if I've upset the apple cart gents.

I just find it strange that my singling out of the two individuals whose advice I followed was questioned.

Indeed as my original post clarified "TT virgin" my knowledge on TT is limited and has now been enlightened somewhat.

The end result is I learned and won extra business. Both of which I am thankful for.

It appears that I have affronted one of the inner circle and the wagons are circling so before this gets silly.

Once again thanks for the lessons and the input.

Best regards to you all.

To fill you in a little there have been some pretty hot debates on this historically. I am firmly in the camp of either get a STABLE TN value of Ra that will operate an OCPD...ie sub 1 ohm.....Or dont,in which case it matters not whether it is 20 ohms or 200 ohms as you are totally reliant on an RCD for earth fault protection,and said RCD will trip just the same at 20 ohms or 200 ohms.I'm also of the opinion that where such Ra values are the case the much hyped STABILITY is overated as we know that our 30ma RCD will be good up to 1667 ohms,which means a sub-200 ohms Ra will have to be UNSTABLE to the tune of 1447 ohms before we need to be concerned. Of couse those values would be less if we had a 100ma RCD as well,but you get my drift?

 

[MBEINST]

"I have returned with this update to thank you all for your input and advice. You have succeeded in enlightening a raw but 2391 trained spark"

 

[richy3333]

To fill you in a little there have been some pretty hot debates on this historically. I am firmly in the camp of either get a STABLE TN value of Ra that will operate an OCPD...ie sub 1 ohm.....Or dont,in which case it matters not whether it is 20 ohms or 200 ohms as you are totally reliant on an RCD for earth fault protection,and said RCD will trip just the same at 20 ohms or 200 ohms.I'm also of the opinion that where such Ra values are the case the much hyped STABILITY is overated as we know that our 30ma RCD will be good up to 1667 ohms,which means a sub-200 ohms Ra will have to be UNSTABLE to the tune of 1447 ohms before we need to be concerned. Of couse those values would be less if we had a 100ma RCD as well,but you get my drift?

Don't anyone say I didn't advocate the wearing of a safety helmet. Run for the bunkers the B52's will start bombing soon...

 

[spark 68]

I bet E54 is loving this lol

 

[RogertheBodger]

I bet E54 is loving this lol

One thing for sure, we'll know either way soon enough lol.

 

[Deleted member 9648]

 

[i=p/u]

I still say under 200 rock on but the lower the better..

 

[SPARTYKUS]

Can you get 30mA time delayed RCDs?:devilish:

 

[richy3333]

Can you get 30mA time delayed RCDs?:devilish:

You can have whatever your heart desires
except anything French, or the Shiant Islands!

 

[baggy61]

My big boy pants are in the wash so I'm too afraid of a bitch slapping!

sad
lad

 

[Engineer54]

It basically comes down to, ....those that will make an effort to install a ''Working'' TT system or those that have no intention of making any effort and taking that 200 ohm value as a lame excuse to do virtually nothing, because they are in there mind, complying. Of course stability would then indeed have to be overrated wouldn't it, regardless of what any of the multitude of papers written on the subject have to say!!

 

[Engineer54]

Can you get 30mA time delayed RCDs?:devilish:

Yes, more than a few well know manufactures provide them...

 

[Deleted member 9648]

It basically comes down to, ....those that will make an effort to install a ''Working'' TT system or those that have no intention of making any effort and taking that 200 ohm value as a lame excuse to do virtually nothing, because they are in there mind, complying. Of course stability would then indeed have to be overrated wouldn't it, regardless of what any of the multitude of papers written on the subject have to say!!

In the highly unlikely event that I ever again have to install a TT to either a commercial or large residential then yes...I would be making an effort to get a TN value.I say highly unlikely because these days TNCS is almost always available in my area. I still do a lot of TT's,but small scale. The most recent being a small unit supplying a few sockets for small fairground/entertainment use on a playing field,and temporary civil engineering supplies on a sea front site.For those I believe the standard UK sub 200 ohm and RCD arrangement is perfectly adequate,and if it was 150 ohms at the time of installation and when I came back for a 3 month re-test it had risen to 160 ohms it wouldnt worry me in the least.
That said as Skelton stated in a previous post....I regularly go back to TT's I have installed over the years and cant ever remember initial readings varying to any great degree.

 

[Engineer54]

In the highly unlikely event that I ever again have to install a TT to either a commercial or large residential then yes...I would be making an effort to get a TN value.I say highly unlikely because these days TNCS is almost always available in my area. I still do a lot of TT's,but small scale. The most recent being a small unit supplying a few sockets for small fairground/entertainment use on a playing field,and temporary civil engineering supplies on a sea front site.For those I believe the standard UK sub 200 ohm and RCD arrangement is perfectly adequate,and if it was 150 ohms at the time of installation and when I came back for a 3 month re-test it had risen to 160 ohms it wouldnt worry me in the least.
That said as Skelton stated in a previous post....I regularly go back to TT's I have installed over the years and cant ever remember initial readings varying to any great degree.

You have often stated in your posts, that soil/ground conditions in you're particular area are not good, and that's fair enough as far as i'm concerned. But you can't go making the same assumptions to those posters that work in and around pretty decent areas, where in some cases i personally know near TN values CAN be attained, in some cases pretty easily too.

Personally i would endeavour to initially treat domestics as i would any other type of installation, only backing off, to let's call it the fall back position, when costs are going to be a major factor.

 

[sparks1234]

We know what it say's, but i'll guarantee you, that virtually every poster that comes on this and other forums, that isn't knowledgeable on TT systems, take that figure in BS 7671 as being the stated maximum and that's what they inevitably will work too!! ...And why i always Poo it off!! lol!!

The whole section on TT earthing needs a thorough sorting out and a bit more guidance wouldn't go amiss either!!

I'm going home (Cyprus) for Xmas this year, and while home, i'll be checking my own TT system. Earlier this year (early summer) it was around 0.93 ohms which has been steadily dropping year on year from around 4'ish ohms.

Here on site, our earth fields were tested middle of last month and recorded 0.17 ohms and 0.21 on the other. The highest value recorded this year was 0.28 and 0.30 respectively, which corresponds to similar test results conducted last year.

It's surprising what can be achieved when you know what you're doing!! lol!!

So that's what you do with your christmas

think I'll eat turkey and have a good time, knickers to the earth rods