Max Ze for TT system

[LeeH]

RCD on a TT must operate within 200mSec. this is achieved by a Zs value of <1667 (30mA RCD).

Of course, my bad.

 

[MBEINST]

Hope this isn't a stupid question,

Given what has already been discussed regarding TT systems, how is it possible to get acceptable Zs readings which will comply with table 2D OSG.

 

[Guest 004]

Hope this isn't a stupid question,

Given what has already been discussed regarding TT systems, how is it possible to get acceptable Zs readings which will comply with table 2D OSG.

Simple you can't

 

[D Skelton]

When i first came into this industry the recognised max for a Roded earth electrode was 10 ohms, FACT!! Never saw one anything like at that value mind, all were generally in the lower single figures.

So now were being sold a complete crock crap that 200 ohms is the max figure to aim for!! If for no other reason, a 200 ohm earth electrode, or anything remotely like it will ''NOT'' provide a stable TT system.

I got a bite! A big one! C'mon lads, get the landing net out ready, this one's gonna be a wriggler!

 

[Guest 004]

Was going to reply, then realised how bigoted some posters are, so will just watch and read with delight.

 

[telectrix]

you seem to be confusing bigoted with banter. we all know eng54's ideas on rodding ( not that sort of rodding, geordie).

 

[Guest 004]

Oh yes you are correct, I feel really stupid now

 

[telectrix]

that gives me an idea. let's ask dan to create a "really stupid" forum. any poster thinking his question might be stupid could post in there and be assured of stupid answers. the mostr stupid response of the week could get a prize of a broken light bulb. :6:

 

[Deleted member 9648]

I got a bite! A big one! C'mon lads, get the landing net out ready, this one's gonna be a wriggler!

 

[SPARTYKUS]

It shouldn't cost a penny, the old regional boards used to convert TT systems for nothing, in fact that was one of the main reasons the electricity boards invested so much cash into PME'ing overhead and later failing underground cables, to provide homes and businesses with a stable means of earthing!!

Seems now the private DNO's think it's fine to charge for this once totally free service. But seeing as it takes about 2 to 3 min's to convert (depending on the service head) it shouldn't cost an arm and

recently quoted 140-160 by the DNO - in the end after tea and biscuits, no charge. And a free isolator. Yippee.

 

[baggy61]

When i first came into this industry the recognised max for a Roded earth electrode was 10 ohms, FACT!! Never saw one anything like at that value mind, all were generally in the lower single figures.

So now were being sold a complete crock crap that 200 ohms is the max figure to aim for!! If for no other reason, a 200 ohm earth electrode, or anything remotely like it will ''NOT'' provide a stable TT system.

With respect, how big were the rods & how close to the ss would that have to be.
I never seem to see much below 30 ohms.
Regards

 

[baggy61]

Sorry, for ss read PMT>

 

[i=p/u]

My first and last one was 14 .8 ohms and 150m from transformer and I got rods in at 3+4 formation

 

[Engineer54]

With respect, how big were the rods & how close to the ss would that have to be.
I never seem to see much below 30 ohms.
Regards

Well they certainly wasn't the short thin twigs you see today!! 10' / 5/8''-3/4'' foot rods were the standard in those days. In fact i have only recently (last year in Cyprus) seen for the first time a 1.2m 5/8'' rod, and was told they only use them as an extension. Myself, i've never used anything other than 3m 3/4'' rods on any of the projects i've been involved on.

As for you only seeing 30 ohms, i can assure you sub 1 ohm values can be gained in the UK in many areas, in some without too much trouble at all...


You can listen to these silly buggers scoff, but you'll not find another country, (certainly none that i'm aware of) that has a ridiculous max Ra of 200 ohms on a roded or any other earth electrode system!! Even the Yanks have a max of 20 ohms for a single rod (oh and they like most other countries still use 10' copper clad rods)!!!

 

[Engineer54]

Originally Posted by D Skelton
I got a bite! A big one! C'mon lads, get the landing net out ready, this one's gonna be a wriggler!

I have no need whatsoever to wriggle, especially on this subject!!