Discuss Max Ze for TT system in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net
Just to clarify,
the max recommended values I gave earlier were for run of the mill and domestic type circuits and not for the more specialised installations.
Edited last post. Not necessarily!
ADS doesn't rely on the customer being the earth! lol
My question was only 'will it work!' :devilish:
Do not need to discuss all the diferent scenarios.
Then the right answer would be - Not always! lol
Final answer?
What about class 2 lighting circuits that have no earth?
So, is your nightmare an illiterate Electrical Trainee, Part P 'registered' trying to 'do' a TT install
Please give people some credit - the wording is not that technical. There's a big difference between 'over 200 ohms can be unstable' and '200 ohms is the maximum permissible value'?
^ yea!!!!!
I'll leave the nightmares to the clever people like of you...
There are a good few real electricians out there that have never touched a TT system in their lives before, and as has been seen from previous threads and posts, that they will also take that 200 ohm figure as meaning the maximum. Like many other areas in BS 7671 things can be a tad on the ambiguous side, especially if you don't take the time to read things through to fully understand what's being stated.
Does rcd not provide fault protection on said circuit with no cpc. Andy leakage and bang trips.
Domestic wise however, I'd be happy with a couple of 4 footers, an Ra value of 200 ohms and a type-s up front. Last year I happily left a domestic with an Ra value of around 250 ohms even after punching in 8 foot of copper into solid chalk. I went back every month for six months in a row to check its stability and the value hadn't budged.
I dunno Mr D, outside of the realms of our normal installations I could think of a few exotic cases where an RCD could be used that wouldn't use an earth per se
Like what?
Certain IT systems use some pretty exotic protection schemas
also some DC systems are another
I will not mention this part again, let the thread continue un-abated
I like a little banter myself but some of the drivel in this thread boarders on people stuck up their own arses trying to score cheap points. Tone it down guys, its not big and its not clever.
Special thanks to Wirepuller and Engineer 54.
Sorry to be thick, but how does an upstream s,type provide more protection, unless you nail the tails ?There are always going to be situations such as you have described due to horrendous soil/ground conditions, and you're solution of an upfront S type, backing up any standard 30mA RCD's is the route i would also take, in such circumstances...
I too have a good amount of chalky soil on my property in Cyprus, but thankfully not to the extent of causing me major problems on my own system...
I was thinking the same, funny worldInteresting how you give special thanks to the two very people that most on here would regard as being at complete opposite ends of the spectrum with regards to their opinions on domestic TT systems yet refer to others opinions as drivel?
I'll put my tin hat on and take coverSorry to be thick, but how does an upstream s,type provide more protection, unless you nail the tails ?
Regards
I'll put my tin hat on and take cover
What was it you said:
"I got a bite! A big one! C'mon lads, get the landing net out ready, this one's gonna be a wriggler!"
Sorry that I'm not interested in winning popularity contests and taking sides in petty arguements.
I thanked everyone on the thread especially those 'wirepuller' & 'Engineer 54' whose advice I followed and which resolved my situation and in fact got me extra work.
However if this leaves you feeling a little under appreciated:
My big boy pants are in the wash so I'm too afraid of a bitch slapping!You can answer If you want.:cheesy:
Sorry to be thick, but how does an upstream s,type provide more protection, unless you nail the tails ?
Regards
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.
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.
I just find it strange that my singling out of the two individuals whose advice I followed was questioned.
It will provide backup in the unlikely...(although some would argue likely)...event of the 30ma RCD failing to trip on an earth fault.After all on a 'normal' uk TT system with an Ra exceeding that which will operate an OCPD you are completely reliant on a single RCD for earth fault protection.
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.
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...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?
I bet E54 is loving this lol
You can have whatever your heart desiresCan you get 30mA time delayed RCDs?:devilish:
sadMy big boy pants are in the wash so I'm too afraid of a bitch slapping!
Reply to Max Ze for TT system in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net
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