Strange Zs Results | Page 2 | on ElectriciansForums

Discuss Strange Zs Results in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

Hey.

For a TT system the max Zs values in 7671 are not applicable, on the next page you will se for TT systems the the max is 1667ohms to enable operation of a 30mA RCD in the desired times at a safe touch voltage of 50V.

Really the RA should be well below 200ohms as this is the accepted value (about 100ohms is spot on) allowing for soil conditions weather etc. As you have 39ohms you have an excellent reading there so no need to worry at all.;)
 
Joe never say sorry for BUMBLING thats what this forum is all about helping each other with the things that bug us in the job. If you learn we succed and how many people have learned from this thread as well the time will come when I will BUMBLE and someone like you is gonna help out:)

Chris
 
Thanks for everyones help on this. I passed my inspection yesterday!! Will definately recomend this site to my sparky mates! ;)
 
Cheers mate. What a nerve-racking 3.5 hours! But he was a nice guy and turned out to be as much of a car-nut as I am so we had a good chat!
 
Hope you passed mate ;). The guy I had was supposed to be a hard cookie from what I have heard from a few mates in the trade. I found him a very easy to talk to guy who is very knowledgeable. I got a lot of questions answered by him about he does things and to be honest, we're all in the same game but they've just got to another level!!
 
Just been reading your thread Joe and wanted to add my congrats. The NIC inspectors are a good bunch even, if they are bookworms.:D Most can quote the regs without even looking it up.
Just wanted to be sure you are clear on a couple of points with regards to your tt readings.
Mainly that you need to relate two methods of fault current protection in a TT system.
a) is your fault current from phase to earth that is dealt with by your 30ma rcd, mainly because with the higher Ze values its the only way to achieve disconnection times. Remember ohms law and the magic triangle V=IxR. The value of 1667 ohms makes sense if you apply it to the 50v rule in other words I= 0.03 x R=1667=V which is our 50 volts.
b) is your fault current from phase to neutral and this is taken care of by your mcb, ok an mcb is quite capable of giving earth fault protection in lower earth resistance path systems like tn-s 0.8 ohms or
tn-c-s (pme) at 0.35 ohms (max recommended) But as said our rcd is coping with that one on TT.
Anyway for phase to neutral we can rely on table 41.3 because our phase to neutral loop will (or should) be much lower and hence our generated pfc much higher,again ohms law will bear this out.

I expect a few of the lads on the forum will be having a chuckle for my waffling on. But I have seen some good sparkies make simple mistakes for years and not realise, just because they haven't grasped the basics early in there careers. For example taking an earth loop and there pfc from the same reading
(Highest pfc will almost always come from phase to neutral) or high ring main continuity (Forgot to null the leads)
Anyway I will shut up now;) Well done to you for getting through.
 

Reply to Strange Zs Results in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

News and Offers from Sponsors

  • Article
As the holiday season approaches, PCBWay is thrilled to announce their Christmas & New Year Promotions! Whether you’re an engineer or an...
Replies
0
Views
329
  • Article
Bloody Hell! Wishing you a speedy recovery and hope (if) anyone else involved is ok. Ivan
    • Friendly
    • Like
Replies
13
Views
886
  • Article
Join us at electronica 2024 in Munich! Since 1964, electronica has been the premier event for technology enthusiasts and industry professionals...
    • Like
Replies
0
Views
857

Similar threads

Evening all, Just after a sense-check before I commit & send the quote. I’ve been asked to run in an SWA to feed a small CU that’ll sit inside...
Replies
0
Views
137
For what OCD? There may be other means of over current protection that allow a Zs of0.45 (HRC Fuse?)
Replies
3
Views
497

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

YOUR Unread Posts

This website was designed, optimised and is hosted by untold.media Operating under the name Untold Media since 2001.
Back
Top