Re: 4mm resistance

[maher]

hi all ,
I am a new B
i am rewiring new ring mians could someone tell me what the ressistance for a 4mm ring main should be to pass
what is the max in homs
and on a 100A mains what is the max amps in brakers i could have.
thank you.

 

[cornburn]

Um, do you have any books to reference? There are many tests that need doing, requiring a low resistance ohmeter, earth loop impedance tester, insulation resistance tester, RCD tester and figures need to be compared to those in the Regs. Do you have any of these, or experience to know how to use them?

 

[maher]

thanks for the reply.
I have the knoledg and experiance in using the tools needed as i am an electritian but in franc not UK and i do not know the exact reqyrment for the UK
I have done the impedance test on the ring on a 4mm twin and earth and i gut 0.45 homs. just wanted to know would this reading will be ok to call a tester to come and certfy my work. or do i need to split the ring to 2 ring mains.
thank you
sorry for the bad english.
best regards
Maher

 

[Doug]

There are several different tests that measure impedance. You could be thinking of Zs (earth fault loop impedance). The max Zs for a circuit depends on the fuse or circuit breaker protecting that circuit. For example, the IEE On Site Guide says that a circuit with a B32 breaker has a max Zs of 1.16 Ohms.

If your reading of 0.45 Ohms is the highest Zs reading for the circuit then you are well within 1.16 Ohms. Of course, if you have a C32 or a B40 breaker or you have been measuring (R1 + R2) then you will be closer to the limit.

The most you can draw using a 100A supply fuse is of course 100A. But the max demand for your installation is likely to be less than the sum of the individual circuit breakers. You can calculate this using diversity.

 

[bugsy]

I think its 1.16ohms, 60898 mcb max cable length 160 m or there abouts ,
this is a 2 bottle pino grigio calculation

 

[maher]

thanks to every one, i have gone to the bock shop and got myself 2 books first one title 17th edition IEE wiring regulation Design and Verification ISBN: 978-0-7506-8721-8 2nd book17 IEE Domestic Electrical wiring ISBN: 978-0-7508-8735-5.
i found the 2 books are very good and verry helpful, it is a must read for any one starting to learn about new regulation
thanks again to all of you .
best of luck
maher