Calculating R1+R2

Length of circuits in meters multiplied by themilliOhm resistance valueof the cable (multiplied divided by 1000 to convert the miiliOhm value back to Ohm).

milliOhm resistance values for cables found in Big Red Book and OSG

[Edited for stoopid mistake]

 

You need to look in GN3 Appendix A.
It gives a list of the R1+R2 per meter for a number of conductor sizes and variations.
2.5mm² T&E with 1.5mm² CPC is 19.51,
6mm² T&E with 4mm² CPC is 7.96
and 1.5mm² with 1mm² CPC is 30.20.

 

Easiest way to calculate R1 + R2 of a ring circuit is divide the end-to-end resistance of the phase conductor added to the end-to-end resistance of the cpc by 4

(r1+r2)/4 =R1+R2

The reason for this is a ring circuit comprises of parallel conductors.

Standard circuits for what you are designing would be as follows:

32A ring circuit 2.5mm2 T&E
32A radial cooker circuit wired in 6mm2 T&E
6A radial lighting circuit wired in 1.0mm2 T&E (1.5mm2 is usually not necessary)
20A (or 16A) radial immersion/heater circuit in 2.5mm2 T&E (not necessary to fuse down but can be on a 13A FCU)
6A radial smoke detector circuit wired in 1.0mm2 T&E (again 1.5mm2 is overkill). For extra brownee points you could specify that it is shared with the lighting circuit which is popular way of doing it. Reason is a lighting circuit failing is more likley to get prompt attention than a stand alone smoke detector circuit which could be left longer).
32A garage supply wired in 6mm2 T&E (or 3-core SWA)
Don't forget main earth conductor 16mm2 (or 6mm2 min on a TT)
10mm2 main bonding conductors.

 

He's designing it, there's nothing to measure yet. If in fact there ever will be.

 

Get in touch with the IEE or the IET as it`s now known as. Ask for publication ELECTRICAL INSTALLATION DESIGN GUIDE. It will tell you all you need to know ffor these calulations and more.

 

At DB position for Ring Final r1 +r2 ..cant you just block (on one leg) the L + CPC together and measure across the L + CPC on t'other leg?..while your at it just whip the N to E also (after disengaging the L)  just to verify continuity on this..?

Observe All Isolation Procedures OP

 

Oh right estimated on paper..sorry Mr Clark dunno owt about all that stuff as it comes under design (pre-deployment  verification of circuit/s)..more applicable to industrial design I would have thought.

 

JP:  Did you used to be in the military?

All this 'deployment' malarkey does my noodle in.

Regards,

S.

ma·lar·key/m??lärk?/
Noun: Meaningless talk; nonsense

 

Unfortunately no you can't do that. You cross connect the phase and cpc then test across the terminals. GN 3 explains. That gives you the R1 + R2 by measurement. This guy is just doing a college design project so needs theoretical value for his college work.

 

Cheers Un for that. Un can you reccommend a good  (not to expensive) book on testing procedures. You know a step by step guide on testing but without a myriad of technical bumpff surrounding the test?..Cheers M8.

 

To be honest J.P. IET publication guidance note 3 reallly is the best book on the subject. It is well written and easy to understand. I am sure you would be okay with it. How about getting one ordered down your local library?

 

Much obliged for the info Un, and I will look into it.

 

J.P. Have given up on thanking people for any replies that may be forthcoming?

 

Being idle on what page in red book are milli/ ohms per meter found easy in on site guide

 

hi today i had to fill in a minor works for some bathroom spot lights, my Zs from a pendant measured 1.56ohm which is good but my r1 +r2 was 1.34ohms, the house is not anything too big, just a 4 bedroom? can anyone help me on if this reading is too high or...? thanks guys

 

Why do you think it is too high?

What is the maximum permissible Zs for your circuit

 

Go away , it's not Monday yet