Chapter 5: Inspection, testing and commissioning

[TheRoadEnd]

basically been given homework from colllage so i will ask a few questions on this rather than make 30 posts if im stuck haha

first one im stuck on

The value of R2 for a ring circuit phase conductor has to be revorded on a schedual of test results form. how do you determine this value?

(fools explanation required HAHA)
Is this just asking how i get my R2 reading, if so how do i do this.

 

[trev]

Think RFC testing mate, what are the first steps you take?
On the test results sheet you're going to have 3 boxes for your end to end tests. Ordinarily they're marked as L-L, N-N and CPC-CPC or something similar (I normally do it without thinking)

 

[MDJ]

Trevs right, when I install a ring main I always test it for continuity without even thinking about it, to ensure it is a ring and theres no break in the circuit, you can do your r1+r2 and r2 at the same time.

 

[Paul.M]

I think what the question is asking is How do you assume or work out the R2 figure before taking a reading?

Do end to end test on R1 and Rn. Lets say you get a measurement of 0.5 Ohms on each. The csa of each conductor is 2.5mm and the CPC/Earth is 1.5mm therefore the resistance of the CPC should be 1.66 times higher than the R1 and Rn (2.5mm divided by 1.5mm = a times factor of 1.66)

So if you times you R1 reading of 0.5 Ohms by 1.66 you get 0.83 Ohms, that is the number you should get when testing the CPC/earth end to end.

If you get a lot higher than 0.83 Ohms, you've got a problem somewhere and needs investigating. If it is just a little bit higher, dont worry about it too much but at least you knw what figure you should get before testing.


For a R1 + R2 you should get result of 1.33 Ohms (0.5 + 0.83).

 

[Sintra]

I think what the question is asking is How do you assume or work out the R2 figure before taking a reading?

Do end to end test on R1 and Rn. Lets say you get a measurement of 0.5 Ohms on each. The csa of each conductor is 2.5mm and the CPC/Earth is 1.5mm therefore the resistance of the CPC should be 1.66 times higher than the R1 and Rn (2.5mm divided by 1.5mm = a times factor of 1.66)

So if you times you R1 reading of 0.5 Ohms by 1.66 you get 0.83 Ohms, that is the number you should get when testing the CPC/earth end to end.

If you get a lot higher than 0.83 Ohms, you've got a problem somewhere and needs investigating. If it is just a little bit higher, dont worry about it too much but at least you knw what figure you should get before testing.


For a R1 + R2 you should get result of 1.33 Ohms (0.5 + 0.83).

Surely for a ring final its (r1 + r2) / 4 = R1 + R2

 

[Paul.M]

Surely for a ring final its (r1 + r2) / 4 = R1 + R2

Yes mate it is but I'm really not feeling well after last night so go easy on me lol.

ps I'm doing a fault find later with Mr. 7677, I'll say hi for you. Btw its a fault that I did I think, he's coming along to take the mick out of me pmsl. I may post it up later if it is relevant to the trainees. Think I'll be doing some rewiring on a Sunday afternoon, great, just what I need.

 

[Sintra]

No probs mate, tell him I said hi also.

 

[Paul.M]

No probs mate, tell him I said hi also.

I did do. Bless him, he brought me a present for my "help" over a certain matter, he got me a new copy of GN7. I cant find anything about a kitchen being a special location Sintra lol



To the op. sorry for taking your thread off topic but sometimes it is the only place I can openly talk like this.

 

[Sintra]

Lol it's not in my GN7 as a special location either. :lol: Some folk just get slightly confused by building regs and wiring regs.