Ring main readings??

[gpz900jim]

On ring mains, am i right in thinking that if you take the loop reading from the live, add it to the loop reading of the earth, divide it by 4, it should equal your r1 plus r2 reading (live and earth cross connected)? Cheers

 

[telectrix]

yes, but you should have used caps for R1+R2. small r denotes end to end resistance.

 

[ezzzekiel]

near enough, wont be exact especially on older installations, higher readings tend to indicate spurs

 

[telectrix]

it gives you an idea of what to expect. as ezzzy says, spurs will give you a higher reading on R1+R2 as the end/end res. of the ring does not see the spur/s.

 

[gpz900jim]

thanks gents, and yes, i will mind my rs as opposed to my Rs

 

[telectrix]

as long as you know your r's from your elbow. but bear in mind, in an exam, just getting that wrong will lose you a lot of marks, and on a certificate would cause confusion, when the 17th amendment is supposed to do that.

 

[Sintra]

And so will calling it a ring main as opposed to a ring final circuit.

 

[telectrix]

picky, but correct, sintra.

 

[PC Electrics]

Yes. Expressed mathematically:

R1+R2 = (r1+r2)/4

where;
r1 = end to end resistance of line on an RFC
r2 = end to end resistance of cpc on an RFC
R1 = resistance of line from MCB to furthest point on any circuit
R2 = resistance of cpc from earth bar to furthest point on any circuit
In the case of a perfect ring, R1+R2 is equal at all points (electrically there is no furthest point - all points are the same)

 

[PC Electrics]

Some may think that getting terminology and symbols wrong doesn't really matter that much, but if you think you are ever going to do your 2391, then you should get used to getting it correct now, because failure to use the correct terminology is always a significant factor in it's high failure rate (see any Chief Examiners report - it's a common theme)

Correct terminology also enables us to discuss technical matters precisely and concisely without confusion. Where terminology is wrong confusion often ensues about what someone 'means'.

 

[Geoffsd]

Some may think that getting terminology and symbols wrong doesn't really matter that much

but they are wrong.

 

[B6 7BU]

And so will calling it a ring main as opposed to a ring final circuit.

Who is right the so called electrician or the customer?

[video=youtube;_YUbpJl63mo]http://www.youtube.com/watch?v=_YUbpJl63mo[/video]

 

[PC Electrics]

Who is right the so called electrician or the customer?

The customer is a lay person and as such is entitled to get the terminology incorrect. Generally there is no need to correct him, just translate in your head.

 

[gpz900jim]

yes you are all correct, terminology is very important

 

[telectrix]

yes you are all correct, terminology is very important

sorry to be picky then, but it's not a ring main, as your title implies, it's a ring final circuit.