continuity of cpc

[flukey]

hi all,
got some testing to do where there are some large expensive looking light fittings that i would rather not remove for testing

what methods do you use to get round this problem as i dont want to get caught up in an only fools and horses type moment

cheers in advance

 

[bahco]

well if that is the case then why have they only realised that now?

they need to make there mind up! haha probably just doing it to **** us off

 

[Spudnik]

Just reading through the bits in the OSG it says:

'test between line and earth at each point in the circuit'.

So that includes fittings and switches.

So they havent really changed their minds like we thought.

 

[flukey]

thats what it said in the old book too.

why would they change the diagram then

as per previous post, thinking logically the switch is the end of the line for the cpc so perhaps like bahco says they must have just realised lol

 

[mrloy99]

hi bahco
thats how i was taught too. the question is now whats the reasoning for the method to be changed in osg and gn3. can only summise that as its continuity of cpc the furthest point will be the switch not the pendant irrespective of how its wired.

If there is any doubt,both readings should be compared.There could be 2(or more)lights off the same switch,and in this case the higher reading is unlikely to be at the switch.

 

[iceman]

hello iv just rewired my house for on of me jobs for nic, i been testing continuity of cpc today on a lighting circuit suppying downstairs after iv linked out at the c/u thn connect my metre leads to cpc and switch line the reading im gettin for R1 + R2 is somethin like 0.67 witch is fine but when i comfirm polarity by flickin the switch im gettin a terrific value somethin like 88.9 ohms lol i always thought there was ment to be no reading at all as the switch is closed, or am i just pickin up the resistence of the cable??? im gettin the same sort of thing when comfirmin polarity for landing light swiched upstaires and downstairs with strappers.

also theres a garage suppy feeding 4 socket outlets and 3 lights when messuring Zs do i take the reading frm the fuse spur suppyin the equiptment?
any help would be great cheers

 

[mrloy99]

hello iv just rewired my house for on of me jobs for nic, i been testing continuity of cpc today on a lighting circuit suppying downstairs after iv linked out at the c/u thn connect my metre leads to cpc and switch line the reading im gettin for R1 + R2 is somethin like 0.67 witch is fine but when i comfirm polarity by flickin the switch im gettin a terrific value somethin like 88.9 ohms lol i always thought there was ment to be no reading at all as the switch is closed, or am i just pickin up the resistence of the cable??? im gettin the same sort of thing when comfirmin polarity for landing light swiched upstaires and downstairs with strappers.

also theres a garage suppy feeding 4 socket outlets and 3 lights when messuring Zs do i take the reading frm the fuse spur suppyin the equiptment?
any help would be great cheers

I think the furthest light,as it would be the extremity of the circuit.
As for your r1,r2 readings,when my meter leads are short circuited it shows 00.0 and open circuit 1(scale to 200) What readings do you get on megohm scale.(I think you meant to say switch is open)

 

[beaver74]

funny you should say that mrloy, just flicking through gn3 and noticed on page 35 that the r1 r2 reading is in fact being taken at the switch.

never noticed that diagram before because ive always taken reading at the fitting as that was the way i was taught, but thinking logically the switch would be the extremities of r1 r2 would it not.

would certainly make my life easier

i would say that switch line to earth at fitting would be the extremities as the feed go from fitting to switch then back co fitting

 

[iceman]

hi i testin the insullation resistence on megohm scale set at 500v and tht was all fine the only probley i had wos a dead short on the garage supply between neutrel and earth it was doin me head thn when i went to do Zs i forgot the luminare wos still fitted, i best not do tht on me assessment or the N I C guy will send me straight to hell lol

 

[Guest123]

also theres a garage suppy feeding 4 socket outlets and 3 lights when messuring Zs do i take the reading frm the fuse spur suppyin the equiptment?
any help would be great cheers

Hey mate.

You would need to measure Zs at - your consumer unit, the socket outlet circuit and the lighting circuit within the garage, not quite sure what you mean with the fuse spur supplying the equipment bit.

Can you clarify?

Cheers.

 

[moorhouj]

Back to switch vs fitting - for a loop in wiring - would have expected R2 to be greatest at switch, as extra CPC from fitting to switch, but R1 greatest at fitting as have to add phase path to and back from switch. So for this arrangement, in 1mm, the fitting should be greater by the resistance of the length of a single cable from fitting to switch, but in 1.5/1.0 this drops to 0.5 of this. But if it's JB wired the relative distances come into play, and any other arrangement can give either as max, so you really do need to measure both unless you are sure how its wired.
Jack

 

[iceman]

hi theres a 20 amp circuit breaker suppying the the garage witch feeds socket outlets and a light circuit the supply comin in goin to a j/b then to a 13amp fuse spur i wanted to knw when messuring Zs do i take it at spur i wouldnt of thought i take it frm light fitting radial sockets cos there are seperate circuits

thanks

 

[Spudnik]

Zs is measured at the furthest point on the circuit.

So, just guessing, at the last light fitting on that 20A radial, or literally, the furthest point from the CU.

 

[iceman]

so i gotta eather take a reading for Zs at the futhest light fitting or the socket outlet witch ever is the greater???

 

[Guest123]

Hi.

Sorry I thought you had a DB in there.

If it's just the one circuit then yes you just find the firthest point on it, and measure your Zs, from there.

Although if coming out of that joint box that you have, a feed to socket outlets and then another feed to a fused spur in turn feeding your lights then I would take 2 readings and record the highest.

Cheers.