continuity of radial circuit conductors

[angus65]

Hi

doing R1 + R2 on lighting circuit green probe on cpc

Red probe on Switch line (switch ON) or Line.Which is correct? Switch line to confirm polarity? .took readings on both .why is switch line reading higher. Thank you for any replies.

Angus

 

[ringer]

I take it you have your temporary link at the DB? And you are measuring at the light fitting (ceiling rose?)? What are the readings you are getting?

You should be clipping to the switched line at both the switch and the light fitting (all relevant points on the circuit, recording the highest measured value). Measuring on the switch at the light fitting, operating the switch will confirm polarity.

The switch line at the light will usually be the highest reading (but not always!) because this is the longest length of cable, and you will always get resistance through the switch contacts.

 

[Sparky Ninja]

You'll need to measure to the switch line to verify functionality of the switch and polarity. The increase in the resistance value is likely to be because of an increased conductor length.
Be aware of potentially higher measurements when you measure through a light switch, as these can sometimes introduce higher resistances from their poor contacts.
If you suspect a high value, then short out the light switch and measure again, seeing if the removal of the accessory itself has contributed towards a reduction in measurement.

 

[ringer]

Widdler, I'm not sure why you would want to short out the switch, unless you just want to prove that it is the switch and not a conductor or other termination that is introducing a high resistance? If the switch introduces an excessive element of resistance to the circuit then it should be replaced. If a switch is in a circuit it then forms part of the fault path, and as such needs to be included in measured values.

 

[DurhamSparky]

Take from Switch Live and CPC...

Reading will be high as already said via the resistance through the switch

 

[SirKit Breaker]

Ringer,

What widdler is trying to get at, is that if you do a con check on the switched line, and get a high reading, it could be due to the resistance of the switch contacts, i.e crap switch manufacturer. As you rightly state, the switch could become a problem, and would need replacing. Dead testing is not a science, and sometimes due to a variety of reasons we get iffy results. I would base my condition of the circuit by looking at the measured Zs, if its OK then its OK. I look upon R1 tests etc as a means to prove that i have continuity/polarity, but much else. I only take any notice if i get a stupidly high reading.

Cheers.......Howard

 

[angus65]

Thanks again for your input .I appreciate the time you have all taken to reply.

Exam on thursday, so i may have a few other questions before then.Thank you again.

Angus

 

[ringer]

What exam are you taking? And for what examining body? Make sure you mention which it is before asking any more questions - will help us to give you the 'proper' answer (as expected by C&G etc, such as always do dead tests) rather than a practical real-life answer. Good luck in it anyway, whatever it is.

 

[malcolmsanford]

Of course as well the switch drop might be in 1.00mm and the loop-in in 1.5mm, I know quite a lot of sparks do this.