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  1. ringer

    Timeswitching two immersion heaters

    Customer, sports ground changing rooms, has two 3kW immersion heaters (one for home team showers and washbasin, one for away team showers and washbasin) and has asked me to fit a timeswitch. Each immersion heater is on its own circuit, 16A MCB, 2.5mm conductors, singles in plastic trunking and...
  2. ringer

    continuity of radial circuit conductors

    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...
  3. ringer

    continuity of radial circuit conductors

    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...
  4. ringer

    continuity of radial circuit conductors

    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...
  5. ringer

    room thermostat

    Why does it have to follow the same route, tel?
  6. ringer

    Rings or Radials

    Are you sure all your downstairs sockets are on the ring? If your house was built in the 70s/80s/90s it may be a ring upstairs and spurs dropped for downstairs sockets.
  7. ringer

    Broken switch on night storage heater - fixable?!

    I am suggesting that you do a dead test on the switch to check the resistance between the incoming terminal and the outgoing terminal on the switch. So far you have only done a live test for voltage. Check for resistance and operate the switch to confirm the switch is actually switching the...
  8. ringer

    Broken switch on night storage heater - fixable?!

    Continuity - isolate the supply, then check continuity through the switch. I take it you have test equipment?
  9. ringer

    Why fit a pull-cord switch for a shower?

    I have been posed the question (by another electrician) "Why do people fit pull-cord switches in their bathrooms (for a shower)?" He challenged me to find a regulation that requires such a device be fitted. The best I could come up with was 537.2.1.1 Every circuit shall be capable of being...
  10. ringer

    Maximum ZS???

    The problem comes when the measured Zs is over the tabulated values and the installer then ignores this and they then rely on the RCD for primary protection. This is laziness and unprofessional. The correct course of action would be to investigate why there is a high Zs and to correct the...
  11. ringer

    2391 March Completed

    Sorry to hear that. If you don't mind saying, do you know why you failed? Was it on any particular issue(s)?
  12. ringer

    Continuity of ring final circuit conductors

    My head hurts, but I think I get it now. Have drawn it out and stretched out the points to make it two conductors in parallel. Each conductor is (0.5 r1 + 0.5 r2) = 0.5(r1+r2) Because the two conductors are in parallel, the resistance is then halved. 0.5(0.5(r1+r2)) = 0.25(r1+r2) The acid test...
  13. ringer

    Continuity of ring final circuit conductors

    Without going into detail, if it is complicated, can you explain why there is this (miniscule) difference with a smaller cpc?
  14. ringer

    Borrowed neutral and how to fix

    Ackbar, you seem to be missing the point. With two lighting circuits each on their own mcb, and a shared neutral at some point on those circuits, if you isolate one mcb you can get backfeed from the unisolated circuit VIA the shared neutral. It is not about overloading a circuit, but ensuring...
  15. ringer

    Continuity of ring final circuit conductors

    Thanks for answering guys. Unfortunately I still don't get it. I understand that by cross-connecting the legs we have effectively created two parallel conductors. I'm now not understanding how when we connect our low resistance ohmmeter, we get a reading of one quarter of the combined...
  16. ringer

    Continuity of ring final circuit conductors

    Why is it when you cross connect the conductors at each leg and then test continuity, the result is one quarter of the combined resistances of the legs? I am usually pretty good at seeing how/why calculations work out, but just cannot in this case get my head around why the value measured is a...
  17. ringer

    please help with this question

    Do you think using this expression might gain bonus marks in a 2391 exam then? :D
  18. ringer

    please help with this question

    I can only assume that they mean confirm the continued integrity after short circuit conditions, which would be by doing an insulation resistance test.
  19. ringer

    please help with this question

    Richard, you risk here putting the OP on the wrong track. The 70oC is likely to be the maximum operating temperature of the cable, though the specific type of cable has not been specified. It might be 90oC cable for all we know! The point is that the note on Table 41.3 states the values given...
  20. ringer

    Sitting 2392 have practice question cant get the right answer help

    R1+R2 = 0.3 (assuming 2.5mm cable for both R1 and R2 over 20m) So they forgot to add the Ze on when they gave the multiple choice answers to the question :oops: No wonder you are struggling to work out the answer. I would complain to your lecturer if I was you.

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