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Re: Insulation Resistence Testing

Adam Kuzack

Re: Insulation Resistance Testing

This may seem like a stupid question, one that is probably abundantly clear, but it's baffling me. 

In a circuit where there is two way switching, the IR test requires that the switches need to be 'toggled. Therefore, the requirement to repeat the test.. Similarly with a circuit with intermediate switching, there is a requirement to operate the switches. 

What is confusing me, (and I have drawn out the wiring diagrams by hand and the various combinations) trying to understand,as to how the switches should be operated and tested. 

i.e with two way switching - IR test, alternate switch on one switch and test, and alternate the 2nd switch and test....or IR toggle both switches and test. 

 i am assuming that on the first test uncertainty exists and there is no way of knowing whether  the circuit is off/on.

Does it matter if the circuit is connected via 3 core system - common in domestic setting where there is a single strapper and permanent line (PL) and switched line (SL) are via l1 and l2 or if it connected via 2 strapper system with PL from switch A  com and Sl from Switch B  Com. 

From my wiring diagrams and tracing it - it seems that with the single strapper system and the two way strapper system - switching works differently and the electrical flow is different. 

How would it be done, combinations with the intermediate switching?

sorry for the   long question..but want to be clear  as to the process. 

Parents
  • 0

    If you do the test as L+N in parallel to E, then the exam question, is are there any lengths of wire not tested in any switch positions .

    Now consider

    here a short to ground on any wire will be found if the bulb is in but if it isn't then in neither of the 2 off states then the bulb live  (here gry) wire will not be energised, and neither will the central (black) wire in one of the 2 'off' states. In the on state, all wires get tested.
    But how do we know - well test, flick one switch, test again.
    Now consider


    here again if the lamp is in the off states get tested. But in either one 'on' state, the unused path is not tested.  Here we need to either fit the lamp, or toggle both switches to be sure.
    Now intermediate switching is more complex. Here again there are 2 ways to wire, plus the intermediate crosses or un-crosses the laterals. At worse, again 2 switches must be operated to cover all cases.

    Note that other things like heating systems have similar untested branches depending for example on thermostat and timer states, but in practice where it is too hard to force the switch states, it is usual to inspect visually and then not worry too much. Very rarely you see things where for example a trip fires when a given heating zone comes on.

    Mike


    Acknowledgement to JW and DIY wiki for their pics.

Reply
  • 0

    If you do the test as L+N in parallel to E, then the exam question, is are there any lengths of wire not tested in any switch positions .

    Now consider

    here a short to ground on any wire will be found if the bulb is in but if it isn't then in neither of the 2 off states then the bulb live  (here gry) wire will not be energised, and neither will the central (black) wire in one of the 2 'off' states. In the on state, all wires get tested.
    But how do we know - well test, flick one switch, test again.
    Now consider


    here again if the lamp is in the off states get tested. But in either one 'on' state, the unused path is not tested.  Here we need to either fit the lamp, or toggle both switches to be sure.
    Now intermediate switching is more complex. Here again there are 2 ways to wire, plus the intermediate crosses or un-crosses the laterals. At worse, again 2 switches must be operated to cover all cases.

    Note that other things like heating systems have similar untested branches depending for example on thermostat and timer states, but in practice where it is too hard to force the switch states, it is usual to inspect visually and then not worry too much. Very rarely you see things where for example a trip fires when a given heating zone comes on.

    Mike


    Acknowledgement to JW and DIY wiki for their pics.

Children
  • 0 in reply to mapj1

    Thank you for the replies. 

    I take Chris’s point that you could test through all the probable combinations. However, I was looking for a method to test all the conductors with the least minimal amount of test.

    With the Mapg1 reply, I am trying to process this. IS is being suggested that to cater for both types of wiring methods (1 strapper v 2 strapper system) the following should be done:

    Two way switching 

    sw1 sw2

    down down  

    down up 

    up up

    Intermediate switching 

    sw1 sw2 sw3

    down down down

    up down down

    up up down

    up up up 



    The above method should ensure that all the conductors are checked, regardless of the method of  system used.

    Is this correct??

    Thanks

      

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