Broken earth testing question

[sparer]

Hi,
I recently exposed some cooker wiring in my kitchen during re-plastering. I pinned the capping back to the wall but before I re-plastered, I checked continuity of all three conductors between the cooker switch and the connection plate and also for shorts, with a cheap multi-meter, to make sure I hadn't damaged the cable. Between conductors was open circuit and each conductor showed short circuit (between switch and outlet) so I plastered up.

Upon having the cooker fitted, the installer measured the circuit and informed be of a fault with the earth conductor. I didn't pay attention to any readings but was a little puzzled because I had checked for continuity and short circuit. In any case I pulled the cable out of the wall there and then and fitted a new one (under his supervision at no extra cost from a well known electrical retailer) and made good later.

I'm still puzzled as to why the earth conductor measured short circuit (between switch and outlet) when clearly there was a fault. What could I have done with my cheap multi-meter that would have exposed the fault?

Thanks

 

[winston1]

Well you have the bit of cable you pulled out so check it again.

 

[sparer]

Well you have the bit of cable you pulled out so check it again.

I did Winston but it still had continuity.

 

[SFK]

Sparer,
regarding your question, >>What could I have done with my cheap multi-meter that would have exposed the fault<<, I think your issue was that you used the "continuity" test, rather than use the meter to measure the "resistance" of the wire.
The "continuity" test sounds a buzzer if there is a continuous wire, but it also sounds the buzzer (sometimes a bit quieter) even if the resistance of the wire is higher than it should be (ie a failed wire). Typically the buzzer sounds until the resistance between the test leads gets to some arbatary and sometimes quite large resistance value.
I would have also tried putting the Multimeter on the lowest "resistance" setting and tested the wire so you would see exactly what the resistance of the wire is, and better determine if one of the wire cores is/was damaged.

(Note that some multimeters also show the resistance value when in "continuity" test mode).
sfk

 

[sparer]

Thanks sfk, yeah i guess i should have looked at the display as the meter will buzz for continuity <200 ohms

 

[SFK]

Sparer,
My pleasure.
Regarding "as the meter will buzz for continuity <200 ohms", I would say that in reality it might be higher than 200ohms, as on mine the buzzer simply continues to sound until the resistance is high enough to reduce the voltage to a point where it cannot operate. So newer batteries, a more tolleratent buzzer, etc, might allow the buzzer to sound well above 200ohms.
sfk

 

[deadshort]

Hi,
I recently exposed some cooker wiring in my kitchen during re-plastering. I pinned the capping back to the wall but before I re-plastered, I checked continuity of all three conductors between the cooker switch and the connection plate and also for shorts, with a cheap multi-meter, to make sure I hadn't damaged the cable. Between conductors was open circuit and each conductor showed short circuit (between switch and outlet) so I plastered up.

Upon having the cooker fitted, the installer measured the circuit and informed be of a fault with the earth conductor. I didn't pay attention to any readings but was a little puzzled because I had checked for continuity and short circuit. In any case I pulled the cable out of the wall there and then and fitted a new one (under his supervision at no extra cost from a well known electrical retailer) and made good later.

I'm still puzzled as to why the earth conductor measured short circuit (between switch and outlet) when clearly there was a fault. What could I have done with my cheap multi-meter that would have exposed the fault?

Thanks

If they did not give you the nature of the fault eg. Non existent earth ? High impedance ? Your meter would not give you that information.
You checked for continuity and shorts.

DS