Value of ohmic resistance

[Ludovic Agathe]

What could be a typical value of the ohmic resistance for contacts in protective devices? I need those for verification of some assumptions made for a loop impedance calculation. If someone could also tell me if there is some measured value for wall sockets (for my general knowledge).

Thanks!

 

[James]

Typical value would be Zero or negligible

 

[Moley]

That's got me thinking which is never a good thing. I'm working away until Thursday night but I'm tempted on Friday to whip out my ductor (micro ohm meter) and actually check some sockets (not connected ones for obvious reasons) and see what sort of readings I get. I've got a feeling they will be quite high, well, high to me. All our connections have to be 10 micro ohm or less. I would assume who it's made by would have an influence too. Maybe the tolerances on the cheaper sockets wouldn't be so tight resulting in higher readings?
If I forget (bloody good chance) someone remind me Friday.

 

[Ludovic Agathe]

Typical value would be Zero or negligible

From measurements made from our end, with a de-energised panel and measuring continuity with a Kyoritsu 6011A multifunction tester, readings of the order of 5 to 8 ohms were registered for both live and neutral, several readings taken. It could be the cables, but my supervisor was telling me to blame the contacts. Is that plausible?

 

[James]

What exactly are you measuring the continuity of?
A diagram might help us.

 

[Avo Mk8]

From measurements made from our end, with a de-energised panel and measuring continuity with a Kyoritsu 6011A multifunction tester, readings of the order of 5 to 8 ohms were registered for both live and neutral, several readings taken. It could be the cables, but my supervisor was telling me to blame the contacts. Is that plausible?

As has already been suggested, one would expect a circuit breaker or residual current trip on a 240V circuit to have a contact resistance of between 10 and 100 micro ohms.

Your test instrument appears to use a current of 25A to measure resistance on the 20 ohm range. I'm not sure it's the right device to try to measure such a low resistance. To make a meaningful measurement manufacturers of the devices you mention would probably measure at 100A.

I will be interested to see what Moley finds if he gets a chance to measure a 13A plug/socket combo!

If you are measuring directly across the terminals of the protective device, there's something up with the measurement technique or the measuring instrument. You have presumably nulled out the leads and got proper contact with the terminals?
One might typically use a 4-wire technique for doing this sort of measurement, the principle of which illustrated below: