Maybe he was thiking of measuring Zs at the load-side terminal of the switch? I guess that would tell one if the switch's contact resistance was ridiculously high, but not much else.
Kind Regards, John
MK Sentry 100A Switch Disconnector recall
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Kind Regards, John
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Am I the only one here who would do these tests?
I mean, the main switch is supplying power to the whole installation. Surely you would check a Zs or Ze reading and an IR reading?
I mean, the main switch is supplying power to the whole installation. Surely you would check a Zs or Ze reading and an IR reading?
In concept, what you say obviously makes sense. However, I think the problem is that the Zs (or 'Zdb', measured on load side of main switch, but not really Ze, since that's meant to relate only to the component of loop impedance which is external to the installation) will not necessarily tell you very much. If, for example, you got an answer 0.1Ω greater 'than it should be', it would very probably still seem very reasonable and would not even 'notice' - yet a 0.1Ω contact resistance in a main switch could be catastrophic (e.g. 360W generated in the contacts at 60A). Even 0.01Ω (36W at 60A) would probably be far too high for main switch contacts, but I don't think that there is any way you'd notice a 0.01Ω 'error' in Zs. In fact, you'd probably be better off just measuring (or trying to measue) the contact resistance of the switch before you installed it.
It's difficult to argue against checking IR - but would you actually do it after, say, changing a light switch?
Kind Regards, John
I suggested Zs.
And when I asked you which side of the switch you would do Ze, and IR, you said I was waffling.
I put it to you that you do Ze upstream of the switch, and that therefore the switch contact resistance is not in the lop, and that therefore the test is of no relevance to work consisting of replacing the switch.
I put it to you that an IR test between (L+N) and E is also not going to test any part of the switch and that therefore that test is also of no relevance to work consisting of replacing the switch.
And when I asked you which side of the switch you would do Ze, and IR, you said I was waffling.
I put it to you that you do Ze upstream of the switch, and that therefore the switch contact resistance is not in the lop, and that therefore the test is of no relevance to work consisting of replacing the switch.
I put it to you that an IR test between (L+N) and E is also not going to test any part of the switch and that therefore that test is also of no relevance to work consisting of replacing the switch.
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... and P.S ... even if you did find some way of usefully interpreting a Zs measurement, it would tell you nothing about the state of the switch's neutral contacts - which represent 50% of the potential 'faults' in the switching mechanism.
Kind Regards, John
Kind Regards, John
If you were really looking to test the switch (rather than looking for stuff to put in boxes on a form) then I think the best test would be a P-N loop test on both sides of the switch. If there is any sigificant difference the switch is faulty.
...except that, similar to what I was saying about Zs (which only tests one side of the switch, anyway) differences (probably of the order of 0.01Ω or less) which could indicate a faulty switch might well be too small to detect with a loop tester (which, typically, will display with a precision of only 0.01Ω
.If you have a sensitive enough voltmeter, you'd probably do better measuring the voltage across the switch (separately for each side) when the CU was under moderate load. With, say, 10A flowing, a 0.01Ω contact resistance would result in a 100mV across the switch.
Kind Regards, John
Or you could have a bit of fun and send in an EIC, with the schedule full of things like "Matter Transporter" for circuit description, "It's a grey one" for device, "fat" & "not so fat" for conductors, "13lbs 5oz" for continuity, "black lace" for IR, and so on.
See if anybody reads it....
See if anybody reads it....
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