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I have recently had the impedance of my electrical circuits tested, and they were found to have increased over the 12 years since they were installed (from about 0.3 mΩ to 0.4 mΩ) and to fluctuate when subsequent readings are taken.

The electrician advised that all the electrical circuits would have to be replaced. My question is... is this really necessary? Could an increase in impedance be simply caused by a loose connection somewhere (for example in the fuse box)?

ThreePhaseEel
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Tom
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    Welcome to DIY.SE! What's the uncertainty on those readings? It's quite possible that there is no significant difference in the readings given the uncertainty. Also, why did you have the impedance tested? – mmathis Nov 02 '16 at 14:08
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    When and why does a person test impedance of home wiring? I've never heard of that. – isherwood Nov 02 '16 at 14:17
  • I would call another licensed electrician and obtain a second opinion. Also echoing what other comments ask..., what event, issue or problem made you call and request this testing? – Tyson Nov 02 '16 at 14:32
  • Hi mmathis6, I'm not sure what the uncertainty was on the readings - the electrician used what I assume is reputable testing equipment - so I assume the uncertainty would be inline with standard testing equipment. The variability in the readings was less than 0.05mOhms - the electrician said that this was unusual. We had the circuits tested because when the fridge defrosting cycle finishes (which is on a separate circuit) our TV switches off momentarily. Similar to previous post - http://diy.stackexchange.com/questions/28002/why-would-my-tv-image-turn-black-when-electrical-appliances-turn-on – Tom Nov 02 '16 at 14:32
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    Yes right - its an unusal testing to have done! We called the electrician because of the problem with the TV/fridge - and the electrician looked at the previous test sheets (one when the flat was built, one when we moved in 11 years later), noticed the impedance had gone up and so tested it again - to find it had gone up more. Then he said we needed to have the entire electric installation replaced - which seemed a bit extreme to me. Absolutely - will get a second opinion! – Tom Nov 02 '16 at 14:38
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    @Tom The uncertainty in a digital readout is typically +/- 1 in the last digit - so, if the measurements were actually 0.3 and 0.4 mOhm, they are statistically the same and not cause for any concern. If they were 0.30 and 0.40 mOhm, on the other hand, there would be a significant difference in the readings. What that significance is, though, I don't know – mmathis Nov 02 '16 at 15:23
  • What country are you located in? Do you have any aluminum wiring? – Carl Witthoft Nov 02 '16 at 15:38
  • Okay that makes more sense. The small 'm' threw me off a bit too but as @Steve says I was thinking of testing insulation resistance (probably tainted by another question just posted about that). Sorry for the confusion on it. – gregmac Nov 02 '16 at 19:52

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Unless you have aluminum wiring, there is no reason to periodically check circuit impedance. For that matter, the resistance of 10 meters of 12-gauge copper wire, often used for 20 amp circuits, is about 50 mohms, so I would question what circuits need to be replaced. The entrance cable? Certainly not your house wiring.

DrMoishe Pippik
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