Wahey! Sparks! Watched this. Got the Megger out. 250V test between two screwdrivers in a glass of water shows 0 ohms! Meter is calibrated and checked on CB200 check box. Our lecturer at college many moons ago got everyone to hold hands and wound up a megger on the last two people in the chain! Great fun. Thanks Dave.
David you bring interesting entertainment to electrical work. From your beer can antics to your dramatic demonstrations. Much appreciated the effort you put into your youtube channel and educational content that you deliver to the derrière! :-)
Regarding air being an insulator, I remember about 25-30 years ago when we used to sometimes get cheap incandescent lamps which lacked a built in fuse so when one failed and with the filament being in a vacuum, sometimes you'd get a nice bright arc inside for a few seconds before either the rewireable fuse in the CU blew or the whole glass envelope separated from the lamp cap and fired out like a rocket!
We still get asked today about breakers tripping when an incandescent lamp dies. It's been a long time since I've seen the glass bulb get fired across the room, but I have experienced it!
(9:15) - Actually, you can use a stanley knife to do that stripping job but it does require a great deal of skill. I remember way back in 1979 when I was doing my apprenticeship, Gordon, that was his name, showed me how he stripped twin & earth. Yes, he used the knife and no, he didn't even nick the inner insulation. What a pro. By the way, how he achieved this was by cutting just a fraction into the outer insulation and the by bending the cable completed the *_cut._* He's long dead now but I hold many dear memories of all his quirks. Most of which, if I am to be totally honest, would not pass muster these days. A *_character._* That's what he was. >
I've been operating on the principle that in general, cables have an insulating layer and then a sheath for mechanical protection. Confusion arises in cables such as 6242Y (T&E) because PVC can be used to perform both functions. It's useful to remember that the rule still applies to cables such as MICC. The insulating white powder offers no mechanical protection but doesn't need to. The copper sheath offers no additional insulation but it doesn't need to. Many other types of cable use other combinations of materials which remind us that there are two clearly defined functions e.g. paper soaked in oil for insulation, and lead sheath for mechanical protection.
Your videos are v.illuminating! But with regard to clamping the outer sheath of the T&E, why would a light fitting fixed into the ceiling be any different from, say, a plug socket fixed into a wall (unless the blind grommet is considered to be a clamp of sorts), given there is no strain on the wires? Is it just because that particular fitting has such a clamp? Also, if putting 1000V thru the testing device does nothing to identify breaks in an electrical cable (in the absence of any conductor between the wires or to earth) how do you identify such, assuming a physical inspection of the wires is effectively impossible? Say, for instance if you’re testing a v.old wiring installation (I’ve seen ones that look like they date from the 1940/50s).
Hello David, nice video, thx for that. However, ik still have some questions regarding measuring Isolation. My name is Philippe from Belgium. In most cases you can't always disconnect all the appliances in the grid, or even so, you can't access them. Do you measure anyway then, or you start on a lower voltage? In Belgium when the inspector comes by too inspect he performs the test on 500V with appliances connected. And he measures between the earth-line and the earth-neutral. If the resistance is greater than O,5 MOhm the test passes. In another video of you (i believe it was fault finding with tripping RCD) you started to measure with the appliances connected and finally your diagnose was a faulty heater. Was that on 250V or 500V? And can you explain briefly when to use wich methode? Thanks on advance. Happy holidays.
Hi Philippe. Happy New Year to you! When I test insulation resistance then it's at 500V unless I suspect a surge protector is present in which case I drop to 250V to avoid a false reading. If I know for sure that no loads are connected, I'll test L-N, L-E, N-E on single phase with an expectation that all results will be greater than 1MΩ. If I suspect loads may still be present, then I'll join L-N together and test between them and earth. The joining of L-N is to avoid squirting 500VDC into any appliance electronics: if the same voltage is applied to both, then there will be no potential difference between them.
They should show the first part of this video on the NAPIT training course. The electrician who did the downlights at my house didn't know how to properly terminate cable
Insurance company : “ So Mr Savery , you were doing what exactly with 10,000 volts arcing between two BBQ skewers when the fire started .....”? .... ... D S : “ Well I was rubbing salt on them .......”
So IR testing is not a foolproof method of testing the integrity of insulation from what I've seen in your video isn't?if it doesn't pick up exposed conductors, how would would better guarantee protection on a rustic colonial house built out of wood please?
(15:00) - I would love to see a high voltage, any high voltage being pushed through glass. This is something that I have never, ever witnessed and to be honest, I have my doubts about. How's that for a challenge ? >
(11:40) - The reason the second test varied so much from the first test was not that the water was *_"settling down there"_* rather than the first high voltage test kind of laid down a carbon tracking path which made for a very easy and convenient electrical route for any further tests. So, the first time, the 1kv insulation test fails with sparks and arcs. The second test fails at a ridiculously low voltage, what was it? 46 volts? In any case, water is an insulator, pure water, that is, but for all intents and purposes, tap water does contain a great deal many ions (or salts). So much so that there actually exists a water heating device that connects to the mains comprising nothing more than two electrodes ! That you could buy off eBay for 99p delivered ! (I don't think they are available these days. That was in the wild-west days of eBay where anything went). The flow of electricity heats up the water ! What a neat trick ! What a fucking stupid trick, for not only does your water get heated while all along suffering the continued peril of being electrocuted, but you end up not just with boiled water, but boiled water plus a whole load of unwanted and likely toxic electrolytes. Enough of my ranting. Not only do I love your RU-vid Channel, I love even more your blog. Please, please, please put up with my petty comments regarding... ...well, you know by now already. I love you man! xxx
(19:10) - Yeah. That smell is ozone. That's what you are making with this contraption. *OZONE.* ( O3 ) [What happened to my subscript ? I formatted it proper, damnit !] Nothing wrong with that at low concentrations. >
