I wouldn't have thought it'll cause any problems at all. Most T&E is stamped to 500V, and IR testing is carried out to twice the circuit rating, so 1KV on T&E ought to be fine.
RCBO Tripping
- Thread starter martinxxxxxx
- Start date
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Always worth a try, I guess - but I suspect that when faults are not seen at 500V, by far the commonest situation (as with Martin) will be intermittency, rather than very marginal deterioration of insulating properties - i.e. when it doesn't show at 500V, it probably won't show at 1000V either. Indeed, if IR is showing hundreds of MΩ at 500V, it's unlikely that (at that moment) any fault would have an effect at 230V.
I'm sure 1000v is fine. IIRC, the dielectric strength of PVC is something around 22 kV/mm. I've just measured some 2.5 mm² T&E, and it seems that the insulation thickness is a bit under 0.7mm - hence, if intact, it should be able to stand around 15kV before breaking down.
Kind Regards, John
from the past found most faults tend too clear for a while and reoccur when bridged by damp or similar 1000v gives that little extra and tends to arc across the damage and show up on the meter, always prefer the analogue needle type for this,
Dates back to my old pyro days of contaminated pots and chafed TandE in damp cellers
Dates back to my old pyro days of contaminated pots and chafed TandE in damp cellers
Also don't forget that IR testers bang DC down the cable, and 1000V is therefore equivalent to only 707V AC.
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[hater-of-lies-and-censorship]It might be worth editing out any testing procedures not suited for DIYers as this post is bound to come up on searches
Plan B - stress the overarching importance of never doing anything which you don't understand, and not be like the plumbers who lie because they cannot be bothered to explain the truth.
Leave everything in.
Tell people not to meddle with what they do not comprehend.
[/hater-of-lies-and-censorship]
all plumbers?
I think he may be using the word "plumber" as a technical term, only understood by electrical-savvy people (and not 'the ignorant') and not necessarily having the same meaning as it would in everyday Englishall plumbers?
.Kind Regards, John
At the moment, sadly, the current test gear inventory prevents me from putting that to the test and providing you with a figure. The only source I have capable of those kinds of voltages isn't very controllable. Should that change you'll be the first to know.
If it's just PVC insulation, rather than specifically T&E, which iinterests you, you can look at thinner insulation, and hence need fewer volts. For example, Cat5e conductors have an average insulation thickness of 0.21 mm, which, per the above, therefore ought to break down at around 4.6 kV if the insulation were in intimate contact with a bare conductor - can you find that many (controllable) volts?At the moment, sadly, the current test gear inventory prevents me from putting that to the test and providing you with a figure. The only source I have capable of those kinds of voltages isn't very controllable. Should that change you'll be the first to know.
Although 'rated' at 30V, Cat5e certainly IRs fine at 1000V (at least, it always has for me!Kind Regards, John
[I presume the red bit should read something like "...more than 1000 times..."]
I totally agree. However, in the TN-C-S/PME case, I think it would be quite easy for a N-CPC fault on an unloaded circuit not to trip the RCBO. Your figures assume a 30A load on other circuits. If it were, say, 3A (e.g. Martin was using a hammer drill as a test appliance), the required impedance ratio would obviously only be 100:1. The direct path from neutral bar to the N/CPC join (at cutout) will often mainly consist of a metre or two of 25 mm cable - a resistance of perhaps 1.75 mΩ - say 2 mΩ to include the very short connection within the CU. To get the unloaded RCBO to trip with 3A on other circuits would therefore require a maximum impedance of the path via RCBO along N to the fault and then back along CPC to the CU to be less than about 200 mΩ (0.2 Ω
. Whether that is achieved will depend entirely on how far the fault is from the CU (i.e. Rn+R2 from point of fault back to CU needs to be <0.2Ω for tripping). Considering, for simplicity, a 2.5 mm² radial, if I've done my sums right, the fault would have to be within about 8.5m of the CU (cable length) for the trip to occur. Kind Regards, John
If it's just PVC insulation, rather than specifically T&E, which iinterests you, you can look at thinner insulation, and hence need fewer volts. For example, Cat5e conductors have an average insulation thickness of 0.21 mm, which, per the above, therefore ought to break down at around 4.6 kV if the insulation were in intimate contact with a bare conductor - can you find that many (controllable) volts?
Kind Regards, John
That's terribly practical John.
And it skips past one big reason for doing it - to see a piece of T&E lose it in style and grabbing a picture of it.
Seriously though, the reason for doing it was just out of interest.
What I really need is a step up transformer that's ideally about 1kv to 1.5kv out. Whether or not its 50Hz mains in is another matter. A mains one would easily plug into the variac but we don't need the power. The high voltage diodes and caps to scale the voltage up further aren't a problem. The test gear to measure the voltage isn't a problem either.
A thoughts? Only has to be a tiddler.
In fact a suitable device with perhaps a stack wound secondary would serve as a source for a multipler and run it off a battery.
Sorry about that!That's terribly practical John.
And it skips past one big reason for doing it - to see a piece of T&E lose it in style and grabbing a picture of it.
I obviously wouldn't be talking about these things if it didn't sound as if you knew what you were doing, since we're straying way above LV voltages.
Given the minimal current needed, if it were me I'd probably be thinking in terms of a low powered inverter (as you say, possibly battery-powered). The main difficulty is likely to be in finding a transformer with a secondary insulated well enough for the sort of voltages we're talking about - you might have to wind your own (or look for a line output transformer of a CRT TV). As you've suggested, you presumably wouldn't need to transform all the way up - you can stick a voltage multiplier on the end of it.
One problem for you would probably be that if you did go down the very low power (well, low current) approach, you probably would not see the cable "loose it in style" - you might actually see little or nothing if/when the insulation breaks down! I'm not actually sure that it would be worth it - people have already determined the dielectric strength of PVC for you, and all you would be doing would be confirming it! Whatever you do, be safe!
Kind Regards, John
12V transformer reversed would be a starting point - gets you the volts bit.can you find that many (controllable) volts?
Sounds like an ideal project for Photonicinduction - maybe he could be tempted...That's terribly practical John.
And it skips past one big reason for doing it - to see a piece of T&E lose it in style and grabbing a picture of it.
Indeed, and one could even put reversed transformers in 'series' if one had to. However, as I said, the problem is likley to be that the secondary winding in one's arrangement (the winding intended as the primary) would quite probably not be well enough insulated to cope with the multiple kV we are talking about.
Kind Regards, John
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