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How is Neutral Wire Neutral in Mains Electricity?

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SeanB:
With regards to that SWA cable, the same construction is used for 11kV, 33kV and 66kV cables, with only a small increase in the number of  overlapped oiled paper insulating sleeve windings used. They do have a very robust overload capability, in that you can have the cable running for decades with the temperature at the melting point of the pitch pour in the seal, provided that your cable ends do not get wet during this time.

I regularly see these in excavations, still powered, and with the pitch covering mostly gone, leaving the steel tapes exposed and corroding away, but the lead keeps it in more or less working condition, till it cracks and lets water in. Then the cable can and will excavate itself, I saw a failed 66kV joint, that blew itself out of the ground, leaving a 6m deep hole where the cable was buried, and turning the cast joint box into an art object. Current practise is not to lead wipe the joints, more due to the lack of any training on the art of lead wiping, and the older experienced people having mostly retired. Instead they use a cast resin joint, generally taking the paper cable to a PVC or HDPE insulated cable for further use, as it is something the electricians are trained to work with, though the core then changes from copper to aluminium in higher current uses, unless the length is short.

As to RCD units, the type with a ground connection was used for a few years here, as the earth connection allowed the unit to detect the loss of supply neutral, tripping on loss of neutral using a 120VAC MOV device, and also incorporating a 480VAC MOV from line to earth as well, which meant you had to disconnect the outputs before doing insulation tests, and you could not back feed them.. the current approved types are smaller, and are strictly 2 wires in and out, and are strictly 30mA RCD, requiring external overload protection. Required on all socket outlets, so typically, as it is rated for use as a disconnector, it is the single main input breaker, so if it trips you are in darkness.

Thankfully with the current Eishkom issues everybody has at ready reach some torches, a cellphone with torch or some form of lighting, as you will have regular rotational load shedding, and you might not get power back for a few hours to a few days if the bit turn on surge into a very cold load kills something upstream.

Electro Detective:
Re RCD mA faith:
 
If the fault current is high enough, fast enough and on a peaky? and or distorted top or bottom cycle/s, there is an extremely high possibilty that ALL the 10, 15, 30 and 100ma 'rated' RCDs will pop

Been there, sometimes the 'faster ones trip first' thinking in theory and in practice ~works~  and you think you got it nailed  :-+

but on repeat tests under the exact same test 'fault simulation' conditions, the whole lot go off, and you never know when   ???

i.e. it's unpredictable and not worth the embarrassment and inconvenience to assume a 10ma fast RCD will pop before the 30ma one at the switchboard 60 meters away.

If you need your lab or bench 'RCD safe' and isolated from upstream/downstream RCDs, then that entire area/zone should be on an large-ish isolated transformer (aka 'Medical Isolation' style)
with the Secondary earth/neutral/chassis bonded together, so the RCD can be plugged into that Seconday output and all the gear into the RCD via a power strip/s board/s etc.

If TESTED and done properly with correct input and output polarity checked, the RCD will trip on faults or tests, but any RCDs elsewhere won't know or care.

This is how I roll with suss scenarios or 'what ifs..'
It saves on a lot of 'reset' walking in the dark with a flat torch, getting rained on, stepping on cat, dog, bird poo..again..  :rant:
and avoids mumbling feeble 'power failure/blackout' excuses no one buys anymore  :-[

richard.cs:

--- Quote from: Electro Detective on February 12, 2020, 09:54:17 am ---If the fault current is high enough, fast enough and on a peaky? and or distorted top or bottom cycle/s, there is an extremely high possibilty that ALL the 10, 15, 30 and 100ma 'rated' RCDs will pop

--- End quote ---

This is well known behaviour. Standard practice here (UK) is to use devices with delays as well as different currents. e.g. instant tripping (well, 40 ms or so) 30 mA devices, with a 100 mA device upstream which has a 100 ms delay, and then if further layers are needed 300 mA 300 ms, etc. It's the delay not the current rating that ensures they trip in order, the increasing trip currents are more about having multiple sub-circuits on each one. Only the <=30 mA instant trip types are considered to offer protection to humans.

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