Electronics > Beginners
How is Neutral Wire Neutral in Mains Electricity?
Monkeh:
--- Quote from: paulca on January 16, 2020, 08:08:35 pm ---
--- Quote from: Monkeh on January 16, 2020, 08:03:08 pm ---Of course there would. If you short N and CPC after the RCD, current in an active circuit can take two paths to return, which is what will cause an RCD to trip.
Oh, and that cable isn't really armoured.
--- End quote ---
No. I pulled the breaker for the downstairs lights and went a cut the garage light cable as I didn't need it anymore. It popped the house RCD. This was not an active circuit the live was disconnected. However the RCD was able to detect the short between the neutral and earth.
--- End quote ---
But because your RCD is common with multiple circuits, and you did not interrupt the neutral conductor with the MCB, you still effectively connected neutral and CPC for all other circuits downstream of the RCD.
--- Quote ---I just stuck the meter into my plug socket.
L->E 232V
N->E 2V
L->N 230V
--- End quote ---
2V across such a low impedance (sub-ohm likely, certainly very, very low ohms) will source more than enough current to trip an RCD!
--- Quote ---I'm fairly sure it is armored. When I worked on a building site NIE (Northern Ireland Electric) would install them quite early on and leave them sticking out of the ground with blue ribbons on them. They were heavy black outer a ring of steam braids and 3 heavy cores.
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A 3-core cable is not the type of cable used to service a single dwelling..
Older installations will be something like PILC - impregnated paper for insulation, a lead cladding providing 'armour' (it's lead - it's soft as butter) and the earth connection. Newer will use a concentric cable - for single phase installations this will be one core, solid or stranded, for the line, and an insulated wrapping of copper conductors under the outer sheath for the CNE. No armour, but if you hit it with a proper digger you should blow a very big fuse before a hole appears in your bucket.
--- Quote ---Besides UK electrical code requires that ALL mains voltage cables put underground are armored.
--- End quote ---
This would be BS7671. The distribution network does not operate under these regulations at all. That which you think you know from house wiring does not apply before the meter.
GeorgeOfTheJungle:
--- Quote from: floobydust on January 16, 2020, 07:57:57 pm ---I'm saying that ground-rod gets connected to neutral inside the breaker panel, at least in North America. There is a "neutral bar" inside the electrical panel joining the two.
--- End quote ---
Is that split-phase 240V thingy what you have in Canada too?
Monkeh:
To steal some images from another site, this is a straight concentric cable supplying a TN-C-S supply to a dwelling:
That's what will be feeding my house. This one looks like 25mm².
And this is a TN-S supply with a split concentric, same idea, but half the outer conductors are insulated for the neutral:
This looks to be 16mm².
Notice the complete lack of armour.
I have nothing immediately to hand to show a lead-clad cable - presumably because those things are sealed with pitch and not easily cleaned for your viewing pleasure..
paulca:
--- Quote from: Monkeh on January 16, 2020, 08:17:42 pm ---A 3-core cable is not the type of cable used to service a single dwelling..
--- End quote ---
You might have a point, I did think it was strange that these were poking up at the kerbs, not at the house where the foundations where already in. So maybe it's a 3 phase distribution cable and they connect single phases to houses later.
Monkeh:
--- Quote from: paulca on January 16, 2020, 08:27:17 pm ---
--- Quote from: Monkeh on January 16, 2020, 08:17:42 pm ---A 3-core cable is not the type of cable used to service a single dwelling..
--- End quote ---
You might have a point, I did think it was straight that these were poking up at the kerbs, not at the house where the foundations where already in. So maybe it's a 3 phase distribution cable and they connect single phases to houses later.
--- End quote ---
Likely - they'll tap off the armour (the CNE) and one phase to each properly, and drive an earth rod at some or possibly all of these joints. The cable to the building will almost certainly have been a straight concentric.
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