General > General Technical Chat
Mains sockets with no earth
JohnnyMalaria:
--- Quote from: michael@metgen.tech on January 19, 2021, 02:26:50 am ---I should probably have said that I originally come from the UK
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"Mains sockets" and "earth" gave you away :)
Monkeh:
--- Quote from: michael@metgen.tech on January 19, 2021, 02:26:50 am ---On the RCD front, I always thought that they were to guard against earth faults... so I don't understand how they can work without a reference to earth.
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They are to protect against current returning to its source (the side of the transformer winding connected to neutral) via a path other than the neutral. Said winding is also connected to earth, and returning via the earth conductor or the greater mass of earth is called an 'earth fault'. They need no reference to this - they measure the difference in current between the line and neutral conductors. Any difference must be returning via an alternate path.
--- Quote from: JohnnyMalaria on January 19, 2021, 02:28:19 am ---
--- Quote from: michael@metgen.tech on January 19, 2021, 02:26:50 am ---I should probably have said that I originally come from the UK
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"Mains sockets" and "earth" gave you away :)
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At least he didn't call them plug sockets..
james_s:
--- Quote from: themadhippy on January 19, 2021, 01:48:33 am ---
--- Quote ---The UK uses a ring circuit for the most part since it allows a narrower gauge of wire to be used for a given power requirement. Radial/spur/star is less common
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slowly the uk is moving away from ring finals,more and more sparks ,mainly the younger ones or those new to the trade ,dont like em and would rather struggle getting 2 larger conductors into a terminal,there fear is of the cable being overloaded if one leg is broken,which whilst true,the chance of a broken wire happening without somebody fiddling were they shouldn't or a badly installed installation are fairly low
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I have mixed thoughts on the ringmain concept. It has clear advantages, although the concerns you mention are valid. Lots of things are ok *IF* properly installed and nobody has mucked with them but that's a big IF, especially in older houses where the likelihood of somebody having messed with something only increases with time. On the other hand it's not like those concerns apply only to a ringmain, over here we have these stupid spring loaded backstab terminals on receptacles and switches, or rather on the cheap hardware sold for domestic use, commercial "spec grade" and hospital grade forbids them. I've had problems on several occasions with those, once in my own house and several I fixed for other people, one that very, very nearly set the house on fire. I can only wonder how many house fires of indeterminate and "electrical" cause have originated with those. The annoying arc fault breakers the NEC mandates now for new construction are a band-aid over the problem, the tradesmen love those push-in terminals because they're so quick and easy to install but I bet most don't use them in their own house.
vk6zgo:
--- Quote from: bdunham7 on January 18, 2021, 03:52:07 pm ---
--- Quote from: themadhippy on January 18, 2021, 12:59:59 pm ---if you dont have an earth your rcd will not work.were does the fault current go as there is no path for it to travel.
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GFI does not depend on having an earth connection, nor does it care what the path is for current to travel outside of the two wires it monitors. If a current is flowing through you, then that amount of current will be missing from the return current in the neutral. GFI sees the imbalance and trips.
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Yes, another name for such devices is "core balance relay".
If the current flow in the L & N lines is equal, the relay is "balanced" & does not operate.
If the currents are not equal, the relay operates, opening the circuit for both L & N.
Ed.Kloonk:
--- Quote from: bdunham7 on January 18, 2021, 05:08:39 pm ---
--- Quote from: themadhippy on January 18, 2021, 04:33:23 pm ---whilst the rcd dosnt have an earth connection it still relies on the circuit somewhere being connected to earth,otherwise theirs nowhere for the imbalance current to flow.If the experiment mentioned above is to scary try putting an rcd on the secondary of an isolating transformer and connect the output to earth ,what happens?
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True, in a truly isolated system the RCD won't trip because there is no fault current. But since there's no fault current, there's no shock and nothing to protect from.
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If you somehow manage to connect your arms/hands to either terminal, even a portion of any isolated mains will do you in. All it takes is enough to fibrillate the heart. However, if the supply is earth bonded and protected with a RCD, chances are much higher that you wont be sitting there becoming burnt toast.
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