Electronics > Beginners
How is Neutral Wire Neutral in Mains Electricity?
Monkeh:
I haven't really seen any cases of our smart meters failing due to design so far, only improper installation (quick, spring up an industry and put people through a week of training, then let them go mess with 100A terminals, nothing can go wrong!).
paulca:
On the functional Earth connection on the RCD (or RCBO maybe) I can only find this:
https://www.electriciansforums.net/threads/what-is-an-rcbos-functional-earth-connection-really-for.51405/
And yes, it does say, worryingly 80A, 240V, 100mA. If 100mA is it's fault current limit it's obviously not going to save a person! I thought these days they were around 6mA and they are only that high because of switch mode power supplies causing nuance trips all the time.
I could probably test that fairly easily, but it would involve putting resistors across Live and Earth which would need to be done extremely carefully.
Out of interest the other Breaker + RCD (not in the photo) for the shower. Why would this not be appropriate protection for an electric shower?
Monkeh:
--- Quote from: paulca on January 16, 2020, 10:12:22 pm ---Out of interest the other Breaker + RCD (not in the photo) for the shower. Why would this not be appropriate protection for an electric shower?
--- End quote ---
Because it's 100mA.
Renate:
My, oh, my, what a can of worms we have here.
To address the question in the OP:
Neutral is a current carrying wire, therefore it will sometimes have a voltage drop across it.
In US-centric terms: 50 feet (one way) 14AWG copper wire will have 1.7V drop on it when you run your 15 ampere toaster on it.
That's an RMS voltage, so the peak is 2.4V, the peak-to-peak 4.8V
The idea of the ground wire (protective earth) is that it should never normally carry any current over it.
Therefore it should not have this couple of volts on it that the neutral does.
How the ground gets connected and where is a separate issue.
In systems where there is lots of metal cases and conduits all hooked together and running in circles
even this ground can get polluted from cross connection to building ground, water pipes, gas pipes, whatever.
That's why we have "IG" insulated ground where an insulated wire runs between a grounding rod all the way to a special orange outlet.
This kind of thing is used in hospitals and electronic facilities where interference is an issue.
paulca:
--- Quote from: Monkeh on January 16, 2020, 10:40:55 pm ---
--- Quote from: paulca on January 16, 2020, 10:12:22 pm ---Out of interest the other Breaker + RCD (not in the photo) for the shower. Why would this not be appropriate protection for an electric shower?
--- End quote ---
Because it's 100mA.
--- End quote ---
Well, yes, as I said, the other RCD not in the photo. However as it turns out it has an I delta N of 30mA. So not life saving either. However a quick google suggests that indeed the regs are for a 30mA RCD for a shower. Maybe there is some expected leakage which would make a 3mA or 6mA RCD un-usable.
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