Electronics > Beginners
How is Neutral Wire Neutral in Mains Electricity?
richard.cs:
--- Quote from: paulca on January 31, 2020, 02:39:17 pm ---
--- Quote from: IDEngineer on January 30, 2020, 11:23:59 pm ---Yes, as discussed ad nauseum herein, GFCI's do not rely on an earth reference to operate, reliably or otherwise.
--- End quote ---
So, explain why some of them DO have an earth reference.
--- End quote ---
All-mechanical RCDs operate on differential current only. The output of the current transformer directly drives the trip coil, the mechanism is sensitively balanced and quite delicate. These are vulnerable to sticking and modern ones often use the CT output to trigger a thyristor and dump a heavier current into the trip coil from the L-N voltage. These therefore don't work in absence of L-N voltage which becomes a safety problem if the neutral is open-circuit upstream of the RCD. A subset of this type therefore use a functional earth connection as a alternate place to pass tripping coil current to.
In UK practice RCBOs are often half the width of an RCD, and sometimes do not switch neutral (this is a rubbish plan but very common). It may be that due the the space constraints these are more likely to have electronic tripping, but in any case it seems far more common for RCBOs to have a functional earth than for RCDs to have them. Also some RCBOs have earth tails that are essentially just there for EMC filtering.
IDEngineer:
--- Quote from: paulca on January 31, 2020, 02:39:17 pm ---
--- Quote from: IDEngineer on January 30, 2020, 11:23:59 pm ---Yes, as discussed ad nauseum herein, GFCI's do not rely on an earth reference to operate, reliably or otherwise.
--- End quote ---
So, explain why some of them DO have an earth reference.
--- End quote ---
The better question would be why some have earth references and some do not. From their presence in the market and their acceptability to (at least) the National Electrical Code, we know that GFCI's without discrete earth references work just fine. So the question becomes why both types are available.
I ran across a discussion of the optional discrete earth connection while replying earlier in this thread, but can't find it again right now. As I recall, GFCI's having discrete earth connections are able to detect yet another type of fault. If so, this would add another "choice" to the range of options in modern circuit breakers and you buy your device based on which of the following options you want: Overcurrent, differential current, arc detection, and now "earth fault" (whatever that last one means). But this thread has focused on the GFCI aspect of operation, and it's crystal clear that an earth reference is NOT required for that.
Monkeh:
--- Quote from: IDEngineer on January 31, 2020, 07:28:32 pm ---But this thread has focused on the GFCI aspect of operation, and it's crystal clear that an earth reference is NOT required for that.
--- End quote ---
Actually, certain people have latched onto such despite them not being the subject..
IDEngineer:
--- Quote from: Monkeh on January 31, 2020, 08:15:23 pm ---
--- Quote from: IDEngineer on January 31, 2020, 07:28:32 pm ---But this thread has focused on the GFCI aspect of operation, and it's crystal clear that an earth reference is NOT required for that.
--- End quote ---
Actually, certain people have latched onto such despite them not being the subject..
--- End quote ---
I checked back and you're correct. YOU first raised the question of breakers not operating properly in this response:
https://www.eevblog.com/forum/beginners/how-is-neutral-wire-neutral-in-mains-electricity/msg2879446/#msg2879446
...wherein you said:
--- Quote ---No, then how do you know the breakers will operate correctly?
--- End quote ---
Prior to that, references to breakers dealt with the OP keeping himself safe. Speaking for me, my comments had been limited to the thread topic, the neutral wire (and its relation to earth), until your query at me about breakers possibly not operating properly. Which I addressed because otherwise casual readers might be misled into believing that breakers require an earth reference, and it's dangerous to leave misinformation uncorrected when dealing with mains voltages.
Monkeh:
--- Quote from: IDEngineer on January 31, 2020, 09:07:42 pm ---
--- Quote from: Monkeh on January 31, 2020, 08:15:23 pm ---
--- Quote from: IDEngineer on January 31, 2020, 07:28:32 pm ---But this thread has focused on the GFCI aspect of operation, and it's crystal clear that an earth reference is NOT required for that.
--- End quote ---
Actually, certain people have latched onto such despite them not being the subject..
--- End quote ---
I checked back and you're correct. YOU first raised the question of breakers not operating properly in this response:
https://www.eevblog.com/forum/beginners/how-is-neutral-wire-neutral-in-mains-electricity/msg2879446/#msg2879446
...wherein you said:
--- Quote ---No, then how do you know the breakers will operate correctly?
--- End quote ---
Prior to that, references to breakers dealt with the OP keeping himself safe. Speaking for me, my comments had been limited to the thread topic, the neutral wire (and its relation to earth), until your query at me about breakers possibly not operating properly. Which I addressed because otherwise casual readers might be misled into believing that breakers require an earth reference, and it's dangerous to leave misinformation uncorrected when dealing with mains voltages.
--- End quote ---
Now search long and hard for 'GFCI', 'RCD', 'RCCB' or 'RCBO' in my post.. I was referring to the function of MCBs, as not all circuits may require or desire residual current protection (unless you have a TT earthing arrangement - which you might well have created with your, uh, interesting approach to performing electrical work).
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