Electronics > Beginners
Single Pole or 1P + N circuit breakers
Monkeh:
--- Quote from: soldar on March 28, 2019, 02:11:12 pm ---
--- Quote from: Monkeh on March 28, 2019, 01:49:57 pm --- Nobody in their right mind uses TN-C outside of distribution.
--- End quote ---
Those diagrams are about distribution. You might want to go back a look at them again. I think you are misinterpreting things.
In America earth and neutral are bonded at the panel.
In Spain this is not allowed and earth and neutral are separate wires all the way to the distribution transformer.
--- End quote ---
So now we're talking about distribution side instead of installation side. Those goalposts move fast. And the relevance to the misuse of a single pole breaker as an isolator in fact still escapes me.
soldar:
It is very simple: faults in the circuit, inside or outside, can make the neutral wire become energized. Having circuit breakers which break all poles offers protection against such thing. The Spanish authorities consider this protection significant enough that they require that circuit breakers to break all poles. I understand it and that is enough for me.
To the OP my recommendation is to follow local code.
Monkeh:
--- Quote from: soldar on March 28, 2019, 02:51:17 pm ---It is very simple: faults in the circuit, inside or outside, can make the neutral wire become energized. Having circuit breakers which break all poles offers protection against such thing. The Spanish authorities consider this protection significant enough that they require that circuit breakers to break all poles. I understand it and that is enough for me.
--- End quote ---
In what circumstance does not having the neutral disconnected by the breaker pose a risk? Merely having it above ground potential is not an issue, because it is a live conductor. You don't have access to it.
Zero999:
The goal posts have not moved. If you reread the the thread, you'll remember, it was about distribution from the first page.
You forget, we're talking about fault conditions. The system is not functioning properly. If the neutral conductor is still live, it still poses a shock and fire hazard. Under normal conditions, the user will not have access to the neutral, but the case of some equipment could be damaged, exposing it or some insulation might have melted, caused it to be shorted to earth and a high current to flow.
The safety regulations are there for a reason, whether you understand why or agree with them or not.
Monkeh:
--- Quote from: Zero999 on March 28, 2019, 03:22:59 pm ---The goal posts have not moved. If you reread the the thread, you'll remember, it was about distribution from the first page.
--- End quote ---
Distribution = all that stuff outside your house. You know, the stuff controlled by large entities following different regulations. This is about an installation, not distribution.
--- Quote ---You forget, we're talking about fault conditions. The system is not functioning properly. If the neutral conductor is still live, it still poses a shock and fire hazard. Under normal conditions, the user will not have access to the neutral, but the case of some equipment could be damaged, exposing it or some insulation might have melted, caused it to be shorted to earth and a high current to flow.
--- End quote ---
But you already said it's not a fused neutral. So you're not offering any protection against combined fault currents from other circuits in an open neutral condition.
If the neutral is exposed, you've already passed two layers of insulation (if the upstream neutral is also open, a double fault..). The line could just as easily be exposed - but an MCB doesn't protect against that either, it protects against overcurrent faults, which your body probably will not create. Especially not from an exposed open neutral.
If the installation or equipment is damaged you isolate it. A single-pole device is not an isolator, so you use the isolator.
--- Quote ---The safety regulations are there for a reason, whether you understand why or agree with them or not.
--- End quote ---
Yes, they are, and they are written by people who understand the application of each type of protective device and the circumstances in which they operate, and hopefully applied by people with equal understanding.
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