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| Single Pole or 1P + N circuit breakers |
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| notsob:
We had a case where a repair technician was hung up [ie. live power on his arm] on a card reader [ the size of 2 washing machines], an operator nearby had to run and drop the main breaker for the building. the breaker on the card reader was phase only - not neutral. However the person that wired the plug under the false floor had wired it incorrectly. So the card reader breaker was actually switching neutral. Very close call, we almost lost that person. So be safe - switch both. |
| Monkeh:
--- Quote from: Zero999 on March 26, 2019, 01:58:26 pm ---Disconnecting the neutral is safer, because it might be live, if it's broken somewhere upstream of the breaker. --- End quote --- This is irrelevant for the purpose of a circuit breaker. It is not isolation, nor is it functional switching - it is overcurrent protection. |
| Zero999:
--- Quote from: Monkeh on March 26, 2019, 09:38:27 pm --- --- Quote from: Zero999 on March 26, 2019, 01:58:26 pm ---Disconnecting the neutral is safer, because it might be live, if it's broken somewhere upstream of the breaker. --- End quote --- This is irrelevant for the purpose of a circuit breaker. It is not isolation, nor is it functional switching - it is overcurrent protection. --- End quote --- No it's not irrelevant. It still has to make the circuit safe, i.e. dead, which won't happen with a single pole device, if there's a break in the neutral conductor. |
| Monkeh:
--- Quote from: Zero999 on March 26, 2019, 10:59:53 pm --- --- Quote from: Monkeh on March 26, 2019, 09:38:27 pm --- --- Quote from: Zero999 on March 26, 2019, 01:58:26 pm ---Disconnecting the neutral is safer, because it might be live, if it's broken somewhere upstream of the breaker. --- End quote --- This is irrelevant for the purpose of a circuit breaker. It is not isolation, nor is it functional switching - it is overcurrent protection. --- End quote --- No it's not irrelevant. It still has to make the circuit safe, i.e. dead, which won't happen with a single pole device, if there's a break in the neutral conductor. --- End quote --- It has to end the condition of overcurrent. Again, it is an overcurrent protective device, not an isolator. |
| ejeffrey:
--- Quote from: notsob on March 26, 2019, 09:15:34 pm ---We had a case where a repair technician was hung up [ie. live power on his arm] on a card reader [ the size of 2 washing machines], an operator nearby had to run and drop the main breaker for the building. the breaker on the card reader was phase only - not neutral. However the person that wired the plug under the false floor had wired it incorrectly. So the card reader breaker was actually switching neutral. Very close call, we almost lost that person. So be safe - switch both. --- End quote --- No. If you are talking about building wiring (i.e., distribution panels), rather than equipment wiring, do it the way your local code and standards specify. Do not install some unapproved non-standard device because some guy on the internet said so. Edit: For instance, in the US it is allowed to have two branch circuits that are fed from opposite phases of the split phase input share a common neutral as long as the wires are run together (same Romex or same conduit). In industrial/commercial settings it is allowed have three branch circuits on three phases share a neutral. These do not use multi-pole circuit breakers but have independent circuit breakers for each branch circuit. If someone listened to this "advice" and went and replaced one of the branch circuits with a breaker that switched both live and neutral, then you would have created a potentially dangerous situation where the other circuit(s) could have live but a broken neutral. In the three phase case, the two remaining phases will try to force current balance causing one circuit to take a potentially severe overvoltage. Even if you think this practice is dumb and that those circuits should be on a single multi-pole breaker, that is not the way it is done or the way anyone would expect it, and unilaterally changing part of the system because of your opinion can cause hazardous conditions. Don't do it. |
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