Electronics > Beginners

Single Pole or 1P + N circuit breakers

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soldar:
I believe the advice to "follow the code" has been repeated several times in this thread. 


--- Quote from: Zero999 on March 30, 2019, 09:02:57 pm --- To clear up the confusion. In many cases a circuit breaker needs to perform both isolation, as well as overcurrent protection, hence the requirement for double pole breakers by some electrical standards. Granted this isn't always necessary, but sometimes it is. If it wasn't, then double pole breakers wouldn't exist.

--- End quote ---

I was just watching Mains Supply And Consumer Unit and that is very different than what we have in Spain. Here the "Mains Supply" cabinet is outside the housing unit and not accessible to the tenant, only to the power company. So the main breaker in the "consumer unit" is what would be used to isolate the installation from the outside.

ETA: BTW, using wood in the mains panel would be totally illegal here. Sounds crazy.

Monkeh:

--- Quote from: bsdphk on March 30, 2019, 09:35:05 pm ---"hire an electrician if you can't answer your own question". That advice often gets me shouted down, however."

Not only if you can't answer your own question, but also because it is the law in all of EU as far as I know.
--- End quote ---

I can't speak for the rest of the EU (and probably really can't soon), but here it is a.. grey area. Unless they've tightened their grip more since I last checked.

They are trying very hard to make it illegal or impractical for people to perform their own work, but this is mostly driven by several large private organisations with immense vested interest in their own profits. But that is very much outside the scope of a technical discussion.


--- Quote ---The derating in USA codes is very much because people are allowed to bodge their own installation and they are not very good at it

--- End quote ---

From my perspective it appears to simply be poorly thought out standards. But they are old, and improving them or adopting anyone elses ideas is heresy there.

Zero999:
To answer the question: why 1P+N, rather than 1P? The main reason is sometimes it's necessary to isolate an entire circuit, so it can be maintained, without shutting everything down. Granted, an isolator can be used as well as a circuit breaker, but if the two are combined into one, it saves cost. It's also safer because two contacts will break the arc more effectively than one and for the reasons mentioned above regarding broken neutrals.

Monkeh:

--- Quote from: Zero999 on March 31, 2019, 08:47:40 am ---To answer the question: why 1P+N, rather than 1P? The main reason is sometimes it's necessary to isolate an entire circuit, so it can be maintained, without shutting everything down. Granted, an isolator can be used as well as a circuit breaker, but if the two are combined into one, it saves cost. It's also safer because two contacts will break the arc more effectively than one and for the reasons mentioned above regarding broken neutrals.

--- End quote ---

So the first point would be the non-safety maintenance point I admitted. No cost is saved by using 1P+N breakers as you still need to isolate the supply to them, so you have an upstream isolator anyway. This is not really a useful thing in a domestic or small commercial environment, just a waste of space and additional points of failure.

The second.. the breaker is required to safely clear arcs up to its interrupt current rating, and I can't see how you can say it's objectively safer to have a breaker which meets a standard than another breaker which meets the same standard.

As for the third point, I still do not see a fault scenario in which it is objectively safer to disconnect neutrals in an overcurrent condition. A different device is required to protect against lost neutrals.

Cubdriver:

--- Quote from: made2hack on March 26, 2019, 09:02:05 pm ---
--- Quote from: Zero999 on March 26, 2019, 08:14:30 pm ---
--- Quote from: ejeffrey on March 26, 2019, 05:07:49 pm ---Certainly in north america standard circuit breakers only interrupt the live conductor.  Neutral is bonded to ground in the panel, so there is no need or desire to break it.
--- End quote ---
Yes, that's mostly the case here too. I say mostly, because I can think of instances where that may not be the case. For example, if there's an outbuilding with a thick cable running to it from the main property, it will have its own distribution panel and will not bond the neutral to earth again there. In that case, to mitigate the danger posed by a poor neutral connection, which would make the neutral float at a dangerous voltage, the breaker should disconnect both the neutral and phase conductors.

--- End quote ---

Is there any reason why I wouldn't be able to bond the neutral and earth in this sub panel?

--- End quote ---

Since I didn't see this answered subsequently in the thread, I'll chime in here - this is one that will depend on your local electrical code. 

For instance, here in the US, you CANNOT by code bond the neutral and earth at a SUB panel - earth and neutral are to be bonded together at the service entrance/main disconnect (where the mains enter the building, usually the main breaker panel, but not always if for some reason it is located more than a few feet from the service entrance).  Any panels that are remote from the main disconnect/earth-neutral bonding point must have separate neutral and earth conductors run to them, and their neutral and earth buses must be kept isolated as well.

So in short, for this answer check the applicable code for your area.

-Pat

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