Electronics > Beginners
Single Pole or 1P + N circuit breakers
<< < (9/12) > >>
Monkeh:
Corner case: Broken upstream neutral, damaged cable with both line and neutral shorted to earth, potential risk of overcurrent in the circuit neutral via other circuits.

The protective device for this scenario is an RCD. If line never shorted the MCB could not clear this fault - an RCD will.

Propose other scenarios.
perieanuo:
Hi, 1p+N if you have triphasic system,otherwise 1P


Envoyé de mon iPad en utilisant Tapatalk
Zero999:
I don't see how disconnecting the neutral, as well as the phase is any more dangerous, than just disconnecting the phase. There can be an argument made for the case that it's not necessary to disconnect both conductors, in most applications, but it's completely wrong to imply it's more dangerous. The fact is, it's clearly safer to disconnect both conductors, this isolating the entire system, whether or not it's absolutely necessary or not.

Any thread involving safety inevitably turns into a shitfest. One should state, their reasoning for why x is safer then y, cite the relevant regulations, then move on and ignore all the dangerous misinformation which follows: hopefully anyone with any common sense will be able to pick through it all.  :horse:
Monkeh:

--- Quote from: Zero999 on March 30, 2019, 07:55:07 pm ---I don't see how disconnecting the neutral, as well as the phase is any more dangerous, than just disconnecting the phase. There can be an argument made for the case that it's not necessary to disconnect both conductors, in most applications, but it's completely wrong to imply it's more dangerous.
--- End quote ---

When have I implied it's more dangerous?


--- Quote ---The fact is, it's clearly safer to disconnect both conductors, this isolating the entire system, whether or not it's absolutely necessary or not.
--- End quote ---

I see no valuable safety benefit to enforcing isolation in an overcurrent device. Only greater expense and an additional point of failure, and yes, MCBs fail. Of course, if you happen to be dealing with a multiple-line scenario with no neutral, the isolation comes for free - but they're still not made for repeated manual operation, and can fail to close again.


--- Quote ---Any thread involving safety inevitably turns into a shitfest. One should state, their reasoning for why x is safer then y, cite the relevant regulations, then move on and ignore all the dangerous misinformation which follows: hopefully anyone with any common sense will be able to pick through it all.  :horse:

--- End quote ---

Regulations are behind a paywall, and I am not an electrician. I note you haven't been citing any, either. My reasoning that it is not necessarily and beneficially safer is that there is no guarantee (in the vast majority of scenarios, not even a possibility) of a device triggered only by the line being able to clear any fault scenario involving the neutral.

I am very open to reasoned fault scenarios I've missed. I have been attempting to tease them out for a while now.
bsdphk:
This is one of the most damaging kind of discussions we have here on EEVblog.

Far too many people seem to assume that in the rest of the world electricity is just like where they live themselves.

Hint: It is not, which is why electrical codes differ.

If you live on a mountain, like a lot of Norway do, there is no way you can get a usable earth potential terminal, "ground" and "mountain" are electrically very different things.

The electrical code of Norway reflects this, having made intelligent choices in the entire system, to provide the best possible compromise for protection.

The "in the entire system" bit is important, personal electrical safety depends on everything the wire is connected to and what kinds of faults and accidents can happen to it.

In USA, a very common failure mode is a car hitting a pole and the 5 or 11kV wires on top shorting to the 110-0-110 wires below.

This is why USA is so hung up about "surge protectors", and rightly so!

In countries where the MV wires are not carried on top of the same masts as LV, class C transient protection is a waste of money because it doesn't provide statistical significant reduction of damage.

(And if you are worried about lightning, class C catches fire like anything else, unless you also have tested and maintained class A and B up-wire.)

These differences in system failure modes are internalized in the electrical code for your country/region/whatever, and even if you truly understand the systems design decision in your local power-grid, you should still do whatever your electrical code says you should do, because anything else is both A) illegal, and B) reason for you insurance adjuster to laugh.

If you want to increase electrical safety in your lab-environment you can do two things:  1) Don't be careless, silly or stupid, 2) Use an isolation transformer until you are sure there are no electrical problems in your DUT.

/rant off

So answer to original poster:  Pick whatever your electrical code tells you to.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod