Electronics > Repair

Repair help; trying to identify hot and neutral

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Monkeh:

--- Quote from: Burnerjack on September 29, 2013, 04:58:27 pm ---You may be able to "Ohm out" the wiring to chassis. The "hot" side should have infinite or nearly so resistance to chassis.

--- End quote ---

Both should be insulated from the chassis.

GEuser:

--- Quote from: mcinque on September 29, 2013, 05:59:37 pm ---
--- Quote from: GEuser on September 29, 2013, 03:47:33 pm ---http://www.docstoc.com/docs/110243318/The-MEN-System-of-Earthing

--- End quote ---

Very interesting. I wonder why we don't use that system here.

--- End quote ---

I dunno? , maybe because your county has been around longer?

So as you see , "if" a fuse was in the neutral leg in the equipment (some do put it in there) it effectively would be useless as it is also tied to earth therefore the only fuse available will be the 10 or 15 or 20 amp mains fuse , or the 2" nail :palm:
 :)

ejeffrey:

--- Quote from: mcinque on September 29, 2013, 03:30:32 pm ---Forgive me for my OT, but I am really curious about why you need to know wich wire is the live and wich is the neutral: in many european countries (expecially in Italy) main sockets can be plugged without worrying about the position of the plug (you can insert the plug also upsidedown, so with the live of the device in the neutral of the socket), while in USA or other countries sockets has an unique insertion way.

--- End quote ---

A couple of reasons.  In some situations there is one contact that is more exposed than the other.  The most prominent case still around are edison lamp sockets.  The shell should be 'neutral' and the center contact hot to reduce the risk of inadvertent contact e.g., while changing a bulb.  I think even in italy permanently wired light fixtures should be arranged this way.  Presumably for plug in lamps you are supposed to unplug it before changing the bulb.

The other reason is that at least in the US it is common to only switch and fuse the live conductor inside a device.  If you use a device like this and the fuse blows or the switch is off while it is plugged in backwards, you disconnect only the neutral and leave the bulk of the circuit at mains voltage. In principle this shouldn't be a problem if the circuit is properly isolated and chassis grounded, but it is still undesirable.  More troubling, if there is a live-chassis fault you actually have no fuse to blow except the main circuit breaker.  The way around this is to use a double-pole switch and two fuses to protect both live and neutral.

mcinque:

--- Quote from: GEuser on September 30, 2013, 03:42:17 am ---"if" a fuse was in the neutral leg in the equipment (some do put it in there) it effectively would be useless

--- End quote ---

That's exactly what I've always thought since I start to understand some basic electrical laws.


--- Quote from: ejeffrey on September 30, 2013, 06:29:44 am ---A couple of reasons.  In some situations there is one contact that is more exposed than the other.
--- End quote ---

This is true, and also here smart electricians apply this security rule to their installations.


--- Quote from: ejeffrey on September 30, 2013, 06:29:44 am ---The other reason is that at least in the US it is common to only switch and fuse the live conductor inside a device.
--- End quote ---

America and Europe share many devices with the same circuitry and only a different transformer: I've seen only fused and switched L cable (at least for color) inside power amplifiers, decoders, vcr etc. but with our simmetrical sockets, it's useless: I can easily reverse L and N.


--- Quote from: ejeffrey on September 30, 2013, 06:29:44 am ---If you use a device like this and the fuse blows or the switch is off while it is plugged in backwards, you disconnect only the neutral and leave the bulk of the circuit at mains voltage

--- End quote ---
Exactly. That's why I think some european (at least Italy, Spain, Finland and Germany) main sockets system is not completely safe.

We should do like US, Australia, Switzerland and UK: a one way insertion main socket as standard and MEN system.

Thank you all for answering my question.

GEuser:
It might not help the US  :-//, 1980 through 1992, 5,348 workers died which is 411 a year and that's not including the average joe blow at home , and that was only until 1992!

Over there it seems either things are very faulty or no-one dies and goes somewhere else?

Also a complete opposite for instance is New Zealand which is just across the pond from here , all basic at home work is fully allowed , the government even promotes it , there are also basic course's to take if one wants and over 20 years or so a at home death is still Zero or abouts ..
http://www.oriongroup.co.nz/your-network/safety/your-safety/home-owners-diy.aspx

"One has to be CAREFUL where one pokes the Finger"  :blah:

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