AC power system basics [RE-wrenches]

[Drake Chamberlin]

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As I said previously, a disconnected neutral wire will carry the 
voltage of the circuit.   AC circuits do not disconnect the neutral 
automatically, this seem to be unique to the ground fault protection 
on PV arrays.

This, combined with the fact that neutral wires from PV arrays can be 
up to 600 VDC creates, in my opinion, a hazard.

I personally never believe a wire is dead, and always check it, no 
matter what color.  In most situations, I use the Fluke field tester, 
which wouldn't even register a DC wire.  Although I get a lot of 
false positives readings, I've never gotten a shock that way.   If a 
possibility exists that DC is present, I'd use a multi meter, and 
test DC as well as AC.

Electricians tend to be more at ease with neutrals, especially in 
residential situations.  I can easily see an apprentice or journeyman 
get thrown across the room or off a ladder while working in a 
residence, thinking he had a neutral wire from a 120 volt system.

Drake

At 06:00 PM 12/10/2007, you wrote:

>Drake:
>
>I am mystified as to why one would think a neutral wire is not 
>dangerous.  First of all a lay person should assume all wires are 
>dangerous-- it's common sense and a very common reaction.  Secondly, 
>an experienced electrician will know that a neutral with a load, 
>when disconnect from the neutral bus, will carry the circuit voltage 
>at whatever amperage the load will support.  Are you under the 
>impression a white wire is or should be intrinsically safe, or did I 
>misunderstand your message?
>
>Furthermore, those of us who have fried appliances by inadvertently 
>disconnected the neutral on a multi-wire branch circuit know even 
>more thoroughly the implications of a disconnected neutral.  (I get 
>most of my lessons the hard way).
>
>It seems to me that white is the logical color for a grounded DC or 
>AC lead and that any conductor should be respected as energized 
>unless proven otherwise.
>
>William Miller
>
>PS:  With all due respect, I am starting to think that, even though 
>there are many very talented people in this industry, there may be 
>some lack of fundamental understanding about standard AC power 
>distribution amongst us.  I recall the recent discussion about 
>powering one apartment by running an extension cord from 
>another.  Basic understanding about how a very common AC power 
>system works should have supplied the answer and common sense should 
>prevent anyone from even attempting that idea.
>
>Again, no criticism meant in regards to anyone on this list.  It is 
>crucial for the good of entire solar industry that all of us have 
>adequate training, but I am wondering how complete that training is.
>
>WM
>
>PPS:  If anyone here has questions about the above and wants to ask 
>me off list, I am happy to elaborate.  Don't be shy, this is 
>important stuff and you need to learn it somewhere....
>
>WM
>
>
>At 05:07 PM 12/10/2007, you wrote:
>
>>We shouldn't continue to have very dangerous wires colored white, 
>>even if they are grounded most of the time.  It can become one of 
>>the two most dangerous wires in a residence, the other being the DC 
>>positive.  I agree that the Code requires the wire to be white, at 
>>present at least.
>>
>>Drake
>
>
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