[Tagging] Powerlines underground

[Ole Nielsen]

On 15/01/2013 15:31, François Lacombe wrote:
> But "aerial line" refers to all the conductors transmitting different
>  lives/phases whereas underground power cable, at high voltage,
> refers to only one phase/conductor.
> http://www.nexans.no/eservice/Norway-no_NO/fileLibrary/Download_540199654/Norway/files/Underground_power_cables.pdf
>
>  *So, many underground cables are needed to set up a line!*
>
> You may have multi-conductors cables up to 150 kV but you still have
>  several conductors.
>
> Insulation is mandatory underground because we can't put enough space
>  between conductors, instead of what is done in the air.
>
> The right question is "*do we map cables separately or lines*"? It's
> all about the vocabulary we use.
> http://2.bp.blogspot.com/-CnkQkGiPmbs/UFM6M2N0lUI/AAAAAAAAArk/IMZxA3i6SmY/s1600/tunnel.png
>
>  If we map cables we must do the same for both aerial and underground
>  lines and I'm not sure it would be really efficient.

Well, I think we need to properly define what is meant by "power=cable".
The wiki page isn't entirely clear on that matter. I'm usually mapping a
underground cable connection as a single way tagged as "power=cable" and
indicating the number of physical cables with "cables=*" (if it is known
to me). Your interpretation is obviously that each physical cable
should be mapped as "power=cable" (which you can't if you don't know the
number of cables).

Considering that "power=line" and "power=cable" are used so extensively
I think it is a bad idea to redefine the meaning of them as it would
break a lot of things and confuse mappers. The distinction between 
'line' for overhead power lines and 'cable' for underground cable 
connections is easily understandable by the average non-expert mapper.

My proposal is to clarify both the 'line' and 'cable' wikis as follows:

"power=line" should represent a connection comprising UN-insulated 
conductors mounted on towers or other supporting structures, normally 
over ground.
"power=cable" should represent a connection consisting of one or more
insulated cables (whether underground, underwater, in a tunnel or 
overground).

The number of physical cables for a cable connection should be indicated 
by "cables=*" when known. I'm currently drafting a wiki page for a 
"circuits" tag to describe the number of electrical circuits, especially 
useful for cable connections having an unknown number of cables, see 
http://wiki.openstreetmap.org/wiki/Key:circuits.

Ole