Burying cables...

[Dave Plowman (News)]

Best way would be to pressurize them slightly.

[Robin]

The Guidelines referenced have red *or* black for HV and LV cable/ ducts/tiles.

[1] that's the NJUG Guidelines on the Positioning and Colour Coding of Underground Utilities? Apparatus

[Roger Hayter]

Thanks. That's useful to know.

[Andrew Mawson]

Nitrogen I believe actually - cylinder at the exchange keeping a slight over pressure

Andrew

[Andrew Gabriel]

They blow dry air down the cable jackets, not the ducts. Many older cables are paper insulated, or more strictly, air insulated, paper spaced conductors.

Ducts are always vented to the outside before they enter the telephone exchange, so that that gas leaks into the ducts can't carry gas into the exchange building. (They often use a streetlamp coloumn without any top on it as the vent pipe.)

Exactly what they do.

Don't know if this is necessary with modern cables, which appear to be packed with petroleum jelly, and don't use air as the insulator (and don't look like air would go through them).

[jrwalliker]

A pair of three-phase 33kV cables running through woodland near here are oil-filled with pressurised header tanks in underground chambers. The conductors themselves seem to be polymer insulated. I got to see the innards of the cables when repairs were being done recently. There had been a slow oil leak for a few years which was finally located. Until then they were topping up the oil tank every few months.

The repair process was quite complex. Rubber lined trench, scaffolding frame to hold up a roof over the work area, safety marshal present some of the time. Liquid nitrogen tank for some phases of the work - presumably to freeze the oil upstream and downstream of the repair and ladles of molten solder to finish the joints which were initially made with metal sleeves with multiple large screws to clamp the conductors. The whole thing was then encased in several bucket-loads of pourable resin.

John

[PeterC]

When Anglian Water repiped the village about 20 years ago it was done in blue MDPE. The foreman told me that AW uased to use HDPE but MDPE is cheaper

- don't know if it's true. The new site in the next village has just had a 25cm water pipe in dark blue, but I couldn't see any markings on it to ID it.