Underground Cabling

NESC [C2-2007] Rule 353:

Minimum radial separation between any cable and other should be 300 mm [12 inches].

However, radial separation should be adequate to permit access to and maintenance of either facility to limit damage to the other.

If your Instructions state Telcom cannot run in the same trench as LV/MV power then I would offer they have a safety policy for this whic states minimum clearances. However, it is not good parctice to run Telcom with or near power as either person from a utility can 'mistake' a cable and cut the wrong one open. Telcom not a hassle. LV/MV I think his eyes may tear up a little and a slight cooking may take place.

BUT, SCADA systems can run in the same jointing pit for connections, if needed and should be segragated from any power cables by means of a physical barrier. If works are being carried out on the power and fibres at the same time, then the power side would be dead and earthed down at the work area as well as at the ends, and breakers locked out.

I advise checking with your safety officer for clearances as they will differ country to country, Simple rule, If you can touch a live cable, or phase, your are probably too close for your own safety, (1100V=1.1kV. Are you meaning 11kV and higher?)

Sorry guys, i must be loosing it. I could have sworn the original questions was telcom cables in the same trench. My apologies. You can work on a simple 120mm separation per 10KV. Unless the cables are laid up to be in trefoil formation. the the trefoil phases can touch each other but the next set of trefoil should be the measurement above, 120/10kv. Look up Nexans, Olex, Prysmian, Pirelli web sites, they offer a load of information for their specific cable types. It is to do with heating, capacitances, dissipation of heat from cables, induction and fault currents. And it all depends on the cable type being used, the soil type the cable is buried in and load cycling on the cables. The above manufacturers have lots of details on cable clearances which is normally downloadable. No idea why I originally read this as telecom and 1100V. Sorry guys!