One rule of thumb when planting roses is about 2'x2'x2' and if you allow another 1'-2'ft in width from the centre of the plant so about 3-5 ft will allow for growth access and non root interference and sinkage not affecting the plant.

if you have to get a lot nearer than the good advice that Drc has given you, then near the rose loosen the soil with a garden fork and remove the soil cairfully by hand ,leaving any roots especaly the fine roots in the air , put the cable down with cair then fill in by the rose by hand'' don't stamp it down the rose will be held by roots you have not disterbed and feed the rose as a reward,

thanks both for the quick and helpful answers - I went about 3 ft from it and didn't hit any roots, so fingers crossed it will survive

I would think that would be ok Rickett

I hope you used armoured cable or put it in a protective sleeve against future digging/disturbances. :o)

when the power companies put a cable down they cover it with a tile ,they don't allways put it at the depth it is surposed to be, but at least you hit the tile with spade or rotavater first befor you do sumthing nasty''