Flat Vs Round Copper

At first the stranded copper conductor is more resistance to any abuse and more

corrosion resistance than the strip.

The copper flat strip could be easily cut by a relative low pressure from above at the edge of a foundation or stone.

Usually steel strips are employed since they are not expensive and can be welded on site easily. But in any corrosive ground their damage is large and their life short.

There are advantages and disadvantages of stranded wire versus flat strip.

For instance : 50 mm^2 of 7 strands of 3 mm diameter the outer surface is 28 cm^2/m 2*25 mm strip presents 2*(2+25)=54 cm^2/m.

Since the exterior surface of strip is about double versus stranded conductor it exposes the strip more to corrosion and the force exercised on the strip is double for the same pressure effort.

If both conductor are small [less than 1/0] the strip is advantageous in a way[as for instance skin effect reduced for high frequency current]. However the minimum cross section recommended for grounding is 4/0[95 mm^2] and for this section the strip is obviously disadvantaged.

Connection and reserve near connection is difficult to achieve in flat strip case.

The presence of bare copper in the ground near buried steel -including concrete reinforcing could damage the steel. So, in some cases a lead or tin covered copper conductor is required. No strip covered is employed-as far as I know.

By using flat one can apply greater earth faults at the connection point. Using round conductor one can go round bends easiers as conductor has a built in curve.

Are you building your 25MW power station now with surge arrestors and isolators? Don't forget to up-size the bus bars to oval lateral indent for greater surface conductivity area of the corona coupler between breakers and earth mat. I suggest sticking with tubular copper pipe for earthing as one can double the fault level current by running the earth faults inside the Cu pipe and for higher levels, on the outside.

The important factor is the FLOW PATTERN of the current in a conductor.

It is known that the current flows in the outer surface of any conductor and not in the centre portion of the conductor. Hence in a circular conductor - flow of current is much less in the centre. This is intensive when the frequency of the current is high/very high and hence some times the conductor will be hollow.

In the case of rectangle/square shape the current will not flow parallel to the surface of the shape and will tend to have a curvature - elliptical shape, which should be off-set.

Hence round shape is preferred. If round shape cannot be used, more area or cross section for the earthing flat is to be provided.

DHAYANANDHAN.S