Even when a shop buys and sells nothing, it still has expenses, e.g. rental, salaries, and so on.
Likewise, Durban Metro Electricity still has expenses even if you do not use any electricity. e.g. repayments on loans for supply network, salaries, streetlighting, vehicles, billing expenses and meter reading, and repairing faults.

The Service Charge that appears on business accounts is to help pay for costs incurred by Durban Metro Electricity even if you do not use any energy.

Why is there a service charge for business customers but not for residential customers?

Before 1992 the service charge for residential customers was in the form of a minimum charge. This basic charge was phased out from the residential tariff and the income that would have come from this is now recovered by an additional charge for each unit of energy sold to residential customers.

This results in s 'lifeline tariff' to those at the lower end of the economic spectrum, but ensures the same income from the whole sector.