A three phase power system provided with a data communications system and associated method of data transmission for transmitting data over a three phase power system between a surface and a sub-surface location for an arrangement such as an oil field electrical submersible pump, the data communications system comprising a cabled connection from a surface system to a sub-surface system; a power module coupled to the cabled connection via a tuned circuit tuned to a first frequency, a data signal module coupled to the cabled connection via a tuned circuit tuned to a second frequency, independently of the coupled power module so as to minimize interference between the power signal module and data signal module during operation.