Rack power distribution: PDUs and power cords

A rack PDU is sized from the input, not from the outlets. A 16 A single phase input carries about 3.7 kVA whatever the number of sockets, so many C19 outlets on a small input cannot all be loaded at once.

Metering decides what you can see. Input metering shows the load on the circuit; per outlet metering and switching show and control each device, and cost more.

Products

Input capacity

Capacity is voltage times current, times the square root of three for three phase. Circuits are often loaded to no more than 80 % of it, by design rule or national practice.

Testing PDUs and cords in Great Britain

Regulation 4(2) of the Electricity at Work Regulations 1989 requires electrical systems to be maintained, as far as reasonably practicable, so that they do not cause danger. The Health and Safety Executive is explicit that the Regulations set no method, tester or interval. Portable appliance testing is not compulsory, its frequency should follow the risk, and there is no legal duty to label tested items or keep records.

That leaves the routine to the site: a check by eye whenever a cord is moved, and an interval set by the risk of the room. Colour coded A and B cords make the check faster, because a cord on the wrong feed shows at once.