What should I consider for electrical distribution with a 3-phase UPS system>

Firstly, please remember that all work should be designed and installed to BS 7671 by a qualified electrical contractor. They will need to consider phase balance, neutral sizing, electrical discrimination, resilience and supply capacity. Aspects that we would cover during a site survey.

For phase balancing, the goal is to spread the IT load as evenly as possible across the L1, L2 and L3 supplies, either by allocating rack PDUs or circuits to different phases or by using three phase rack PDUs. A heavily loaded phase runs hotter and stresses the UPS.

In terms of neutral sizing, the switch-mode power supplies powering IT servers create harmonic currents that add together in the neutral, so the neutral conductor may need to be the same size as the phase conductors, or larger.

Electrical discrimination requires coordination of the the breakers so a fault on one server rack circuit trips only that circuit, not the UPS output breaker. This is in case of fault (short circuit) or overload condition.

Resilience in terms of electrical supplies concerns using A and B power feeds to dual-cordded servers and the use of a separate or common bypass supply, and coordination of the UPS system with a local standby generator.

Supply capacity refers to the incoming supplies and main LV board and sub-distribution circuits to ensure they can carry the maximum UPS input current.