Five-Year Arc Flash, Coordination and Short Circuit Updates for Two Buildings of an Oilfield Equipment Plant, Humble (2025)

In spring 2020 we issued arc flash studies for two buildings of a plant in Humble that makes pressure control equipment for the oil and gas industry. NFPA 70E asks for an update at least every five years, and in March 2025 we issued both.

Two buildings, two models

The main facility takes one utility feed at 34.5 kV, stepped down by four transformers, and has an on-site generator. The rubber mixing and manufacturing building has two 34.5 kV feeds of its own and two step-down transformers. For the updates we did the walkdowns and obtained the utility data ourselves, and each model has six scenarios for the ways the system can be run. Where a breaker could not be read it was modeled with no trip function, and where a cable could not be traced its size was estimated from what it serves.

The main facility

The 2025 model held 340 buses: 298 at 480 V, 21 at 208 V, a few at 240 V and 120 V, and 12 at 690 V. Twenty-five buses were above 8 cal/cm² and nine above 40. The highest, about 96 cal/cm², was on the line side of a large press, followed by the secondary of a maintenance transformer at about 88 and the switch for a smaller press at about 74. The 690 V incoming bus came out near 61.

The rubber building

The smaller model, 85 buses at 480 V and 208 V, showed a sharper split. Ten buses were above 8 cal/cm², and all ten were also above 40. The highest, about 128 cal/cm², was at a 3,000 A switchboard with a bolted fault current near 44 kA, with two other switchboards near 88 and a disconnect switch near 77. The largest bolted fault in the building, about 52 kA, was at the secondary of a pad-mounted transformer. The other 75 buses were at 8 cal/cm² or less.

What the numbers mean on the floor

Neither update called for setting changes, and the labels were reissued from the new models. At the 19 locations above 40 cal/cm², no arc rated clothing is considered adequate, so the labels steer work there to de-energized conditions. The rest of the plant can be worked under the clothing and boundaries each label lists.

Related work

The original studies are described with two other plants in our manufacturing plant arc flash studies. For the modeling side, see our arc flash study services.