Jeffrey Cheney

Featured interest

Data center electrical work

This is a professional interest. It is not a claim that Jeffrey has worked in a data hall.

A data center is a building whose product is computing that is not allowed to stop. The electrical system is designed so a single failure, and often a planned maintenance shutdown, does not take the computers down. That is a different brief from a typical commercial tenant fit-out, even when the voltages look familiar.

Redundancy

  • N means just enough capacity to carry the load. One failure takes something offline.
  • N+1 adds one spare module: one extra UPS module, one extra generator, one extra cooling unit. The spare covers a single failure or lets one unit come out for service if the rest can carry the load.
  • 2N is two independent paths, each able to carry the full load. A server with two power supplies, each fed from a different path, can lose an entire side.

Uptime Institute Tier ratings use the Institute’s own published criteria. Writing “N+1” on a drawing is not the same thing as holding a Tier certificate.

Simplified A and B power paths Two parallel paths, each with utility, generator, UPS, and a PDU, feeding a dual-corded rack. Utility AGeneratorUPS APDU A Utility BGeneratorUPS BPDU B Rack
A 2N sketch: two paths, each able to carry the load, meeting at a dual-corded rack.

The equipment

  • Switchgear and switchboards. Service and distribution. Switchgear in the ANSI/UL 1558 sense uses drawout breakers and is built for higher fault duty. Switchboards (often UL 891) are a different listing. The name on the drawing should match the gear that shows up.
  • Generators and transfer switches. The generator starts when utility fails. An automatic transfer switch moves the load. Open transition has a brief gap. Closed transition overlaps the sources and has to be listed and coordinated so two sources are not paralleled by accident. The UPS covers the seconds while the engine comes up.
  • UPS. Rectifier, batteries or another energy storage, inverter. Maintenance bypass lets the UPS be serviced without dropping the load, if the bypass path is healthy. Static switches move the load quickly between inverter and bypass.
  • Busway. Overhead bus with tap boxes above the rows, used instead of a forest of conduit whips. The bus has to be supported, jointed, and bonded the way the manufacturer and Article 368 describe.
  • PDUs and remote power panels. They step 480 volts down to the voltage the racks want, often 415/240 or 208/120, and break it into branch circuits. Whip cables or busway tap boxes finish the run to the cabinet.

Hot aisle and cold aisle

Racks are lined so the cold faces look at cold faces and the hot exhausts look at hot exhausts. Containment keeps the two from mixing. Electricians feel that layout in the power path: busway, whips, and tray have to stay out of the airflow and still reach the cabinet. A whip that blocks a tile or a door is a cooling problem and a safety problem.

Commissioning

Mission-critical jobs test the system on purpose before computers depend on it. A common sequence, named in the project spec and often lined up with ASHRAE commissioning guidance, runs from factory witness, to installation checks, to startup, to functional tests of each piece, to an integrated systems test. The integrated test is the one people mean by “pull the plug”: load banks on the UPS, a transfer to generator, a failure of one path, and a check that the other path holds. The test script, not a memory of the last job, says what “pass” means.

Lighting in the halls and support spaces still has to meet the energy code. That is the lighting controls page, including the fact that controls must not fight the lighting an operator needs during an alarm.

What's happening now

The 2026 reporting on this topic is remarkably consistent: owners are trying to build computing buildings faster than they can hire people to wire them.

Code section numbers, energy-code rules, and utility practices change by edition and by city. The authority having jurisdiction, and the employer’s written program, decide what applies on a given job.