NECA/IEEE Joint Publication on Arc Flash in Data Centers: Key Takeaways

Data centers break the assumptions that underpin standard arc flash assessments in three ways:

• Low-impedance sources. Modern data centres run parallel UPS modules, each contributing fault current. A facility with four 500 kVA UPS units can deliver combined prospective fault currents exceeding 60 kA at the main distribution bus — comparable to heavy industrial switchboards but in a facility that does not look or feel like a steel mill.
• Continuous operation mandate. Unlike manufacturing facilities that can schedule shutdowns, data centres operate 24/7/365. Maintenance on energised equipment is not a convenience — it is an operational requirement. This means arc flash exposure hours per year are significantly higher than in facilities that can de-energise for maintenance.
• Equipment density. PDUs (Power Distribution Units), RPPs (Remote Power Panels), and busway systems pack high-current conductors into compact enclosures with bus gaps sometimes as small as 20–25 mm. The IEEE 1584:2018 model shows that smaller bus gaps can increase incident energy for certain electrode configurations.

The most significant finding in the NECA/IEEE guidance is the DC arc flash risk that many data centre operators have never assessed.

Data centres routinely operate DC bus systems at 48 V (legacy telecom), 380–400 V DC (modern high-efficiency architectures), and battery systems ranging from 192 V to 540 V. The critical physics: a DC arc will sustain at voltages above approximately 80 V. Once initiated, the arc does not self-extinguish at current zero as AC arcs do every half-cycle — it burns continuously until interrupted by a protective device or until the conductors separate beyond the arc’s reach.

Implications for data centre arc flash assessments:

• 48 V DC systems are generally below the arc sustaining threshold and do not require arc flash assessment (though they can deliver extremely high bolted fault currents that cause thermal burns through direct contact)
• 125 V DC and above can sustain an arc. Battery banks at 192 V, 384 V, or 540 V are serious arc flash hazards, particularly because battery systems deliver fault current for the duration of the arc — there is no upstream breaker that sees overcurrent, because the battery itself is the source
• 380–400 V DC distribution architectures (increasingly common for efficiency) combine high voltage with high available fault current from rectifier modules. These systems require arc flash assessment using the DC arc flash calculation methods in IEEE 1584:2018, Annex D or the method published in the NECA/IEEE guidance

The NECA/IEEE recommendation is unambiguous: every DC distribution system above 125 V in a data centre requires an arc flash hazard assessment. Facilities that have assessed only their AC distribution have an incomplete picture of their arc flash risk.

The NECA/IEEE publication provides actionable guidance specific to data centre environments:

1. Assess both AC and DC. Perform arc flash studies on all distribution above 125 V, including UPS bypass buses, battery cabinet distribution, and DC power shelves. Use IEEE 1584:2018 for AC systems and the recommended DC calculation method for DC systems.
2. Account for all fault current sources. Include contributions from all parallel UPS modules, standby generators (during transfer), and battery banks. The prospective fault current at a data centre main bus with all sources paralleled can be significantly higher than any single source rating suggests.
3. Review PDU and RPP bus gaps. Measure actual bus gaps in server room PDUs — do not assume manufacturer defaults. The electrode configuration and bus gap directly affect the arcing current and incident energy calculation in IEEE 1584:2018.
4. Implement maintenance switching. Where continuous operation prevents de-energising, install maintenance bypass switches that allow technicians to transfer load before performing work. The cost of a bypass switch is trivial compared to the cost of an arc flash injury.
5. Label everything. Arc flash labels on every panel, PDU, RPP, battery cabinet, and busway tap-off. The guidance specifically calls out battery cabinets as frequently unlabelled in existing facilities.

Standards referenced: IEEE 1584:2018 (AC arc flash model and Annex D for DC), NFPA 70E:2024 (Article 130), NFPA 70:2023 (Article 645 — IT equipment), NECA/IEEE joint publication on data centre electrical safety (2025).