– Dave G. Loucks, PCM Solution Manager with Eaton Corporation (www.eaton.com), says:
No company should begin powering their data center at 400V before making careful preparations aimed at protecting their employees. The following will discuss five essential safety steps that data center managers should consider taking.
Perform a hazard analysis. Proper arc flash safety is impossible without accurate measurements of the potential energy release associated with arc flash events. An arc flash hazard analysis can help you calculate those incident energy values, while also identifying arc flash risks along the power chain and strategies for mitigating them.
Select appropriate personal protective equipment. Technicians in a 400V data center should never come within range of a potential arc flash incident unless they’re wearing appropriate personal protective equipment (PPE), such as flame-resistant clothing, eye protection and gloves. For example, if live bus work is exposed, personnel should remain at least 10 feet away unless they’re wearing appropriate PPE. The specific type of PPE worn depends on the calculated incident energy values. PPE shields wearers from the heat and light produced by arc flash explosions, and to a lesser extent from shrapnel and noise as well.
Conduct employee safety training. While providing appropriate PPE is a vital part of safeguarding technicians from arc flash hazards, thorough safety training should also be part of every company’s strategy for mitigating arc flash dangers. When delivered by experienced and knowledgeable instructors, arc flash safety training can also help data center managers calculate potential short circuit currents, Hazard Risk Categories and safe boundary distances based on the IEEE 1584-2002 and NFPA 70E standards. Organizations should also ensure that any vendors or third-party service providers working in their data center have received thorough safety training as well.
Leverage parallel redundant architectures. Many organizations currently use parallel redundant power chain architectures in their data centers. At their most thorough, such schemes provide multiple, independent power paths all the way from utility mains to electrical load, so that if one path becomes unavailable due to a component failure or routine maintenance, the others can keep critical applications up and running.
Use circuit breakers instead of fuses. Generally speaking, organizations have two options when selecting overcurrent protection technologies in a data center power system: fuses and circuit breakers. Though data center managers should consider a range of factors before making their choice, circuit breakers provide significant advantages with respect to arc flash safety due to the faster fault clearing time they provide during the kind of fault that occurs most commonly in a data center—ground faults. In fact, IEEE Std 493-2007 (Gold Book), Table 10-32 states that the likelihood of a ground fault is 2.5 to 70 times more likely than a phase-to-phase fault. Since ground fault current typically flows through non-copper conductors, the overall magnitude of the fault current is reduced. Under these lower current conditions, the very steep time-overcurrent curve typical of a current limiting fuse works against it.
Furthermore, though technicians can turn fusible switches on or off remotely, changing or inspecting a fuse requires them to go into the panelboard, where they’re exposed to potential arc flash events. Circuit breakers, by contrast, rarely require replacement and can be reset safely from outside the panel.
Conclusion
Long common elsewhere in the world, 400V data centers are slowly gaining popularity in the U.S., at least partly because they eliminate 480V to 120V transformers and thus offer superior energy efficiency. Yet operating a data center at 400V poses arc flash risks far more severe than those found in a 120V data center. To protect their employees from disabling and even lethal injuries, organizations contemplating a move to 400V must carefully study the potential hazards and supply their people and facilities with appropriate PPE, circuit protective devices and training. By doing so, they will position themselves to enjoy all of the power-saving benefits 400V operation offers without needlessly endangering lives.
