System Maintenance and Design for Arc Flash Safety
Under ideal circumstances, preparations for arc flash safety take place long before live electrical work needs to be performed. By designing electrical systems with safety in mind, and by maintaining them in good working condition, many arc flash risks can be minimized or eliminated before they even appear.
Designing for Arc Flash Safety
Fault current and clearing times are the two major contributors to the magnitude of an arc flash incident. Both can be controlled with safety-conscious system design. The design phase is, in fact, often the only time steps can be taken to reduce available fault current.
Using several small transformers and substations, rather than a single larger one, can often lower the fault currents available at various points in the system. This design has the added advantage of improving system reliability in the event of a malfunction.
Careful selection and coordination of overcurrent protective devices is a key step in reducing fault-clearing times. In addition to installing current-limiting fuses and breakers (see our Safety Devices page for more information), a number of methods can be employed to ensure that faults clear rapidly. These include:
- Use appropriate fuses. Installing the lowest-ampere fuse required for downstream loads (including inrush currents from motor startup) makes it more likely that the fuses will operate in the current-limiting region in the event of a fault.
- Use zone interlocking. This breaker feature communicates between main, tie, and feeder breakers to ensure a quick fault-clearing time by signaling upstream breakers that a fault has occurred, causing them to switch to a more sensitive setting.
- Use adjustable breaker settings. By setting the short time delay setting correctly, quick fault clearing times can be achieved even when current is below the breaker's instantaneous region.
Finally, installing protective devices like IR viewports, voltage sensors, or remote controls during the initial construction of an electrical system saves the cost and difficulty of retrofitting the system at a later date. Some facilities with extraordinarily high incident energies may even design their systems so that energy released in an arc flash is channeled away from workers into safe areas outside the workspace.
Real-world advice and insight into preventing arc flash accidents.
NFPA 70E and System Maintenance
Even a well-designed system can pose unnecessarily high dangers if it is not maintained properly. Improperly maintained circuit breakers can lose functionality over time, and may even become completely inoperable. In the event of an arcing fault, such devices will not be available to interrupt power, which can lead to long fault-clearing times and extreme levels of incident energy.
Proper maintenance can not only keep incident energy to a minimum; it can even prevent arc flash incidents from occurring. Many arc faults are associated with loose connections or gaps in insulating materials. Regular, careful inspections and thermography can catch these problems before they cause an accident.
A footnote in NFPA 70E refers to the industry maintenance standard contained in NFPA 70B, "Recommended Practice for Electrical Equipment Maintenance." NFPA 70B compliance is not mandated by OSHA, and remains entirely voluntary. However, proper preventative maintenance can greatly contribute to worker safety, as well as saving companies the high costs associated with serious arc fault incidents.