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Stage Two - Protection Review / Update

Typically, one of the simplest ways to reduce high arc flash energy levels and risks is to examine the settings on the protection devices. There is evidence that during the life of electrical system the protection settings are sometimes changed i.e. to allow starting of motors, or to prevent nuisance tripping due to overloads. Quite often these changes are not properly recorded which can lead to problems like a lack of discrimination between the protective devices as well as to increased arc flash energies.

Apart from the protection settings being changed, there is another factor that often affects the arc flash energies – available short circuit currents. Changes to the electrical system, like reducing available generation on-site or increasing the impedance of the system e.g. replacing LV cable with longer cable of the same type due to switchboard relocation, can lead to lower fault levels and higher arc flash energy as described in Arc Flash Studies. Arc flash risk can be often overlooked in this case as apart from the cable, all equipment remains unchanged, the protection settings are considered appropriate and no further consideration is given to the arc flash energies.

Once the arc flash levels are calculated during the initial study, operation of protective devices can be evaluated to validate whether the required discrimination margins are achieved between the devices. Should discrimination allow, further recommendations to the protection settings can be made to reduce the achieved arc flash energies. There are cases where lack of discrimination between the relays can be also considered in favour of lower arc flash energies, however the standard approach is not to cause deterioration of the protection discrimination.

As indicated earlier, the good news is that in a large number of cases the arc flash energies can be drastically reduced by simple adjustment of the protection settings. In some cases changing the settings will require a few button pushes on the protection relay, or adjusting the dial with screwdriver, some more complicated examples would include replacing the fuse with fuse of smaller rating.

Further protection related solutions and considerations are explained in Hazard Reduction.