DGUV Information 203-077e - Thermal hazards due to electric fault arcing Guide for selecting Personal protective equipment

Abschnitt 5 - 5 Hints for practical implementation

Worksheets (Excel) have been developed to assist in applying this process. These are available in the Download section on the Internet website of the DGUV Department of Subcommittee Electrical Engineering and Precision Mechanics (www.dguv.de ;Webcode: d1183022). g_bu_1890_as_16.jpg

The alternative steps below can be used when applying the calculation methodology in order to achieve more precise results.

  • If the maximum value kP max was used to determine normalized arc power kP in the initial calculation, it is considered a safe calculation, but may go well beyond the target in practice. In this case, it may be worthwhile to calculate using a typical reference value or by considering the system configuration in actual practice.

  • When determining the current limiting factor kB, a (worst-case) value of 0.5 can be assumed for electric arcing in the low voltage network. As a rule, a calculation of the current limiting factor according to the more precise method [21] results in a kB value > 0.5 and, therefore, can lead to significantly low arc energy levels, e.g. when the short-circuit shutdown occurs due to fuses with trip times < 1 s (refer to the examples in Annex 5).

  • The geometry of the real installation is entered into the calculation. The transmission factor kT, which is normally determined during the initial approximation, can be adapted based on the actual geometric system conditions and the working environment. If a deviation from transmission factor kT = 1 is intentional, this determination must be justified.

If application of the risk assessment in Phase 3 determines that the protection afforded by the PPEaA selected for the work process under consideration is not adequate, the following exemplary measures could be considered in more detail in Phase 4:

  • The characteristics and corresponding trip time of the protection device have a significant influence on the potential electric arc energy in the event of a fault. Replacement of the upstream circuit protector with a fast-acting safe-work fuse or the adjustment of the circuit breaker tripping characteristics during the work period might be worth considering.

  • A separate electric fault arc protection device detects the arc fault via a sensor system and immediately initiates a bolted short-circuit, thereby triggering the upstream protection device. Consequently, the duration of arc combustion is reduced to just a few milliseconds. These devices may already have been considered for permanent installation during the system planning stage.

  • Working distance has a significant influence on the PPEaA protection level. Therefore, it always makes sense to consider whether the working distance can be increased through the use of additional auxiliary devices.

  • Short-circuit power at the workplace can be reduced by means of modified circuit variants, dependent upon the system configuration (e.g. disconnecting a mesh network switch, removing a parallel connection). It should be noted that the exposure to electric arcing must also be taken into account where it could impact the associated switching operations.

  • Use tested PPEaA for higher levels of incident energy.

The following basic conditions should be considered when using PPEaA in practice:

  • The requirements of DGUV Regulations 3 and 4 "Electrical Systems and Equipment" [4] must be taken into account, particularly with respect to the use of additional PPE for working on or in the vicinity of electrical installations.

  • This process addresses merely that protection provided against the thermal effects of an electric fault arc. Experience has shown that these can result in the most severe consequences. Electric fault arcing in high-energy systems can lead to additional hazards, such as shock waves, acoustic shock, optical radiation or escaping electric arc gases.

  • The manufacturer's instructions must be observed to ensure the PPEaA provides the appropriate protection in the event of a fault. In particular, it is essential to adhere to the instructions for proper usage, including those specified by the manufacturer for proper care and maintenance, as well as parts replacement criteria.

If the risk assessment reveals that the residual risk is too high (red area) and no further measures can be implemented, then work must not be performed on the installation.
The installation must be isolated.