G5/4 is an Engineering Recommendation used when planning to add loads and capacity to an existing electrical installation. When expanding an installation there is a requirement to limit harmonic emissions for nonlinear loads and generation plant onto the electrical supply system. This requirement is design to limit voltage distortion in the distribution network. Harmonic limits are not governed by statue but are used by the DNO when considering the connection agreement. The harmonic limits are defined for both harmonic voltage distortion and current harmonics.