05: 51 Common Rules (126)

Question 1

A generating set used as an additional source of supply in parallel with another source, and is installed on the load side of all the protective devices for a final circuit, the additional requirement not applicable is (551.7.2 p.209)

a) A generating set shall be connected by means of a plug and socket
b) An RCD providing additional protection in the final circuit
c) The line and neutral conductors of the final circuit and of the generating set shall not be connected to earth
d) Iz ≥ In + Ig

Answer 1

a) A generating set shall be connected by means of a plug and socket

551.7.2 p.209
A generating set used as an additional source of supply in parallel with another source shall be installed:

– on the supply side of all the overcurrent protective devices for the final circuits of the installation, or

– on the load side of all the overcurrent protective devices for a final circuit of the installation, but in this case all the following additional requirements shall be fulfilled:

(i) The conductors of the final circuit shall meet the following requirement: Iz ≥ In + Ig

where:
Iz: is the current-carrying capacity of the final circuit conductors

In: is the rated current of the protective device of the final circuit

Ig: is the rated output current of the generating set

(ii) A generating set shall not be connected to a final circuit by means of a plug and socket-outlet

(iii) The line and neutral conductors of the final circuit and of the generating set shall not be connected to
Earth

(iv) Unless the device providing automatic disconnection of the final circuit in accordance with Regulation 411.3.2 disconnects the line and neutral conductors, it shall be verified that the combination of the disconnection time of the protective device for the final circuit and the time taken for the output voltage
of the generating set to reduce to 50 V or less is not greater than the disconnection time required by
Regulation 411.3.2 for the final circuit.

This regulation does not apply to an uninterruptible power supply provided to supply specific items of current-using equipment within the final circuit to which it is connected.