Off-load isolators

NERs can be fitted with manual or motorised off-load isolators, either singly or in interlocked pairs if the purpose is to switch between resistance earthing and solid earthing.

Vacuum contactors

For medium-voltage power generating schemes which have multiple diesel generating sets, it is necessary to ensure that one (and only one, to avoid the possibility of circulating currents) of the neutrals of one of the running generating sets is earthed at all times. This can be most economically achieved by using a single earthing resistor of the appropriate rating (usually the full-load current of one phase) connected to each of the neutrals with a vacuum contactor which is controlled from the generating set panel.

Cressall have standard cabinet designs to house 1, 2,3, 6 and 9 contactors, for generators of 3.3 to 24kV system voltage.


11kV manual off-load isolator	NER with single vacuum contactor

NER with nine vacuum contactors

Cressall Resistors Ltd, Evington Valley Road, Leicester, LE5 5LZ U.K. Tel: (+44) (0)116 273 3633