NR RT/E/C/19011 ISSUE 1 PDF

The principles specified in this document shall apply to new designs and alterations to existing circuits, where silver to silver contacts of d.c. polarised moving iron relays are used to cut off the supply to relays and other inductive loads.

PURPOSE

Technical Investigation Report 95040 identified that in certain circuit designs, silver to silver contacts of d.c. polarised moving iron relays are used to cut off the supply to relays and other inductive loads. Such designs have been found to contribute significantly to damage and possible welding of contacts. This document includes advice on methods of minimising the risk of damage and the welding of contacts due to induced back emfs.