The purpose of EGN 4 is to set safety standards and ensure that those who select, use and maintain mains isolating transformers in technical areas and workshops are aware of their responsibilities under BBC Requirements and the Electricity at Work Regulations 1989. It is intended to cover the selection, maintenance and use of mains isolating transformers in all these areas and in particular will apply to Resources, N&R, News, World Service, Radio & Music, Technology and Broadcast.

This guidance does not apply to auto-transformers (which should not be used), transformers used on building sites (110V or 50-0-50V) nor to isolating transformers used in vehicles e.g. OB Scanners and satellite trucks.

The Mains Isolating Transformers covered by this Guidance Note will be various types and will be found:

As free standing units in workshops
Built in to workshop bench supplies and marked as 'isolated supply'
In Radio and TV Studios
In use with Performers' equipment in studios

Note that in the BBC the name often used for this piece of equipment is a Safety Isolating Transformer (see Special cases- Performing Band electrical and musical equipment).

This EGN replaces all previous safety documentation with regard to the selection, use and maintenance of Mains Isolating Transformers issued by BBC Safety or by the former Engineering Management Safety Committee. It does not however, replace documents issued at Divisional or Departmental level, although such documents must neither conflict with nor set standards which are not as rigorous as those given here.

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