Appliance Safety Testing - Construction and Repair

Sometimes it is necessary to build, repair or modify potentially hazardous electrical equipment that will be used in the Physics Department. Potentially hazardous equipment includes all equipment in hazard classes C, D and E defined below (230V mains equipment is usually class C). For safety, and to ensure Physics complies with all legal requirements, it is essential that any such work is carried out to high safety standards by competent people using suitable parts.

Physics has a 'sign-off' system in place requiring that any work on potentially hazardous electrical equipment is checked by an approved Physics Department electrical supervisor before the usual electrical safety inspection and test (PAT) required for all mains powered appliances can take place. This check is documented on a form requiring the signature of the person carrying out the work; the electrical supervisor and the appliance tester. The completed form should be handed to the appliance tester who will arrange for it to be filed. This sign-off system may also be used to confirm the safety of equipment without CE marking or a certificate of compliance that is brought into Physics. Work on potentially hazardous electrical equipment by Physics Electronics staff is similarly checked and documented.

The electrical supervisor will expect new built equipment to be of a safety standard at least equivalent to that required by the relevant BS EN standard. If suitable equipment cannot be bought commercially then it may be best to get the Physics Electronics group to build it for you as they have experience in constructing safe mains appliances, their standard build methods are documented in a guide which may be useful to you if you decide to do the work yourself. It is always advisable to discuss safety requirements with an electrical supervisor before starting work.

Please do not expect electrical supervisors to offer step by step instruction or to spend time repeatedly rechecking an item until it is acceptable - anyone undertaking work on potentially hazardous electrical equipment is expected to be fully competent to do the work and the supervisors job is simply to check and approve it.


Links to Documents

Sign-off form

Physics Electronics Group Construction Guide

Physics Electrical Supervisors etc


Electrical Hazard Class Definitions

Class A. Safety Extra-Low Voltage

Circuits operating at <42.4V peak ac or <60V dc (extendable under fault conditions to <71V peak ac or <120V dc for a maximum of 0.2 seconds). Stored energy to be <20J and available power to be <240VA.

Class B. Limited Current

Circuits operating below the Class D limits where no hazardous currents flow in normal or likely fault conditions. Currents up to 2mA dc or 0.7mA peak ac up to 1kHz rising linearly with frequency to 70mA peak ac. at 100kHz are permissible. In circuits operating at <450V the circuit capacity is to be <0.l microfarad. In circuits operating at >450V the circuit capacity is to be <0.05 microfarad.

Class C. Hazardous Low Voltage

Circuits operating at <650V peak ac or <l000V dc which fail to meet the Class A or Class B definitions.

Class D. High Voltage

Circuits operating at >650V ac or >l000V dc

Class E. High Current

Circuits operating at >l00A and all pulsed magnet systems producing peak fields >0.1 Tesla.

Class F. Building Wiring

All building lighting circuits and all power distribution circuits designed as part of the building services and terminating in a socket or equivalent termination.

(Classes A and B are regarded as non-hazardous and Class F should only be worked on by Building Services electricians and UED.)