Electrical Hazards

See also Part 3 of the University Health and Safety Policy - Electrical Equipment.

In this Division, committed to working with and constructing electronic equipment, it must be recognised that the main hazard is one of electrical shock or burns.

Students are not permitted to work alone in laboratories.

Trained staff working with equipment with exposed mains or EHT voltages must ensure that there is at least one other person present.

The primary cause of injury or death is the passage of electric current through the body. Consequential injury, possibly severe, can result from violent muscle reaction to the current.

The current can be supplied from a number of different sources 240V AC; DC supplies; EHT voltages. Someone electrocuted and still attached to a supply is still `live'.

Current over 10mA passing through the body is painful; current in excess of 100mA passing through the body is lethal.

The amount of current passed through the body is determined by the points of contact, the voltage applied and the skin condition (moist or dry). Skin resistance may vary from under 1000 ohms for wet skin to 500Kohms for dry skin.

Death has been caused by as little as 40 Volts.

Students in this Division are not allowed to have access to equipment with exposed voltages of over 30 Volts.

Students are not permitted entrance to the electronic workshops (where technical staff may be working with equipment with exposed mains and EHT voltages) unless approval has been obtained from the Head of Division or his authorised representative.

The Electrical Switchroom in the North Computer Hall is OUT OF BOUNDS to all students. In the event of the Main Supply dropping out for any reason, ONLY specific authorised personel are allowed to re-apply power. In the event of a power failure outwith normal working hours the appropriate person should be contacted using the Emergency Duty Roster which is mounted in the servitors' box. This must be done in conjunction with the Work's Division electrician who is responsible for the Machine Hall ventilation equipment, which will also have tripped out. The duty servitor or security officer will make the necessary telephone calls.

Safe working procedures must be aimed towards not contacting any live electrical conductor. In practical terms the following points should be noted:

• Do not attempt to modify or service electrical equipment unless it is disconnected from the supply or you are working under the supervision of trained personnel.
• Live electrical terminals must be shielded.
• Always ensure that electrical earths are continuous; connection to a chassis must be clean and checked.
• Temporary connections made for experimental reasons must be safe and properly insulated. Permanent connections should be made as soon as possible.
• Fuses of the correct rating must be fitted to all electrical equipment.
• Three Phase supply connections are the responsibility of the Works Division and should only be made by the Works Division Electricians; they should be permanent connections.
• Electrical isolators have a live side even in the switched off position - be aware of the danger.
• Single pole switches, if used, must be on the `live' side of the supply; always use double pole switches if at all possible.
• High current supplies can, in addition to the electrical hazard, give rise to arcing which can cause fire, electrical burns and ultra violet radiation, excercise care if wearing rings or metel chains.
• Disconnect high current supplies only when power is switched OFF.
• Always work with dry hands, standing on a dry floor, in a dry environment.
• The outer cover of any mains cable must always be securely held by the cable grips on the plug.

One of the main problems for technical staff working with electricity is over- familiarity. It is very easy to become so used to handling electrical and electronic circuitry that one loses the awareness of the potential dangers involved. One might be working on a piece of TTL circuitry, exposed to nothing more harmful than 5 volts, where you can have your hands all over the components with impunity, then change to a VDU where you may be exposed to 20 K/Volts. ALWAYS be alert to the danger and possibility of injury should you touch a high voltage conductor. Develop a sense of Safety Consciousness regarding electricity.