Transcript Work on Electrical Equipment (Revision 1)

Procedures for work on
Fixed Electrical Installations
Toolbox Talk 3:
Work on Electrical
Equipment
Main Points:
•
Hazards and risks associated with work on electrical systems
•
Procedure for work on electric cables
•
Procedure for work carried out adjacent to exposed live conductors
On average, 20 people are killed in the UK every year by electrical accidents
whilst at work - most of these accidents are preventable.
The Electricity at Work Regulations 1989 requires precautions to be taken
against the risk of death or personal injury from electricity in work activities.
The purpose of these procedures is to put in place a system of control measures
to prevent injury to University Staff and contractors from the hazards and risks
associated with work on electrical systems at the University.
HAZARDS AND RISKS ASSOCIATED WITH WORK
ON ELECTRICAL SYSTEMS
Electric shock
Electric arcing
Fire
Electrical explosions
Electric Shock occurs when a person makes
contact with a live conductor while
simultaneously in contact with an earthed
object or another live conductor at a lower
potential and current passes through the body.
The effects of electric shock include:
• Muscular contractions causing involuntary gripping of the live
source and being unable to let go.
• Cardiac arrest.
• Electric burns
• Momentary loss of control or balance
Factors in the surrounding environment that
can increase the likelihood of electric shock
include wet or damp conditions or areas where
there is a high proportion of earthed metal in
cramped surroundings.
PROCEDURE FOR WORK CARRIED OUT ON OR NEAR LIVE
CONDUCTORS WHICH MAY FORESEEABLY GIVE RISE TO DANGER
Scope of this procedure
This procedure covers work on or near live electrical conductors which may foreseeably
give rise to danger. Work includes electrical testing and work activities that are not
electrical in nature but are carried out near live electrical conductors. Work on or near live
conductors which may foreseeably give rise to danger will rarely be permitted by the
Estates Section.
How to decide whether the work will ‘forseeably give rise to danger’
When carrying out any work on or near live conductors the electrician who will carry out
the work must carry out an initial risk assessment of the work based on the following
factors:
• The amount of exposed live conductors (e.g. metalwork).
• The possibility of electric shock from physical contact with the exposed live conductor,
arcing whilst being in proximity to the exposed live conductor, or dropping something onto
the live conductor.
• The location where the work is to be carried out (i.e. can the area be easily secured or is it
in a busy place?).
Authorisation for work
In view of the strict requirements laid out in the Electricity at Work Regulations and
the potential risks, cases where the risk assessment highlights a foreseeable risk of
danger from the live conductor must be referred to the Assistant Estates Director
with responsibility for the work prior to the work being carried out.
The Assistant Estates Director will decide if the work can proceed based on the
three conditions necessary for work on or near live conductors which may
foreseeably give rise to danger listed in the Electricity at Work Regulations 1989.
Question:
Which of the following is NOT a factor in deciding whether work would
“foreseeably give rise to danger”:
a) Whether it is single phase or three phase a) Single phase can still electrocute you!
b) The location
c) The amount of exposed live conductors
d) The possibility of physical contact with the conductor.
Question:
Why might this electrical equipment
foreseeably give rise to danger?
Minimum precautions required for all work on or near live conductors
which may foreseaably give rise to danger
Risk assessment and method statement
The authorised person supervising the work must carry out a written risk assessment for
the work. A method statement must then be written detailing exactly how the work will be
carried out and the safety precautions to be taken.
Personal protective equipment
Required
• Insulated tools – to BS EN 60900: 1994
Optional (depending on results of risk assessment and the precautions required)
• Rubber gauntlets (rated 1000V) – to BS EN 60903:1993 Note: Ensure that the
replacement date stamped on the gauntlet has not expired.
• Visor
• Arc proof boilersuit
In addition to the above PPE loose metal jewellery should be
removed. Metal objects kept in pockets such as coins, keys, lighters
etc must be removed to prevent anything falling out onto live parts
during the work.
Area where work is to be carried out
The work area must be checked to ensure that:
(i) There is adequate working space. The HSE publication HSG85 Electricity at Work
Safe Working Practices states that where there are exposed live parts at 400V or
above, the clear working space should not be less than 1m. Where there are live
parts exposed on each side of the working space the clear working space should not
be less than 1.4m.
(ii) Floors are free from any slip and trip hazards.
(iii) Lighting levels are adequate.
(iv) In some areas effective barriers may be required to keep unauthorised persons
away from the work area.
(v) Warning notices must be posted at the entrance to the area to prevent
unauthorised entry.
(vi) Protective screening may be required to screen live parts. Any protective
screening used must be suitable for that purpose.
Accompaniment of person carrying out the work
The person carrying out the works must be accompanied at all times by another
Estates Section electrician with the competence to keep unauthorised persons away
from the area, recognise danger, switch off power in the event of an emergency, radio
for assistance and provide first-aid to the injured person.
Question:
Assuming this is work on live conductors which may foreseeably give
rise to danger, what is wrong in this picture?
Answer:
• Nothing to stop anyone opening door
• No barriers
• No PPE
• Trip hazards on floor
• No standby person
Removal/replacement of covers designed to shroud exposed live conductors
Covers which shroud live conductors should not be unscrewed or unbolted whilst
the equipment is still live. The reason for this is that what is behind the cover is
unknown and any loose parts (e.g. screws, cables etc) or the cover itself could
come into contact with the live conductor. The same would apply to replacing
covers which shroud live parts.
Examples include:
• Screwed or bolted covers on distribution boards and consumer units.
• Covers on power sockets and light switches.
Covers which shroud live conductors may sometimes have to be removed in
order to carry out live fault finding on equipment. The equipment should be
isolated and locked off before unscrewing or unbolting the cover. The equipment
should also be isolated and locked off before screwing or bolting the cover back
into place.
PROCEDURE FOR WORK ON ELECTRIC CABLES
Electric cables must not be worked on unless they have been proved dead and can be
traced from the point of work all the way back to a SECURE ISOLATION at the
switchboard.
Methods of tracing cables
The following methods of tracing cables are
acceptable:
• Visually tracing the cable all the way back to
the switchboard. Note: Pulling at cables is not
an acceptable method of tracing cables as
other cables can be wrapped around the cable.
• In cases where the cable terminates at a
socket - using a fuse finder to locate the fuse
or circuit breaker for the cable.
• In cases where the cable is found to be live and does
not terminate at a socket outlet - using a non-contact
voltage detector on the cable and an Estates electrician
switching off circuit breakers/pulling fuses until the circuit
breaker/fuse for the cable has been located.
Notes:
1. The voltage tester being used must be suitable for the type of cable being tested (refer
to manufacturers instructions for suitability).
2. The non-contact voltage detector must be proved against a known live source before
and after testing the cable. The cable must be separated from other cables when the tests
are carried out.
3. Using the non-contact voltage alone without actually going and tracing the cable back
to its source is not acceptable as the final means of proving whether a cable is live or dead.
The cable must be labelled stating who proved it dead, when it was proved
dead and the circuit breaker/fuse for that cable.
When using a non-contact voltage detector to
trace cables, always prove against a known live
source first.
Redundant cabling
Cabling that is no longer required must be
stripped out back to the switchboard.
Exceptional cases where this is not possible
must be referred back to the Estates Section
person commissioning the works. Should the
person commissioning the works decide that it
is unreasonable to remove the cable, the cable
must be physically disconnected at both ends,
tied up and labelled.
Under no circumstances should cabling be left
connected to a power source once it has been
disconnected from the equipment it originally
supplied.
Question:
Before working on an electrical cable which of the following must be done?
a) Apply a non-contact voltage detector to the cable. If it does not light up then
proceed with work on the cable.
WRONG – This test only proves that the cable is dead at the time of the test,
It does not prove that the cable is not still connected to a power source which
could be re-energised at any time.
b) Visually trace the cable all the way back to the switchboard and ensure
that the circuit is isolated and locked off.
CORRECT
c) Pull at one end of the cable where the other end cannot be seen.
WRONG – Cables can get tangled or snagged on other cables. Cables need to be
physically traced.
PROCEDURE FOR EARTHING LOW VOLTAGE EQUIPMENT
Additional local earths may be required if:
1. The point of work is remote from the point of isolation.
2. There is a chance that the equipment or circuits may retain an electrical charge (due to
capacitance or induction) after disconnection from the power source. Examples include
switchboards fed from transformers on a high voltage system and large motors.
Should electrical staff be in any doubt whether additional local earths may be
required they should contact the Senior Maintenance Electrician/Chargehand
Electrician.
The following PPE must be worn when connecting and disconnecting
leads:
• Rubber gauntlets (rated 1000V) – to BS EN 60903:1993 Note: Ensure
that the replacement date stamped on the gauntlet has not expired.
• Visor
The following sequence of operations must be carried out when connecting
and disconnecting leads:
1. Carry out checks to ensure that the equipment or circuit is dead and has been
securely isolated (see section 5.1).
2. Check portable leads for any defects, check that leads have are suitably rated to deal
with any short circuit currents.
3. Connect leads to earth before connecting to each phase conductors, then link up
each of the phase conductors.
4. Check that good contact has been made. Leads must be labelled to identify them as
an additional earth.
5. When removing portable leads, disconnect leads from phase conductors first and
then from earth.
HIGH VOLTAGE EQUIPMENT
The University owns a number of high voltage installations - a specialist contractor
maintains these.
Estates Section electrical staff are not permitted to work on any high voltage
equipment.
Estates Section electrical staff must not enter any HV substations unless authorised
and accompanied by the Clerk of Works (Maintenance), Senior Maintenance
Electrician, Chargehand Electrician or M&E Project Engineers.
Note: for the purposes of these procedures high voltage is classed as any voltage
above 650V ac.
POTENTIALLY EXPLOSIVE ATMOSPHERES
There are several areas around the University where there is the potential for an explosive
atmosphere to develop due to the nature of the items being stored (e.g. solvent or chemical
stores). “Hazardous area” fittings have been installed in these areas.
University Maintenance staff are not permitted to work on the “Hazardous area” safe
fittings in these areas.
All works in these areas to be carried out by a specialist contractor with the permission of the
Technical Resources Officer responsible for the area.