Transcript Electrical Isolations (Revision 0)

Procedures for work on
Fixed Electrical Installations
Toolbox Talk 1:
Electrical Isolations
Main Points:
•
Hazards and risks associated with work on electrical systems
•
Procedures for carrying out electrical isolations
•
Procedure for padlocking off and posting of caution notices on isolations
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.
PROCEDURES FOR CARRYING OUT ELECTRICAL ISOLATIONS
Note: The Senior Electrician/Chargehand Electrician must be contacted prior to any work being
carried out if the distribution board or consumer unit is found to be unsafe to work on (e.g.
covers missing leaving live parts exposed).
1. Identify the circuit to be isolated (refer to circuit charts or use a fuse finder if charts
are poor or do not exist).
2. To isolate the circuit carry out one of the following:
a) Switch off circuit breaker or isolator and lock off OR
b) Remove the fuse and carrier. Apply locking device to the fuse carriage and
lock off.
Note: Fuses that have been removed must be retained by the person responsible for the
isolation and not left lying on distribution board shelves or rooms.
If neither of the above is possible contact the Senior Electrician/Chargehand Electrician
(Maintenance) prior to carrying out any work.
Post caution tags on the circuit breaker OR on
the lock in the fuse carrier.
Note: Taping over fuse carriages or posting
caution tags on the distribution board door is
NOT acceptable.
The caution tag must state the person carrying
out the isolation and the reason for the isolation.
To test the circuit to prove that it is dead the following must be done:
Note: Authorised equipment MUST be used (see section 4.0).
(i) If using a multimeter ensure that the
correct function (voltage testing) has
been selected. Note: All multi-meters
issued to staff will be a type that will not
give rise to danger if inadvertently put to
an incorrect setting.
(ii) Prove the test meter by applying the
leads to the test unit.
(iii) Apply the testing leads to the electrical equipment to be worked on in this order:
Each phase & earth
Each phase & neutral
Each phase to phase
Neutral to earth (if the neutral has been disconnected)
Prove the test meter again by applying the leads to the test unit.
Note: In the case of testing that a
socket has been isolated a Martindale
plug in tester may be used. The plug in
tester must be proved on a live socket
before and after the check on the
socket that is being proved dead.
Question:
Which of the following is an acceptable isolation for an electrical contractor:
a) Switch off the circuit breaker/isolate and post a caution on the door
b) Remove the fuse and put some tape over the holder
c) Switch off circuit breaker and apply a maintenance padlock before handing
over the isolation to a contractor
d) Switch off circuit and apply a maintenance padlock and contractors padlock
(if contractor to work on circuit)
Procedure for the electrical isolation of a motor or pump
1.Switch off the isolator serving the motor.
2. If it cannot be confirmed that the isolator is a 2 pole isolator (for single phase) or 4-pole type isolator
(for 3 phase), then open the isolator cover to check that the neutral link has been physically separated.
If the neutral link has not been physically separated, drop the neutral link (this is assuming the isolator
has a neutral which can be dropped). Note: should any covers be broken or missing exposing live parts
the Senior Electrician/Chargehand Electrician (Maintenance) MUST be contacted before the works
proceed.
3. Lock off and post caution tag.
4. Remove cover of the motor and prove that power supply to the motor is dead.
De-isolation of motor
Re-connect the neutral link prior to the de-isolation being carried out.
After carrying out a de-isolation check that the motor is operating in the right direction by
momentary switching the motor on.
Note: The above test should be satisfactory for most applications. In rare cases where
phase rotation tests are required (i.e. tests which are carried out with covers removed and
there are exposed live parts where there is a foreseeable risk of danger) then the
procedures listed for “Work on or near live conductors which may foreseeably give rise to danger” will
apply.
Procedure for the isolation of main switches on incoming low voltage switchboards
In addition to the isolation and locking off of the main switch the following must be
carried out:
1) Uninterrupted Power Supply (UPS) to be shut down and isolated:
• Procedure for shutting down the UPS system listed in the operating manual to be
followed.
• Switch off and isolate the power supply from the UPS. Lock off and post caution tag.
• Switch off and isolate the power supply to the UPS on the main LV board. Lock off and
post caution tag.
2) Standby generator to be isolated and locked off:
• Push stop buttons (external and internal)
• Turn selector switch from ‘auto’ to ‘stop’/off
• Switch main circuit breaker to off position
• Disconnect battery tails
• Senior Maintenance Electrician/Chargehand Electrician to apply personal padlock and
caution tag.
• Senior Maintenance Electrician/Chargehand Electrician to remove key and place in
lockout box.
De-isolations
Tests required prior to the system being de-isolated
Systems or equipment which have been worked on must not be de-isolated until
copies of the tests required by BS7671: 2008 (the IEE Wiring Regulations 17th Edition)
have been supplied to the person carrying out the de-isolation.
Re-connection of the neutral conductor
In cases where the neutral conductor has been disconnected (e.g. in an older type
isolator), the neutral conductor must be re-connected prior to the de-isolation being
carried out.
Neutral conductors on older circuits
On older circuits the dangerous practice of borrowing neutrals may have been carried out.
A borrowed neutral which has been used in another circuit could be live when
disconnected (or become live if the other circuit is switched off at the time of disconnection
but subsequently re-energised).
For disconnection
Against disconnection
the neutral conductor the circuit to be
worked will be isolated from any source
of potential power
a neutral which has been borrowed can
become live once it is disconnected risk of electrocution
fire if a neutral conductor which was
disconnected on a 3-phase board is not
reconnected when the board is
reenergised
Neutral conductors on older circuits (continued)
For this reason work involving older boards will need to be considered on a case by case
basis, however the following guidelines will apply:
• Staff should be aware that on older circuits borrowed neutrals could be an issue.
• Neutrals should be treated as being potentially "live". Tests should be carried out
between neutral and earth for any voltage if the neutral is disconnected. Note: the test
will only work if the other circuit is energised at the time the neutral is disconnected.
• ALL neutrals which have been disconnected should be terminated into separate
terminal blocks. They should be treated as being potentially ‘live’ when being
reconnected.
Neutral link in place
Neutral link dropped
PROCEDURES FOR PADLOCKING AND POSTING OF CAUTION NOTICES ON ISOLATIONS
Padlocks used by Estates Section staff
Estates Section staff are only permitted to use
padlocks that have been approved by the
Senior Maintenance Electrician/ Chargehand
Electrician.
All padlocks used by Estates Section staff will
have unique keys with no duplicate keys being
held.
Work on low voltage installations (general)
The padlocks of all persons (including contractors) working on the low voltage
installation must be applied at each point of isolation. The Estates electrician
carrying out the isolation must apply a caution notice at each point of
isolation. The padlock of the Estates electrician carrying out the isolation
must be the first padlock applied to the isolation and the last padlock
removed prior to de-isolation.
Work on mechanical equipment
Where isolations are required to enable work to be carried out on an item of
mechanical equipment (e.g. pump), the padlocks of all engineers working on
the job must also be applied at each point of isolation.
What is wrong in this picture?
Isolations where multiple padlocks cannot be applied
On some small lighting and power circuits it may not be possible to apply multiple padlocks
at the point of isolation. In this case the padlock of the Estates Electrician will be applied,
the key for the padlock must then be put in the lockout box and the padlocks of all those
involved in the works (including contractors) applied to the lockout box. The lockout box
must then be taken to nearest electrical workshop. The Estates Section electrician must
apply a caution notice at the point of isolation.
Lockout box for use when multiple padlocks
cannot be applied to a circuit. Put key for
maintenance padlock on circuit breaker into
box...
...then apply contractors and maintenance
padlocks to box.
Isolations where it is not possible to apply a padlock
Where it is not possible to apply a padlock (e.g. older type switchboards with fuse
carriers which cannot be locked off), the Senior Electrician or Chargehand Electrician
must be contacted. The phase cable to the fuse carriage must be disconnected, the
end taped and a caution tag applied to the end of the cable - taping over fuse
carriage holders and leaving the circuit cables connected is NOT acceptable.
Note: this work must be done with the switchboard dead and securely isolated. The
fuse carrier should then be put back into the board without the fuse, this will ensure
that the live parts of the board are covered.
Question:
What is wrong
in these two
photos?
Question:
1. Where multiple padlocks cannot be applied for an isolation for Projects work
which of the following should be done:
a)
Apply a maintenance padlock to the circuit then handover to the
contractor.
WRONG
b)
Apply the contractors padlock to the circuit then handover to the
WRONG
contractor.
c)
Apply a maintenance padlock to the circuit, put the key into a lockout
box, then apply both maintenance and the contractors padlock to the
locked box.
CORRECT
Removal of padlocks in the absence of the owner
The removal of padlocks will only be permitted in exceptional circumstances
(i.e. the consequences for the University of not removing the padlock are
operationally or financially unacceptable). The removal of a padlock MUST be
authorised by an Assistant Estates Director.
PROJECTS ISOLATION REQUEST FORM - GUIDANCE ON COMPLETION FOR AN
ELECTRICAL ISOLATION
• The only Projects staff who are authorised to complete a request for an electrical
isolation are the M&E Project Engineers. If any other staff (e.g. Building Clerks of
Works) require an electrical isolation it must be referred to one of the M&E Project
Engineers.
• Maintenance staff will normally isolate electrical services on behalf of Projects. On
some occasions it may be more efficient for one of the M&E Project Engineers to carry
out the isolation themselves. In this case a Projects Isolation Request Form will still
need to be completed by this person.
• An individual form is required for each area to be electrically isolated (i.e. electrical
isolations for two completely separate areas require two separate forms). Requests for
isolation of other services (e.g. fire alarm, water etc) must not be put on the same form.
• Forms must not be faxed.
SECTION 1 OF FORM
Parts 1-6
The M&E Project Engineer requesting the
electrical isolation, or carrying out the
isolation, must complete parts 1 to 6 of the
form. The information in parts 1 to 6 must
contain sufficient detail for the isolation to
be carried out (location, circuit board
number, circuit number etc).
Maintenance staff carrying out isolations must only isolate the electrical services listed on
the form. If additional services require isolation a new form must be completed.
Part 7
The isolation may not proceed until:
- The Clerk of Works (Maintenance) has checked Parts 1-6 of the form and signed Part 7 of
the white and yellow copy of the form. Note: If the Clerk of Works (Maintenance) is
unavailable then the Senior Electrical Engineer, Chargehand Electrician or Assistant Estates
Director (Maintenance) should carry out the checks and sign this part of the form.
- The Building Clerk of Works responsible for the area has signed part 7 of the form.
SECTION 2 OF FORM
Part 1
This must be completed by the Senior Electrical Engineer or Chargehand Electrician
confirming that the electrical isolation may proceed. Permission for the isolation should not
be granted if the information in Parts 1 to 7 of the form are either incomplete or do not
contain sufficient information.
Part 3
Part 3 must be completed by the electrical contractor who will actually be carrying out the
work. The isolation must only be carried out if there is an electrical contractor there to
accept it.
SECTION 3 OF THE FORM
Part 1
Electrical de-isolations MUST NOT be carried out until copies of the dead tests for the work
required by BS7671: 2008 (IEE Wiring Regulations 17th Edition) have been forwarded to
the person who will carry out the de-isolation.
FILING OF PROJECTS ISOLATION REQUEST FORMS
The Projects representative must collect each of the copies of the form and file these
together in file H PRO ISO kept in the Estates office.
Questions:
1. Who can accept an electrical isolation?
a)
A building Clerk of Works
WRONG
b)
An electrical contractor
CORRECT
c)
The principal contractor (building) for the works
WRONG
Question
2. Who can complete a request for an electrical isolation?
a)
A building Clerk of Works
WRONG
b)
The Clerk of Works (projects)
WRONG
c)
M&E Project Engineers
CORRECT
d)
Project Managers
WRONG