To safely work on electrical circuits, they must be isolated and tested to ensure they are dead. This involves switching off the power supply, disconnecting cables or using an isolating switch, locking off the isolator with a padlock, posting warning signs, and testing for voltage with a certified voltmeter. Proper isolation, locking, signage, and voltage testing are all required to confirm a circuit is dead before beginning any work.

1. Safe isolation of electrical
installations

2. The safest way of working on an electrical circuit
is to make sure that the circuit is ‘dead’.
A ‘dead’ circuit is a circuit which cannot cause
harm.
NEVER ASSUME THAT A CIRCUIT IS ‘DEAD’.
ALWAYS CHECK THE CIRCUIT YOURSELF!

3. Safe isolation means:
SWITCH OFF
This means the supply to the circuit is switched
off.
ISOLATION
This means the disconnection of the supply
cables, or using an isolating switch.

4. POST WARNING NOTICES
Warning notices must be shown on any
isolator that has been switched off. The reason
is that you do not want anyone re-energising a
circuit whilst you are working on that circuit.

5. POSTING WARNING NOTICES
Warning notices also need to be posted on the
approaches to the site of work. They must
make it clear to anyone that they must stay
away from the area where the work is being
carried out.

6. LOCKING OFF
Many electricians believe that ‘locking off’ a
circuit is a case of overkill when warning
notices have been posted on isolators. But,
‘locking off’ stops accidents happening to
people who ignore the notices or people who
cannot read.

7. LOCKING OFF
Isolators must be able
to be ‘locked off’. This
is done with a padlock
and key.
Or the handle can be
made removable in the
OFF position and the
person can take it with
them once the circuit is
switched off.

8. CIRCUIT TESTING
Do not assume a circuit
is ‘dead and safe’ to
work on until it has
been proved.
You use a voltage
indicating tool like a
voltmeter. This
measures the potential
difference (voltage)
between the circuit and
earth.

9. CIRCUIT TESTING
Any test instrument
used must be proved to
be in good working
order and safe to use.
The instrument and its
associated test leads
must comply with the
health and safety
guidance note GS38.

10. CIRCUIT TESTING
A visual inspection of
the instrument and its
leads should always be
made before it is used.
This should be followed
by proving the voltages
shown are the right
values. This is done by
using a voltage proving
unit or by testing on a
known supply first.

11. CIRCUIT TESTING
Once the instrument has
been checked as safe to
use you can test the circuit
for the presence of a
voltage.
Having tested the circuit
and confirmed that it is
‘DEAD’ you should retest
your instrument with the
proving unit (or the known
supply) to check it has not
been damaged while being
used.

12. Now it is safe to work on