In this section
Electrical safety is very important in hospitals as patients may
be undergoing a diagnostic or treatment procedure where the
protective effect of dry skin is reduced. Also patients may be
unattended, unconscious or anaesthetised and may not respond
normally to an electric current. Further, electrically conductive
solutions, such as blood and saline, are often present in patient
treatment areas and may drip or spill on electrical equipment.
Injuries received from electric current are dependent on the
magnitude of current, the pathway that it takes through the body
and the time for which it flows.
The nature of electricity flowing through a circuit is analogous
to blood flowing through the circulatory system within the human
body. In this analogy the source of energy is represented by the
heart, and the blood flowing through arteries and veins is
analagous to current flowing through the conductors and other
components of the electric circuit.
The application of an electric potential to an electric circuit
generates a flow of current through conductive pathways. This is
analogous to the changes in blood pressure caused by contraction of
cardiac muscle that causes blood to flow into the circulatory
system. For electric current to flow there must be a continuous
pathway from the source of potential through electrical components
and back to the source.
Electrical components and systems are encased in non conducting
insulation, to ensure that the electric current is contained and
follows the intended pathways. If the insulation deteriorates or
breaks down, current will leak through the insulation barrier
and flow to earth. This may be through the
protective earth conductor or through the operator.
Medical equipment and clinical areas are fitted with a number of
protective devices to protect the patient and operator from harmful
Extension leads are not permitted in clinical areas of RCH
organisations. They may cause high earth resistance
and excessive earth leakage current. An extension lead
can allow equipment to be powered from areas other than the
relevant protected treatment area. The power from the other
area may not be protected to the same level as the power in
the treatment area.
As the connection between the extension lead and the equipment
mains cable is often on the floor there is a high danger from
fluid spills, tripping and damage to the mains cable by
trolleys when an extension lead is used.
Double adaptors must not be used in RCH organisations. They
may not sit securely in a wall outlet, may not be able to provide
adequate earth protection and may cause overloading, overheating,
fire or loss of electrical supply.
There are several methods of providing protection for operators
and patients from electrical faults and harmful leakage
Class I equipment is fitted with a three core mains cable
containing a protective earth wire. Exposed metal parts on
class I equipment are connected to this earth wire.
Should a fault develop inside the equipment and the exposed
metal comes into contact with the mains, the earthing conductor
will conduct the fault current to ground. Regular testing
procedures ensure that earthing conductors are intact, as the
integrity of the earth wire is of vital importance.
Class II equipment is enclosed within a double insulated case
and does not require earthing conductors. Class II equipment is
usually fitted with a 2-pin mains plug. An internal electrical
fault is unlikely to be hazardous as the double insulation prevents
any external parts from becoming alive. Class II or double
insulated equipment can be identified by the class II symbol on the
Class II Symbol:
Some medical equipment within the hospital is classified
as defibrillator proof. When a defibrillator is
discharged through a patient connected to defibrillator
proof equipment, the equipment will not be damaged by the
defibrillator's energy. Defibrillator proof equipment can
remain connected to the patient during defibrillation.
It is identified by one of the following symbols.
Defibrillator proof symbols.
Most patient care areas in the hospital are fitted with
protective devices. These devices are regularly tested, in
accordance with the relevant guidelines published by Standards
Australia. The level of protection provided is dependent upon the
device and the area in which it is located.
RCD's (safety switches) are used in patient treatment
areas to monitor and protect the mains supply.
RCD's sense leakage currents flowing to earth from the
equipment. If a significant leakage current flows, the RCD will
detect it and shut off the power supplied to the equipment within
40 milliseconds. Hospital RCD's are more sensitive than those
fitted in homes. A hospital RCD will trip at 10 milliamperes
Power outlets supplied through an RCD have a 'Supply Available'
lamp. The lamp will extinguish when the RCD trips due to excessive
Resetting a RCD
In critical life support applications where loss of power
supply cannot be tolerated, special power outlets powered by
isolation transformers are installed.
Line Isolation Monitors are installed to continually
monitor electrical leakage in the power
supply system. If an electrical fault
develops in a medical device connected to an isolated power outlet,
the LIM will detect the leakage current. The LIM will alarm
and indicate the level of leakage current, but will not shut off
the electric supply.
The faulty equipment can be identified by un plugging one item
of equipment at a time from the supply until the alarm stops
sounding. Equipment that is not faulty may be reconnected.
Faulty equipment should be appropriately labelled and sent to
Biomedical Engineering for repair.
The LIM also monitors how much power is
being used by the equpiment connected to it. If too much
power is being used, the LIM will alarm and indicate that there is
an overload. The power used must be reduced immediately by
moving some equipment to another circuit as soon as possible until
the alarm stops sounding. Failure to reduce the load on the
LIM will result in the circuit breaker tripping and loss of power
to the circuit.
Equipotential earthing is installed in rooms classified as
'Cardiac Protected' electrical areas. Equipotential earthing in
treatment areas used for cardiac procedures is intended to minimise
any voltage differences between earthed parts of equipment and any
other exposed metal in the room.
This reduces the possibility of leakage currents that can cause
microelectrocution when the patient comes into contact with
multiple items of equipment, or if the patient happens to come into
contact with metal items in the room whilr they are connected to a
All conductive metal in an equipotential area is connected to a
common equipotential earth point with special heavy duty cable.
This policy aims to provide guidance to
those who find that they need more electrical outlets than those
available, or that the existing electrical outlets are
As extension leads and multiple outlet
power boards can introduce additional hazards into an area the
following procedures should be observed.
Approved extension leads (AS 3760,
1996) may be used in some areas within the hospital but MUST NOT BE
USED IN PATIENT AREAS. All electrical extension leads must be
tagged with an Engineering Department maintenance tag, and require
a yearly safety inspection and test, via the Engineering
Double adapters may cause overloading
or equipment earthing problems and are not to be used in WCH
The only mains extension device that is
to be used in "Patient care areas" is the 4-way or 8-way portable
Core Balance Unit.
The Biomedical Engineering Department
must approve all units prior to use. These units contain a safety
switch and can detect excessive leakage current and disconnect
the power in the event of a hazardous situation.
Care must be exercised in the use of a
portable Core Balance Unit. It should be located off the floor and
in a position that will protect it from physical abuse and possible
entry of fluids. These devices are expensive and easily damaged.
The device must be sent to Biomedical Engineering every 6 months
for safety testing.
Approved multiple-outlet power boards
can be used across RCH but must not be used in patient care areas,
except areas approved by the Biomedical Engineering Department.
The power boards must have overload
protection, be fitted with internal safety shutters that protect
unused outlets and be fitted with an on/off switch for each
All of the above mentioned devices are
intended to overcome a temporary inadequacy in the electrical
installation. If a Department/Unit is likely to have a long term
need for such mains extension devices a Project Initiation Request
should be submitted to the Engineering Department for the
installation of additional power points.