TECHNICAL KRAUS & NAIMER KRAUS & NAIMER TECHNICAL

Identifying “On Load Isolators” AS/NZS 60947-3 Switch-disconnector Switch Disconnector

by the product label Popular Name On Load Isolator Switch Off Load Isolator
On Load Isolators are easily identified
Complies with the Complies with the
by the above symbol on the switch label,
Isolation Function and Rated to make and Isolation Function.
which is compulsory. It is logically a Description
is rated to make and break Loads. Not rated to make and
combination of the “Switch”, and the
break loads. break loads.
“Disconnector” (Isolation) symbols,
explained to the right.
Symbol
On Load Isolators are labelled with both
an AC-21 Amp rating, and an AC-23

ISOLATOR
kW rating. The AC-21 Amp rating is Rated to make, break &
applicable for resistive loads and the carry loads, i.e. AC-23
AC-23 kW rating for inductive motor loads.
The table to the right lists a few examples Complies with the
of common electrical loads. Isolation Function tests

Off Load Isolator – Selecting an On Load Isolator by Application.

SELECTION
Disconnector Utilisation Category and
Identified with the Isolation symbol only, Application Electrical Description Rating Selection
off load isolators are not rated to make or
break loads. These isolators have utilisation Isolator for elements Resistive or Inductive Load AC-21 Amp Rating
categories AC-20 / AC-21 or DC-20 /

MADE EASY
Isolator for motors Inductive Load AC-23 KW Rating
DC-21 and can carry the thermal current
of the load in the closed position only.
A group of electrical loads, both
An off load isolator must be linked to a AC-21 Amp rating of the total
resistive and inductive. Add all
device that makes the load after the electrical load, and;
Main Switch for combined inductive and resistive loads
isolator's main contacts close, and breaks
machines for AC-21A Amp rating and; equal or AC-23 kW rating of the largest
the load before they open. This is generally
exceed the locked rotor current of the motor in the machine
achieved by a Late Make Early Break
largest motor for the AC-23 kW rating
auxiliary contact on the isolator that is wired
to a drive, soft starter or circuit breaker.
The additional complexity of installing Off
Load Isolators for single load installations,
small machines and domestic installations
is over complicated and has significant

Isolators are relied on by T he purpose of isolation is to provide

protection against electrical hazards
normal conditions and specified overload
conditions and also pass electrical and
additional cost.
Should the Isolator be switching the load Should a fault or accident occur and
electricians, maintenance such as electric shock, burns and
ballistics (the effects of arc flash), and
mechanical tests to comply as isolators.
Example; these switches cannot be
directly ensure it has the Switch
Disconnector Symbol.
the process needs to be shut down
immediately, all devices identified by a
personnel, plant operators and the unintentional start-up of machinery. turned to OFF (handle moved to the off Auxiliary contacts on Isolators provide
Red and Yellow colour combination will be
capable of stopping the process.
Commonly referred to as Isolating position) unless all the main contacts
domestic property owners to switches, an “On Load Isolator” is the have physically opened. Should there
important functionality and shall be
discussed in a later article. Best practice is to install Isolators with
be one welded contact, the OFF position
isolate everything from a hot water most common piece of equipment used to
achieve isolation. They are switch devices cannot be reached, and a padlock device
Red handles and Yellow surrounds if it is
intended that the isolator be available for
cylinder or heat pump at home, to that cut off a circuit or equipment from cannot be fitted, even with three times the
normal operating force being applied and
Padlock Device Colours use in an emergency, or other coloured
handles if not, to eliminate confusion
a source of power and ensure that the Isolators from all manufacturers have
heavy industrial machinery in the electrical circuit or equipment is completely when released the handle returns to ON.
This communicates very effectively that different handle colours and combinations:
during an emergency situation.
isolated in order to conduct maintenance,
workplace or farm. servicing, modification or repair.
isolation has not been achieved and that grey, black, black and red, all of which

For the above applications, a 1 pole

the circuit or equipment is not safe, and
has not been isolated. In addition to the
identify the isolators as "Main Switches"
which safely isolate a load.
How to ensure you have selected
isolator for single phase, or a 3 pole physical handle test, there are electrical However, the red and yellow handle the right Isolator for your application.
isolator for three phase are generally threshold tests to ensure current will not combination has international significance, Install only correctly rated and type of Big or small, any reputable switch
installed. They are electrically capable jump the contact gap or track to earth identifying the device as an 'Emergency isolator from reputable manufacturers that manufacturer will have tested and marked
of making and breaking the load under under specified fault conditions. Switch" suitable for use in an emergency. are fit for purpose. their switches accordingly.