1. Selecting the current
rating
of an RCD
1 Revision 01

2. AS/NZS 3000:2007 (Amendment 2)

3. 3 Revision 01
To Calculate the loading for the lighting portion of the installation use
Load group A (i) - lighting
• A lighting point is where the
fixed wiring terminates
• E.g. a twin Fluorescent light
fitting is counted as one
point ClipsalClipsal

4. 4 Revision 01
Load group A - lighting
Loading is calculated on the basis of:
–Average size lamp
–Not all lights will be on at the same
time
–As part of the overall diversity of the
installation

5. Lighting
For example if a domestic installation has 46 lights this equals 46 points
Using the above table A(i) allows:
3 A for the first 20 points (1 to 20)
2 A for the next 20 points (21 to 40
2 A for the remaining 6 points (41 to 60)
7 A total maximum demand for A(i)

6. Load group A – lighting
Particular attention must be paid to the footnotes when
using table C1

7. To Calculate the loading for the lighting portion of the
installation use
Load group B – socket outlets
• Load group B covers All
socket outlets for
general purpose use
• Permanently connected
equipment not covered
in other load groups
• One point represents
one outlet
• E.g. a 4 gang outlet is
equal to 4 points
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8. 8 Revision 01
If an installation has 10 double and 12 single socket outlets the
maximum demand would be
10 x double outlets = 20 point + 12 single outlets = 32 points
B(i) allows
10A for first 20 outlets (1 to 20)
5A for next 12 outlets (21 to 40)
Total demand = 15A for this portion of the installation.

10. Example 2.1
To calculate the
current rating of
this RCD the
maximum demand
of this portion of
the installation
must be calculated
using Table C1
From the switchboard schedule in example 2.1
CCT 4 has 12 points (socket outlets)
CCT 5 has 13 points (socket outlets)
CCT 6 has 20 lighting points
Note: Individual final sub circuit loadings calculated
using table C8 are not used to calculate the maximum
demand of a portion of an installation.

11. Maximum demand for this portion of the installation
Step 1; calculate the socket outlets maximum demand using Table C1
Total points = (CCT 4),12 points + (CCT 5),13 points = 25 points for this portion of the
installation
Maximum demand calculation
10A for first 20 points (1 to 20)
5A for next 5 points (21 to 40)
15A is the maximum demand for the sockets outlets in this portion of the
installation

12. 12 Revision 01
Step 2; calculate the lighting maximum demand using Table C1
CCT 6 = 20 points
Maximum demand calculation A(i)
3A for first 20 points therefore maximum demand for the lighting of this portion of
the installation = 3A
Step 3 add the socket outlet max demand 15A to the lighting max demand 3A the total
maximum demand of this portion of this installation is 18 Amps

13. AS/NZS:3000:2007 Clause 2.6.2.1 General
Any device for the provision of additional protection shall be capable of interrupting the part
of the circuit protected by the device when an earth leakage current is above a
predetermined value.
The load current rating of an RCD shall be not less than the greater of the following—
(a) the maximum demand of the portion of the electrical installation being protected by the
device; or
(b) the highest current rating of any overload protective device on the portion of the electrical
installation being protected.
As the calculated maximum demand for the portion of the installation
being protected by the first RCD has been calculated to be 18A and the
highest rated circuit breaker being protected by the RCD is 20A the RCD
must have a minimum current rating of 20A
If the maximum demand was calculated to be above 20A then the
maximum demand value would be the minimum RCD rating