A
mpSize
Menu
Tasks
Size a cable for a shed
The smallest cable that carries the load over the run to a shed.
Check a long run for voltage drop
The voltage drop on the run, against the limit.
Fill a conduit
The space factor of the cables in the conduit.
Add an instrument loop
A cable for the signal over a 150 m route.
Earth a cable screen
Where to earth the screen and the drain wire.
Check solar voltage rise
The voltage rise on the cable from a 5 kW inverter.
Check disconnection time
The loop impedance of the circuit, against the maximum Zs.
Work out commercial maximum demand
The maximum demand of a tenancy from Table C2.
All tasks
Tools
Cables
Cable Size
Voltage Drop
Loop Impedance
Fault Rating
Conduit Fill
Voltage Rise
Underground Cable
Segregation and Separation
Maximum Circuit Length
Simplified Selector
Minimum Conductor Size
Imperial Cable
Comms Cable Selector
Aerial Clearances
Site Cord Length
Loop Power Budget
DC Cable Size
Protection
IDMT Protection
RCD Selection
Switchboard Form
Loads
Maximum Demand
Full Load Current
Motor
Battery
Circuit Loading
Max Demand by Phase
EV Charger Circuit
Power
Three Phase Power
Transformer
Generator
Safety
Arc Flash
Construction Site Supply
Show and Carnival Wiring
Earthing
Earthing and Bonding
Screen and Drain Earthing
Testing
Test Results
Test and Tag
Fire
Sounder Level
Fire Alarm Cabling
Fire Alarm Battery
Detector Spacing
Regulatory
Regulatory Pathway
Assessment Intervals
Hand-held Supply
All tools
Wizard
Guides
Domestic
15
guides
Commercial
18
guides
Industrial
5
guides
Instrumentation
1
guide
Automation
3
guides
Solar
4
guides
Engineer
9
guides
Estimator
8
guides
Apprentice
13
guides
Homeowner
1
guide
All guides
Learn
Conduit fill and installation methods
Current-carrying capacity and derating
MEN system: multiple earthed neutral explained
Voltage drop basics
AS/NZS 3008.1.1:2025: what the AU part covers
IB ≤ IN ≤ IZ: the overload rule on a 32 A circuit
IEC 60364 and the Wiring Rules
Loop impedance and disconnection time
All learn
Standards
Glossary
Library
Pricing
‹
Learn
Home
/
Learn
/
Advanced
Advanced learn pages
Switchboard fault ratings, harmonics in the neutral, and the numbers behind an arc flash label.
19 Sept 2026
·
4 min read
Industrial switchboards: fault rating, form, IP
What the three ratings on an industrial switchboard or motor control centre mean, how each one is chosen, and which AmpSize tools feed the numbers behind them.
Calculators these guides use
Cable fault rating calculator
Check that a conductor can withstand the fault current.
Motor calculator
Find motor full load current, starting current and torque.
Full load current calculator
Calculate full load current from power, voltage and phase.
