SPD chart displaying SPD minimum conductor sizes, minimum impulse withstand voltage and permissible power frequency stress voltage. SPD's and their applications of use and location of installation. Type 1, type 2 and type 3 SPD devices.

1. SPD surge protection
SPD Protective conductor sizes
Type Name Location Protective Conductor CSA Protection
1
Equipotential bonding or
lightning protection
current SDP
Origin of installation
16mm minimum. Length of tails
ideally <0.5m but no longer than
1mtr
Protection against flashover from
direct lightning strikes to structure or to
LV overhead supply
2 Overvoltage SPD Distribution board
4mm or equal to CSA of circuit
conductors
Protection against overvoltage's
which can stress the electrical
installation
3 Overvoltage SPD Terminal equipment
2.5mm or equal to CSA of circuit
conductors
Protection against overvoltage's and
high currents on items of equipment
Required minimum impulse withstand voltage kV (L-E)
Nominal Supply
Voltage
Cat IV Equipment with
very high impulse
voltage
Cat III Equipment
with high impulse
voltage
Cat II Equipment with normal
impulse voltage
Cat I Equipment with reduced impulse
voltage
230/240 6 kV 4 kV 2.5 kV 1.5 kV
277/480 6 kV 4 kV 2.5 kV 1.5 kV
400/690 8 kV 6 kV 4 kV 2.5 kV
1000 12 kV 8 kV 6 kV 4 kV
Permissible power frequency stress voltage
Duration of
earth fault in HV
system (t)
> 5s
< 5s
Printed from the Electrical Tools & Reference App
Permissible power frequency stress voltage on equipment in LV installation
Uo + 250V
Uo + 1200V
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