7P.20.9.350.0020 FINDER, 7P.20.9.350.0020 Datasheet - Page 17

• Manufacturer Part Number: 7P.20.9.350.0020
• Description: 55T0824
• Manufacturer: FINDER

Specifications of 7P.20.9.350.0020

• Current Rating: 100mA
• Supply Voltage: 350VDC
• No. Of Poles: 1
• Mounting Type: DIN Rail
• Rohs Compliant: Yes
• Svhc: No SVHC (20-Jun-2011)

SURGE VOLTAGE PROTECTORS
Surge voltage protectors (such as Finder’s Surge Protection Devices, SPD)
are intended to be installed in electrical systems, to protect people and
machines from surge voltages that can occur on the electrical supply
line and which would otherwise have disastrous consequences. These
surge voltages can be atmospheric (lightning) or can originate on the
electrical system due to, for example: the opening and closing of large
loads, short circuits, or the switching of large power factor correction
capacitors. The SPD can be described as a switch that is in parallel with
the electrical system’s supply line - which it is protecting. At the
nominal network voltage (e.g. 230 V) the SPD appears as an open
switch, having a very high impedance (almost infinite). But, under an
overvoltage condition its impedance rapidly falls to near 0 Ω. This
effectively applies a short circuit across the supply lines and
immediately “drains” the overvoltage to earth. In this way the supply
line is protected wherever SPD are installed. When the overvoltage has
passed, the SPD impedance rises rapidly and resumes the state of an
open switch again.
Figure 1: Ideal operation of an SPD
SPD technologies
Finder surge voltage protectors use either varistors or spark gaps.
Varistor: this can be considered as a variable resistance that at
nominal voltage has a very high ohmic value. But the resistance
rapidly falls to near zero as the voltage surges. In this way the
varistor applies a near short circuit which clamps the surge voltage. The
varistor is however subject to progressive degradation due to the small
leakage current that occurs at the nominal voltage, and with the
number of interventions. With every overvoltage that occurs the
leakage current rises and accelerates the end of life for the device - which
is ultimately indicated by the change from green to red in the
signal-window.
Spark gap: this comprises two electrodes separated by air, or a gas.
When a surge voltage occurs an electrical arc bridges the gap and a
surge current flows to limit the surge voltage to a low and constant
level. The arc extinguishes only when the surge current falls below about
10 ampere. The gas guarantees a constant level of breakdown voltage
since the arc is struck in a protected environment; not exposed to
pressure or humidity variations or impurities as would happen if it had
occurred in air. There is however, a delay before the device arcs and
the surge current is diverted, and this is dependent on the magnitude
of the original voltage surge and on its rate of rise. Therefore, the
voltage protection level can vary, although it is guaranteed to be less
than U p .
7P Series - Surge Protection Device (SPD)
Figure 2: SPD component characteristics.
Installation (Overvoltage) categories
Choosing the SPD requires the matching the Rated Impulse Voltage of
the SPD with that of the equipment to be protected. This in turn relates
to the Installation category (Overvoltage category). Installation categories
are described within IEC 60664-1, which for a 230/400 V
installation prescribes as follows:
- Installation category I: 1.5 kV for “particularly sensitive”
- Installation category II: 2.5 kV for “user” equipment subject to
- Installation category III: 4 kV for equipment that are part of a fixed
- Installation category IV: 6 kV for equipment installed at or near the
Lightning Protection Zones and installation considerations
International standards refer to the various Lightning Protection Zones
by the letters LPZ followed by an appropriate number.
LPZ 0A: An external area, where a direct lightning strike is possible
LPZ 0B: An external area, but below a lightning conductor providing
LPZ 1:
LPZ 2:
LPZ 3:
On the following picture (Figure 3, representation is not binding) is
shown that the transition from a protection zone to the next is through
the installtion of SPD. SPD Type 1 must be connected upstream the
system, at the point of delivery connection. As alternative is possible
to use SPD Type 1+2. The grounding conductor must have a minimum
section of 6 mm
mm
made to CEI 81-10/4 for the correct dimension of the cable).
Figure 3: Typical relationship between Lightning Protection Zones,
Component
equipment (e.g. electronic devices like PC or TV set);
“normal” impulse voltages (e.g. household electrical appliances,
mobile items);
installation (e.g. switchboards, switches)
origin of main incoming supply mains (e.g. energy meters).
Spark gap
Varistor
2
Ideal
for SPD Type 3 (If the building has an LPS, reference should be
e.g. energy meters
and where there is total exposure to the electromagnetic field
induced by the lightning.
direct lightening strike protection. There remains total
exposure to the electromagnetic field.
Area within a building – therefore protected from direct
lightning strike. The electromagnetic field will be attenuated,
depending on the degree of shielding. This zone has to be
protected by SPD type 1 device(s) at its boundary with the
LPZ 0A or 0B zone.
An area, typically a room, where the lightning current has been
limited by preceding surge protectors. This zone has to be
protected by SPD type 2 device(s) at its boundary with the LPZ 1 zone.
An area within a room where the lightning current has
been limited by preceding surge protectors (typically the
wiring after a socket or an area within a metal enclosure). This
zone has to be protected by SPD type 3 device(s) at its
boundary with the LPZ 2 zone.
LPZ 0
(6 kV)
Installation Categories and SPD types
IV
Symbol
2
for SPD Type 1, of 4 mm
Very Low
Leakage
current
e.g. switchboards,
0
0
switches
(4 kV)
LPZ 1
III
dissipated
Medium
Energy
High
High
electrical appliances,
Response
Medium
e.g. household
mobile items
time
Fast
Fast
(2.5 kV)
2
LPZ 2
for SPD Type 2, and 1.5
II
Voltage/Current
characteristic
e.g. electronic devices
like PC or TV set
(1.5 kV)
LPZ 3
I
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