some components can retain charge sufficient to create a shock hazard. Prior to touching any part of the
inverter please ensure surfaces and equipment are under touch safe temperatures and voltage
potentials before proceeding.
- This product was not tested to section 5 of AS/NZS 4777.2:2020, and is not to be used in multiple
inverter combinations without additional measures taken within the installation to ensure continued
compliance to requirements.
2.2 PE Connection and Leakage Current
PV System Residual Current Factors
-
In every PV installation, several elements contribute to the current leakage to protective earth (PE). these
elements can be divided into two main types.
-
Capacitive discharge current - Discharge current is generated mainly by the parasitic capacitance of the
PV modules to PE. The module type, the environmental conditions (rain, humidity) and even the distance
of the modules from the roof can effect the discharge current. Other factors that may contribute to the
parasitic capacitance are the inverter’s internal capacitance to PE and external protection elements such
as lighting protection.
-
During operation, the DC bus is connected to the alternating current grid via the inverter. Thus, a portion
of the alternating voltage amplitude arrives at the DC bus. The fluctuating voltage constantly changes the
charge state of the parasitic PV capacitor (i.e capacitance to PE). This is associated with a displacement
current, which is proportional to the capacitance and the applied voltage amplitude.
-
Residual current - if there is a fault, such as defective insulation, where an energized cable comes into
contact with a grounded person, an additional current flows, known as a residual current.
Residual Current Device (RCD)
-
All Fox inverters incorporate a certified internal RCD (Residual Current Device) to protect against
possible electrocution in case of a malfunction of the PV array, cables or inverter (DC). The RCD in the
Fox inverter can detect leakage on the DC side. There are 2 trip thresholds for the RCD as required by
the DIN VDE 0126-1-1 standard. A low threshold is used to protect against rapid changes in leakage
typical of direct contact by people. A higher threshold is used for slowly rising leakage currents, to limit
the current in grounding conductors for the safety. The default value for higher speed personal protection
is 30mA, and 300mA per unit for lower speed fire safety.
Installation and Selection of an External RCD device
-
An external RCD is required in some countries. The installer must check which type of RCD is required
by the specific local electric codes. Installation of an RCD must always be conducted in accordance with
local codes and standards. Fox recommends the use of a type-A RCD. Unless a lower value is required
by the specific local electric codes, Fox suggests an RCD value between 100mA and 300mA.
-
In installations where the local electric code requires an RCD with a lower leakage setting, the discharge
current might result in nuisance tripping of the external RCD. The following steps are recommended to
avoid nuisance tripping of the external RCD:
1. Selecting the appropriate RCD is important for correct operation of the installation. An RCD with a rating of
30mA may actually trip at a leakage as 15mA (according to IEC 61008). High quality RCDs will typically trip at
a value closer to their rating.
2. Configure the trip current of the inverter’ internal RCD to a lower value than the trip current of the external
RCD. The internal RCD will trip if the current is higher than the allowed current, but because the internal
inverter RCD automatically resets when the residual currents are low it saves the manual reset.
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