ISOPV425-D4-4 Bender

ISOMETER® isoPV425 
with coupling device AGH420
Insulation monitoring device for unearthed
DC circuits (IT systems) for photovoltaic installations 
up to 3(N)AC, AC 690 V / DC 1000 V
ISOMETER® isoPV425 
with coupling device AGH420
Device characteristics
• Monitoring for unearthed AC and DC 
systems with galvanically connected 
rectifiers or inverters
• Measurement of the nominal system 
voltage Un (True RMS) with undervoltage 
and overvoltage detection
• Measurement of DC voltages system to 
earth (L+/PE and L-/PE)
• Automatic adaptation to the system 
leakage capacitance up to 1000 μF
• Automatic device self-test with connection 
monitoring
• Selectable start-up delay, response delay 
and delay on release
• Two separately adjustable response value 
ranges of 1…500 kΩ (Alarm 1, Alarm 2)
• Alarm signalling via LEDs (AL1, AL2), a 
display and alarm relays (K1, K2)
• N/C operation or N/O operation selectable
• Measured value indication via multifunctional
 LCD
• Fault memory can be activated
• RS-485 (galvanically isolated) including 
the following protocols:
– BMS interface (Bender measuring device 
interface) for data exchange with other 
Bender components
– Modbus RTU
– isoData (for continuous data output)
• Password protection to prevent 
unauthorised parameter changes 
Certifications
Product description
The ISOMETER® of the isoPV425 series monitors the insulation resistance of unearthed 
AC/DC main circuits (IT systems) with nominal voltages of 3(N)AC, AC, AC/DC 0…690 V or 
DC 0…1000 V.
DC components existing in AC/DC systems do not influence the operating characteristics. 
A separate supply voltage allows deenergised systems to be monitored as well. The maximum 
permissible system leakage capacitance is 1000 µF.
 i The isoPV 425 determines the leakage capacitance through an impedance measurement 
whose frequency is adjusted to the most accurate insulation measured value possible. 
The measurement signal is affected if it goes through a rectifier or inverter, and this can 
lead to phase errors that may result in an incorrect leakage capacitance value.
Application
• AC, DC or AC/DC main circuits
• Solar systems with directly connected inverters
• Solar systems with high system leakage capacitances
• Solar systems with high but slow voltage fluctuations
• Systems including switch-mode power supplies
Function
The currently measured insulation resistance is indicated on the LC display. The response 
value of the ISOMETER® is factory-set to AL1 10 kΩ and AL2 5 kΩ. When the value falls below
 the preset response values, the response delay “ton” starts. Once the response delay 
“ton” has elapsed, the alarm relays “K1/K2” switch and the alarm LEDs “AL1/AL2” light up. By 
means of two separately configurable response values/alarm relays, the messages can be 
evaluated separately. If the insulation resistance exceeds the release value (response value plus 
hysteresis), the alarm relays return to their initial position. The point of fault L+, L- or the 
symmetrical insulation resistance is indicated on the display. In the menu, the alarm relays
 can also be assigned to the point of fault. 
If the fault memory is enabled, the alarm relays remain in the alarm state until the reset 
button is pressed or until the supply voltage is switched off. The device functions can be 
checked using the test button. Device parameters are assigned via the LCD and the control 
buttons on the front of the device, as well as the RS-485 interface (BMS or Modbus RTU).
Connection monitoring
The connections to the electrical system (L1/+ / L2/-) and earth (E/KE) as well as the connecting 
wires from the insulation monitor to the coupling device are periodically monitored every 
24 hours after pressing the test button and connecting the supply voltage. In case of line 
interruption, the alarm relay K2 switches, the LEDs ON/AL1/AL2 flash and a message appears 
on the LC display:
“E.0x” for a fault in the connecting wires between both devices or system fault,
“E.02” for a fault in the connection to the system,
“E.01” for a fault in the connecting wires to PE.
After eliminating the fault, the alarm relays switch back automatically or by pressing the 
reset button.
Measurement method
The ISOMETER® isoPV425 uses the AMP and PCP measurement method.