Accessories are required depending on the type of installation on which the device is installed.

Accessories list

Accessory Catalog number
Cardew C “250 V” surge limiter 50170
Cardew C “440 V” surge limiter 50171
Cardew C “660 V” surge limiter * 50172
Cardew C “1000 V” surge limiter * 50183
Cardew C base * 50169
ZX impedance 50159
IM400-1700 voltage adaptor *


PHT1000 voltage adaptor * 50248
P1N ground adaptor PHA6326700
Voltage transformer See Note
  • P1N ground adaptor is applicable for IM400THRN.

  • For information regarding automatic and mobile insulation fault locating accessories, see Locating.

  • Voltage transformers must be selected appropriately depending on system voltage. Refer to the Schneider Electric Medium Voltage Transformer catalogue.

Cardew C surge limiter


Cardew C is used if the insulation monitoring device is connected to the secondary connection of an MV/LV transformer (according to the rules and conventions that apply in the various countries).

It protects the low-voltage (LV) installation against over voltage hazards. It is connected to the secondary connection of the transformer. Cardew C can be used on the following systems:

  • U < 1000 V AC

  • U < 300 V DC

Selection table

Un: Nominal Phase-to-Phase Voltage of AC System

Ui: Arcing Voltage

Type of Cardew C

Accessible neutral

Not accessible neutral

U ≤ 380 V

U ≤ 220 V

400 V < Ui ≤ 750 V

250 V

380 V < U ≤ 660 V

220 V < U ≤ 380 V

700 V < Ui ≤ 1,100 V

440 V

660 V < U ≤ 1,000 V

380 V < U ≤ 660 V

1,100 V < Ui ≤ 1,600 V

660 V

1,000 V < U ≤ 1,560 V

660 V < U ≤ 1,000 V

1,600 V < Ui ≤ 2,400 V

1,000 V



  • Cardew C mounted directly on busbars

  • Mounting with plate-mounted base


ZX limiting impedance


ZX limiting impedance enables you to create an installation with a high-impedance grounded neutral system (1500 Ω at 50 Hz).

ZX limiting impedance remains connected during insulation fault locating at 2.5 Hz:

  • 1500 Ω at 50 Hz

  • 1 MΩ at 2.5 Hz

The ZX impedance must be used on systems with U ≤ 500 Vac.



On mounting plate


Voltage adaptor

The optional voltage/ground adaptors are:

  • IM400-1700

  • PHT1000

  • P1N


The IM400-1700 and PHT1000 voltage adaptors can be used to connect a IMD to ungrounded systems higher than 480 V AC. The wire connecting IM400-1700 or P1N to IMD has to have the same voltage rating as the monitored network. The P1N ground adaptor must be connected with the system for the operation of IM400THRN. The compatibility of voltage adaptors with insulation fault location is as follows:

  • The IM400-1700 and P1N voltage adaptors are not compatible with insulation fault location.

  • The PHT1000 voltage adaptor is compatible with insulation fault location.






On DIN rail On mounting plate On mounting plate


Wiring diagram Wiring diagram Wiring diagram

(1) Voltage adaptor connected to a phase

(2) Voltage adaptor connected to neutral

S3 subassembly (retrofit)

Insulation alarm thresholds of the device has to be set higher than 2 kΩ to take into account internal impedance of the no longer commercialized S3 subassembly.

QR Code is a registered trademark of DENSO WAVE INCORPORATED in Japan and other countries.

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