ABB ESP M1R Installation Instructions Manual page 29

This should help to reduce any spurious tripping of such
devices due to transient overvoltages. Where ESP units
are installed after (or downstream) of RCDs, special
transient hardened RCDs (type 'S') should be used (e.g.
ABB F 200 A selective type series).
9.3 Insulation tests (flash testing)
The ESP unit should be fully disconnected from the
circuit before testing. Otherwise the ESP unit will treat
the insulation test as a transient overvoltage and control
the voltage to a low level - thereby defeating the object
of the test.
9.4 Duplex configuration
For systems demanding extremely high reliability, ESP
units can be connected in duplex format. The use of two
units will achieve an improvement in performance and
increased lifetime over a single ESP unit at high
discharge current levels. Each unit should have its own
(separate) wiring and its own isolation.
Installation instructions for mains wire-in protectors | 9/2