Combined SSE CT Chamber and RCD Rated at 2500A with Outer Cabinet

Overview

As part of the enabling works on one of the UK’s major construction projects, the Blakley team have supplied a series of 2500A CT chambers each with close coupled RCD, which are to be located within ISIA series GRP site intake cabinets. The combined CTC/RCD assemblies are fitted to substantial, floor fixing, angle-iron frames, with the ISIA cabinet standing over, to protect the inner unit from the elements (the CTC/RCD assembly alone weighs 650kgs and is too heavy to be mounted on to the wall of the ISIA cabinet). See below for a drawing of the overall general arrangement.

The assemblies are to provide Temporary Builders Supplies for a series of work sites, with each one fed from a dedicated 1500kVA, 11000:400V transformer. A total of 11 no. bunched wavecon cables will be required to connect a transformer to a CTC/RCD and suitable terminations are provided within the CT chamber for this arrangement. The CT chamber incorporates shelves and removable links for the DNO’s current transformers.

The CT chamber enclosure is all-insulated and close coupled to the outgoing 2500A 4P MCCB, which has an associated MRCD series, core balance, modular RCD providing protection in accordance with BS EN 60947-2 Annex M. The MCCB has a wide adjustment range and can be set as low as 1000A. The RCD sensitivity can be adjusted from 0.3A to 30A and has a time delay adjustment range of 0 to 10 seconds. The outgoing termination arrangement allows a total of 4 no. cables per phase to be terminated.