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In recent years, the number of major projects specifying Mains Distribution Assemblies (MDA) with Form 4 Type 3 segregation has increased dramatically. Although Form 4 assemblies are larger and more expensive than conventional MDAs, the practical benefit of being able to connect or disconnect an outgoing circuit without the need to isolate the whole assembly is seen by many as an essential requirement for high current, primary MDAs supplying critical loads.

Our Form 4 MDAs are of modular design, which enables us to build site specific MDAs without having to design from scratch every element of the enclosure, bus bar system, etc. In addition to the basic switchgear, the assembly shown in the image incorporated many of the features commonly specified, which include:

  • Facility to terminate multiple incoming cables (up to 6 cables per phase)
  • Surge protection
  • Variable RCD protection for each outgoing way
  • Test sockets for the incoming supply and each outgoing way (enabling RCDs to be tested with an independent test set)
  • An anti-condensation heater in each compartment (controlled by a common thermostat)
  • Web enabled kilowatt hour meters for the incomer and each outgoing circuit
  • Door stays for when the panel is used in windy conditions

To address the client’s concern that inset panels (or shield plates) are not always re-fitted when load cables are terminated or disconnected, this Form 4 MDA also incorporated hinged outgoing inset panels. The arrangement eliminates the use of screw-fixed inset plates, which have to be removed and re-fitted whenever a cable is connected or disconnected.
Instead, with this new design, the outgoing inset panels remain fixed in position and a hinged section gives access to the MCCB terminals, which eliminates the requirement to re-fit screw fixed inset panels. It is anticipated that this addition to the range of options will further enhance on-site safety.

Please contact the Blakley Projects Team if you have a possible requirement for a Form 4 MDA and would like to discuss the specification in detail.

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Mains Distribution Assemblies



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