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Disaster recovery offices.

I must install a number of 32 amp single phase ceeform sockets in a presently empty open plan office area. The exact use is unknown as it for emergency re-location. It is presumed that typical office equipment will used from portable distribution units that consist of 6 twin 13 amp sockets, each incorporating an RCD. Additional, non RCD 4 way extension leads may be plugged into the RCD sockets to allow for large numbers of small loads. 

The total floor area is just over 400 square meters. If hypothetically, standard 32 amp ring finals had been installed instead, then the floor area would suggest five such circuits. In fact 6 of the 32 amp circuits are proposed.


A single 32 amp ring final is proposed in addition, covering the entire area, this being primarily for power tools and cleaning equipment. This circuit on a 32 amp RCBO.


There is no permanent heating or air conditioning installed. Therefore provision must be made for portable electric heaters and air conditioning. Six outlets, each 16 amp ceeform are proposed for this purpose, each on its own 16 amp RCBO.


All wiring to be surface SWA. Cheap is important. Available supply is 200 amps, 3 phase, but that is to also serve a small catering kitchen, and toilets and showers.


For the kitchen, two ring finals and two 32 amp ceeforms are proposed. Type of equipment unknown, but large numbers of basic hot meals and hot or cold drinks is a reasonable assumption. I have guessed at one domestic type electric cooker, one 6KW water boiler, at least three large fridges and several microwaves, toasters and the like.


Hot water for kitchen, toilets, and showers from existing cylinder with 12KW Three phase immersion heater.


The space is relatively long and narrow, with windows along one long side. Furniture layout completely unknown.


Load calculated as follows

Total of 11 circuits each 32 amps, the "worst" phase will have 4 circuits. 100% of FLC for one circuit plus 50% of the remainder = 80 amps


Total 6 circuits each 16 amps for heating or air conditioning, simultaneous use likely, so allow 13* amps per socket=26 amps


Water heater, no diversity, presume 16 amps per phase.


Lighting, allow 10 watts per square meter 500 square meters, including kitchen, toilets etc, might not be well balanced=16 amps


Total loading per phase is about 140 amps.


*it might seem odd to presume a 13 amp loading on each 16 amp socket, but I expect the use of the largest loading portable appliances that just about work on a 13 amp socket, so less than 13 amps is a bit optimistic, but a full 16 amps unduly pessimistic.

Can anyone see any obvious flaws in the proposed arrangements.

  • On the surface it sounds generally not unreasonable (although I can' say I've checked your calculations).


    I presume all your 32A sockets will have 30mA RCD protection - with so many unknowns I would have thought a written risk assessment showing that RCD protection was unnecessary won't be forthcoming.


      - Andy.
  • Without full and complete details of the loads that will be connected, it is impossible to be 100 per cent sure that the design is fit for purpose. At best it will be educated guesswork.


    Z.
  • Yes, every circuit will be on an RCBO, the inclusion of RCD socket outlets in the portable distribution units is firstly a "second line of defence" and secondly seems a wise precaution in case the equipment is re-used in another building in which the 32 amp sockets are not RCD protected.


    The intention is to provide one 13 amp socket per person for the greatest number that could reasonably be accommodated. A four way extension lead per person would permit use of a laptop PC, a cellphone, and any two other low loading appliances.


    Detailed loading information is not available due to the unknown use. I have made reasonably pessimistic assumptions, and expect the existing 200 amp 3 phase supply to suffice. 100% generator backup is required and a good used diesel generator has been delivered, rated at 180KVA for prime power, or 210 Kva standby.


    A staff room has now been added, but I expect little extra loading from that facility. 13 amps for a heater or an air conditioner, 1 amp for lighting, and 2 amps for charging portable electronics.

  • I understand that this facility may now be used due to the coronavirus.

    As living accommodation, not sure if as an emergency medical facility, a hostel for key workers, or otherwise.