cable sizing to BS7671

Hello all! Would some kind sparky type have a quick look at this and give me some practical advise?
We have a problem with a supply: a distribution board with 30A BS88 fuses
supplying a consumer board of 63A RCCD feeding two MCBs of 32A (has a total 28A load) and 16A (2Amp load). The connection between the two is wired in 20 meters of 2.5mm2 twin & earth. Is this OK? I ask because the 28A load (Switch mode power supplies) causes all sorts of flickering and volt drops across the other load at switch on and usually will not power up (unless individual equipment is powered up one by one).
My questions are: Is this cable OK? What size should the cable be?
Thank in advance for any help given! Jake
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The 2.5mm cable is NOT large enough for the current draw and requires immediate disconnection (unless run on perforated cable tray!). The current capacity of a cable is determined by "how" it is run. If it is run in insulation, 2.5mm is rated at 18.5A, in trunking or conduits 23A, clipped direct to a non metallic surface 27A or on a perforated cable tray 30A. Also, cable length plays a factor in the selection of cable (volt drop). You may find for a 30A? (32A) BS88 fused supply, you may require 6mm twin and earth cable to compensate, although if you are pulling 30A from the supply it may be worth upgrading to 10mm or even 16mm to allow for further expansion. My advice, consult a local electrician (NICIEC) to have a look at your needs and the existing supply, sooner rather than later!! Regards, PF

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