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16A 3 Phase supply in SWA

Former Community Member
Former Community Member
Im looking to run in 2 16a 3 phase supplies, 25m long.

From what I can understand 1.5mm SWA is suitable up to 23A (table 4e4a, clipped direct)

1.5mm cable has a volt drop of 27mV/A/M =  10,800mV - 10.8v (table 4e4b, 3 Phase AC), Less than 5%.

So why do I see many people talking of 4mm installs?

I must be missing something?



  • 0
    The only observation that I would make is that the terminals and enclosure should be suitable for 90 deg C when you use thermosetting cable at full capacity. Mind you, thermoplastic is still rated at 18 A.


    Voltage drop is slightly less at 10.0 V.


    So no, you are not missing anything, but I cannot answer the other question.
  • 0
    Larger cable may be used for several reasons.


    1) Because the client or consultant says so. A lot of contracts state "minimum conductor size of 4mm for power circuits"

    2) To reduce energy losses on a long hour load.

    3) To reduce voltage drop, remembering that a lot of the 5% may have been already used up in ub mains etc.

    4) Due to derating for grouping, thermal insulation or high ambient temperatures.

    5) To future proof the circuit in case needs change.

    6) Because it was what was in the back of the van.
  • 0
    What's the circuit supplying? Are there any starting conditions that might need taking into account?

       - Andy.

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