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Current carrying capacity of XLPE/SWA cables

M Gilmore
Hi, I keep coming across the same issue in regards to the current carrying capacity of a XLPE/SWA cable. I always use the de-rated current carrying capacity when I am not sure if all associated equipment is rated at  90°c, which is all the time. So as an example, a 4 core 150.0mm² XLPE/SWA cable clipped direct is rated at 386 Amps from table 4E4A column 3 in BS7671:2018. A standard 4 core 150.0mm²  PVC/SWA is rated at 306 Amps from table 4D4A column 3. This is a big difference! If this was protected by a 355 Amp BS 88 I would flag the conductor as being undersized.


There is a note by table 4E4A that points out Regulation 512.1.5. This is regarding compatibility and says equipment should not be connected to conductors intended to operate at a temperature exceeding 70°c unless the equipment manufacturer has confirmed that the equipment is suitable for such conditions. 99% of the time I wouldn't have the available data on site. Most circuit breakers I have checked are rated at 70°c.


Any thoughts? I just want to make sure I'm providing the correct information. I don't want to provide an observation if the conductor is ok to be rated at full capacity. Cheers in advance.


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  • 0
    And if you believe that line from whatever cowboy film it was said at a card game that "a Smith and Wesson beats four aces"  (*) then in much the same way a

     

    .. storm of acrimony and argument based entirely on "What Iffery"




    conjecture can sometimes  be beaten  by real measurements, in the form of those stickers that change colour to indicate peak temperature, as a sort of high tide marker- only really good on large diameter stuff, but then on large diameter lugs and bussbars,  the cost of rework and or over sizing becomes  most significant. Looking at the stickers every xx months reassures everyone it has not been overheating yet.


    * I'm not suggesting that people should be shot for their electrical work,  well only a few anyway.


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  • 0
    And if you believe that line from whatever cowboy film it was said at a card game that "a Smith and Wesson beats four aces"  (*) then in much the same way a

     

    .. storm of acrimony and argument based entirely on "What Iffery"




    conjecture can sometimes  be beaten  by real measurements, in the form of those stickers that change colour to indicate peak temperature, as a sort of high tide marker- only really good on large diameter stuff, but then on large diameter lugs and bussbars,  the cost of rework and or over sizing becomes  most significant. Looking at the stickers every xx months reassures everyone it has not been overheating yet.


    * I'm not suggesting that people should be shot for their electrical work,  well only a few anyway.


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