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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
    CE marked kit for connection to the mains should be type tested by the makers and declared to meet IEC 61000 - 4.

    The standard itself is expensive, but a guide to how the testing is done is   here  .

    Responsible manufacturers aim to exceed the requirements of test level 4 by a reasonable margin ( 4000V transients 8us rise, 20uS fall into a low impedance or 1.2uSrise  50us fall time into a high impedance ) between any pair of cables with a mains connection. As a corollary, some milspec kit is tested to a far higher limit.

    Makers of some cheap LED fittings seem to omit this testing altogether before applying CE stickers to their product. We see the effect of this in early failures.

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  • 0
    CE marked kit for connection to the mains should be type tested by the makers and declared to meet IEC 61000 - 4.

    The standard itself is expensive, but a guide to how the testing is done is   here  .

    Responsible manufacturers aim to exceed the requirements of test level 4 by a reasonable margin ( 4000V transients 8us rise, 20uS fall into a low impedance or 1.2uSrise  50us fall time into a high impedance ) between any pair of cables with a mains connection. As a corollary, some milspec kit is tested to a far higher limit.

    Makers of some cheap LED fittings seem to omit this testing altogether before applying CE stickers to their product. We see the effect of this in early failures.

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