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SY Cable containment

GHEC

I know the subject of SY cables in fixed power installations pops up a lot but please bear with me.

I know that SY cable does not meet any British or harmonised standards and is 'discouraged' under BS 7671, but can be installed and noted as a departure on the installation certificate. 

As it will need to be 'safe' under BS 7671, should SY cable be installed in metallic containment such as steel trunking?

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    My main concern regarding the use of this cable type is the rather high and variable resistance of the braiding. This matters little as regards effective earthing of the connected load since one of the copper cores can be and in most circumstances should be used as the CPC.

    That however does not tell the whole story. Consider the consequences of a fault between phase and the earthed braid, perhaps as a result of impact damage, part way along a long run of SY. The resistance of the braid might limit limit the fault  current to a value too low to promptly operate the fuse. A high resistance arcing fault could persist for long enough to start a fire.

    An RCD should save the day, but not all circuits require one. AFDD likewise.

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  • 0

    My main concern regarding the use of this cable type is the rather high and variable resistance of the braiding. This matters little as regards effective earthing of the connected load since one of the copper cores can be and in most circumstances should be used as the CPC.

    That however does not tell the whole story. Consider the consequences of a fault between phase and the earthed braid, perhaps as a result of impact damage, part way along a long run of SY. The resistance of the braid might limit limit the fault  current to a value too low to promptly operate the fuse. A high resistance arcing fault could persist for long enough to start a fire.

    An RCD should save the day, but not all circuits require one. AFDD likewise.

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