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90 degree cable and equipment terminal operating temperatures

Luke Swanborough

Morning 

This is a query about when 90 deg cable CCCs can be used in the cable calculations.

BS 7671 states that switchgear, protective devices and accessories shall not be connected to conductors intended to operate at a temperature exceeding 70 degrees unless the equipment manufacturer has confirmed that the equipment is suitable for such conditions. Hence we use the 70 deg CCC values when using XLPE 90 deg cable.

The confusion is that the switchgear for example is tested under BS EN 61439-2 which allows a 70 degree rise on the terminals - BUT - with a maximum ambient temperature of 35 degrees. Therefore the terminals during testing could potentially be at 105 degrees...?

We have asked many manufacturer about this and generally get the response that its tested to BS EN 61439-2 which allow for 70 deg above a max ambient of 35 deg.....

Is there a minimum ambient temperature the terminals are tested to?

Thoughts please on when we can use 90deg cable CCC values in calculations?

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    This depends on the rest of the cable route, and the termination detail.  a multi core cable with the 3 or 4 cores side by side may reach 90C with a given current flow, in a given environment - say attached to a wall or in a duct. The hottest part of the cable must be kept below 90C, but that may not mean the  ends are that hot..

    It is not going to be the same once the cores have been split out, as generally that is cooler, or need  if part of the cable or cores is clamped to something that is a better heatsink than the rest of it.
    And then the box with terminations itself may be in a hotter or colder place. It is not a simple matter to determine.
    Mike

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  • 0

    This depends on the rest of the cable route, and the termination detail.  a multi core cable with the 3 or 4 cores side by side may reach 90C with a given current flow, in a given environment - say attached to a wall or in a duct. The hottest part of the cable must be kept below 90C, but that may not mean the  ends are that hot..

    It is not going to be the same once the cores have been split out, as generally that is cooler, or need  if part of the cable or cores is clamped to something that is a better heatsink than the rest of it.
    And then the box with terminations itself may be in a hotter or colder place. It is not a simple matter to determine.
    Mike

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