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Max Zs for adjustable MCCB's

Gareth 1

When determining the max permitted Zs for an MCCB with variable settings.

Do you have to apply the Zs value for the maximum possible settings, regadless of actual settings.

OR

Is it permissible to apply the Zs value for the actual settings, despite the fact that these could be increased at a later date.

Many Thanks

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  • 0

    It rather depends if you think the settings are likely to be changed by an incompetent person; It is possible to seal the settings on some designs, either with wire seals or paper ones, and changing the settings is then a deliberate act, perhaps requiring tools- after all in that case, in a conventional CU, someone could unscrew a fixed rating say 32A MCB and fit  40A one in its place without much more effort.

    You can only base your design on the settings you sensibly expect  to be used, and the rest is a matter of clear labeling and instructions.

    Mike

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  • 0

    It rather depends if you think the settings are likely to be changed by an incompetent person; It is possible to seal the settings on some designs, either with wire seals or paper ones, and changing the settings is then a deliberate act, perhaps requiring tools- after all in that case, in a conventional CU, someone could unscrew a fixed rating say 32A MCB and fit  40A one in its place without much more effort.

    You can only base your design on the settings you sensibly expect  to be used, and the rest is a matter of clear labeling and instructions.

    Mike

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