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Clarification of Table A444.2

Ben Gregory

Hello folks,

Thinking about BS guidance for separation distances for EMC. 

BS EN 50174-2:2018 gives a nice formula for working out distances between power supplies /control cable, with criteria to be met. 

BS 7671 Table A444.1 gives some minimum values which I'm Ok with, as I can arrive at the same values using the criteria and formula from BS EN 50174-2:2018.

however BS7671 goes on to state that if the criteria for Table A444.1 cannot be met then Table A444.2 should be used. I find Table A444.2 more problematic as I cannot understand where the values were derived from, and it means I can't use the formula in 50147 for anything over 600A , or IT application unknown, when actually 50174 allows for both those scenarios. 

What is the source material for Table 444.2?

Why does it use obsolete nominal voltages 240 and 415V?

Why does it consider voltages (the left side of the table) for separation when EMC is current driven?

Is the 600A mentioned three phase or single phase?

Many thanks for anyone taking the time to humour me and my ruminations.

Ben

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    Ben Gregory said:
    it means I can't use the formula in 50147 for anything over 600A , or IT application unknown, when actually 50174 allows for both those scenarios. 

    Is it not the case that A444.4 states (1st para);

    Where both the specification of the information technology cable and its intended application is known, the requirements of BS EN 50174-2 and BS EN 50174-3 are appropriate.

    A444.4 then goes on to describe some more detail ... and then says 'If the above conditions do not apply ...' meaning the conditions where both the specification of the information technology cable and its intended application is known' then go ahead an follow the older rules of thumb if you need to.

    So I read it as though if you can use BS EN 50174-2 or BS EN 50174-3, then do so, otherwise, use the rules of thumb.

    More pertinent, however:

    It is wholly incorrect to say 'it means I can't use the formula in 50174 for anything over 600 A', because the whole of Annex A444 is informative, which means it is only guidance, and not necessary to comply with BS 7671. If there are normative requirements in BS EN 50174 series for this particular aspect, it would be proper to use those; if the requirements are informative, they would be equally valid.

    However, please refer to BS 6701 Telecommunications equipment and telecommunications cabling. Specification for installation, operation and maintenance as this modifies certain aspects of BS EN 50174-2, particularly in terms of separation (segregation) of power and telecommunications cabling.

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  • 0
    Ben Gregory said:
    it means I can't use the formula in 50147 for anything over 600A , or IT application unknown, when actually 50174 allows for both those scenarios. 

    Is it not the case that A444.4 states (1st para);

    Where both the specification of the information technology cable and its intended application is known, the requirements of BS EN 50174-2 and BS EN 50174-3 are appropriate.

    A444.4 then goes on to describe some more detail ... and then says 'If the above conditions do not apply ...' meaning the conditions where both the specification of the information technology cable and its intended application is known' then go ahead an follow the older rules of thumb if you need to.

    So I read it as though if you can use BS EN 50174-2 or BS EN 50174-3, then do so, otherwise, use the rules of thumb.

    More pertinent, however:

    It is wholly incorrect to say 'it means I can't use the formula in 50174 for anything over 600 A', because the whole of Annex A444 is informative, which means it is only guidance, and not necessary to comply with BS 7671. If there are normative requirements in BS EN 50174 series for this particular aspect, it would be proper to use those; if the requirements are informative, they would be equally valid.

    However, please refer to BS 6701 Telecommunications equipment and telecommunications cabling. Specification for installation, operation and maintenance as this modifies certain aspects of BS EN 50174-2, particularly in terms of separation (segregation) of power and telecommunications cabling.

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