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Band I / Band II cct separation

Farmboy
Does the principal of Band I / Band II  cct separation re 528.1 apply within equipment? A DETA mechanical chime with internal transformer has LV and ELV wiring right near each other within the same enclosure (the lid of which is easily removable without tools), which seems to moot the requirement to have them separated as per the reg?


F
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    Yes the general safety principle of separation does apply here, but comes under manufacturing rules and regs. You do not want any possibility of the nasty dangerous mains Voltages reaching a rain soaked door bell push on the front door frame.


    Z.
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    So can a Din rail bell transformer be installed within a consumer unit?


    Andy B
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    Sparkingchip:

    So can a Din rail bell transformer be installed within a consumer unit?


    Andy B




    You asked the question, which doesn't answer the question, so what's your answer to either question?


    F

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    Inside equipment, because it can be type tested for approval (think of a megger-like test) you can show that an alternative arrangement is possible.

    For example on a PCB with primary and secondary votages on the same side, I'd expect clearances to be to IEC-60950-1

    it very quickly gets confusing. c


    Of course you can fit  transformer in a CU. But unless the bellwires at 12 V or whatever coming out are over-sleeved to a standard that can hold off mains, you should really bring the ELV out in mains flex.
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    mapj1:

    Inside equipment, because it can be type tested for approval (think of a megger-like test) you can show that an alternative arrangement is possible.

    For example on a PCB with primary and secondary votages on the same side, I'd expect clearances to be to IEC-60950-1

    it very quickly gets confusing. c




    Agreed - BS 7671 does NOT apply to pre-manufactured assemblies, which should comply with appropriate standards (Regulation 113.1).


    BS EN 62368-1 (IEC 62368-1) supersedes BS EN 60950-1 (IEC 60950-1) and BS EN 60065, both of which are due to be withdrawn this year.






    Of course you can fit  transformer in a CU. But unless the bellwires at 12 V or whatever coming out are over-sleeved to a standard that can hold off mains, you should really bring the ELV out in mains flex.




    Agreed - subject to:


    • Regulation 536.4.203 - i.e. is the transformer stated as suitable for installation in that CU by the manufacturer, or are you happy to take responsibility for the safety and EMC performance of the whole assembly?

    • Regulations 444.6.1 and 444.6.2 i.e. is there adequate separation for electromagnetic compatibility of the Band I circuit? Regulation 444.4.1 lists switchgear as a "source of electromagnetic disturbance". It depends what the transformer is supplying, but an electronic door bell, for example, is unlikely to have been manufactured to consider the disturbances from switchgear, and it's possible that spurious operation of the bell, or damage to the electronics, could occur if there is not adequate physical separation. In the absence of further information, if we consider a 100 A DBO, Table A444.2 would recommend 600 mm separation distance from circuits carrying 100 A, 500 mm from circuits carrying 50 A, and 450 mm for 230 V circuits carrying less than 50 A.

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    Well consider a motor control centre where voltages of any size may be present. The controls from automation equipment and telemetry are likely to be present and cables carry no volts at all are common monitoring whether a contactor is open or closed for example. 


    I know some design goes into this to ensure some separation where possible but often it is not possible in an MCC...........- the design of which -  I'm no expert, but I think one way to enable this mixture of voltages in the same finger trunking to is ensure that what ever cables are used are rated (insulation is rated) for the highest voltage present. 


    More Knowledgeable people than me I'm sure will comment on this shortly I'm sure. 

     

    Kind Regards


    Tatty
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    Farmboy:




    Sparkingchip:

    So can a Din rail bell transformer be installed within a consumer unit?


    Andy B




    You asked the question, which doesn't answer the question, so what's your answer to either question?


    F


     




     

    It’s not a question I have had to answer, hardwired door bells have gone out of fashion in favour of cordless door bells.


    Bu now people want a 24 volt supply for Ring door bells and the like, I have only done one and the transformer was remote from the CU.


    So lets start at that font of knowledge, The Screwfix website.


    As I read it BG bell transformer can be installed in the “Hi-integrity” split of a consumer unit without any RCD protection for it or the cables it supplies that may be concealed in a wall.


    So another question, how should the bell wire be run through and out of the consumer unit?


     Andy Betteridge 


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    tattyinengland:

    Well consider a motor control centre where voltages of any size may be present. The controls from automation equipment and telemetry are likely to be present and cables carry no volts at all are common monitoring whether a contactor is open or closed for example. 


    I know some design goes into this to ensure some separation where possible but often it is not possible in an MCC...........- the design of which -  I'm no expert, but I think one way to enable this mixture of voltages in the same finger trunking to is ensure that what ever cables are used are rated (insulation is rated) for the highest voltage present. 


    More Knowledgeable people than me I'm sure will comment on this shortly I'm sure. 

     

    Kind Regards


    Tatty




    This is definitely the case. The difference, with respect to EMC, is the fact that EMC testing has been carried out for that application, whereas I doubt many domestic-market products have been tested for use in switchgear or controlgear assemblies, or where cables supplying them are sourced from, or routed close to, a switchgear or controlgear assembly.

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    I thought that had been answered, use sheathed 2 core 0.75 flex. I very much doubt that a din rail TX has ever been type tested in a CU, and can see no reason to do so. There are reasonable limits to apply here, read the type testing document and you will see why.
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    davezawadi:

    I thought that had been answered, use sheathed 2 core 0.75 flex. I very much doubt that a din rail TX has ever been type tested in a CU, and can see no reason to do so. There are reasonable limits to apply here, read the type testing document and you will see why.




    The transformer like a SPD cannot be mounted over a consumer unit busbar, you will either have to create a gap or put them on the other side of the main switch, then route the bell wire and possibly alarm wires from the SPD out of the consumer unit avoiding an potential risks.


    Andy Betteridge 

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