Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • Replies 34 replies
  • Subscribers 44 subscribers
  • Views 632 views
  • Users 0 members are here
Options
You may also be interested in

My war against dual rcd boards

Newfutile
As each (RCD) Residual Current Device must not have more than 30% leakage current on it.
It's hard to see how dual (RCD) Residual Current Device boards can be fitted at all these days.
i come across so many dual rcd boards with solar, evse and heat pumps on them, these have all been recently installed.
i wonder if BS7671 should state: Dual (RCD) Residual Current Device boards shall not be fitted, unless it can be shown (and documented) that they are suitable for the combined leakage currents expected .
otherwise developers will keep specifying them and i will have keep educating them on the many reasons a type A rcd should not be shared with other equipment!.
maybe manuafactuers instructions should also state : not suitable for a shared rcd, for certain equipment.
Parents

  • I have a 15 way dual RCD board on my home installation. I have lots of electronic equipment plus a full range of kitchen and laundary appliances, an outside workshop with machinary and a amatuer radio station. I have a standing earth leakage of 11mA acroos the 2 RCDs. Never had a nuisance trip other than the senior management pooring water over her steam iron, this got replaced with an early wedding present (she was lost for words and no dinner for me that night).

    JP

Reply

  • I have a 15 way dual RCD board on my home installation. I have lots of electronic equipment plus a full range of kitchen and laundary appliances, an outside workshop with machinary and a amatuer radio station. I have a standing earth leakage of 11mA acroos the 2 RCDs. Never had a nuisance trip other than the senior management pooring water over her steam iron, this got replaced with an early wedding present (she was lost for words and no dinner for me that night).

    JP

Children
  • in reply to John Peckham

    Are the RCD type AC?  The type AC could mask/blind the nuisance trip

  • in reply to Sergio Fernandez
    Sergio Fernandez said:
    Are the RCD type AC?  The type AC could mask/blind the nuisance trip

    That's an interesting point ... if, with the loads connected, the RCD is still able to operate within parameters from a Type AC RCD test (simulating a supplemental fault over the standing conditions), is that OK?
    (I'm fully aware that what I'm proposing here is very "loose", but certainly a discussion point.)

    However, we also need to consider that, in the "blinding" situations, currents, such as smooth DC, changing/pulsating DC, and/or high frequency AC, need to appear as a residual current ... and not all protective conductor currents, nor all 'leakage' currents are 'residual currents' in the live conductors.

    And ... not all Type AC RCDs are 'blinded' in the same way, to the same thresholds. 

    The actual blinding from some electronic equipment might only occur during a fault downstream of some electronics - as shown in Fig A53.1.

  • in reply to gkenyon
    gkenyon said:
    And ... not all Type AC RCDs are 'blinded' in the same way, to the same thresholds. 

    Agreed

    But we do know they (Type AC RCD) get blinded or may become blinded to a greater or less degree.  Now consider the domestic dwelling for the scenario a light bulb fails (lamp to engineers) Home owner/occupier replaces it.  Firstly the original lamp could of been filament or halogen or florescent/compact florescent the replacement surely by now will be LED thus the resistive load now becomes an electronic load with or without a certain amount of DC leakage.  

  • in reply to Sergio Fernandez

    Firstly the original lamp could of been filament or halogen or florescent/compact florescent the replacement surely by now will be LED thus the resistive load now becomes an electronic load with or without a certain amount of DC leakage.

    How can you have any leakage from anything with a 2-wire connection, like a BC or ES lampholder? (and no other connection to terra firma).

       - Andy.

  • in reply to Sergio Fernandez
    Sergio Fernandez said:
    Firstly the original lamp could of been filament or halogen or florescent/compact florescent the replacement surely by now will be LED thus the resistive load now becomes an electronic load with or without a certain amount of DC leakage

    Isn't that a matter for the product standards, and relevant legislation such as the Electrical Equipment (Safety) Regulations and the Electromagnetic Compatibility Regulations? A product manufacturer ought not to assume an electrical installation conforms to the current version of the national wiring code? They can, however, provide information and guidance for users and installers that highlight certain issues, I guess - but in the case of a general product with a standard plug, or a GLS replacement lamp, would the user even understand the information?

    This debate about compatibility could go on and on in other directions. We do know that older RCDs (BS 4293 and BS 7288 prior to 2016) weren't necessarily tested for Electromagnetic Compatibility to the current levels - this could also be the case for RCDs to earlier versions of BS EN 61008 and BS EN 61009 than the current versions (although I haven't checked as of posting this) ... so are they safe for continued use if modern electronic devices are used in the premises?

  • in reply to AJJewsbury
    AJJewsbury said:
    How can you have any leakage from anything with a 2-wire connection, like a BC or ES lampholder? (and no other connection to terra firma).

    Capacitive is possible in the cabling to the ceiling rose  ... but that would rule out DC, and would be generally low-level 'leakage'.

    However, if the lamp is damaged, and the user is being protected against accidental contact with live parts, say after the rectifier, would the type AC RCD operate is perhaps another question?

  • in reply to gkenyon

    I presume the rcd would still operate after all when we test we test on 0 and 180 which I assume to be positive and negative going cycles

  • in reply to gkenyon
    gkenyon said:
    However, if the lamp is damaged, and the user is being protected against accidental contact with live parts, say after the rectifier, would the type AC RCD operate is perhaps another question?

    The RCD almost certainly will not trip, as the current drawn by the lamp will probably be less than what is required to trip a 30 mA RCD.

Community Rules & Guidelines