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

  • State Not Answered
  • Locked Locked
  • Replies 30 replies
  • Subscribers 26 subscribers
  • Views 11850 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

Use of RCD protection in industrial and commercial installations

Andy
Hello All

We all know the benefits of RCD protection and how the regulations are changing regarding domestics. I am constantly being asked if RCDs are required for normal switched socket circuits in industrial installations apart from the obvious use of RCDs for areas likely to cause a reduction in resistance (sockets that could conceivably be used out side). So are RCDs required for general office circuits, for dedicated IT equipment (computers etc), work areas such as clean dry packing areas and so on.


Given RCDs require testing regularly and the results recorded which causes disruption to production equipment, IT equipment, Data centers etc are RCDs really required especially if they are installed within steel conduit or steel trunking on walls or under floors?


Any advice welcome


Andy
  • 0

    How about an RCD assembly incorporating a switchable parallel feed (by a special key?) which could be put in circuit whilst the RCD is tested?  Straight away I can see that for the duration of the test the circuit may not conform to regs, but maybe with a Risk Assessment and suitable control measures in place this could be overcome.    Just an idea.....



    I wonder if I can improve on that idea - two RCDs side by side and an all-poles make-before-break change-over switch between the RCDs and the load - you'd then be able to test one RCD at a time without disconnecting the load or losing protection. If one RCD failed you could leave the system switched to the other until a convenient time for replacement.


      - Andy.
  • Former Community Member
    0 Former Community Member
    two RCDs with a make before break switching arrangement wont work and you would drop your load. parallel paths would imbalance the currents through the rcds which would operate and drop your load.
  • 0


    two RCDs with a make before break switching arrangement wont work and you would drop your load. parallel paths would imbalance the currents through the rcds which would operate and drop your load.



     



    Ah yes, good point. Same problem with a single RCD and a by-pass switch then too. Back to the drawing board....


       - Andy.

  • 0

    AJJewsbury:





    two RCDs with a make before break switching arrangement wont work and you would drop your load. parallel paths would imbalance the currents through the rcds which would operate and drop your load.



     



    Ah yes, good point. Same problem with a single RCD and a by-pass switch then too. Back to the drawing board....


       - Andy.


     




    How about a purpose made assembly using two RCD's with tripping mechanisms that are disabled during switching, an interlock to make sure that both were not left on together and a system for provision of testing the one out of circuit.  It's getting a bit complicated now!

  • 0

    Foffer:




    AJJewsbury:





    two RCDs with a make before break switching arrangement wont work and you would drop your load. parallel paths would imbalance the currents through the rcds which would operate and drop your load.



     



    Ah yes, good point. Same problem with a single RCD and a by-pass switch then too. Back to the drawing board....


       - Andy.


     




    How about a purpose made assembly using two RCD's with tripping mechanisms that are disabled during switching, an interlock to make sure that both were not left on together and a system for provision of testing the one out of circuit.  It's getting a bit complicated now!


     




    Or back to the switching between twin RCDs idea, but with the switching done by electronics at the zero-crossing point? So the load side of the RCDs aren't connected together and the load never notices the switching.

      - Andy.

  • Former Community Member
    0 Former Community Member
    again zero point only valid for resistive loads, but with modern switchmode and inductive  capacitative loadings that zero point would be hard and the switching timeframe tiny. sometimes we chase a solution and become blinded by the desire to identify that solution, when the reality is that it could be done simpler and easier through planning the work and having buy in from others. there is no process that can not be interrupted for a short time if all the required planning and adjustments are in place.
  • 0

    Ruggedscot:

    again zero point only valid for resistive loads, but with modern switchmode and inductive  capacitative loadings that zero point would be hard and the switching timeframe tiny. sometimes we chase a solution and become blinded by the desire to identify that solution, when the reality is that it could be done simpler and easier through planning the work and having buy in from others. there is no process that can not be interrupted for a short time if all the required planning and adjustments are in place.




    I must admit I hadn't thought enough about different load characteristics and how this will alter switching loads and timings.   Maybe that's why I was a maintenance electrician and not a designer!  I also understand what you say about planning although as someone who worked in a 24/7 manufacturing environment, installing anything which needs to be turned off would be avoided if possible.  There will be planned maintenance downtime when the shut will be as short as possible and there is never enough time to do what you want normally without adding new jobs (RCD testing).  New satelite equipment would normally be hard wired from a control panel without RCD protection.  I realise that BS7671 would not apply in such a situation but think that RCD protection would be considered more often if testing did not involve switching the load off.  


     

  • 0

    lyledunn:

    Interestingly the National Rules for Electrical Installations in Ireland (ET 101:2008) permit omission of RCD protection for socket outlets for IT equipment and socket outlets used for isolation of fixed equipment. Caveats apply. Not sure if this will alter in the new edition scheduled for publication in January 2020.




    Apologies that I didn't see your post earlier, but non-standard socket-outlets are a requirement for such an approach to be adopted.

  • 0
    Agreed RB, I did say caveats apply. Providing non-standard sockets is not an automatic get out in 7671 2018 as it seems to be in ET101 2008. 

    By the way, purely out of academic interest, I have only just recently began to identify differences between the two sets of regulations. Both are HD based but it is interesting to note the difference in the various omissions, inclusions and approaches in both documents. I am not sure which, if any, of the regulations in ET101 are SNCs but in relation to the OP, it would seem that the intention of both national standards is that non-RCD protected circuits supplying sockets of standard construction are not acceptable even if the intended use is specifically for IT equipment unless other measures are considered.
  • 0

    again zero point only valid for resistive loads



    Zero voltage crossing perhaps, but what if it were zero current crossing?

      - Andy.

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines