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 18 replies
  • Subscribers 32 subscribers
  • Views 2064 views
  • Users 0 members are here
Options
You may also be interested in
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

MCCBs

richard64
Ok, no showers on this one.

Where can I find max zs and time current characteristics for mccbs.

There's nothing in the BBB covering them (as far as I can see).

Thank you.
  • 0
    I would personally look at the fault level/discrimination curves to verify selectivity, but then that is the way I have always done it. If you follow Mike's guidance then as he says, "it won't be perfect, but will protect you from most credible faults". Perfection costs time and therefore money (and sometimes can't be achieved anyway).

    Alasdair
  • 0

    OMS:

    Who owns that main supply - ie is it a DNO fuse ?


    Regards


    OMS




    Aah, sorry. When I said Main Supply, I meant the customer's supply to the Main DB. Not the DNO cut out.

  • Former Community Member
    0 Former Community Member

    richard64:


     


    OMS:

    Who owns that main supply - ie is it a DNO fuse ?


    Regards


    OMS




    Aah, sorry. When I said Main Supply, I meant the customer's supply to the Main DB. Not the DNO cut out.

     


     




     

     

    OK - well, if the customer is already operating fuse technology, then be careful about suddenly introducing MCCB's  - however, I'd be reasonably happy to accept a supply protected by BS 88's and then use MCCB's for the next two tier of distribution and MCB's for the final tier


    Regards


    OMS
  • 0

    OMS:


     

    I'd be reasonably happy to accept a supply protected by BS 88's and then use MCCB's for the next two tier of distribution and MCB's for the final tier

     


    Absolutely agree with that (though not circuit breakers and then fuses as it causes all sorts of headaches with discrimination.....)

    Alasdair

  • 0
    Thank you for all the advice.

    I'm sorry for all the questions...it's been a long while since I've done this kind of stuff, so just clearing out the rust from my brain and checking my memory.


    It would seem that the client is steaming ahead with...'what they always do'... and I'm playing catch up verifying it all.


    Thanks again,

    Richard.
  • 0
    Do not worry about asking, it is far better for all of us to ask the apparently daft question on here in more or less anonymity, than to see headlines asking why the life support  supply was cut off when only the light in the loo failed.


    BTW it was OMS who brought up the concept of only considering the more 'credible faults ' though I agree entirely with the sentiment - incredible faults may bulk up the Risk Assessment, if you are paid by weight of paper, but measures to avoid them are largely nugatory but can be comical.

    Risk " nuclear powered missile lands on substation, causing loss of power to dryers and lights in adjacent toilet block and welfare area"

    Mitigation  "nothing we can do could stop it really" 

    Probability " incredibly unlikely" 

    Action fit EM light in toilet and welfare areas, ensure spare toilet rolls are kept in fireproof cupboard..

    Reviewer Notes " if this happens I won't be around to worry about it, and the site facilities office no. will  go direct to answerphone "



  • 0

    mapj1:

    Do not worry about asking, it is far better for all of us to ask the apparently daft question on here in more or less anonymity, than to see headlines asking why the life support  supply was cut off when only the light in the loo failed.


    BTW it was OMS who brought up the concept of only considering the more 'credible faults ' though I agree entirely with the sentiment - incredible faults may bulk up the Risk Assessment, if you are paid by weight of paper, but measures to avoid them are largely nugatory but can be comical.

    Risk " nuclear powered missile lands on substation, causing loss of power to dryers and lights in adjacent toilet block and welfare area"

    Mitigation  "nothing we can do could stop it really" 

    Probability " incredibly unlikely" 

    Action fit EM light in toilet and welfare areas, ensure spare toilet rolls are kept in fireproof cupboard..

    Reviewer Notes " if this happens I won't be around to worry about it, and the site facilities office no. will  go direct to answerphone "



     




    If that happened, I'd like better access to the toilet rolls...I hope the RA ensures that the fireproof cupboard isn't locked :-0

  • Former Community Member
    0 Former Community Member

    mapj1:

    BTW it was OMS who brought up the concept of only considering the more 'credible faults ' though I agree entirely with the sentiment - incredible faults may bulk up the Risk Assessment, if you are paid by weight of paper, but measures to avoid them are largely nugatory but can be comical.





     



     

    OK - for clarity, I wasn't suggesting that we don't design for all of the faults that may occur within a system (electrical protection from O/L, SC and E/F should be achieved throughout) - just that were a fault to occur at a particularly unusual position, then we might not achieve discrimination - ie we would say we would have partial co-ordination. So an example might be someone driving a silver stake through a cable about 2m downstream from the panel - which in reality means someone has climbed up to reach the cable tray/ladder and given the cable a bloody good insult - at that point I wouldn't worry unnecessarily that the feeder breaker and the main panel device have raced each other to the final and both operated, leaving some healthy circuits off - in most cases, it would be so rare that it would be tolerable - and if it ain't then it needs more money spending to absolutely ensure full discrimination at any point in the system (so add £XX thousands for things like bus bar protection zones, line differential protection on feeders, fail to trip schemes, restricted earth fault protection zones, circuit breaker restraint schemes (with the consequent increase in switchboard fault rating (eg increase from 1 to 3 second protection)) etc etc


    Regards


    OMS

Community Rules & Guidelines