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 11 replies
  • Subscribers 40 subscribers
  • Views 3629 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

MCB Change on Socket Circuit - No RCD

Bees2699

Hello All,

I have a question which I'm sure will have lots of opinions, so look forward to hearing them. 

After having carried out an EICR some welding sockets have failed, some due to the size of the MCB in relation to the cables current carrying capacity and some due to Zs. The loading is not an issue so we are looking to downgrade the size of the breakers which will sort out both issues. However as these are feeding sockets if we change the MCB will these have to become RCD protected. Although they have a specific intended use I cannot guarantee they wouldn't be used for anything else. However due to cost implications the customer is not willing to pay for either 3 phase RCBO's or individual RCD's mounted by the board or for replacing the sockets to include RCD's. By the changing the MCB we would only be making the circuit safer and up to the standard when it was installed, however I would usually try and bring any circuit I work on up to current standards. But as there are about 8 three phase circuits affected its not a simple or cheap option to replace them all. 

Look forward to any opinions or articles relating to this matter.

Thank you 

Bees 

Parents
  • 0

    When you say the welding sockets "have failed" do you mean they have been burnt out,  damaged by overload or just that you have not given them an EICR pass ?

    If the former then really they should be changed for the next size up, or the overload removed.

    If you mean you have found a 16A socket on a 20A D curve breaker and really you would prefer to see a 16A C type, then it may well be that no instant action is really required, if the load on the sockets is in practice known and not likely to be changed.


    Also, the problem of the high Zs may be made acceptable in some cases by lowering R2 relative to R1 - i.e. supplementary earthing, so that during an L_N fault at the far end, the R1/R2 voltage division gives a touch voltage that stays below 50v - then we do not need to worry about disconnection times in quite the same way.

    It is not often done, and it may not be the normal way to think about things, but so long as the highest touch voltage under fault conditions is less than 50, or whatever the safe shock limit is for the situation,  the  disconnection time can safely be extended to "never" . Of course in reality it would still go off in a few seconds, and you would really  want it to, if not from a shock perspective, then  from considerations of hot wires and a large electricity bill !!

    Mike

Reply
  • 0

    When you say the welding sockets "have failed" do you mean they have been burnt out,  damaged by overload or just that you have not given them an EICR pass ?

    If the former then really they should be changed for the next size up, or the overload removed.

    If you mean you have found a 16A socket on a 20A D curve breaker and really you would prefer to see a 16A C type, then it may well be that no instant action is really required, if the load on the sockets is in practice known and not likely to be changed.


    Also, the problem of the high Zs may be made acceptable in some cases by lowering R2 relative to R1 - i.e. supplementary earthing, so that during an L_N fault at the far end, the R1/R2 voltage division gives a touch voltage that stays below 50v - then we do not need to worry about disconnection times in quite the same way.

    It is not often done, and it may not be the normal way to think about things, but so long as the highest touch voltage under fault conditions is less than 50, or whatever the safe shock limit is for the situation,  the  disconnection time can safely be extended to "never" . Of course in reality it would still go off in a few seconds, and you would really  want it to, if not from a shock perspective, then  from considerations of hot wires and a large electricity bill !!

    Mike

Children
No Data

Community Rules & Guidelines