Consumer unit's live bus bar for msbs

[arturas]

Hi there,today my mate asked my to connect his tower rail and toilet pump to cu,he has one spare 16amp mcb,but the live bus bar has been cutted before it,and there's no chance to get one today,but he needs to use the toilet,everything was wired in 2.5mm twin & earth,and will use about 4amps,is it wrong to temporary link the live bus bar with a bit of 2.5 to last mcb??nothing else will be connected on this mcb

 

[telectrix]

as a temporary link, no problem, but be sure to make the connection in the MCBs tight. if you're not carefull, the 2.5mm will not be gripped . give it a good tug after fitting, and don't forget to go back and do a more permanent job.

 

[Rockingit]

The problem that you have is that whilst what you've described would work in practice as a temporary measure, the theory is that each part of the circuit has to be able to withstand the limits of the proceeding bit of protection. For example, if something went wrong with the pump which was so catastrophic that it destroyed the MCB in the board (and presumeably also the RCD feeding it), then the cable in between has to be capable of withstanding the temporary fault current to the next bit of protection - and in a standard setup that's the Distributors fuse. What would actually happen in practice will be all down to the maths of the rest of the Ze etc.

If we are talking about temporary measures, is there a way in which you terminate the cable NOT into the MCB in the board, but instead put a 13A plug on it and just run it from a socket? That way, it's protected and you also avoid having to disturb the board until you're ready. BUT - you MUST make sure that the board is fully enclosed and safe, so don't try to get inventive with covers and wires.

 

[arturas]

Thanks for advices!It was double rcd cu,and this circuit was the last last mcb on second rcd, i couldn't convert it into a plug because the guy who did all the cu like couple months ago ,installed the cable into cu ,stripped it,and left it unconnected,because the bathroom was not finished,but then cutted bus bar too short for some reasons ,even the spare fuse was in the cu. So i could extend the cable and not close the cu properly or do a link with a bit of a cable,i asked him to wait but his frends coming to stay in for couple days so they needed a toilet.. i choose to make a link,and next weekend will change it to new bus bar..

 

[Mr.Ian]

Surley if it's wired in 2.5mm from CU to load then feeding the additional mcb with 2.5 for a temp period shouldn't be unsafe (as long as a good connection is made). The 2.5mm supply to load from the mcb must be big enough to take the fault current expected to trip the mcb and heaven forbid if there is a fault as soon as it's tripped the 2.5mm temp supply to it will have no more loading stress than the rest of the circuit feed.

 

[topquark]

Surley if it's wired in 2.5mm from CU to load then feeding the additional mcb with 2.5 for a temp period shouldn't be unsafe (as long as a good connection is made). The 2.5mm supply to load from the mcb must be big enough to take the fault current expected to trip the mcb and heaven forbid if there is a fault as soon as it's tripped the 2.5mm temp supply to it will have no more loading stress than the rest of the circuit feed.

What would happen in the event of a say 1.5kA fault from outside? Would the CU survive with that temp link?

 

[Mr.Ian]

What would happen in the event of a say 1.5kA fault from outside? Would the CU survive with that temp link?

How would the 2.5mm temp link to a low load circuit have any detrimental effect on CU survival from an outside 1.5ka fault?? I'm not being funny just wondering what you mean.

 

[davie spark]

Any temp link should be at least the same CSA of the busbar to render the same degree of current carrying capacity from a safety point of view but as it's at the end of the busbar it's not going to be handling the rest of the current flowing in the busbar so purely as a temporary measure it should be ok if connections are electrically and mechanically sound but it should not left long term. Having said all that the only 100% safe answer is to replace the busbar or whole C.U. It would not pass a 17th ED. inspection otherwise.

 

[Knobhead]

If you’ve got a bit of 16mm earth and lugs I would suggest using that. With a bit of brown tape obviously. Just thinking of what you may have kicking about.