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  1. spsparks
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    spsparks Regular EF Member

    100A Square D QOE Isolator on dist board with 25mm tails from service head (100A), then a 16mm sharing the incoming side of the isolator to a 2nd DB.

    The dummy then sticks a 6mm2 in along with them to a 63A RCCB for solar DB......... NICEIC reg. company apparently.
    Guess he couldnt fit another 25mm in there. Only wish I had taken a photo.
     
  2. Earthstore
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    Earthstore Guest

    The experts will answer this I dare say.
    Depending on the size of the PV system, and the length of the AC run, a 6mm cable sounds fine (has to have <1% drop) as the PV circuit should not be on a shared circuit.
    Unless the system is mounted in another building, or has a long cable run, you would never need 25mm cable.
    Of course, how he made the connection, only you have seen that, by the sounds of things it could have been better.
    And you are right a photo would have been good.

    I hope this helps.
     
  3. spsparks
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    spsparks Regular EF Member

    dont think you got the gist of this ..........service fuse 100A then 6mm to 63A rccb in shared terminal with 25mm tails and 16mm tails. No suitable overcurrent protection on 6mm cable IMHO
    What happens if there is a fault on 6mm ?..........
     
  4. GaryM
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    GaryM Guest

    6mm2 is probably fine supplying a 1 way CU with a maximum demand of 16A.
    What isn't fine is a 25, 16 and 6mm conductor in the same terminal. There's no way you can guarantee a sound mechanical connection.

    What kind of fault on the 6mm?

    Imagine a 400A busbar chamber supplying multiple 63A isolators. Are you suggesting all supplying conductors to the isolators should be capable of carrying 400A?
     
    Last edited by a moderator: Feb 25, 2012
  5. Earthstore
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    Earthstore Guest

    I am not a sparky, I do not work on electrical systems, but I do understand PV systems, so just trying to help.
    I think I understand what you are saying now about the overcurrent protection for the 6mm.
    But as a pv system is a supply,and a dedicated circuit, with a maximum output (normally 3.68KW on a domestic installation) and the grid voltage is regulated, there is no possibility of overcurrent, unless as you say the 6mm cable goes faulty.
    So, not too sure, one of the experts will be on here later, and probably tell you which reg applies.

    Just trying to help.
     
  6. spsparks
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    spsparks Regular EF Member

    We are not discussing the merits of 3 phase distribution. But are discussing a single phase situation that COULD lead to a dangerous situation and doesnt comply with Regs. It was signed of by an NICEIC reg. company.
    As I said it runs to a 63A RCCB from the isolator. Two mcbs 16A and a 6A in small CU............but thats a minor detail.

    BS7671 chapter 43 and best practice guide 3.
    I wonder what supplier would say to a 6mm being run from their service fuse.
     
    • Like Like x 1
  7. GaryM
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    GaryM Guest

    Nothing, if all it feeds is a 2 way consumer unit with a 16A and 6A circuit.
    You need to understand that the main fuse protects the cable coming in from the street, not the consumers installation.

    What's the danger to the 6mm conductors in this instance?
     
  8. spsparks
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    spsparks Regular EF Member

    I appreciate the feed back Earthstore. I also understand that practically their is unlikely to be a problem with the cable. If this is the way these systems are being installed then they dont comply with regs requirements for protection from over current. I will ask the supplier what tails they spec (usually 25mm). As this is an indirect connection to these. I think its a poor quality job when the solution is to use a couple of 3 way 100A JBs and run 25mm tails to the RCCB. That does comply with regs and would be a better solution. I reckon he used 6mm as it was all he could get in the terminal.
     
  9. spsparks
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    spsparks Regular EF Member

    Then to that logic you are using a 63A RCCB to protect a 6mm cable ????
     
  10. GaryM
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    GaryM Guest

    Why doesnt it comply with overcurrent requirements? Have you got a direct link to a regulation? Bet you don't find one!
    Why would the DNO be interested?

    I've seen many 1 way CU's supplying showers with 6mm2 DI tails from a henley block. Nothing at all wrong with them.
     
  11. GaryM
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    GaryM Guest

    Nope, the circuit breakers combined will have a maximum demand of 22A. An RCCB won't provide overcurrent protection.
     
  12. spsparks
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    spsparks Regular EF Member

    You obviously cant be bothered to look for yourself and based on your reponses that doesnt surprise me.
    433.1.1 (ii) but many more in the whole section you should read.
     
  13. GaryM
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    GaryM Guest

    Will have a look. It's not that I can't be bothered, it's just that I think you're wrong. No offence intended so lets keep it to a friendly debate.
     
  14. GaryM
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    GaryM Guest

    Just looked. You don't agree that two protective devices - 16A and 6A won't offer protection against overload of a 6mm2 conductor? Don't you think either will trip if their respective circuits generate more than 16A or 6A for a long duration?
     
  15. JD6400
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    JD6400 Trusted Advisor

    Location:
    ?
    Not done the calcs yet as the weekend and all the books are at the office , 6mm on a 63amp breaker sounds to large at the moment and as for squeezing them all into the incoming side of the main switch instead of a Henley block is just plain and simple rough as a Brock let alone any of the regs that i am sure you would find that just simply say NO ! I would hope ?
    But there is absolutely no reason not to use the 6mm if it is covered by a appropriate protective devise on the incoming load side ? (To limit the load draw down the 6 mm )
    I hope that last bit made sense .
     
    Last edited: Feb 25, 2012
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