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Doubled 2.5mm cable instead of 4mm

Discussion in 'Electronics & Electrics' started by craigcurtin, Feb 24, 2021.

  1. craigcurtin

    craigcurtin Member

    Joined:
    Jul 1, 2012
    Messages:
    28
    Guys,

    Just in the process of doing some renovations and have found that our spa which has both a heater and a swimjet in it has been wired with twin 2.5mm cables (i.e. in parallel) rather than 4mm

    This has been installed in conduit over about 25mm - part of the way is embedded in a concrete slab.

    It has a 32amp breaker at one end on the switchboard and a isolation switch at the other end - before it splits out to the swimjet and heater.

    Is this OK to be like this - or should we attempt to get it replaced with a 4mm ?

    Just worried about where it is embedded in the slab as i do not know if we will be able to get it around any bends etc to pull the new cable through

    THoughts ?

    Craig
     
  2. Technics

    Technics Member

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    Location:
    Brisbane, AU
    IANAS (I am not a sparky) and I'm sure one will chime in as there are a few around here. IIRC wiring in parallel is okay provided the wires are running the same length and will share the current evenly (so you're probably fine there based on shared conduit) and provided the conductors are 4mm or larger (so it seems questionable in this case). It also has implications for temperature de-rating if they share a conduit. I'd wait till a real sparky gives there $0.02 though because I could be wrong about the 4mm requirement.
     
    Last edited: Feb 24, 2021
  3. OP
    OP
    craigcurtin

    craigcurtin Member

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    Thanks for the quick reply - will wait to hear back from one of the experts

    Craig
     
  4. rickbishop

    rickbishop Member

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    Someone like Symon would know better than me, but I was always told that running two cables was a very bad idea, because if there's a break in one, the other one carries all the load and is a fire risk. The breaker is there to protect the cable, and 2.5mm is ok for 20 amp, but definitely not 32 amp.
     
  5. Symon

    Symon Castigat ridendo mores

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    You aren't permitted to parallel cables <4 sqmm in size, so what you have there is not compliant (clause 3.4.3 for those that want to check).

    How long is the run? If you actually need 32A I suspect you will need 6 sq mm.
     
    CacTuar, jpower and terrabyte like this.
  6. Privatteer

    Privatteer Member

    Joined:
    Mar 19, 2006
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    +1
    Are they directly connected together or on separate poles of a double pole switch/MCB?
    If your lucky it may be possible to have heater and pump on the separate cables depending on their load.
     
  7. ArmoureD

    ArmoureD Member

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    Get it redone. 4mm is not permitted when installed as per your conditions. 6mm is the required size.

    Alternatively, can it be wired as 3 phase?
     
  8. blindy

    blindy Member

    Joined:
    Mar 22, 2017
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    61
    Since you have 2 wires, you have double the chances of getting a string through if one breaks:lol:
     

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