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Thread: Underfloor heating circuits

  1. #1
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    Underfloor heating circuits

    Hello all,

    I got a licensed Electrician in to help me with a CoC for a client of mine. I didn't do the house wiring but doing other work so I said I would organise and supervise it.

    He had an issue with the Underfloor heating. The 2 rooms downstairs are combined to one 20A CB in the DB, and the 2 upstairs are on another 20A CB in the same DB. Both are on the ELPD feed.

    He says each underfloor heating element / room mus be on its own CB in the DB.

    According to what I can find relevant in the SANS regs:

    6.16.4.1 Heating and cooling
    .1 Dedicated circuits should be provided for fixed space heating and cooling (air Con units) that are rated more than 16A. There may be more that one unit on each circuit and the power supply to each shall be controlled by switch-disconnector

    6.16.4.2 Underfloor Heating
    .1 The circuit that supplies underfloor heating shall be protected by an ELPD that has rated EL tripping current <= 30 mA

    And according to

    http://www.jcheat2tile.co.za/calculations.html

    I am estimating about 6 amps per room, so that is 12 amps per CB so that is under the 16A above, assuming Under Floor Heating applies to this Even so, does one need the Switch-Disconnecter only if more that 16A? Is that the wall mounted stove type? surely doesn't have to be in the DB, is the Switch Disconnector needed for each unit at all?

    Earth Leakage, no problem, but I cant see how he can insist on rewiring so that each room unit has its one CB in the DB. Am I missing something? The plot maybe?

    Can anyone shed some light or share experiences in this regard please. I have asked the Electrician doing this (allegedly a Master) to advise under which regs his request if referenced to, but thought I would float it here as well


    Thanks in advance.

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    Diamond Member AndyD's Avatar
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    I can't think of any reg that would forbid 2x rooms of underfloor heating on a single circuit. I'd ask the sparky for the reg that gave him cause for concern. A switch disconnector is a device capable of breaking the full load current of the circuit, it must also break the live(s) and neutral. AN SP+N circuit breaker or an earth leakage breaker or any isolator switch that's rated as on-load can be used as a switch disconnector. The full requirements for a switch disconnector are found in SANS 60947-3 or IEC 60947-3.
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    Site Caretaker Dave A's Avatar
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    I suspect the answer is in your post -

    Quote Originally Posted by kosmonooit View Post
    There may be more that one unit on each circuit and the power supply to each shall be controlled by switch-disconnector
    Each unit requires its own switch disconnector (as opposed to own circuit).

    If that is not currently the case, the question moves to the best way to correct the problem.

    Quote Originally Posted by kosmonooit View Post
    Even so, does one need the Switch-Disconnecter only if more that 16A?
    You need a switch disconnector if the fixed appliance (of this nature) is connected directly into the installation (as opposed to via a socket outlet).

    What the reg is trying to imply (between the lines) is that if the load is greater than 16A you may not use a socket outlet and must wire in directly.

    Perhaps also worth mentioning that a socket outlet qualifies as a disconnecting device.
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    Thanks for the replies, but it just seems this is unclear:

    ".1 Dedicated circuits should be provided for fixed space heating and cooling (air Con units) that are rated more than 16A. There may be more that one unit on each circuit and the power supply to each shall be controlled by switch-disconnector"

    Does this mean you only need a switch-disconnector only if its rated at more than 16A?

    Say now each underfloor does require a switch-disconnetor, regards of rated current, this could be solved by either a 2 pole Sw-Discon in the db for each circuit. or fitting a 100x50 box in the wall above the controller and putting the Sw-Discon there.

    And if this is required, a single pole CB in the db will not be complaint, since the codes specify a Sw-Discon (which breaks Phase and Neutral)

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    If the second part sentence of .1 above does not follow on from the first sentence (ded cir req for > 16A), then why is it not .2 under 6.16.4.1?

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    Site Caretaker Dave A's Avatar
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    Quote Originally Posted by kosmonooit View Post
    Thanks for the replies, but it just seems this is unclear:

    ".1 Dedicated circuits should be provided for fixed space heating and cooling (air Con units) that are rated more than 16A. There may be more that one unit on each circuit and the power supply to each shall be controlled by switch-disconnector"

    Does this mean you only need a switch-disconnector only if its rated at more than 16A?
    No. As I cover in post 3, if it is connected directly and not via a socket outlet you will need a switch-disconnector for this type of fixed appliance regardless of the load.

    What sentence one of this section is actually trying to stress is that you should have a dedicated circuit (as opposed to a mixed circuit or supplied off a plug top) if the load is greater than...

    Quote Originally Posted by kosmonooit View Post
    Say now each underfloor does require a switch-disconnetor, regards of rated current, this could be solved by either a 2 pole Sw-Discon in the db for each circuit.
    Perhaps* Yes if that circuit only supplies one appliance. Certainly No if that circuit supplies more than one appliance.
    *I need to check if the isolator is allowed to be in the db in this instance (in which case it would need to be lockable), or whether it must be within arms reach... (and I don't have the code with me right now).

    Quote Originally Posted by kosmonooit View Post
    or fitting a 100x50 box in the wall above the controller and putting the Sw-Discon there.


    Quote Originally Posted by kosmonooit View Post
    If the second part sentence of .1 above does not follow on from the first sentence (ded cir req for > 16A), then why is it not .2 under 6.16.4.1?
    Because it applies to "heating and cooling", and not just "under floor heating".
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    Thanks Dave that is a bit clearer, I assume the On / Off switch in the control box would not satisfy the requirement for a Switch-Disconnnecter

    I must also say the code should/could be clearer on this, this is ambiguous. They are badly written in general. which is why I struggle to pass Installation Rules!

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    Quote Originally Posted by Dave A View Post


    Because it applies to "heating and cooling", and not just "under floor heating".
    6.16.4.1 is Heating and Cooling

    6.16.4.2 is Underfloor Heating

    The above .1 is under 6.16.4.1

    What i was saying is that 6.16.4.1.1 could have been broken down into two parts since they second part is not a condition on the first, and that is the ambiguity.

    Should we also assume that the regs for Heating and Cooling apply to Underfloor Heating?


    Sorry to labour these points but how must one try make sense of this if its written in an ambiguous and unsuccinct manner. Seems like its open to interpretation.

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    Site Caretaker Dave A's Avatar
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    Quote Originally Posted by Dave A View Post
    *I need to check if the isolator is allowed to be in the db in this instance (in which case it would need to be lockable), or whether it must be within arms reach... (and I don't have the code with me right now).
    So I've just checked. There being no specific clause on location of the disconnecting device for "heating and cooling" and "under floor heating", thus the general rule of 6.16.1.5 would seem to apply - being within 1.5 m of the appliance or in a distribution board (if the switch-disconnector is lockable).

    Quote Originally Posted by kosmonooit View Post
    Should we also assume that the regs for Heating and Cooling apply to Underfloor Heating?
    Absolutely. Underfloor heating is a subset of Heating and Cooling and has additional requirements specific to that type of fixed appliance. Heating and Cooling is a subset of Fixed Appliances and has specific requirements in addition to the general requirements for Fixed Appliances.

    The full requirement for any particular component is built in layers...

    Quote Originally Posted by kosmonooit View Post
    I must also say the code should/could be clearer on this, this is ambiguous. They are badly written in general. which is why I struggle to pass Installation Rules!
    Once you grasp the fundamental principles of how they are structured, it does become a lot easier to understand.

    If you want to start getting into "ambiguous", the real discussion on that front is the meaning of "should"!
    Does that mean "mandatory" - or just that it's good practice, but ultimately optional.
    Last edited by Dave A; 24-Oct-16 at 02:39 PM. Reason: typo
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    Thanks Dave, I will break the good news to the client that I am going to have to cut boxes into their nice walls. Yes, I do have problems grasping the the fundamental principles of SANS 10142 with the way its written.

    The client is asking how come did they get a CoC when they bought the house with these circuits like this, I have said it was probably overlooked. But that is not all, there is 1.5mm sq cable supplying a sub db in the flat onto which a geyser and electric stove is installed! And this is in plush suburbs of Jhb. Replacing that with 10 mm sq,

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