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Thread: Mixed circuits

  1. #1
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    Mixed circuits

    Lets talk about mixed circuits ... what is a mixed circuit?

    Can a Sub DB ... a plug circuit ... a light circuit ... an isolator feeding a fixed appliance ... all be fed from a single breaker ... labelled "mixed circuit"

    Lets say we have an aircon on a isolator ... a couple of socket outlets and a couple of lights connected directly to a day/night switch ... all fed from a 20 amp MCB using 2,5 mm wire ... labelled "mixed circuit" ?

    Share some of the common example that you have experienced and see what everyone thinks?

    It would be handy to have someone on the "technical board" from the ECA or ECB or even better SANS offering some feedback.

    Thins kind of discussion is very important in our industry if we want to improve the industry.

    I encourage the youngsters who are busy studying the Regs to become an installation or master electrician to join in these discussion ... I ask a lot of what some people would refer to as really dumb question ... and I am master electrician with many many many years of hands on experience (40+ years) ... yet I still have so much to learn ... everyday I go to work I learn something new ... I am faced with new challenges ever single day ... if you dont ask you will never know.

    I am glad to see sparks replying to posts ... the industry can only improve if we all make an effort.
    Comments are based on opinion...not always facts....that's why people use an alias.

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    Diamond Member Justloadit's Avatar
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    What about a circuit breaker supplying lights on a day/night switch and a gate motor.

    This happens in older homes where there was no provision made for electric gate motors, but have outside lights
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    HI

    Thought I would place the relevant regulation down to help and I have highlighted relevant bits that stick out in red.


    6.15.4 Mixed loading of circuits
    6.15.4.1 Except as allowed in 6.15.4.2, 6.15.4.3 and 6.16.3.2.3, there shall
    be no mixed loading of circuits.
    6.15.4.2 Except as required in 6.16, a non-dedicated single-phase circuit that
    has overcurrent protection rated at not more than 20 A may supply a mixed
    load of a combination of any socket-outlets rated at not more than 16 A,
    luminaires and fixed appliances.
    NOTE 1 The number of points need not be limited, but the diversity of loads should be
    considered.
    NOTE 2 Mixed circuits should be carefully considered since this may result in nuisance
    tripping.
    6.15.4.3 Socket-outlets rated at 16 A or more that are connected to circuits
    with mixed loading shall comply with the earth leakage requirements of 6.7.5.
    NOTE 1 See 7.1 for the conditions under which a socket-outlet may be installed in a
    bathroom.
    NOTE 2 See 6.16.1.6 for the conditions under which a socket-outlet may be used for
    the connection of fixed appliances.


    6.16.3.2.3 A cooking appliance circuit may also supply one socket-outlet if
    the rating of the socket-outlet does not exceed 16 A and if the following are all
    contained in one control unit (see also 6.15.4.1):
    a) the socket-outlet;
    b) an earth leakage protection device including overcurrent protection for
    protecting the socket-outlet; and
    c) the switch-disconnector required for the cooking appliance (see 6.16.1).

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    Can a Sub DB ... a plug circuit ... a light circuit ... an isolator feeding a fixed appliance ... all be fed from a single breaker ... labelled "mixed circuit"
    Not a sub DB - specifically states sockets , Luminaries and fixed appliances ( 6.15.4.2) - The C/breaker cannot be rated at more than 20 Amps
    The 20 Amp stipulation would exclude stoves - Aircons rated above 16Amp ( 6.16.4.1.1) need to be on dedicated circuit

    Lets say we have an aircon on a isolator ... a couple of socket outlets and a couple of lights connected directly to a day/night switch ... all fed from a 20 amp MCB using 2,5 mm wire ... labelled "mixed circuit" ?
    You would need to take into account 6.15.4.2 note 1 and note 2 - Needs to be carefully considered

    I would use a mixed load circuit for a swimming pool if getting access to the DB was a problem . The " pool DB" is actually a motor control center for the fixed appliance , being the pool.The minute I feed lights ( I would put the pool light as part of the pool) or plugs from the pool DB then it is no longer a motor control center but automatically becomes a sub DB and can no longer be on the circuit.

    I would mix load to a gate motor and lights at the boundary wall.

    Would use it for a garage that is stand alone and used for parking a car and using a socket for the vacuum cleaner. If the garage is going to be a laundry or workshop , then I would think twice.

    Would use for a braai Lapa set up in the middle of the garden .

    Personally think they are valid uses for mix loading but would not use it for general use and not trying to cut prices .The note about taking into account diversity and nuisance tripping are going to come back to haunt.

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    Further to above
    Definitely not allowed on mixed circuits would be

    6.16.2.2 Dedicated circuits shall be provided for water heaters and there may
    be more than one water heater on each circuit.

    6.16.3.2.1 A dedicated circuit(s) shall be provided for cooking appliance(s)
    that are rated at more than 16 A.

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

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    Dave A (17-Oct-21)

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    Diamond Member AndyD's Avatar
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    I've seen 'mixed circuits' a few times in DB's where physical space is an issue and they've shoved a light circuit and a radial socket circuit into the same 20A MCB as a quick fix..
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    Quote Originally Posted by AndyD View Post
    I've seen 'mixed circuits' a few times in DB's where physical space is an issue and they've shoved a light circuit and a radial socket circuit into the same 20A MCB as a quick fix..
    So long as the circuit breaker is rated for the thinner cable ... I have seen 16 amp breakers used for this type of application.
    Comments are based on opinion...not always facts....that's why people use an alias.

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    A quick question ... can you use a 16 amp breaker with 1.5 mm wire for a plug circuit ... I am sure there is something in the regs about 2.5 and plug circuits.
    Comments are based on opinion...not always facts....that's why people use an alias.

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    by the way thanks for the responses ... I have been hectic busy and it doesnt look like it is going to ease anytime soon/.

    GCE thanks for attaching the regs.
    Comments are based on opinion...not always facts....that's why people use an alias.

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    Quote Originally Posted by ians View Post
    A quick question ... can you use a 16 amp breaker with 1.5 mm wire for a plug circuit ... I am sure there is something in the regs about 2.5 and plug circuits.
    Reg 6.15.3.b Single phase circuits that only supply socket outlets rated at 16A shall use conductors that are rated at not less than 16A.


    The only time that the rating of 1,5mm wire dips below 16A, is if it is in conduit inside a wall. ( 14,5A )
    In all the other installation methods, the rating is above 16A.

    So to answer your question, it is perfectly in order to use 1,5mm with a 16A breaker if the circuit is not in conduit in a wall.

    Peace out .. Derek

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