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Thread: Incoming Supply and Prepaid metering.

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    Incoming Supply and Prepaid metering.

    I have come across many prepaid meters installed by the municipality that is quite sub-standard. They are mostly mounted next to the existing distribution board. and a piece of concrete plaster knocked out of the wall or a slot cut in the DB cover to route the mains through them. If the mains are too short, an extra piece of wire is joined on and the connection taped up. The part that concerns me most however is the fact that they usually feed the existing main breaker from the load (output) side. Although this is probably not illegal, it is not the conventional way. In my experience the main switch was supplied from the top and then a bridge inserted from the bottom (load) side to supply the rest of the installation on the top (supply side). Most breakers are not marked, so I assume that any side could be used for supply. It seems that the reason they do this is is to save space in very crowded distribution boards. In a few instances I have also come across double pole isolators supplied from the "conventional" load side. Is this practice acceptable? (Reg.6.8.2.3)

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    Morning Henthal

    This is a very interesting point.

    I don't believe that you would be able to use any side as a 'live' or 'load' side unless clearly indicated by the manufacture.

    I have attached a picture of the inside of a circuit breaker and you will see label 12 which is the bottom is the output/load.

    I know that most breakers don't have live and load on them but they do have a diagram on them and normally numbers, 1 on to then 2 underneath on the diagram and so on.

    Click image for larger version. 

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    Thank you SeanM. The interesting part is that I don't think it will make a difference to the tripping. The load or overload will be sensed through the whole conductor, load or supply side. I am more concerned about the ethical issue. We are so used to the conventional wiring that someone may assume a wire on the load side is "dead" with the breaker switched off. I just feel that it is bad practice not to follow convention. Also, I am not sure if all breakers are insensitive to the way you wire them. There may be a technical issue of which I am not aware.

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    Conventions vary from place to place, in SA residential installs it's the norm to have supply at the top and load at the bottom, in the UK for example it's vice versa and in the USA the breakers are often mounted horizontally in 2 columns with the busbar in the centre which is similar to them being supplied from the top in this country. As Sean mentioned, whether it's electrically acceptable to supply a circuit breaker from the top or the bottom would depend on the diagram on the breaker itself and the manufacturers data sheet information, some are designed to have the supply on either side and some only from one side.
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    Sorry it took me so long to respond Andy. Yes, I am aware of the trends in the UK and USA. I think the Germans also Use the UK method. The breakers all seem to be versatile and very few are marked to indicate load side. I just do not think that it is sound practice to wire your breakers in opposition to the norm. No matter in which country you are. Reg. 6.8.2,3 seems quite clear on this. If maintenance is performed and the maintenance personnel are not wide awake, nasty accidents can result. Not mentioning expensive damage to test instruments. I think it is poor workmanship to wire in opposition to the norm.

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    The reg states it's not recommended to deviate from the 'norm' of supply at the top and load at the bottom but it can be done if the device manufacturer approves of that wiring orientation, it's labelled accordingly and without visible contradiction.

    I'm not really buying into it being poor workmanship, the counter argument would be it's downright dangerous workmanship by any electrician who damaged his equipment or himself because he didn't test properly for safe isolation before continuing with other tests. There's also an argument that establishing or even favouring local 'norms' like this in the regs could be at least partly responsible for making electricians 'assume' things rather than establishing things beyond doubt by testing.....hence even recommending a norm and then giving acceptable exceptions in the following sentance is part of the problem rather than the solution.

    I'd agree I don't see any reason it should be done in a standard domestic DB but it's fairly common practice in commercial or industrial distribution and control panels and also in internal machine wiring.
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    I was specifically referring to domestic installations. I do not think it is good practice to divert from the normal practice just because it is easier and you do not have to extend the wires.
    I do not suffer fools lightly, but at least afford them a fighting chance (referring to assumptions). I think there are very few qualified electricians that had not at one time or another made the expensive mistake of testing Voltage on the Ohms scale. Doing this inadvertently makes it so much worse. I, for one, will stick to the norm.

    Regards
    Henthel

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    Hi Henthal

    In your opening post you mention both a breaker and a main switch. Is the mains an isolator or circuit breaker? We were taught supply in top of circuit breakers but supply in bottom of isolators. Not sure if this is still the norm these days but that's what we were taught as appies in the 70's and I've been doing it like that ever since.

    Derek

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