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Thread: House main DB Modifications?

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    House main DB Modifications?

    Afternoon All,

    I have been silently "lurking" on this forum for quite some time and found the advise to be given really helpful and I myself have learned quite a bit as well.
    Now it's my turn - I have a query for the learned members on this forum regarding my own house main DB.

    The DB in the house that I bought 9 years ago has always been an eyesore but I've managed to successfully pretend it didn't exist until recently. How it managed to get a CoC when I bought it is a mystery but considering the previous owner was the estate agent and her husband the conveyancing attorney, I suspect some special arrangements were made.

    After a recent heavy and damaging downpour in my town, the main incoming municipal cable was damaged. A colleague of mine, the local sparky, who did the repair mentioned that I really need to sort my DB out - he's told me this on a few occasions.

    Now the questions:

    1. I have too many breakers for the existing panel, it has been modified as the house was extended to squeeze a few extra's in. I am considering placing a surface mount box on top of the existing flush mounted box - probably a larger dimensioned box to fit two rows of breakers. Is this allowed?

    2. Leading on from the above, some of the circuits (lights, plugs) have two wires out of the single pole breaker - is this allowed? (Another reason to fit a bigger box. Also to incorporate additional ELCB's to eliminate nuisance tripping, which I have occasionally)

    3. As I anticipate the wiring to be too short, is it legal to fit a terminal rail into the DB, which will allow the use of shorter, extension pieces from the CB's to this terminal rail? (Terminals such as Weidmuller SAK 2.5 or 4 or equivalent legal terminals - I'm an Instrument Tech by trade, hence my familiarity with using terminals in JB's.)

    I hope the above makes sense?

    Many thanks,
    Shaun.

    p.s. - I have no intention of doing the work myself. I just want to be able to make an educated decision when scoping the job.

  2. #2
    Diamond Member AndyD's Avatar
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    Comments in red;

    Quote Originally Posted by desertburner View Post
    Afternoon All,

    I have been silently "lurking" on this forum for quite some time and found the advise to be given really helpful and I myself have learned quite a bit as well. Always good to see a lurker spring to life
    Now it's my turn - I have a query for the learned members on this forum regarding my own house main DB.

    The DB in the house that I bought 9 years ago has always been an eyesore but I've managed to successfully pretend it didn't exist until recently. How it managed to get a CoC when I bought it is a mystery but considering the previous owner was the estate agent and her husband the conveyancing attorney, I suspect some special arrangements were made.

    After a recent heavy and damaging downpour in my town, the main incoming municipal cable was damaged. A colleague of mine, the local sparky, who did the repair mentioned that I really need to sort my DB out - he's told me this on a few occasions.

    Now the questions:

    1. I have too many breakers for the existing panel, it has been modified as the house was extended to squeeze a few extra's in. If your circuit breakers are older generation it may be possible to replace the breakers with new ones which are smaller in width, this alone may free up sufficient space for the extra circuits. Maybe post a couple of photos of the DB if you can.

    I am considering placing a surface mount box on top of the existing flush mounted box - probably a larger dimensioned box to fit two rows of breakers. Is this allowed? Yes, it can be done but it's not in the realms of DIY work so maybe have a discussion about it with your sparky. Is it not possible to remove the old DB and neatly cut in a larger new flush mount enclosure? Surface mount DB's tend to be obtrusive.

    2. Leading on from the above, some of the circuits (lights, plugs) have two wires out of the single pole breaker - is this allowed? Difficult to say without more details but generally this would be bad design at best and downright non-compliant at worst and most times I've come across this it's the latter.

    (Another reason to fit a bigger box. Also to incorporate additional ELCB's to eliminate nuisance tripping, which I have occasionally) One word....testing!! Again, another reason you need to discuss the design with a sparky. The majority of nuisance tripping faults are because of faults on circuits and/or appliances. Without testing and remedying of faults there's a high liklihood that adding earth leakage circuit breakers won't cure the problem.

    3. As I anticipate the wiring to be too short, is it legal to fit a terminal rail into the DB, which will allow the use of shorter, extension pieces from the CB's to this terminal rail? (Terminals such as Weidmuller SAK 2.5 or 4 or equivalent legal terminals - I'm an Instrument Tech by trade, hence my familiarity with using terminals in JB's.) Extending of circuits can be done using DIN mount terminals in some circumstances but properly indent-crimped ferrules insulated with 2 layers of heatshrink would be a better result in my (old fashioned) opinion, especially if access to the connections is limited or unavailable in the future. Wago connectors or the Helacon or similar are also great although somewhat bulkier, just depends on space and personal preference. Some of the DIN mount terminal blocks aren't good for single solid conductors, they're primarily designed for panel wire which is fine stranded.

    I hope the above makes sense?

    Many thanks,
    Shaun.

    p.s. - I have no intention of doing the work myself. I just want to be able to make an educated decision when scoping the job.
    _______________________________________________

    _______________________________________________

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    Thanks for comments AndyD, much appreciated.
    My responses below:

    1. I have looked at different breakers, since my DB is a mixed bag but they are mostly the miniature size. My aircons are also SP which I believe is incorrect? In any case, changing the breakers is unfortunately not going to give me the quick win I was hoping for.
    The old DB is built into the wall - hence my calling it flush mount. It is also inside a cupboard space - probably also illegal - so cutting may also not be an option. Since it is out of plain sight, I thought a surface mount may suffice?

    2. As for 2 circuits fed from a breaker, I suspect it was due to alterations and lack of DB space that led to this. I have no intention of DIY'ing any of this - I just want to know the legal implications so I can have an educated discussion with the electrician.
    The reasoning for additional ELCB's is because I have already had one fitted for the outbuildings due to damp weather causing the whole house to trip because of a garden light.
    Since it's a reasonably large house with many PC's, I thought that more individual protection may be better and more in line with what seems to be accepted practice? The sparky seems to think along those lines as well. (So no actual problem that I'm trying to hide - just trying to think ahead.)

    3. Thanks for the heads up regarding ferrules and heat shrink - never thought of that.

    Regards,
    Shaun.

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  4. #4
    Site Caretaker Dave A's Avatar
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    Quote Originally Posted by desertburner View Post
    2. Leading on from the above, some of the circuits (lights, plugs) have two wires out of the single pole breaker - is this allowed?
    6.1.5 of SANS 10124-1 places a general limit of 3 conductors connected to any one terminal (provided that the terminal has the correct rating).

    6.6.1.11 of SANS 10124-1 effectively limits the number of neutral conductors connected to a terminal to one where the cross section of any one of those conductors exceeds 4mm2.

    Quote Originally Posted by desertburner View Post
    My aircons are also SP which I believe is incorrect?
    Per 6.16.1.4, this is not a problem provided there is a disconnecting device within 1.5 meters of the fixed appliance.

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    Thanks Dave A, much appreciated.

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    i would take a surface db , cut out as much of the back plate as possible and mount it directly over the flush db. if you design it nicely a lot of the wiring will be long enough. as dave mentioned ,3 wires per terminal are acceptable for live conductors . i would install at least 2 earth leakage relays excluding one for a pool or outbuildings etc. only once the job is complete then start looking for earth faults.
    i have done many db upgrades where the nuisance earth faults have disappeared after adding ELCB's. its the accumalative earth fault current that pushes it over 30ma.

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    Good advice bergie, thanks. Will definitely consider it.

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    Hi, I'm a semiskilled working with a registered electrician but he doesn't explain much.Recently we where working at a church building which applied for 3phase supply and he used 40A 4pole main breaker to feed 4 subDBs all with 63A double pole main breakers,he says the transformer size of Eskom determines the Main breaker i.e 40A... I really don't understand as I should. Can someone explain

  9. #9
    Diamond Member AndyD's Avatar
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    Supplying 60A subDB's from a 40A main would usually be poor design. In the case of an overload the main will trip first causing the fault to be cleared but also causing unnecessary power outage on the other two subDB's.
    Circuit breakers within a DB are generally sized according to the current carrying capacity of the final circuit cable they're supplying, which is calculated from the conductor size, the cable length and the installation method.
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