Wiring distributuion box

[Gnome]

125% of 16a = 20a so in essence, the regulations make it impossible to fit more than a 20a breaker on a plug circuit unless all the plug outlets can handle more than 16a (which normal sockets can't).
Or each plug is protected by a circuit breaker.

 

[Geoff.D]

125% of 16a = 20a so in essence, the regulations make it impossible to fit more than a 20a breaker on a plug circuit unless all the plug outlets can handle more than 16a (which normal sockets can't).
Or each plug is protected by a circuit breaker.

Thanks for posting the relevant sections of the regulations. I am not at home and do not have access to my copy.
The latest amendments are in the 2017 version, these deal mainly with alternative power sources, such as standby generators, solar power systems etc.

Note that older installations that complied with previous versions of the regulations where 4 mm square cabling was used for power sockets, allowed for 30A CBs.

What is important also, is that as is indicated in the quoted regulations you can install a power socket on smaller cables provided the correct sockets, CBs are used and that the sockets are suitably marked for the purpose intended.

My home has a separate circuit for freezers and fridges, another for the stoves, geezer, other water heaters, as well as a dedicated circuit for security systems , none of which go via the E/L unit.

 

[Pitbull]

Reading this thread all I can think of: "Jusus this is going to end badly and he won't be able to claim at all if the house burns down due to not being qualified to wire the DB board"

 

[JerryMungo]

Reading this thread all I can think of: "Jusus this is going to end badly and he won't be able to claim at all if the house burns down due to not being qualified to wire the DB board"

It will still cost to have it inspected and the certificate issued, but less than having the whole place rewired. That said, it all depends on what you bill yourself out at. It might be more.

 

[Swa]

Note that older installations that complied with previous versions of the regulations where 4 mm square cabling was used for power sockets, allowed for 30A CBs.

So how does this apply to fitting a new DB? Nothing in the circuit itself has changed so it should still be compliant. The way I see it it's about the wire and not the socket itself. 4mm wire can handle 36A so with a factor of 0.71 it can safely do just above 25A.

 

[Swa]

How would you connect wires except through a wire nut? Also there's a pair going to the garage/outbuildings. Would the best place to connect them be through the E/L? I'm guessing if I go that route it doesn't need a separate E/L.

 

[Goobie]

I would bypass the E/L for the wire going to the outbuilding then add a sub DB with its own E/L in the outbuilding.

I prefer having a sub DB in a garage/outbuilding especially if you are welding etc from that sub DB; if it overloads it trips just the garage and not the entire house.

 

[Swa]

I would bypass the E/L for the wire going to the outbuilding then add a sub DB with its own E/L in the outbuilding.

I prefer having a sub DB in a garage/outbuilding especially if you are welding etc from that sub DB; if it overloads it trips just the garage and not the entire house.

There is a DB but it doesn't have an E/L. If I wire it from the main E/L it doesn't need a separate one unless I'm missing something. Remember the E/L trips on ground leakage and not on overload. A major overload is going to trip the main DB anyway but that has never happened.

 

[Geoff.D]

I agree with the previous comment. Extend power to a sub DB board in the out buildings and then install another E/L unit in that sub DB .

If you should choose not to do so, then you can rely on the main E/L unit in the main board, BUT ensure that the sub DB board has at least a double pole isolator installed before any distribution to power sockets etc in the outbuildings.

 

[Swa]

I agree with the previous comment. Extend power to a sub DB board in the out buildings and then install another E/L unit in that sub DB .

If you should choose not to do so, then you can rely on the main E/L unit in the main board, BUT ensure that the sub DB board has at least a double pole isolator installed before any distribution to power sockets etc in the outbuildings.

Exactly what do you mean by "extend" power? It was running from the main switch to the sub-DB but there's no E/L. Or are you saying I should extend it directly to the DB and then install the mains and E/L, but then it will no longer be a sub-DB?

 

[JerryMungo]

Exactly what do you mean by "extend" power? It was running from the main switch to the sub-DB but there's no E/L. Or are you saying I should extend it directly to the DB and then install the mains and E/L, but then it will no longer be a sub-DB?

AFAIK he's saying that if you extend (run a cable) to a remote building, rather put in a DB at the remote building with it's own EL. I'd do the same. Earth faults at the remote building won't affect the main home. Rather spend the money on a separate EL IMO. If you don't, make sure you put in a double pole isolator at the outbuilding DB side right after the input from the main building before you run circuits to sockets or lights.

In your case you already have the DB so either put in EL or a double pole isolator if you don't already have one (first in line in the circuit).

 

[Geoff.D]

AFAIK he's saying that if you extend (run a cable) to a remote building, rather put in a DB at the remote building with it's own EL. I'd do the same. Earth faults at the remote building won't affect the main home. Rather spend the money on a separate EL IMO. If you don't, make sure you put in a double pole isolator at the outbuilding DB side right after the input from the main building before you run circuits to sockets or lights.

In your case you already have the DB so either put in EL or a double pole isolator if you don't already have one (first in line in the circuit).

Exactly what do you mean by "extend" power? It was running from the main switch to the sub-DB but there's no E/L. Or are you saying I should extend it directly to the DB and then install the mains and E/L, but then it will no longer be a sub-DB?

Correct +1 thanks

 

[Swa]

AFAIK he's saying that if you extend (run a cable) to a remote building, rather put in a DB at the remote building with it's own EL. I'd do the same. Earth faults at the remote building won't affect the main home. Rather spend the money on a separate EL IMO. If you don't, make sure you put in a double pole isolator at the outbuilding DB side right after the input from the main building before you run circuits to sockets or lights.

In your case you already have the DB so either put in EL or a double pole isolator if you don't already have one (first in line in the circuit).

Yeah but do you connect it directly or to the main switch (not the one outside)? Latter would be easier. I'm also still looking for a way to connect 4 or 5 wires and can only see a busbar as a safe option. I've seen boxes with multiple ones but the one I was able to get only has an earth and one neutral which rather limits the installation.

 

[JerryMungo]

Yeah but do you connect it directly or to the main switch (not the one outside)? Latter would be easier. I'm also still looking for a way to connect 4 or 5 wires and can only see a busbar as a safe option. I've seen boxes with multiple ones but the one I was able to get only has an earth and one neutral which rather limits the installation.

Plenty of options for connectors - just get 60a terminal blocks.
Connect via your home's isolator. The only reason not to do it is if you want to be able to isolate the home without isolating the outbuilding - but then I would get a second mains isolator on the home side so that you can isolate it from the main home as well as on the outbuilding side.

 

[Gnome]

What is important also, is that as is indicated in the quoted regulations you can install a power socket on smaller cables provided the correct sockets, CBs are used and that the sockets are suitably marked for the purpose intended.

Assuming that at the maximum current of the breaker rating, the voltage drop is no more than 5% as per the regulations.
There is also a temperature requirement of the cable and derating based on where the cable is installed.

The reason decent electricians use 2.5mm for plugs is likely because if you calculate the value it'll become nearly impossible to comply with all the conditions in the regulations and use less than 2.5mm.

At least for 16A plugs.

So how does this apply to fitting a new DB? Nothing in the circuit itself has changed so it should still be compliant. The way I see it it's about the wire and not the socket itself. 4mm wire can handle 36A so with a factor of 0.71 it can safely do just above 25A.

The new regulations do not allow it.
Altering a new installation means you need to comply with the latest version of the regulations.
Fitting a new distribution board obviously means altering the installation.

Your breaker cannot be rated more than 125% of the lowest rated socket outlet on the circuit run.
Since SA doesn't have sockets more than 16a, the absolute maximum is 20 amps.

 

[Geoff.D]

That is correct. Not for normal power sockets but for specialised circuits. Such as security systems.

BUT here is the real problem . property developers housing estate developers and the like do terrible things using barely acceptable components and cabling that scrapes through the regulations leaving future owners of those properties with issues that can take years to resolve.

Like a place we saw recently only equipped with the new 5A sockets only and therefore leading to power circuits done with 10A breakers and 1.5 mm square cabling!

 

[Swa]

The new regulations do not allow it.
Altering a new installation means you need to comply with the latest version of the regulations.
Fitting a new distribution board obviously means altering the installation.

Your breaker cannot be rated more than 125% of the lowest rated socket outlet on the circuit run.
Since SA doesn't have sockets more than 16a, the absolute maximum is 20 amps.

Well that is where the controversy is as there is no definition of what an alteration is and whether or not it's only the alteration or the whole installation that must be certified. Some people seem to think that changing like for like is not an alteration while others seem to think it is or should be. Then there's even those thinking the addition of an earth wire where there wasn't one before to make it safe isn't an alteration.