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House and DB wiring sizes


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Hi Guys

What is typically the wiring sizes used in house wiring and DB wiring?

1) The size of wiring used in light and plug fittings

2) The size of the wiring used in DB for stuff like geyser and oven.

3) What is the best way to bridge wiring on DB circuit breakers when using the thick wiring (geyser/oven) when you need two of the thick wires into one CB or even busbar+thick wire? Best practice, what is safe and what not, etc. Is there a limit (regulations) on how much stripped wire can stick out above the CB, etc.

Just need to confirm based on what I have seen in my DB. 

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57 minutes ago, Tsa said:

Hi Guys

What is typically the wiring sizes used in house wiring and DB wiring?

1) The size of wiring used in light and plug fittings

2) The size of the wiring used in DB for stuff like geyser and oven.

3) What is the best way to bridge wiring on DB circuit breakers when using the thick wiring (geyser/oven) when you need two of the thick wires into one CB or even busbar+thick wire? Best practice, what is safe and what not, etc. Is there a limit (regulations) on how much stripped wire can stick out above the CB, etc.

Just need to confirm based on what I have seen in my DB. 

1)  1.5 and 2.5 mm

2) depends on power rating of both: 2.5 or 4 mm (see attached)

3) Use cross connecting link (solid copper link) for as many CBs as required.

Aberdare_649.pdf

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10 hours ago, Tsa said:

Hi Guys

What is typically the wiring sizes used in house wiring and DB wiring?

1) The size of wiring used in light and plug fittings

2) The size of the wiring used in DB for stuff like geyser and oven.

3) What is the best way to bridge wiring on DB circuit breakers when using the thick wiring (geyser/oven) when you need two of the thick wires into one CB or even busbar+thick wire? Best practice, what is safe and what not, etc. Is there a limit (regulations) on how much stripped wire can stick out above the CB, etc.

Just need to confirm based on what I have seen in my DB. 

Good afternoon Tsa

As per SANS 10142:2006 the maximum allowable current for PVC insulated cables in a single phase installation when the cable is enclosed in conduit fixed to a wall or trunking fixed to a wall are as follows. For Multi-Phase the currents are lower.

For GP cable - That is the individual Black, Red, Blue, White, Yellow, Yellow and Green cables which are not bundled together with a second insulation over the individual cores and with 1 solid core or multiple thick strands

1.5 mm2: 17.5A, 2.5 mm2: 24A, 4.0 mm2: 32A, 6.0 mm2: 41A, 10.0 mm2: 57A, 16.0 mm2: 76A, 25.0 mm2: 101A

For Surfix and Twin and Earth  - A cable with more than 1 cores with 1 solid core or multiple thick strands individually insulated with a second insulation over the individual cores

1.5 mm2: 16.5A, 2.5 mm2: 23A, 4.0 mm2: 30A, 6.0 mm2: 38A, 10.0 mm2: 52A, 16.0 mm2: 69A, 25.0 mm2: 90A

The maximum cable operating temperature are not allowed to exceed 70 degree Celsius, if the temperature exceeds 70 degree Celsius a thicker cable must be used.

Cabtyre -A flexible cable with thin strands used for appliances, power tools, extension leads etc are not allowed in a DB.

The gap between the clamp of the MCB and the start of the insulation may not exceed 2mm.

There is also a limit of the number of cables entering or leaving an MCB and that limit is 3.

Another point that is misunderstood is that the MCB protects the cable and not the load supplied by the cable.

If a cable leaving the DB is joined and the cable that is joined is thicker or thinner than the other cable then the MCB must be rated for the thinner cable, for example a gate motor is to be installed and the cable leaving the house is 2.5 mm2 but you cannot get a 2.5 mm2 cable only 1.5 mm2 is available then the MCB must be rated for the 1.5mm2 cable.

Circuits are not allowed to be mixed on the MCB's eg Lights and Socket outlets on the same MCB.

Open spaces in the cover of the DB must be closed off so that you are protected from a electric shock and to keep insects, bugs, spiders, bees and wasps out of the DB.

MCB's must be marked with indelible ink or a proper label which is not easily removed.

If a DB is supplied by another DB then the sub DB and the supplying DB must be properly marked the same way MCB's are marked.

A Switch Dis-connector (isolator) must disconnect both L & N for single phase installations and all P's & N for multi-phase installations.

A 2 pole or 4 pole MCB are not allowed to be used as a switch dis-connector (isolator).

A MCB must trip all P's for multi-phase installations if there is a over current in any of the phases.

An Earth leakage must disconnect both L & N for single phase installations and all P's & N for multi-phase installations

PS CB is short for Miniature Circuit Breaker.

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Posted (edited)
On 2020/05/29 at 5:54 PM, GerhardK83 said:

Circuits are not allowed to be mixed on the MCB's eg Lights and Socket outlets on the same MCB.

I have a few interesting violations there, that even passed a recent CoC...

The laundry room is powered by a single breaker, which covers all the plugs and lights. There is a conduit running to an exterior light, and then someone siliconed/glued an extension onto this conduit to power a fish pond pump from that same circuit.

So on the face of it, there is a plug running from a light connection, but because all the lights in the room are technically running from the plugs circuit... I'm not actually sure what is wrong here, if anything. It certainly is unconventional...

I would think lights from a plug circuit is less of an issue than plugs from a light circuit.

But then, on the other end of the house where the former owner had a fridge behind the bar... there's a plug circuit running from lights... obviously more of a concern than the other way round.

So at the moment everything is safe, but not everything is right... I do however have a CoC for this mess 🙂

Here is me checking that old dangling fridge cable (and getting the definition of CoC wrong) one night during load shedding when I realised it's not powered from where I thought it was...

 

Edited by plonkster
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2 hours ago, plonkster said:

I would think lights from a plug circuit is less of an issue than plugs from a light circuit.

Yes I agree. It is perfectly fine to plug in a light into a plug. You can't do it the other way around (legally).
I guess it is all up to how the laundry is labeled in your DB?

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Posted (edited)
On 2020/05/29 at 5:54 PM, GerhardK83 said:

An Earth leakage must disconnect both L & N for single phase installations and all P's & N for multi-phase installations

So, a question around this specifically, if I have two separate DB's on two seperate incoming phases (serving completely different CBs) can each DB simply have it's own Earth Leakage, or must there be a shared Earth leakage between the two incoming phases and neutral ? E.g. a three-way EL breaker  (L1, L2, and N) ?

 

In my case, I have a DB for "critical load" with an inverter setup, and another DB for "general" load, geyser, stove ETC, fed from two different CityPower phases, with a shared neutral.

My split is simply two DB's one fed from each of the different Live phases, and each DB with it's own Earth leakage, and mains disconnectors. This seemed logical to me until I read GerhardK83's comment.

 

Edited by TheRoDent
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3 hours ago, TheRoDent said:

must there be a shared Earth leakage

I believe the shared RCD is only necessary if there are three phase loads. Then a leakage on one phase must disconnect all three (because a dropped phase on a three phase load is generally not a good thing).

Single phase get their own RCDs, and there is no upstream 3-phase RCD (otherwise a leakage on another phase trips this one as well, which will serve no purpose and be annoying as hell).

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5 hours ago, TheRoDent said:

So, a question around this specifically, if I have two separate DB's on two separate incoming phases (serving completely different CBs) can each DB simply have it's own Earth Leakage, or must there be a shared Earth leakage between the two incoming phases and neutral ? E.g. a three-way EL breaker  (L1, L2, and N) ?

In my case, I have a DB for "critical load" with an inverter setup, and another DB for "general" load, geyser, stove ETC, fed from two different CityPower phases, with a shared neutral.

My split is simply two DB's one fed from each of the different Live phases, and each DB with it's own Earth leakage, and mains disconnectors. This seemed logical to me until I read GerhardK83's comment.

Hi @TheRoDent if the supply from the utility is multi-phase and the multi-phase supply is broken down into single phase supplies then it is fine with only an earth leakage per phase, as long as the load is only a single phase load.

If the load is a multi-phase load and the load has bare metal exposed where one might get an electric shock if there is an electric fault on the load then there must be a multi-phase earth leakage installed for the multi-phase load as well.

Usually what they do in multi-phase installations is they split the incoming supply from the utility up with 5 bus-bars 3P+N+E and from there they supply 4 earth leakages 1 3P+N and 3 1P+N all wired in parallel, if you wire the earth leakages in series and there is an earth fault then the 1 with the lowest earth fault current will trip first which might be annoying and or problematic.

Your setup is correct because each of your single phase DB's are protected by a single phase earth leakage.

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On 2020/06/03 at 1:06 PM, plonkster said:

Circuits are not allowed to be mixed on the MCB's eg Lights and Socket outlets on the same MCB.

Not completely correct, unless the law has changed. Circuits may be mixed, and different size wires used on same breaker, only if the rating of the breaker does not exceed the rating of the smallest wire in that circuit, and as long as the circuit breaker is labeled correctly. In the case of mixed plug an light circuits, the breaker size may not exceed 15 Amps

EDIT: Under Correction, Ive done this stuff years ago.. 

 

On 2020/05/29 at 5:54 PM, GerhardK83 said:

Circuits are not allowed to be mixed on the MCB's eg Lights and Socket outlets on the same MCB.

 

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1 hour ago, GerhardK83 said:

Hi @TheRoDent if the supply from the utility is multi-phase and the multi-phase supply is broken down into single phase supplies then it is fine with only an earth leakage per phase, as long as the load is only a single phase load.

Your setup is correct because each of your single phase DB's are protected by a single phase earth leakage.

Thanks so much for confirming! This is indeed the case. Each phase is split to seperate DB's and each (non-mixed) phase only powers a certain set of CB's.

Now, to add to a bit of the line of questioning (many thanks for your feedback so far). Is it OK for sub-db's hanging off the individual phases to also have an Earth leakage CB? That seems logical as well...

 

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Posted (edited)
1 hour ago, Jaco de Jongh said:

Not completely correct, unless the law has changed. Circuits may be mixed, and different size wires used on same breaker, only if the rating of the breaker does not exceed the rating of the smallest wire in that circuit, and as long as the circuit breaker is labeled correctly. In the case of mixed plug an light circuits, the breaker size may not exceed 15 Amps

This seems logical as well. I don't see any particular reason to have to "plug in a light" into a socket, in order to not have lights and plugs mixed.

 It provides no protection above the normal CB? Of course, earthing for plugs are important, so I suppose that is a "general" reason for not mixing them, but if a circuit is fully earthed to the point of a plug, and then powers a light from there-on, I don't see how it would be different from having a non-earthed light circuit with a seperate CB ?

Again, not an expert around wiring code, but it seems logical to be able to mix lights and plugs on a CB, as long as all the plugs are properly wired with an earth ?

As for the mixing of wire-guages, it also seems sensible that if a single CB protects different guage circuits, that it has to be rated for the thinnest guage wire.

 

Edited by TheRoDent
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On 2020/05/29 at 5:54 PM, GerhardK83 said:

A 2 pole or 4 pole MCB are not allowed to be used as a switch dis-connector (isolator).

I'm busy looking at SANS 10142-1: 2017, but I can't find this requirement anywhere. Do you perhaps recall under which section it is stated?

 

 

On 2020/05/29 at 5:54 PM, GerhardK83 said:

The gap between the clamp of the MCB and the start of the insulation may not exceed 2mm.

Looking at my main DB I see multiple violations of this, and it has passed two CoCs that I know of. Is this a SANS 10142 requirement?

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