Size of cables in ducting

[Cashboy]

I am put the ducting in the walls.

I have noticed that there are basically three main sizes of round plastic ducting:

 

3/8" = 15mm   = outside diameter about 18mm

1/2" = 18mm  = outside diameter about 22mm

3/4" = 20mm = outside diameter about 26mm

 

I need to run the mains cable ( 3 No 16mm ) in ducting.  

Will I manage to get those in the 1/2"  ?

 

I ask because I had to drill through the concrete floor and keep hitting steel and don't want to chop out the steel but can get the 1/2" through no problem.

 

On the 4,500 watt electric shower I am going to use ( 3 N0 4mm) in ducting.

Will I manage to get those in the 3/8" ducting.  ?

 

I ask this because I have to chase the bathroom ducting in those small clay walls so don't want to weaken the wall

 

Can I get 6 No 16mm cables in 3/4" ducting 

 

 

 

 

 

 

[carlyai]

This may not be much help but from what I can remember the white plastic ducting is not as high as it is wide. I think you will gave trouble with the .5" ducting, specially with bends etc. I'd get a metre of the cables and go to an electrical shop and see if they will fit in the ducting. There's also a heat factor that may need to be considered when you lay cables in ducting, so I would go for a ducting size that lets the cables lay comfortably in it. 

Someone will probably come along who i working with cables and give you an exact answer. 

Edited May 3, 2020 by carlyai
Sorry, I see you are using that round white plastic ducting. Another thought may be to use 3 conductor NYY cable then you probably won't need the ducting.

[Crossy]

1 hour ago, Cashboy said:

I need to run the mains cable ( 3 No 16mm ) in ducting.  

Will I manage to get those in the 1/2"  ?

 

You won't get one 16mm² in a 1/2" duct/conduit and get it to go round any bends.

 

16mm² VCT is 8mm outside diameter.

 

Are you talking about conduit (round) or trunking (rectangular)?

 

[Crossy]

1 hour ago, Cashboy said:

Can I get 6 No 16mm cables in 3/4" ducting 

 

What on earth are you feeding with that lot?

[bankruatsteve]

1 hour ago, Cashboy said:

I ask this because I have to chase the bathroom ducting in those small clay walls so don't want to weaken the wall

Most (all?) Thai construction doesn't have load bearing walls, so you don't have to worry about that.  But, I've never heard the term "small clay wall".  Does your bathroom have different wall construction than the rest of your house?

[Crossy]

9 minutes ago, bankruatsteve said:

But, I've never heard the term "small clay wall".

 

I assume he means the small Thai bricks which tend to have more mortar than brick ????

 

@Cashboy I wouldn't worry about weakening the walls, as Steve notes it's not load bearing anyway and in reality most of the actual strength comes from the render.

[Cashboy]

OMG

 

I only have lying around 2.5mm and 1.5mm cable.

I can see that I can easily get 6 x 2.5mm through the 1/2" (15mm) SCG round plastic conduit.

 

However I have no 4.0mm (for shower) or 16mm cable ( I don't mean that aluminium cable from the pylon) but the copper cable to check.

No bends expected in the 4.0mm or 16mm or if I did was going to use that flexible plastic ducting.

 

In response to questions; the reason I was thinking of 5 x 16mm through 3/4" was the government mains coming in and generator mains coming in.

 

The, what I termed "clay bricks" are those small little bricks they use in bathrooms.  The rest of my house I used 15cm G Con blocks (Thermalites to British).

 

Ducting pipes are all round.

 

I am correct with 16mm copper for mains in with the 50 Amp government supply as I read that 1l6mm is good up to 80 Amp and if I recall that was quite common in Do Home, Global House etc.  I am talking about the single 16mm cable rolls available in different colours.

 

 

Edited May 3, 2020 by Cashboy

[Cashboy]

1 hour ago, Crossy said:

 

You won't get one 16mm² in a 1/2" duct/conduit and get it to go round any bends.

 

16mm² VCT is 8mm outside diameter.

 

Are you talking about conduit (round) or trunking (rectangular)?

 

I do not need to go round any bends, just a short straight 3 meter run from a 100 amp switch through a concrete floor into a consumer unit.

[bankruatsteve]

17 minutes ago, Cashboy said:

In response to questions; the reason I was thinking of 5 x 16mm through 3/4" was the government mains coming in and generator mains coming in.

Do you have 3-phase?

 

What size generator are you planning? 16mm² would be about right for 15kVA single phase.

Edited May 3, 2020 by bankruatsteve

[Crossy]

What's confusing me is the need for three x 16mm², single phase would need 2 plus a reduced ground, 3-phase would need 4 plus ground unless it's a 380V machine.

 

Anyway for 3 x 16mm² VCT you're looking at at least a 1.25" tube (no bends). Could you drill for three (or however many) 1/2" tubes and run one wire in each? 

 

In reality, I'd just cut the re-bar, you're not going to significantly weaken anything.

 

Our incoming supply (16mm2 x 2) runs down the wall in 2.5" square plastic trunking (there's other stuff in there too). Done carefully it's neat and easy if you want to get another cable in.

[bankruatsteve]

30 minutes ago, Cashboy said:

The, what I termed "clay bricks" are those small little bricks they use in bathrooms.

You might consider running the conduit on the outside and come in through a hole.  Cutting a chase through those bricks is a real bitch.

[bankruatsteve]

9 minutes ago, Crossy said:

In reality, I'd just cut the re-bar...

I'll bet more than just me would love to hear how to do that.  ????

[Crossy]

4 minutes ago, bankruatsteve said:

I'll bet more than just me would love to hear how to do that.  ????

 

Depends how big it is, in a floor it will likely just be mesh, cut it with a big pair of bolt cutters.

 

If it's a column or beam you shouldn't be doing anything to it, run round the outside.

[Cashboy]

40 minutes ago, bankruatsteve said:

Do you have 3-phase?

 

What size generator are you planning? 16mm² would be about right for 15kVA single phase.

Single phase !

Mains is government 50 Amp single phase ( live, neutral and earth)

and generator would probably only be a 6 kilowatt single phase (live, neutral and earth)

Hence 6 cables or wires.

[Cashboy]

21 minutes ago, Crossy said:

 

Depends how big it is, in a floor it will likely just be mesh, cut it with a big pair of bolt cutters.

 

If it's a column or beam you shouldn't be doing anything to it, run round the outside.

No way would I drill a hole through a beam.

 

I am either hitting the steel raw bar in the pre-made concrete floor slabs you put down before you put down the wire mesh and concrete the floor or the wire mesh.

 

I think the only way I can cut the steel is with just a blade from a metal saw.

[bodga]

1 hour ago, Crossy said:

 

What on earth are you feeding with that lot?

Seems  pretty  obvious to me!

[bankruatsteve]

8 minutes ago, Cashboy said:

Single phase !

Mains is government 50 Amp single phase ( live, neutral and earth)

and generator would probably only be a 6 kilowatt single phase (live, neutral and earth)

Hence 6 cables or wires.

You wouldn't need more than 4mm² for that generator and earth not necessary.

Unless you are establishing your earth connection in the 100a switch, I don't see why you need that.  In any case, you could go with at most 10mm².

[Cashboy]

56 minutes ago, Crossy said:

What's confusing me is the need for three x 16mm², single phase would need 2 plus a reduced ground, 3-phase would need 4 plus ground unless it's a 380V machine.

 

Anyway for 3 x 16mm² VCT you're looking at at least a 1.25" tube (no bends). Could you drill for three (or however many) 1/2" tubes and run one wire in each? 

 

In reality, I'd just cut the re-bar, you're not going to significantly weaken anything.

 

Our incoming supply (16mm2 x 2) runs down the wall in 2.5" square plastic trunking (there's other stuff in there too). Done carefully it's neat and easy if you want to get another cable in.

What do you mean "reduced ground"

Isn't the earth cable also 16mm cable from the earth rod?

 

If you are saying that 16mm cable is 8mm in diameter, then 3/4" (20mm) round internal should be able to squeeze 3 cables in I would imagine in a straight run.

 

The mains supply coming in is 2 x  25mm aluminium cables (live and neutral) I assume.

I shall be coming into the loft with that and immediately go into a 100 Amp switch where the earth from the copper rod will also meet.

Then I was going to run 3 x 16mm copper wire (live, neutral and earth) through the ceiling to a 63 Amp MCB and then to 3 consumer units.

 

 

Edited May 3, 2020 by Cashboy

[bankruatsteve]

2 minutes ago, Cashboy said:

should be able to squeeze 3 cables in

You never want to squeeze cables in conduit or anything else.

[Crossy]

A fact of life, you are not going to get 3 x 16mm2 in a 20mm conduit. It may theoretically "fit" but you'll never pull it through.

 

Actually I would run 2 x 25mm2 from your 100A isolator to the CU, then when you want to upgrade to a 100A supply you don't need to rip anything out.

 

Run 10mm2 from the main earth bar in your CU directly to your ground rod via whatever route is most convenient. 

 

For your 6kVA genset, 4mm2 would be fine, 10mm2 if you want to future-proof. How are you arranging genset/mains transfer and load shedding? Since this is a new design far easier to organise it now rather than later. You may consider an "essential" CU and an "others" CU which would make things really easy.

 

Also, don't forget to install at least one RCD/RCBO.

 

 

 

[Cashboy]

2 minutes ago, bankruatsteve said:

You never want to squeeze cables in conduit or anything else.

 

Seriously,  why not?

When wires (live, neutral and earth) are in a cable, that is tight.

So what is the difference to wires being tight in a conduit make?

 

[Crossy]

This PEA document may prove useful Groundwire Mk2 book-Manual.pdf

 

You need to do it this way to pass the PEA inspection (unless you already have a permanent meter).

 

The important diagram with translations.

 

[Cashboy]

1 minute ago, Crossy said:

How are you arranging genset/mains transfer and load shedding? Since this is a new design far easier to organise 

 

 

 

 

 

[Crossy]

Looks good, apart from the fact they are $10 on AliExpress (supply your own box). If you organise your essential supply you can use a smaller transfer switch and save some $$$. Things like water heaters can go on non-essential and not be powered by the genset.

 

I would also have a look at this thread 

 

[Crossy]

10 minutes ago, Cashboy said:

So what is the difference to wires being tight in a conduit make?

 

You won't get them in!

 

2/3 full is the maximum recommended fill ratio, even then it's a wrestle.

[bankruatsteve]

12 minutes ago, Cashboy said:

 

Seriously,  why not?

When wires (live, neutral and earth) are in a cable, that is tight.

So what is the difference to wires being tight in a conduit make?

 

Well, because you have to pull the wires through the conduit.  If they are packed tight, it is impossible to pull them without damage (insulation tear, wire stretch, potential of short).

[Cashboy]

This is my plan.

 

The 25mm aluminium cables come into the loft of the two story house.

I bring an earth supply from a ground rod up as well.

I have a 100 Amp switch in the loft.

 

I then run a live, neutral and earth in 16mm from the loft to a box on Floor 2 with a 63 Amp MCB and "changeover switch" in case I want to attach a generator to the system.

 

I then take a live, neutral and earth to a consumer unit on Floor 2 and also down to Floor 1 to two consumer units.

[Crossy]

Good that you have split-load CUs.

 

I would dedicate 1 half of one CU to non-essential (mostly water heaters) and wire that to bypass the transfer switch.

 

I would bring the earth directly to the primary CU, then you will be able to show the inspector the MEN connection as he is expecting to see it.

 

[Cashboy]

9 minutes ago, Crossy said:

Good that you have split-load CUs.

 

I would dedicate 1 half of one CU to non-essential (mostly water heaters) and wire that to bypass the transfer switch.

 

I would bring the earth directly to the primary CU, then you will be able to show the inspector the MEN connection as he is expecting to see it.

 

Cheers for that.  Learned quite a bit from this electrical forum but still have to decide if I should connect the neutral to the earth which still baffles me and seems crazy.

 

Not even sure if there is a point in running an earth on the 6 Amp lights as most light fittings don't have an earth by the looks of things.  There seems to be plenty of cable with live and neutral available, but no earth in it.  In the loft to the second floor lights would make sense to only use that.

 

Edited May 3, 2020 by Cashboy

[Crossy]

14 minutes ago, Cashboy said:

I should connect the neutral to the earth which still baffles me and seems crazy.

 

In your home in the UK it's almost certainly connected (unless you are TT or TNS), you just don't see it as it's hidden in the service head.

 

If you don't do MEN in the Thai way you won't pass inspection. Nothing to stop you changing to TT once you have the permanent meter of course.

 

Our lights don't have an earth, they are either Class-2 or well out of reach.

 

By the way, please don't wire ring-finals on 32A breakers, make everything 2.5mm2 radials on 20A breakers. That's what the locals will expect and there's no danger when Grandad plugs his welder in (no plug fuses here).

 

Also, if you want an English language standard to use I suggest AS/NZ 3000 rather than BS7671, the Aussie system is much closer to the Thai system than the UK is.