Pvc Conduit

[padawan]

Hi guys  I would just like to seek some clarification on running multiple circuits in conduit.

This is for a domestic installation, installing 2 new circuits, one of which is 6a lighting circuit and the other a 32 a ring main. Both circuits will be run in round pvc conduit which will be surface mounted.

Am i right that due to it being a domestic installation, and both circuits not running constantly at full capacity then there is no need to derate the cables, and that spacing factors are not really required? essentially as long the cables/conductors can all fit inside the conduit then there is no problems?

With regards to running the conduit i have a couple of questions about best working practices.

1. Do you suggest running both circuits in the same conduit system and then dropping down to the relevant sockets or light switches?

2. Is it better practice to run each circuit in there own independent conduit system?

3. What size conduit would i need to run a ring main and lighting circuit in the same conduit? will 20mm or 25mm do the job?

4. Is it ok to run T&E in conduit?

My thoughts are:

1. It could be more economical to run both circuits in the same conduit where possible. It could also make the job look a lot neater.

2. It would be more clear to the customer or any future electricians working on the installation, when doing any additions/alterations/testing.

3. Tbh i don't know, and I'm not sure how to work out the max capacity for conduit, any advice on how to do this would be great. Obviously if both circuit was in an independent conduit system i would run 20mm, but for 2 circuits in the same conduit is 20mm still ok? would 25mm be better?

4. I know T&E would be a lot more difficult to pull, but for the short run of the lighting circuit it would be a lot more economical to run T&E.

I would like to hear what you guys think, as always any advice is much appreciated.

 

[Dairyspark]

I can answer question 3 for you lol

Check your onsite guide (appendix E)

The way it works is each cable size has a factor, solid and stranded cables have different factors so make sure you choose the right one.

Each conduit size has a maximum capacity factor and as long as you don't exceed that capacity then that's the size you need

For example; 10 X 1.0mm solid core singles

1.0mm factor is 22 and if 20mm conduit is to be used it has a maximum capacity factor of 460

So....10 X 22 = 220 and 220<460 so 20mm has lots of space lol

For more than one size of cable, add the total factors together (5x1.0 + 6x2.5)

Hope this makes sense lol I'm tired and it's early in the morning.

 

[pewter]

bunching calculations are not required if the cable is using <30% of its current carrying capacity.

 

[Evans Electric]

Before I read any further Padawan , forget running Twin &Earth in conduit . ( Unless you were sheathing a drop to a socket perhaps  , straight length only)

Is this in a garage or something  as you're using surface conduit ?

Thing with conduit is , you erect the whole system first before wiring .

Then you wire with 6491X  grade cable .

To make life easy , use 25mm cond.  & tee off with 20mm .

Don't use elbows & tee pieces always use boxes or pull a bend in.

I assume you are not an electrician.

 

[padawan]

I can answer question 3 for you lol

Check your onsite guide (appendix E)

The way it works is each cable size has a factor, solid and stranded cables have different factors so make sure you choose the right one.

Each conduit size has a maximum capacity factor and as long as you don't exceed that capacity then that's the size you need

For example; 10 X 1.0mm solid core singles

1.0mm factor is 22 and if 20mm conduit is to be used it has a maximum capacity factor of 460

So....10 X 22 = 220 and 220<460 so 20mm has lots of space lol

For more than one size of cable, add the total factors together (5x1.0 + 6x2.5)

Hope this makes sense lol I'm tired and it's early in the morning.

Yep, makes perfect sense thanks

I ran the calcs based on running everything in singles.

2.5mm = 6 x 43 = 258
1.5mm = 6 x 31 = 186
Total = 444
 
So just over the 20mm conduit threshold.
 

bunching calculations are not required if the cable is using <30% of its current carrying capacity.

Thanks i will keep it in mind.

I assume for lighting circuit usage I use P = VI

How do i calculate socket ring/radial circuit usage? 

Before I read any further Padawan , forget running Twin &Earth in conduit . ( Unless you were sheathing a drop to a socket perhaps  , straight length only)

Is this in a garage or something  as you're using surface conduit ?

Thing with conduit is , you erect the whole system first before wiring .

Then you wire with 6491X  grade cable .

To make life easy , use 25mm cond.  & tee off with 20mm .

Don't use elbows & tee pieces always use boxes or pull a bend in.

I assume you are not an electrician.

Its a utility room. Reason for using conduit is the customer requested it, as it seems the electrics was an after thought.

I have run conduit a few times before, but as my boss is letting me have more of an input in designing installations, i keep second guessing myself.

Im not an electrician yet, I'm currently working towards my NVQ and doing my city and guilds. But i i will get my gold card one day lol