Pulling in swa

[rainstorm]

Good evening all
Got a 200m run of 3 core 10mm swa to install in a trench. Rather than pulling it through a duct, was wondering if anyone has ever pulled the duct over the cable, then dropped in into trench.
Duct is 50mm internal diameter flexible type. Might be a non starter, just weighing up options.
Thanks for any help.

 

[pc1966]

Single socket maybe?

Well 5% drop and 10mm single phase comes to 12.3A over 200m so not far off it!

 

[DefyG]

Single socket maybe?

Doubt it could be that, I just did a quick VD calc and 5% is exceeded at a load of 13A over that distance for 10sqmm

 

[DefyG]

I calculated 7.54v at 13A over 200m but at 12.3A it could be slightly under 5%

Well 5% drop and 10mm single phase comes to 12.3A over 200m so not far off it!

but either way certainly nowhere near 3% for lighting!

 

[pc1966]

I calculated 7.54v at 13A over 200m but at 12.3A it could be slightly under 5%


but either way certainly nowhere near 3% for lighting!

~12A is a lot of LED illumination!

Football park?

 

[Mike Johnson]

If pulling a 200m length of duct over a 200m length of SWA with a 200m pull cord you need 400m of space in a straight line to do it, and that is only if the draw cord is already in the duct, I did this with an alarm cable, but only 100m, would be easier in 50m sections with draw pits.

 

[pc1966]

And the sand wont be cheap! 200m at 200mm thick (100mm below cable and 100mm over the top) and say 200mm wide trench = 8cu m (8 builder bags worth)!

Yikes!

Just looked at that on some web site. Even at 5cm surround (10cm x 10cm) it is saying 5 bulk bags at ~£50 each. Going to a safer/easier to pour in 20xm x 20cm (i.e. 10cm safe margin) it is 4 times that and almost £1,000

Might be cheaper to look at 90mm or 110mm twinwall duct? 200m of that is around the £400 mark.

 

[DefyG]

12A is a lot of LED illumination!

Agreed but the OP is being a bit coy as to what the cable is being used for. Assuming a mixed load it 'should' still meet 3% guideline if only 1A of lighting!

 

[pc1966]

Agreed but the OP is being a bit coy as to what the cable is being used for. Assuming a mixed load it 'should' still meet 3% guideline if only 1A of lighting!

Well the regs still say that but really it is a hang-over from the days of filament lamps and their significant voltage/illumination sensitivity.

I personally would be OK with 5% drop on "mixed" if it is LED lighting. Which it almost certainly would be.

 

[pc1966]

From here it has the light versus voltage law for halogen lamps as more or less cubic (V^3):

Halogen lamp - Wikipedia

en.wikipedia.org

LED lamps are more or less linear output with V if a simple current-limiting resistor is used, even less sensitive if some DC-DC coveter/driver that regulates the output.

So best-case LED cares not as long as in-specification, worst case LED is 3 times less sensitive to small changes in voltage (i.e. if 3% limit VD for halogen lamp, then LED equivalent is around 9%)

 

[DefyG]

Well the regs still say that but really it is a hang-over from the days of filament lamps and their significant voltage/illumination sensitivity.

I personally would be OK with 5% drop on "mixed" if it is LED lighting. Which it almost certainly would be.

I probably would too which is why I put 'should' in ' ' and guideline, and is justifiable if not filament/discharge lights.
I would probably aim for 4% though which would limit the OCD to perhaps 10A for 10sqmm!

 

[pc1966]

I would probably aim for 4% though which would limit the OCD to perhaps 10A for 10sqmm!

I'm not sure I would bother with lowering the supply OCPD, it just has to be able to provide overload & fault protection for the SWA.

R1+R2 is going to be about 0.94 ohms for that run of cable, assuming 0.8 ohm as max Ze for TN-S then you are looking at max MCB of something like a 20A B-curve, or a 25A BS88 fuse if it is a sub-main (i.e. with 0.4s disconnection and and RCD planned for the far end, etc).

Ultimately what matters is the OP/customer is not needing load(s) much above 10A or anything with very big start-up surges!

 

[Rockingit]

OP might have a happier time by installing 2 x 6mm in parallel, 10mm singles..... etc
There are so many alternatives available after a little maths!

 

[rainstorm]

10A supply requested to supply comms kit. Not sure what exactly!
Probably a bit excessive but that is what asked for.

 

[MJPD29]

10A supply requested to supply comms kit. Not sure what exactly!
Probably a bit excessive but that is what asked for.

You've already done the prior planning without our input thankfully

 

[pc1966]

10A supply requested to supply comms kit. Not sure what exactly!
Probably a bit excessive but that is what asked for.

Do they need any network cables along with the power? That would be a good reason to use some duct!