URGENT CAN WATER MAIN & ELECTRIC SUPPLY GO TOGETHER

Kel

No you should not put cable and pipework in the same duct. You can put the pipework and cable in the same trench but you must put them at different depths and use yellow warning tape laid over the cable duct to warn of Cables Below. Your groundworker should know all this if he is worth his salt.

Roy

 

Just a thought. Is the pipework for your water blue MDPE? And are you using steel wire armoured cable?? If so you need not put this in duct! Just put the water pipe in trench and lay the swa separately. Just a thought. If its your own private garden there is no hard and fast rule for laying the services in duct. It would be different if in a highway. 750mm depth is good for both the water and the electric. You should be okay if its like that and means you can get the job finished. Best to surround the cable in sand too.

Roy

 

Yes the water is blue MDPE.

The eletric was going to be normal 8mm cable run to
the garage (into a fuse box) then out of the garage
in 4mm to our shed/summerhouse at the bottom of the
garden which would just have a socket and a light.
This is why we were planning on putting the electric
as well as the water in ducting.

Kel

Not sure that you have the electric arrangement designed properly. Have you got RCD's? Consumer unit at shed end? Would you like some assistance?

I would just lay the MDPE directly in to the trench and use the duct for your cables. If you are plannning on pulling the cables through remember to put draw cords in or you will never get the cables through! I would strongly recommend that you consider swa. It will last longer and be safer. Post a reply with your current plan of action and we can help.

Roy

 

go to an electrical wholesaler and buy some nice big amroumed cable
200ft is about 60m afaict so for a 40A feed (which is what i find is generally advised for outbuilding suppllies) you need to be using 16mm (due to volt drop)

the armoured cable can be run directly in the ground eliminateing the need for ducting

only problem i can see is getting it on a sunday maybe one of the sparkys here would sell you some (at a significant markup ofc ) the parts other than the cable can be purchased later

using the same size cable for the whole outdoor run is probablly less hassle and keeps the calculations simpler

start from a 40A breaker in the non rcd side of the house CU

from here run in 10mm twin and earth to a metalclad 2 module din rail box with a 40A rcd fitted

in the garage gland both the cables into a big metal adaptable box and inside this fit henly blocks to join the 2 runs of SWA and the tails to a CU (the adaptable box is needed because the single insulated individual cores from the SWA must not be exposed

from here run with the 16mm armoured to a metalclad switch CU in the garage



from here run a lighting cuircuit from a 6A mcb a ring from a 32A mcb

in the shed fit another switched metalclad CU and run another ring and lighting cuircuit

 

ok corrected version

go to an electrical wholesaler and buy some nice big amroumed cable
200ft is about 60m afaict so for a 40A feed (which is what i find is generally advised for outbuilding suppllies) you need to be using 16mm (due to volt drop)

the armoured cable can be run directly in the ground eliminateing the need for ducting

only problem i can see is getting it on a sunday maybe one of the sparkys here would sell you some (at a significant markup ofc ) the parts other than the cable can be purchased later

using the same size cable for the whole outdoor run is probablly less hassle and keeps the calculations simpler

start from a 40A breaker in the non rcd side of the house CU

from here run in 10mm twin and earth to a metalclad 2 module din rail box with a 40A rcd fitted

from here run with the 16mm armoured to the garage

in the garage gland both the cables into a big metal adaptable box and inside this fit henly blocks to join the 2 runs of SWA and the tails to a CU (the adaptable box is needed because the single insulated individual cores from the SWA must not be exposed

run with 10mm twin and earth from this adaptable box to a metalclad CU in the garage

from here run a lighting cuircuit from a 6A mcb a ring from a 32A mcb

in the shed fit another switched metalclad CU and run another ring and lighting cuircuit

 

i would still use the 16mm armoured though in the way i specified before

maybe its just me but i don't really trust ducting

you need the 16mm because of the insane lengths involved (and the insanely small allowed volt drop in uk electrical regs)

 

Can we still take you up on your offer of help with
the electric arrangment design, please see my earlier
message for details showing our measurements.

Good morning Kel, Plugwash has given some sound advice in his post. Look at carefully and see if there is anything you could use.

With regard to the depths we know it should be 750mm
water and 450mm electic but could we put them both at
750mm.

Yes that would fine. Keep the ducts apart and put both in the bottom of the trench. As you say the depths quoted are minimum and no harm going deeper!

With regard to still using swa even in the ducting is
this essential. ...is very expensive for such a long run especially in
16mm as someone else recommended and Screwfix don't
do 16mm or long rolls. We live in Tolleshunt D'Arcy,
Essex which is near Maldon and Colchester if you can
recommend anyone cheaper.>

Well according to my calculations at 40A you could get away with 10mm armoured as this would be good for 52m. (6mm armoured is only good for 31.5m).

As previously advised you should really use swa for the best job. pvc cables in duct would be more susceptible to groundwater long term. I would suggest using a 32A breaker in the fuseboard instead of a 40A for the outside circuit supply. This should be ample taking diversity in to account and this will get your cable size down to 10mm comfortably (and this should be much cheaper than 16mm.)

Using a 32A breaker to protect the circuit allows you up to 65m of cable at 10mm for voltage drop compliance.

Roy

 

Consumer unit in house on 1st floor to back of house
at ground level is 15 metres. Want to take feed from
here to garage.
Back of house to garage is 20 metres. We want to fit
another consumer unit in garage with RCD's to give
protection to garage, shed & garden. So in total from
consumer unit in the house to the consumer unit in
the garage would be approximately 35 metres.

Okay thats no problem. Use a 40A breaker in the fuseboard and 16mm T&E to get to the garage. This is necessary to limit volt drop from house to the garage as you are going to need max voltage at garage befire you continue cable up to the shed/summerhouse.

to take a feed from the comsumer unit in garage to
shed/summerhouse. Hubby will want to use power tools
in the garage.

> Garage to shed/summerhouse is approx 50 metres. In
shed/summerhouse we want to have a double socket for
plugging in garden equipment like strimmer or
shredder or maybe small electrical appliance if
having a barbeque. Also a single socket to power a
light (flu probably) to save running a lighting
curcuit as well.>

Yes that all looks good. As my previous post I would definitely use 10mm to get up the garden as you are not going to be using very much current at all. As its a job you only do once 10mm gives plenty of scope to expand at shed if you need and 16mm is overkill so I think we've sorted it.

Kel I am going out doing leaflet drops now so wont be around for a few hours. Good luck and hope you get it all finished.

Roy

 

Use a 40A breaker in the
fuseboard and 16mm T&E to get to the garage. Then use a 32A breaker at the garage CU for the cable going to the shed.

 

Ducting is the way, even if you have the cable ready!!