Long armoured cable

[GateOpener]

Hi, hope someone out there might have an answer, I would like to get power to an outbuilding across a field, I know I will need to use armoured cable and be buried 18 inch min, that is no problem. What I need to know is if the distance is possible - load will prob not exceed 2Kw but is about 100 metres away, is this poss and what size cable would be advised ? Thanks for any info.

 

[ban-all-sheds]

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http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html
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Tell it you're using PVC cable, even if you're not, or it will assume you can run it at 90°, and tell it you're using 2-core cable, even if you're not, or it will do 3-phase calcs....
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[davy_owen_88]

And because you said 'probably won't exceed' I would not go for less than 10mm² to give yourself some room to upgrade in the future as 6mm² is right on the limit with regards to voltage drop.

 

[GateOpener]

Hi, thanks for advice, not knowing any different I tried the calculater using 3 core pvc, 2Kw, 100m and it came up with 6mm, when used 2 core pvc, 2Kw, 100mm result 10mm is that the expected result ? I'll measure cable run properly in the next couple of days so I can get an idea of costs/viability if a goer then will get someone qualified to qote for connections at either end, Thanks again.

 

[Taylortwocities]

This field. Yours I guess?

What is the use of the field?. Read reg 705.522
there's special requirements for cables in/over agricultural land where vehicles & agri machines are used.

 

[GateOpener]

Thanks, anyone enlighten me as to what 705.522 says, I dont have copy of regs so dont know. Thanks.

 

[ericmark]

Although there are a number of factors volt drop is normally the most limiting so 2kW at 230 volt = 8.69A so 11.5volt (5% of 230) divided by 8.69 x 100meters = 13.225 mV/A/m as max volt drop permitted and 4mm² cable has mV/A/m of 11 so that cable would fit the bill. However since the MCB is limiting factor rather than what you are using if we look at a 10A MCB then we go just over the 11mV/A/m (11.5) so it would require 6mm² at 7.3mV/A/m and at 16A we just exceed the 7.3 (7.18) so we would need 10mm² at 4.4mV/A/m all a case of simple maths.
705.522 Selection and erection of wiring systems in relation to external influences
In locations accessible to, and enclosing, livestock, wiring, systems shall be erected so that they are inaccessible to livestock or suitably protected against mechanical damage.
Overhead lines shall be insulated.
In areas of agricultural premises where vehicles and mobile agricultural machines are operated, the following methods of installation shall be applied:
(i) Cables shall be buried in the ground at a depth of at least 0.6 m with added mechanical protection
(ii) Cables in arable or cultivated ground shall be buried at a depth of at least 1 m
(iii) Self-supporting suspension cables shall be installed at a height of at least 6 m.
Eric
PS The (7.18) should have been 7.18 in brackets but seems this can't be displayed sorry.

 

[BS3036]

(7.18)

 

[PaulAdman]

Hello ericmark
Thanks your info. Really your info usefull me and our members.

 

[ban-all-sheds]

Paul - laws-of-physics stuff like voltage drop, current carrying capacity of cables etc must be the same, but our Wiring Regulations don't apply to you, particularly with respect to directly buried armoured cable...

 

[Taylortwocities]

Thats assuming the USA has something exactly the same as (eg) 6mm XPLE armoured cable - which I doubt...

So, you canna change the laws of physics but all of the parameters will be different if the CSA of the cable, the supply voltage and the sheath & insulation is different in Thanksgivingland.

 

[GateOpener]

Guys (ericmark/ban-all-sheds), Can't thank you enough for all your help and info, taken an actual measurement across the field with a bit extra and it is 100m, as suggested I think I would go for the 10mm to give a bit of over capacity although it will only be running 3 or 4 75w flouros and a couple of small maybe 100/200w pumps and thats it. I a digger attachment so a trench 600mm deep is no prob, as for extra protection would 100mm pvc drain pipe suffice bedded on/in pea gravel ? Once again many thanks BB.

 

[ban-all-sheds]

Thats assuming the USA has something exactly the same as (eg) 6mm XPLE armoured cable - which I doubt...

I thought they did have an equivalent cable type, but on further investigation I don't believe they do. What they call armoured cable is actually flexible metal conduit with singles inside ( it comes already "assembled" but you can pull the cores out and draw new ones in)


http://books.google.co.uk/books?id=...=X&oi=book_result&resnum=2&ct=result#PPA23,M1

Type U looks like flat split-con, but isn't approved for use underground.

So, you canna change the laws of physics but all of the parameters will be different if the CSA of the cable, the supply voltage and the sheath & insulation is different in Thanksgivingland.

Clearly there are AWG-mm² conversions needed, but they'll all have to be rated for use at at least 220V, PVC is PVC, XLPE is XLPE...

 

[skenk]

The armoured cable itself should be sufficient mechanical protection, i'd have thought. It should be layed in sand with gravel on top of the sand and warning tape above.

 

[Taylortwocities]

And at least at the depths specified for the environment.