Armoured cable sizing

[The Bear]

! wouldn't normally ask this here but I''m having problems getting hold of my electrician, I have a feeling he is on holiday, and I need the answer.

I'm currently renovating the house and have a trench open that goes from the house right past the detached garage. This garage is destined to be my new workshop if I ever get my machines out of storage. The current supply is way too small for the machines I have so this is an ideal time to upgrade the armoured cable even if it sits unconnected for while. Eventually I will install and connect it to a new consumer unit in the garage. The rush is due to the fact it was -6C here last night and part of the trench also carries the water main. With the overnight temperature I want to get the trench filled in asap to prevent it freezing and bursting.

Everything is single phase. The biggest woodwork machines I have are 3hp (2200kw) I will only ever use one at once but will also have dust extractors running at the same time. The main extractor is also 2200kw and when I run the table saw I also have a 1800kw extractor running as well. (prob the only time I run both extractors together). In addition there are the lights, power tool batteries charging, radio, a fridge freezer and I will in future use this supply to provide power to the garden for lights and hopefully one day electric gates.

Distance from house consumer unit to garage consumer unit is about 30m, but maybe up to about 40 if I put the garage unit where the current small one is.

Any sparks, electrical engineers, competent persons know what size cable I need?

I addition I'm considering dropping an armoured cat 5/6 cable in as well for future use. Is it ok to put in same trench as the supply or are there interference or any other issues?

Thanks

Mark

 

[slate1234]

I don't know whether the length makes any difference, I have got a 10mm armoured cable going to my workshop and I have got a bench saw and planner running on 16amp supply running separately but with with the extractor lighting and chargers ect it works fine, we are refurbing a large house in work at the present and have put a 10mm armoured cable to the garage 30m away from the house and 60m down to the gates with cat 5 for intercom I'm in no way a sparky so please wait for someone in the know to confirm.

 

[flying haggis]

10mm swa should be good for a 40A supply at 40m distance

put the cat 5/6 and any phone or alarm cables in ducting about 100mm away and you will be fine. with a draw rope for additions if you foresee any

you can buy armoured cat 5 but that is a bit of an overkill

or put in ducting now and then pull the cable in later

 

[n0legs]

Using the Doncaster Cables Calculator.
For a 32amp supply at 40 metres laid direct in the ground they say 6mm.

I've said it before and I'll say it again, go as big as you can afford.
From TLC ,done very quickly:-

6mm £70.80
10mm £94.00
16mm £161.20. Exc VAT
That's for 40 metres of 2core.

Its easier to uprate protection and switching hardware to uprate a supply than change a smaller cable. The 16mm will happily run at 32 amps forever. It will run up to 110 amps depending on install method, this gives you loads of potential for a bigger supply later on.

 

[flying haggis]

if you use three core swa the earth is not dependent on the cable armour which could fail if water gets in and corrodes the armour

 

[n0legs]

if you use three core swa the earth is not dependent on the cable armour which could fail if water gets in and corrodes the armour

That's a valid point and in all honestly I only lay 3 core in this instance.
There is however no reason not to use the armour as the earth. But saying what the rules state is cold comfort after 30 years of finding poorly terminated or rotted off armours on cables.
There are other factors depending whether he can export the earth to an outbuilding, but this is best left to his spark to decide.

 

[siggy_7]

Cable sizing depends on maximum current and permissible voltage drop - this is why long runs to outbuildings sometimes need larger cable sizes than you might expect from a current carrying perspective. TLC have a handy calculator to do the work for you:

https://www.tlc-direct.co.uk/Technical/ ... eDrop.html

 

[The Bear]

Thanks all
Cable purchased this morning, put in trench and partly backfilled.
They gave me 4 core for the price of 3 as they'd run out of 3 core. What can I use the 4th core for?
Mark

 

[n0legs]

They gave me 4 core for the price of 3 as they'd run out of 3 core. What can I use the 4th core for?
Mark

You could if you're not transporting the earth bunch or pair the conductors. In effect doubling the cross section of the conductors. Speak to the spark.

Or if you are transporting the earth out double up on the CPC/earth. This will lower the impedance, good for the Ze. Talk to the spark.