4mm armoured

Discussion in 'Electricians' Talk' started by mr p nuss, Nov 21, 2008.

  1. mr p nuss

    mr p nuss New Member

    Hi,need some advice please.

    How much power can you pull through 4mm armour at 30 metres and what kind of voltage drop,also is it ok to double up cores as it 4 core and run a 10mm seperate earth along side.

    Asking as i need to put the cable in ground before i backfill footings of house ex and this will go to garage.

    Thanks Paul
     
  2. spike

    spike Guest

    As much as you like depending on how long you want it to last.
    Recommend getting someone who knows what there doing round like perhaps a professional electrician.
     
  3. JP.

    JP. Screwfix Select

    VD around 7.5v

    Max load around 26 Amps

    The above not for parallel and not precise.

    Why not just use 10mm 3 core SWA? and be done with it OP?
     
  4. mr p nuss

    mr p nuss New Member

    Dont need one thanks,found my answer elsewhere 7 kw is plenty without doubling up,why would i need a sparky to drop the cable in the ground thats not too technical,i will leave him to do the rest of the work.
     
  5. mr p nuss

    mr p nuss New Member

    Thanks for the above,i must learn to type faster,I already have the 4mm and it will be fine.

    Thanks
     
  6. JP.

    JP. Screwfix Select

    What a joke.

    30 meters..all the work involved burying the cable to reg depth.

    I don't care what anyone says - the installation is crying out for 10mm min.
     
  7. BillytheSpark

    BillytheSpark New Member

    Mr Russ,

    Dropping a cable in the ground is not difficult I agree. Knowing the minimum depth that it can be buried is slightly improtant, and the use of the warning tape is also usefull information.

    If my customers want to dig the trench, I tell them to get on with it, then I lay the cable.

    PS - Armoured cable usually uses the armouring as the earth. 10mm will decrease the ZS though.
     
  8. general matter's

    general matter's New Member

    4mm2 SWA would carry 40a no problem! XLPE maybe around 45a? (again no literature on me at present) i normally put 4mm2 on a 32a mcb!

    as for VD? assuming its 30 metres and fully loaded, it will be around 10.5v. but diversity can significantly improve VD!

    NB SWA underground temp can increase Iz, so check the Iz against the 'free air' method to get a better, more realistic current carrying capacity!
     
  9. Young Scud

    Young Scud New Member

    While doubling up isn't necessary from the point of view of current carrying capacity, it would help with voltage drop.
     
  10. Logic0104

    Logic0104 New Member

    funny I came across this question as I had exactly the same issue 3 years ago and spent hours researching and speaking to qualified electricians about this and the best answer I found was actually quite surprising and really came down to common sense. firstly ask yourself why are you concerned about voltage drop. (what is the installation for) . I was reliably informed that voltage drop will be minimal at my 4mm armoured 3 core installation over a distance of 45 meters. mmmmm you may say. (when Edison discovered how to use electricity he unknowingly used DC, dc needs higher voltages to travel longer distances but a clever Serbian/American named Nikola tesla discovered that by using AC the high voltages were not needed over distance but it needs a return to complete a circuit, hence alternating current or it alternates between the supply and the receiver hence a live and a neutral, up the live back down the neutral , the earth is for safety reasons) the important thing is to use a reliable and correct RCD's. I used a 40amp RCD with a 32amp breaker for sockets and 6 amp breaker for lights. and as for the armouring of the cable being used for earth well BEWARE this is not entirely true in household installations and is mainly only used on industrial 3 phase or 400v installations as additional safety on 4 core cable. so now to how deep to bury the cable. again I was reliably informed that in contractual or industrial installations the rules are clear and state that a armoured cable must firstly be placed inside a heavy duty conduit (pipe) laid in sand at a minimum depth of 2 feet with an awareness tape laid above to a minimum of 1 foot. this is common sense and is for the reason of other service contractors may dig in the same place later. but in your home there is not actually a set of rules and common sense must be used, for example I was told to bury in the garden 50% deeper than a spades depth and still use warning tape, conduit is not necessary as armoured cable is armoured for a reason, I laid a course of dense engineering brick over mine at 2 feet then still used warning tape at 1 foot depth then in future if by any chance someone unknowingly digs that deep they will be warned of the cable. so back to amps and handling capability. as said earlier what do you want to run from your sockets and find out the current those tools or applications will draw. you will be very surprised at how many things you can run at once before you hit 32amps load but again the importance lies in adequate breakers and earthing. electrical heaters use the most then motors (drills, sanders, laths, lawn mowers etc.). so there you are and finally my installation was tested and passed with flying colours using 4mm 3 core armoured over a distance of 45 meters up to my workshop I have a 40amp breaker on the consumer unit in the house (supply) and a 40amp RCD on a garage unit at the workshop with 32amp for sockets and 6amp for lights. good luck and always get it tested. don't cut corners and use twin and earth for outside always use armoured.....;)
     
  11. PJ Wales

    PJ Wales Member

    Logic, check the forums dae, I think he has solved his issue already by following the advice or gone on his own accord and ignored the advice..
     
  12. dale76uk

    dale76uk Member

    someone point me to the ' minimum depth ' please?


     
  13. Logic0104

    Logic0104 New Member

    yeaa I did see the date but this will probably help people in future....:cool:
     
  14. Logic0104

    Logic0104 New Member

    Hi read my previous thread mate.... answer yourself , is it at your own property (domestic installation). is it in the garden. is it going to be covered in concrete. if you want to be thorough 2 feet in heavy duty conduit (plastic pipe) and always use warning tape.... as my thread says THIS IS FACT "there are no set rules for personal domestic installations" but as said previously common sense is important,,, hence if you bury it in a garden where you may dig later you need it deeper than the depth of a spade. the best thing would be to have the warning tape as deep at a spades depth then the cable twice that, as I said previously "I laid bricks over the cable so if by any chance you do decide to dig that deep you will firstly hit the warning tape which clearly states "Warning Electric cable below" then you will hit solid bricks so if you or anyone else hit and cuts the cable then, well you can only make things Idiot proof to a certain level, and am sure you are no idiot. but there are lots of them out there :confused: . go as deep as is practical and if expense is not an issue use sand and conduit. DO NOT USE TWIN and EARTH in conduit... MAKE IT SAFE. anything over 30 milliamps can KILL DEAD GONE NOT COMING BACK NO SECOND CHANCE AND YOUR DEAD FOREVER.....:( you can be pulling 35 to 38 amps up your cable (you probably wont but if you are go for 6mm). view electricity like a river , AMPS are the speed it flows, Volts are the Pressure pushing the flow, watts is a measure of that which an appliance will use... or the amount of water used.. respect it, understand it and never play with it unless you know what you are doing. another pointer may be to draw a map of the cable and its direction as I did then if I move and sell my house I will pass this on to new owner and tell them where it is.BE SAFE
     
  15. JP.

    JP. Screwfix Select

    Does a full SWA submain (no joins onto t+e in house etc) require rcd protection Logic?
     
  16. Lectrician

    Lectrician Screwfix Select

    Both Logics posts give odd and incorrect advice. Lots of "I was told". Nothing at all to do with the actual requirements of the regulations.

    And you can't say "anything above 30mA can kill". Factually incorrect. You cannot compare the 30mA to the 30 odd amps being drawn by the load either. 30 amps is not going to flow through you.

    Current is not "the speed of flow" either, it's more like "the volume".

    I would take both posts with a huge pinch if salt. Neither makes much sence.
     
  17. Logic0104

    Logic0104 New Member

    Why would you want to come straight from sub main to a garage without protection ??? . the answer is obvious ," of course" most sub mains are 80amp and will or should have 80amp bottle fuse or wire (depending on age) but a fuse does not protect against injury or death a RCD should react fast enough to prevent serious injury and that is also why your earth should be adequate. it is illegal to use mains power without RCD in domestic installations..... if what you mean is can I bypass the meter and distribution unit ???? then I cannot answer that all I will say is ALWAYS USE RCD and RCB . I personally would put protection at every point of a Join again common sense (I have a 40amp RCB feeding from dizzy in house then a garage unit with 40amp RCD and 32amp RCB for sockets and 6amp RCB for lights) you would be better using 25mm meter tails onto the 80amp fused connector at the sub main then to a dizzy/ consumer unit but use a RCD which is the same rating as the cable to feed the garage shed etc. then a standard garage dizzy/ consumer unit, again with correct RCD and RCB's but in this case I would also add 10mm earth wire also directly onto sub main from the consumer unit at source. again common sense. you could even double earth from the garage back consumer unit at source too this would ensure correct protection and does not cost that much more. in lamens terms you only require an RCD rated at what you will pull from source not what the source pushes.
     
  18. Logic0104

    Logic0104 New Member

    so post a reply and correct it instead of picking fault, and amps or current are rate of flow .... troll. what I said about 30milliamps is correct, and absolutely correct you cannot compare 30milliamps with 30odd amps or so considering that a milliamp is 1/1000 of an amp. and correct 30amps will not flow through you but if you complete the AC circuit it will probably be that which your body can conduct until the RCD trips but that would not matter if not using an RCD would it. so either give these people some constructive advice or sod off and watch tv or sod off to face book and cause arguments on their. oh funny that you have not replied to any of the questions regarding this issue is that because you are an electrician who is Pixxxd at not getting the work :confused:. sorry pal but you should not be telling people on here not to take sound and factual safety advice unless you are gonna correct that same advice , tut tut .... so either correct it or stop trying to be clever. only thing worse that a thick git is a thick git who thinks he is clever.
     
  19. JP.

    JP. Screwfix Select

    So what you are saying Logic is that all types of SWA sub mains (correctly deployed) from house intake to garage require RCD protection at house intake position? also SWA sub circuits
     
    Last edited: Apr 27, 2014
  20. Cheburashka

    Cheburashka Active Member

    What is an RCB? I must be a thick git too.
     

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