SWA cable, long run how to join

[choppachimp]

what an excellent resource for DIY info these forums are!

...right down to biz

Providing 32A power to my new workshop. So have gone with a 4mm
3 core SWA. However the longest reel of cable I could get was 25m/82ft.

Unfortunatley the workshop is 35m/114ft from the house.

What is the best way to join two lengths of SWA? (or should I find a supplier of single run, 35m SWA). External plastic/rubber box? or other method?

Do I need an earth rod due to the length of run?

anything else I should be considering due to the length?



TIA

 

[Spark123]

You can join SWA using cold-pour resin joints, 4mm is a bit on the small side though, assuming a design current of 32A it gives a volt drop of 12.3v which is too high. The next size up which is 6mm gives a volt drop of 8.2v which is acceptable but leaves little room for volt drop on sub-circuits. 10mm is probably the most viable giving a volt drop of 4.9v. This is also not taking into account future expansion.
It depends on a number of factors wether it is better to go to sink an electrode and go for a TT, these include your supply type and wether or not there are any extraneous conductive parts in the outbuilding, there is some further information about this subject here: clickme
Also, please note this work will be notifiable to LABC under part P of the building regs, further info here: clickme

 

[Deluks]

35m should easily be able to get hold of from any electrical supplier. The sheds and SF only do 25m cos it's heavy to transport and ship out. but a good electrical supplier will sell by the metre.

10mm 3 core here

What exactly will you be running in the workshop?

 

[Belle427]

dont join,single run is best

 

[RF Lighting]

dont join,single run is best

Hear hear

You should avoid the unnecessary jointing of cables when ever possible (not just on SWA)

 

[nobbee]

protect workshop circuit with 30ma rcd due to it being outside of equipotential zone far safer. if tt system earth rod would be advisable. if you live in built up area it is unlikely you have tt system.

 

[Big_Spark]

You can join SWA using cold-pour resin joints, 4mm is a bit on the small side though, assuming a design current of 32A it gives a volt drop of 12.3v which is too high. The next size up which is 6mm gives a volt drop of 8.2v which is acceptable but leaves little room for volt drop on sub-circuits. 10mm is probably the most viable giving a volt drop of 4.9v. This is also not taking into account future expansion.
It depends on a number of factors wether it is better to go to sink an electrode and go for a TT, these include your supply type and wether or not there are any extraneous conductive parts in the outbuilding, there is some further information about this subject here: clickme
Also, please note this work will be notifiable to LABC under part P of the building regs, further info here: clickme

Good advice..use it..

Further, as others have said, use a single length of cable sourced from an Electrical Wholesaler and not a shed. It should also(in an ideal world) be protected both ends by an RCBO..supply end should be 300mA, the workshop end should be 30mA for a single device, but if you want a decent install then I would suggest a 100mA main switch RCD with any power circuits protected by individual 30mA RCBO's with the lighting on standard MCB's. It's all a matter of cost and your choice.


Edit...
Note: There is no Regulation demanding this level of protection, however it is required that at some point the final circuits in your workshop be protected by an RCD, hopw you choose to achieve this is your decision.

 

[Spark123]

Long time no hear Big-Spark??

 

[plugwash]

hes back and still advising hugely over the top RCD arrangements.

i do not belive there is any reg requiring properly installed underground SWA cables to be RCD protected.

 

[dingbat]

There isn't.

 

[Big_Spark]

hes back and still advising hugely over the top RCD arrangements.

i do not belive there is any reg requiring properly installed underground SWA cables to be RCD protected.

Never said there was Plug, perhaps if you read my post you will see that I suggest that level of protection, I did not state it was a Reg.

However the cable is OUTSIDE the zone and requires a level of protection commensurate with the potential for mishap that a buried cable presents.

If the cable is submerged into the ground in the correct way, then an MCB should provide the level of protection needed, but how often do people actually bury the cables correctly? How often do SWA's buried in gardens get dug up..quite often.

Personally, I believe there should be a regulation demanding this protection..but I don't write the regs so can only make a suggestion.

 

[Big_Spark]

Long time no hear Big-Spark??

Been busy with the real world...got a bit more time to myself now so can spend some online again.

 

[plugwash]

However the cable is OUTSIDE the zone and requires a level of protection commensurate with the potential for mishap that a buried cable presents.

which is imo quite low in a garden.

1: even if people do hit the cable it will most likely be with a blunt spade which is unlikely to penatrate the armour.

2: even if people do manage to cut the armor the armor will earth whatever cuts through it so when a live conductor is hit disconnection should happen very rapidly even with just a MCB for protection.

having said that you should certainly install the cable properly at the reccomended depth and with proper warning tape above it (best to put the warning tape about half way down so you don't dig it up too often but you have some warning between hitting the tape and hitting the cape).

 

[Big_Spark]

Plug, I understand your points, and certainly agree with your comments about how to bury the cable, unfortunately personal experience tells a wholly different story. Many certainly do take precautions with cables, however there are a great many that are not as dilligent, as a result we get cables laying on the surface or within a few inches of the topsoil, most of these cables are bootlaces, with most being 6mm² at best, and I can assure you that a decent garden spade will penetrate the armouring very easily on cables of this size.

I often encounter cables which have not relied on the armouring for an earth path..it is very common..they contain an extra core for this. It is perfectly acceptable to do this, however a glancing blow from a garden tool can easily penetrate the armouring and a single core without damaging the earth core..in this situation it is highly unlikely that the MCB would trip, but I can assure you the RCD would..

It's horses for courses really, and lot of it is down to personal choice and your budget.

 

[plugwash]

yeah but the people without the diligence to install the cable properly are certainly not going to be the ones that spend hundreds of pounds on rcds.

i can see if you are trying to sort out an existing f*ckup using more RCDs to compensate for badly installed cable may be an option but for a new installation i'd advise justing installing the cable properly