SWA too short !

user786786 · Apr 29, 2021

Hi
Fitting a consumer unit in garage . Unfortunately the 16MM SWA is too short to reach consumer unit
So i have done as follows .

Glanded SWA into a metal adaptable box .
earthing nut earthed with 10mm crimped and run to earth block .
2 cores of SWA Brown and Grey ( oversleeved BLUE) run to single pole Henley blocks
25mm LIVE and Neutral tails to consumer Unit main switch through Same 32 mm hole
3rd core of SWA ( oversleeved earth ) to earthing Block in consumer unit .

Everything is being boxed over ( acessable ) so the single insulated cores of SWA will be covered.

Does this seem ok?

Also at the supply end is it okay 25mm tails from henley to 100amp double isolator to feed swa after glanding in a adaptable box .
Thanks

MJPD29 · Apr 30, 2021

user786786 said:
Thanks for reply Everyone

Garage /outbuilding end

Swa is coming out of concrete but too short too gland directly into the Metal CU so
the Swa has been glanded into a metal adaptable box then then outer sheathing removed to show the three single cores . two of them have been run ( for about 10 inches )into seperate henley boxes . third core used as earth to garage cu . swa and henleys all trunked over .

then 25mm tails to the consumer unit length about 450mm each.

the consumer unit in garage is a crabtree starbreaker and has two 6amp rcbos / and two 32 amp rcbos protecting the outgoing circuits .

main House end

The utilty supply comes from the Main Fuse which is sealed but i suspect a 80amp .
This goes off to a 100amp isolator which the utility company fitted .
From here we have 25mm tails to henley blocks , from the henley blocks we then have 25mm tails to the main house consumer unit . ( 7 circuits protected by Rcbos)

The earthing Is TN . 16mm earth wire from utilty supplier to earth block . then 16mm to house CU 10mm to gas 10mm to water .

the SWA run starts here
I wanted to run two 25mm tails from henley to a Wylex 100amp isolator ( couldnt find a lower amp one) connect the Swa which runs to the garage

Have you got a pic? Hard to visualise

user786786 · Apr 30, 2021

Julie. said:
OK

There are a number of issues, if you have used an isolator, this is merely a switch, and provides no protection to the cable.

This cable must be provided with both overload and fault protection, usually via a fuse switch (assuming swa all the way).

One way of back-checking your work, is to imagine what an experienced person would assess the work both as an initial installation and as an eicr. If you did this it would attract a C2 for both missing fault and for missing overload protection (2×C2).

I still don't quite understand the boxed in part, if this is proper trunking then that's one thing, however if not and it's a matter of being behind metal/plastic/timber covering that looks architectural then there are further issues, firstly as the cable has only a single layer of insulation this would attract a C2 - a second layer must be applied, a colouring sheath would not meet the requirements as it should not be removable without tools/destruction and is generally not of the required thickness/insulation.

In addition, now this cable is hidden less than 50mm in the building structure, rcd protection is required, some would code this as a C2 some C3, I would normally consider it C3, however as a substantial supply to a sub-main I would give this a C2 - driving a nail into a 1mm^2 - 2.5mm^2 cable protected by a 6A/32A mcb is one thing, into a 16mm^2 unprotected cable is another!

If it's a matter of a few ft, can you not move the garage cu? Or install proper steel conduit/trunking

Thanks again everyone have been very helpful and have brought up some issues which i will adapt .

---house end do not use 100amp isolator ,instead replace with a 63 amp wylex fused switch will protect the live feed of the SWA .

--- garage end the wiring is already in situ so i dont fancy digging up or extending CU . so i will use a large adapatable box to put the exposed single cores and henley boxes in . That should be up to regulations ?

--i was understanding that i dont need RCD protection for the SWA as the armor is earthed at both ends. Will that not be sufficient ?

user786786 · Apr 30, 2021

here is the garage end

Julie. · Apr 30, 2021

user786786 said:
--i was understanding that i dont need RCD protection for the SWA as the armor is earthed at both ends. Will that not be sufficient ?

Correct, but at the extended end it is not SWA all the way to the CU.

If you took the SWA into the CU then it would be OK

user786786 · Apr 30, 2021

Julie. said:
Correct, but at the extended end it is not SWA all the way to the CU.

If you took the SWA into the CU then it would be OK

Ahh okay so if put in large adapatable box of metal construction next to the consumer unit will that be appropriate.?

timhoward · Apr 30, 2021

user786786 said:
Ahh okay so if put in large adapatable box of metal construction next to the consumer unit will that be appropriate.?

Sounds ok to me.
If I was having to sort that out I'd probably go for slightly larger box than that one, longer double insulated tails (supported), appropriate grommet, and solder/crimp, tape and heat shrink the joints inside the box, and dispense with the Henleys.
But just throwing a metal box or trunking around it would achieve the same.

Julie. · Apr 30, 2021

user786786 said:
Ahh okay so if put in large adapatable box of metal construction next to the consumer unit will that be appropriate.?

Yes, as long as the cable run has mechanical protection all the way from the one end from the fuse switch through to the CU that would be OK.

Ideally metallic, but plastic can be OK if not concealed

brianmoooore · Apr 30, 2021

Maybe not quite how I ould have done it myself, but the only thing I can see that is non compliant is the lack of a double sheath on the exposed SWA conductors.
If you have any left over 16mm2 or 25mm2 tails, suitable lengths of the outer sheath slid off and slipped over the exposed brown and grey ends of the SWA will do the job.

westward10 · Apr 30, 2021

You can't possibly leave it like that aside from looking awful those conductors are not enclosed. No amount of sleeving will make any difference as you will never be able to completely cover them it will always be exposed where they exit the cable. Crimp some 16.0 6181Y within the adaptable box then bring out through a gland.

user786786 · Apr 30, 2021

timhoward said:
Sounds ok to me.
If I was having to sort that out I'd probably go for slightly larger box than that one, longer double insulated tails (supported), appropriate grommet, and solder/crimp, tape and heat shrink the joints inside the box, and dispense with the Henleys.
But just throwing a metal box or trunking around it would achieve the same.

Great thanks

brianmoooore · Apr 30, 2021

Why will the ends be exposed anymore than the ends of tails when they connect to service blocks at the DNO service end?

westward10 · Apr 30, 2021

brianmoooore said:
Why will the ends be exposed anymore than the ends of tails when they connect to service blocks at the DNO service end?

At the cable end which is poking out of the box. To sleeve them the sleeve would have to enter into the cable or it just sits on top.

brianmoooore · Apr 30, 2021

Sleeve should be pushed on all the way back to the SWA gland in the bottom of the adaptable box. I've done this myself to terminate SWA sub mains into flimsy plastic CUs that wouldn't take a SWA gland direct.

buzzlightyear · Apr 30, 2021

The op wins a crackjack pencil for trying.

user786786 · Apr 30, 2021

westward10 said:
You can't possibly leave it like that aside from looking awful those conductors are not enclosed. No amount of sleeving will make any difference as you will never be able to completely cover them it will always be exposed where they exit the cable. Crimp some 16.0 6181Y within the adaptable box then bring out through a gland.

going to use a large adaptable box . and large trunking . the asethetics are not that important on this occasion as its a garage . i just want to make sure everything is safely carried out to regs .

thanks

westward10 · Apr 30, 2021

Aesthetics are always important.

loz2754 · Apr 30, 2021

westward10 said:
Aesthetics are always important.

Professional pride too.

pc1966 · May 1, 2021

westward10 said:
Aesthetics are always important.

Often they follow from a job well done.

Darkwood · May 1, 2021

I will add a few points in addition to others concerns of exposed single insulated cables.

You tell us the supply is TN but what I was getting at is whether is is TNS or TNCS, this can matter, it may mean you garage requires equipotential bonding installed or isolation from electrical earth and rodding as a TT set up.
-Do you have a metal structure or support to the garage that is attached to the ground?
-Do you have any metallic pipes like service pipes (gas - water) coming up through the ground into the garage?

If the answer is yes to any of these questions then you may need to take specific measures in your earthing arrangements in the garage.
To note here that this will not be a concern if the garage is structurally part of the house and not a separate entity away from the house itself.

user786786 · May 1, 2021

Darkwood said:
I will add a few points in addition to others concerns of exposed single insulated cables.

You tell us the supply is TN but what I was getting at is whether is is TNS or TNCS, this can matter, it may mean you garage requires equipotential bonding installed or isolation from electrical earth and rodding as a TT set up.
-Do you have a metal structure or support to the garage that is attached to the ground?
-Do you have any metallic pipes like service pipes (gas - water) coming up through the ground into the garage?

If the answer is yes to any of these questions then you may need to take specific measures in your earthing arrangements in the garage.
To note here that this will not be a concern if the garage is structurally part of the house and not a separate entity away from the house itself.

Hi

it is seperate at back of garden . No metalic structure /support to ground .
no metalic pipes only a plastic MDPE water pipe.

The electrician who did the intial 1st fix work didnt ask to get a steel rod on the shopping list he left me .So i am assusing that he is using the main earth supply via swa 3rd core

I will confirm with the electrcian when they come to energise and test the installation /supply as i dont have knowldge of testing and havent invested in the equipment yet .

Is there a way to distinguish between TNS or TNCS or is it only via testing ?

thanks

Darkwood · May 1, 2021

Confirm it with the Electrician, I didn't realise you were in tally with an electrician, don't worry about the supply characteristics then as this should have also been taken into account by your electrician, in hindsight it would have been better to get them in to do the extended joint as in its present state it would not comply as others have mentioned.

brianmoooore · May 1, 2021

The CPC and neutral are connected to the same block of brass in the DNO service head on a TNCS system, so any Ze you measure at the CU will be just the resistance of the two tails, which for a 'normal' set up will be very close to zero.
On a TNS system, the connection point between the two is further back the line, so you should be able to measure a significant resistance.

SWA too short !

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