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A

ash2020

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I'm just about to wire a sub-main from an entrance hall into a flat, about 4-5 metres away. I guess it'll have to be in 25mm which in SWA is going to be like a broomstick?

As it's my first crack at it, how difficult is the termination going to be at both ends and are there any particular pitfalls/tips from anyone.

Thanks for any advice or help.
Cheers
Andy
 
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S

sparkyork

it doesnt have to be in swa if im correct in saying so. if youve come from your meter tails to an fused isolator then you can run tails from your isolator. just a thought to give you some more ideas, plan your route then crack on!!
 
A

ash2020

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  • #3
Thanks sparkyork (is that spark york as in Yorkshire or sparky Ork as in Lord of the Rings? just wondering!)

I would gladly run the tails in bendy electrical string rather than SWA, especially as it's not outside and no-one's going to put a spade through it.

How would you recommend protecting it? Metal trunking? Plastic trunking? It's going to run up the wall by the edge of a staircase and then through a 12" brick wall.

2 X 25mm tails + 16mm earth is still going to be fairly hefty, but not nearly as bad as 3 core 25mm SWA.

Cheers
Andy
 
S

sparkyork

bit of nice pvc trunking maybe 50x50? id use a bit of plastic pipe to take it though the wall with and also be aware that you may need to provide fire barriers in thsi hole as well.

ps yeah from york mate, not so much ork as dork!! lol
 
S

spark-doctor

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  • #5
Technicaly you cant hang another 100A supply of the same incomer fuse. If you have a problem in the future and it blows the main fuse, you could be in trouble with your DNO.

I take it as 100A as you say you are using 25mm tails
 
S

sparkyork

hey up doctor, forgive me but where does it say he's got essentially 2 supplies coming off same fuse? sure hell tell us in a mo!!
 
S

spark-doctor

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  • #7
hey up doctor, forgive me but where does it say he's got essentially 2 supplies coming off same fuse? sure hell tell us in a mo!!
Because he says he is putting in a SUB MAIN of his main supply ie 2 supplies.
 
S

sparkyork

i interpreted that as been his main supply as in dno fuse and that he was installing a new sub main??
 
A

ash2020

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  • #9
Thank you to that man from York. (nice city) I'm assuming he's a man, but there are one or two of the other types doing sparky work now. (the ones with fun bumps).

Anyway, as sexism is now illegal, I'll get on with it.

Two meters have been put under the stairs in the entrance hall to two upstairs flats, basically because that was the easiest place for them to get to. I now have to run each supply 3-4 metres up to the top of the stairs and then into each flat.

I obviously want the CUs to be actually inside the flats so I've got to run either long tails or sub mains (thanks sparkyork!)
Cheers
Andy.
 
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S

spark-doctor

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  • #10
i interpreted that as been his main supply as in dno fuse and that he was installing a new sub main??
LOL i interpreted it as he was coming of his main panel in the hall to a flat above.

Hope he clarifies:D
 
S

sparkyork

ahh so you got 2 seperate supplies into the property and your running 2 separate supplies from each supply to each flat!?

ps i wish i was a woman sometimes! id have one of them usb things stuck some where warm all day!!
 
S

spark-doctor

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  • #12
ps i wish i was a woman sometimes! id have one of them usb things stuck some where warm all day
Could not be a woman, would sit at home all day fondeling my breasts:D

As for the tails, do you need a 100A supply to each flat. If you only need 60A you could drop the cable to 16mm.
 
A

ash2020

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  • #13
Of course, the other thing is that these new tiny meters have a 100A isolator switch on the right hand side that anyone can operate with a screwdriver, (or even a lolly stick in an emergency) so maybe that counts as a switch and they're more forgiving about the length of tails.
Andy.
 
E

EasyFox

  • Thread Starter Thread Starter
  • #15
Switch fuse at the meter end then
Use 25mm 2 core swa & a seperate 16mm mec.
Or
25mm 3 core swa
Or
25mm/16mm tails in earthed trunking.
 
J

jibspark

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  • #18
arnt 3-4 meter tails too long? i thought there was a limit on length but i cant remember what.....
 
M

Mike P

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  • #19
Mechanical protection not needed on any thing over 4mm.

I refer of course to the MEC
 
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Jurassic Spark

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  • #20
Why are you using 25mm SWA? 16mm SWA is adequate for 100amp supply - use 3-core with one core used as earth to supplement the armouring.
 
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ash2020

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  • #21
I guess 16 will do, it's a smallish flat. I wasn't sure about being able to use the armouring for the main earth. Are you saying it's not enough? The calcs for it are mind boggling. (543.1.3 17th ed) How the hell do you work out the CSA of the armouring?
And is I in the equation the same as max PFC?
 
M

Mike P

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  • #22
I only use the armour as a way of beefing up the earth and mech protection.
If your not running three core 16mm yoy should run a seperate 16mm MET
 
M

ms&electrical

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  • #23
I only use the armour as a way of beefing up the earth and mech protection.
If your not running three core 16mm yoy should run a seperate 16mm MET
I would do it this way to. 3 core 16mm swa with 60amp switch fuse isolator.
 
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ash2020

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  • #24
Sorry to bang on about it but where does it say about running a separate earth and why isn't the armouring sufficient.
 
S

Spudnik

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  • #25
Sorry to bang on about it but where does it say about running a separate earth and why isn't the armouring sufficient.
There is no requirement if you are using 3 core SWA, but obviously you need one if using 2 core plus seperate earth.

However, if there is no need for mechanical protection and it is going to be run in trunking, then i would suggest you ask your supplier for 16mm split concentric cable.

Doddle to run and terminate with standard plastic compression glands.

Have a look here:

Electrical Cable - Split Concentric Cable BS7870
 
J

jibspark

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  • #26
There is no requirement if you are using 3 core SWA, but obviously you need one if using 2 core plus seperate earth.

However, if there is no need for mechanical protection and it is going to be run in trunking, then i would suggest you ask your supplier for 16mm split concentric cable.

Doddle to run and terminate with standard plastic compression glands.

Have a look here:

Electrical Cable - Split Concentric Cable BS7870
wow! never seen that before! whats with all the neutrals???
 
S

Spudnik

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  • #27
wow! never seen that before! whats with all the neutrals???
The neutral conductors csa together form 16mm2. As the same with the CPC's.

Centre core is 16mm line conductor.
 
S

sparkyork

last time i used some of this stuff we had to heat shrink the neutrals and earth
 
S

Spudnik

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  • #29
last time i used some of this stuff we had to heat shrink the neutrals and earth
No need if they are terminated into an enclosure!

Plus, 10mm earth sleeve is available.
 
S

sparkyork

they were terminated into consumer units from sw/fuse isolators down in the mains room. both ends were heat shrinked, neatrals were carefully bared off and twisted together, and heat shrinked. looks professional, rather than seeing a load of seperate neautrals etc.
 
A

ash2020

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  • #31
D'you think it would be ok to run split con through a communal entrance hall (all indoors) into the flats without trunking, just clipped to the surface? If not, would plastic trunking be OK?
 
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spark-doctor

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  • #32
Sorry to be the bearer of doom but if you used Split-Con you would have to RCD protect the cable, bury it greater than 50mm or protect it with earthed capping/conduit, as it does not have a earthed protector and the Neutral is classed as a Line conductor.

Trying to get all the neutrals into the termination would be a pain as well.

As for not sleeving them, would you not sleeve CPC and Neutral conductors in a CU?
 
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S

Spudnik

  • Thread Starter Thread Starter
  • #33
Sorry to be the bearer of doom but if you used Split-Con you would have to RCD protect the cable, bury it greater than 50mm or protect it with earthed capping/conduit, as it does not have a earthed protector and the Neutral is classed as a Line conductor.

Trying to get all the neutrals into the termination would be a pain as well.

As for not sleeving them, would you not sleeve CPC and Neutral conductors in a CU?
There is no requirement to rcd protect a split con cable that is surface mounted, providing it is out of reach and cannot be damaged. No different from t&e.

Obviously if it is buried then yes, but to be honest, i would do everything i can to avoid an RCD on the front end of it, even if it meant trunking. Its a piece of cake to work with and looks a lot neater.

There is no problem getting the neutrals into a termination point. Just a little care and time taken to do the job.

Why would you need to sleeve a neutral conductor in a cu?

CPC's yes.
 
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