Yet Another Submain / Name Calling Ect Banned.

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sirsparkabit

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I am being brave posting this after reading all other posts on this subject so here goes.

Small workshop

20mtr run

Needs 4 S/O + 4 Five foot double florries.

13 amp welder, grinder hand tools ect to be used,(by one person!!)

House (small 2 bed) Has tncs system. Board has RCCB main switch so i will not be coming off spare way!.

My design is 20amp fused switched isolator fed from henley block

4mm 3 core swa to rcd garage unit with 16amp breaker to 2.5mm radial for sockets and 6amp mcb 1.0mm to lights.

I did talk this one over as originally i was going to tt the garage but after chatting to a learned friend he said if max Zs tables are not exceeded he did not see why the earth could not be Exported over this distance.

I do intend to contact local DNO for their views, of course all your views are respected and most welcome as usual.PrayPray

 
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Oh dear. The general view seems to be

DON'T EXPORT THE EARTH

How much is a rod going to cost if you TT the 'small workshop/shed/husband hideaway'. Very little.

Now if you reply quickly promising to nock a rod in we can all sleep soundly

:D

 

sirsparkabit

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Oh dear. The general view seems to beDON'T EXPORT THE EARTH

How much is a rod going to cost if you TT the 'small workshop/shed/husband hideaway'. Very little.

Now if you reply quickly promising to nock a rod in we can all sleep soundly

:D
Hi apache i was waiting for that comment but larger and in red from steps.

I am not adverse to knocking a rod in if it gets you a good nites sleep, however i just spoke to my helpline and when i said i was going to tt the garage they said why?.

I have just spoken to EDF who said yes you can but your never sure if they know what is what as they do not have a technical dept anymore.

 

M107

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personal prefrence.

I'd TT the shed.

Use10mm for the submain.

Up the submain ocpd.

It's then future proof for those extra circuits you'll be asked to put in at a later date.

 

Theorysparky

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personal prefrence.I'd TT the shed.

Use10mm for the submain.

Up the submain ocpd.

It's then future proof for those extra circuits you'll be asked to put in at a later date.
agreed

but its not only the extra circuits

its the three kids going to the workshop to do a project with everything plugged in.

EON still have a technical help line ,,,sorted out my meter tail problem

 

sirsparkabit

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Thanks for replys m1o7 and theory i have visited this workshop and cant see the need for 10mm,

originally with vd ect calc came out at 2.5 so i upped it to 4mm i think with 20amp sw fuse ect no need to go larger unless client wants to put in extra circuits which he does not . This is a clued up guy not your average punter who wants to sneak things in after you have gone.

He is capable of doing this himself but wants cert to cover his insurance ect.

 
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What is the construction of the workshop?

Does it have any Extraneous Conductive Parts that could introduce an earth potential that would need bonding?

If you need to supp bond any bits in the workshop..

then you have got to avoid parallel earth paths and thus need to TT!

but if it is it all brick & concrete floor.. NO water pipes?

bit like an integral garage in your average semi?

it could be argued it ain't much different from the house itself? :|

for example my house has concrete garage floor..

and brick walls... just happens to be physically joined to the building? ;)

 

sirsparkabit

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[

What is the construction of the workshop?]could have some steel girders into the concrete ok i will tt it.Does it have any Extraneous Conductive Parts that could introduce an earth potential that would need bonding?

If you need to supp bond any bits in the workshop..

then you have got to avoid parallel earth paths and thus need to TT!

but if it is it all brick & concrete floor.. NO water pipes?

bit like an integral garage in your average semi?

it could be argued it ain't much different from the house itself? :|

for example my house has concrete garage floor..

and brick walls... just happens to be physically joined to the building? ;)
 

sirsparkabit

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Sorry specs i tried doing that [ ] thing but am carp on these things.

O.k i think it does have some steel work in the construction now you mention it so i will TT it in any case.

Do you think the design is o.k (i respect your opinion) :x

What make of switch fuse isolator would you use, as usual good one but not to expensive?

 
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Hi apache i was waiting for that comment but larger and in red from steps.
There's time yet :D

.13 amp welder, grinder hand tools ect to be used,(by one person!!)
its the three kids going to the workshop to do a project with everything plugged in.
I wouldn't let your 3 kinds grind and weld all at once! Could be dangerous!

 
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I would not use 20 amp B type MCB to supply building as welder could trip it out. When I do submains to exterior buildings I use 10mm 2 core Swa and rod it at the other end no matter what supply is.

Batty

 

sirsparkabit

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I would not use 20 amp B type MCB to supply building as welder could trip it out. When I do submains to exterior buildings I use 10mm 2 core Swa and rod it at the other end no matter what supply is. Batty
Its only a small mig but point taken batty perhaps 32 with a 6mm swa would do the trick?.Pray

 
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..............so i will TT it in any case...............
Ah!! Steptoe will be a happy man tonight then;\ :^O

Do you think the design is o.k
ok... lets have a look through your facts...

Small workshop 20mtr run

4x S/O

4x5ft double florries. 4x(2x58w tube)=464watts (2.02A)

13 amp welder' date='

grinder hand tools ect to be used,(by one person!!)

House Has tncs system... [ TN-C-S {pme} MAX Ze <=0.35Ω

My design is 20amp fused switched isolator

4mm 3 core swa [/quote']

CURRENT

As you say the 4.0mm SWA can carry upto 37A method 'D' 'buried'

or greater clipped direct..

VOLTDROP

The 4.0mm SWA bit will have a voltdrop of 11mv/A/m

lets assume it is running as your full 20Amp load..

11x20Ax20m/1000 = 4.4volts @ the SWA termination at workshop CU!

As max permissible Volt drop is (from pg 124 OSG / appendix 12 BS7671)

lights max 3% = 6.9V

other max 5% = 11.5V

6.9v - 4.4v = 2.5v can still be dropped down your 1.0mm

11.5v - 4.4v = 7.1v can still be dropped down your 2.5mm

so taking extremes again...

LIGHTS:

IF the lights were taking 6A

1.0mm has 44mv/A/m

so 2.5v=(44x6xMeters)/1000

2.5=0.264xMeters

so max length of cable = 9.47m

BUT your florries are only 2.02Amp.

lets say customer also asks for 500watt Halogen floodlight outside.

add another 2.18Amps total 4.2A..

checking the above calc again with 4.2A gives approx 13.5meters?

not sure if this is long enough?

If you did the same to calcs but with 1.5mm cable.. (29mv/A/m)

you would get:-

14m @ 6A

20.5m @ 4.2A

SOCKETS:

IF the sockets were taking 16A

2.5mm has 18mv/A/m

so 7.1v=(18x16xMeters)/1000

7.1=0.288xMeters

so max length of cable = 24.65m

So basically IF everything was running FULL wack!

your lights circuit on 1.0mm bit cannot exceed 10m-13m from SWA CU termination to furthest light!

OR

your lights circuit on 1.5mm bit cannot exceed 14m-20m from SWA CU termination to furthest light!

AND

your sockets on 2.5mm bit cannot exceed 25m from SWA CU termination to furthest sockets!

Zs

R1+R2

20m 4.0mm =0.19Ω

25m 2.5mm =0.49Ω

13m 1.0mm =0.47Ω

20m 1.5mm =0.61Ω

At these lengths, and if Ze is 0.35Ω

then Zs on sockets will be around 1.03Ω

Zs on lights @1.0mm will be around 1.01Ω

Zs on lights @1.5mm will be around 1.15Ω

CABLE COSTS:

4.0mm to 6.0mm costs 66p more per meter @ TLC prices
 

sirsparkabit

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SpeshThat was a work of art !!!

Applaud Smiley
May i also applaude such great work,drat no smileyies left.

I really wish i had taken more notice of my maths now,Blushing

i do find it hard and think i will have to brush up on it:_|

But i really do think that you guys are so helpfull that with perseverance i will get there in the endPray.

I like to think with the right teachers anyone can arrive at the same conclusion eventually, many thanks to you all and the forum that works so hard to make us all more competant.

P.S to those who would smite a lesser spark,

If i don't know how to do it ,i won't do it.

With a little help from our friends, great things are possible:x:x;)

 
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SpeshThat was a work of art !!!

Applaud Smiley
dohh!Blushing

its just a load of individually small calcs..

bundled up together to look big & clever..

but down at the grass roots its just a systematic logical approach! :p ; )

Actually its a classic example of how..

Gut instinct & experience.. (e.g. Battys reckoning that 6mm SWA probably best?)

Matches up with formally calculating something out to assess best solution.

And the real world is always a case of working between sensible costs.. {don't go too big}

and sensible electrical tolerances.. {don't go too small}

Spose the whole of this thread could be a good text book example of that balance between..

customers requirements / the regs & calcs / applying experience and knowledge to get the best results.

;)

And anyway if it has helped anyone reading to perhaps look at things from a wider or different angle then great!

That is the great thing about this Forum!!

and all of its members!

AND THE COMPLIMETARY DRINKS IN THE VIRTUAL BAR!!!Blushing:p:^O

Guiness DrinkGuiness Drink

 
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I would not use 20 amp B type MCB to supply building as welder could trip it out. Batty
Quite right. Me and a few of my friends restore/mod cars as a hobby and a 100A mig (the smallest type) will trip out a 20A B type breaker. You will have to fit a minimum of a 32A supply. You can export an TNCS earth under certain circumstances, Here's that IEE document again

http://www2.theiet.org/Publish/WireRegs/WiringMatters/Documents/Issue16/2005_16_autumn_wiring_matters_electrical_installations_outdoors.pdf

 
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Forgot to mention that the above article was written to the 16th edition so ignore the RCD parts. I tend to wire jobs like this in 10mm SWA so there is always a main bond to go back to the MET. Up here in London i rarely see TT systems but any supply earth is always going to be better than TT.

 

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