Outbuilding

[Traineeboy]

I’m aware of that but does that mean the Electricians guide to building regs not count ? That isn't a Sarcastic question I’m just wanting to clarify. 

 

[Murdoch]

I’m aware of that but does that mean the Electricians guide to building regs not count ? That isn't a Sarcastic question I’m just wanting to clarify. 

we design, test and install to BS 7671 18th edition

 

[binky]

I’m aware of that but does that mean the Electricians guide to building regs not count ? That isn't a Sarcastic question I’m just wanting to clarify. 

it's a guideline figure, ie for soft ground likley to be dug with a spade, 500 / 600mm is a reasonable depth, but if you were laying cable under a solid concrete driveway, what's the chance of cutting through cable with a spade?  There are different depths for high ways and ploughed fields, where digging is more likely.

I installed lighting on a listed church building, dig any deeper than 300mm and it becomes notificable as an 'archaeological dig' - so that didn't happen!  Like wise an historical feature that had solid granite paving, the paving turmed out to be about 500mm thick (and firkin heavy). The paving is listed, so no fixings will ever be made to it, like drilling holes for a litter bin. To feed a cable we ended up drilling a small hole through the granite block . Cable is now protected by 300mm of solid granite, can't do much more than that. One thing I would say is that when not following guidelines, a Risk Assessment may be needed to cover arse! 

 

[Evans Electric]

How come you measured your cable run in feet  Traineeboy ?    I make it about 121 mtrs  for the sake of calcs .  

I think I'd forget the existing outbuildings and run back to the main supply if you can .     Work out your design current , feed a metal switch fuse  from the Henley blocks  , gland your  SWA into the sw/fuse .            Have you decided what the heating load will be? 

I would then not earth nut at the new building end but install an earth rod. Would this be the correct thing to do ? 

I don't see that you need to do all that stuff ,  run a  3 core SWA  ,  earth your glands in the usual way .    You say its a TN-S supply  I think.     

 

[Murdoch]

Measuring in feet suggests a very mature trainee.

why is it so many people think they need to TT outbuildings ?

 

[Evans Electric]

Its the dreaded  ,  " Exporting  the PME  earth  to outside the bonded zone "       Many have no knowledge of it , many ignore it .  An Assessor I spoke to knew nothing of it . 

As far As I know it arose from when PME  started to appear ,   the  fear that a break in the earthed neutral on the supply side would result in current flowing between L & E  in the premises .  

It used to be hard to track it down in various Regs books   ( Or was that just me?)      But  its become an issue now with the advent of EV charging  points mounted outdoors . 

It seems no one bothered when it was just an outside garden socket.                   It doesn't seem to bother anyone when its a TPN  supply .  Imagine a small building added within a hospital ,  a supply would be taken  from an existing building  DB   to the new building , including the earth .  No  rods at new  building .  

 

[Traineeboy]

Measuring in feet suggests a very mature trainee.

why is it so many people think they need to TT outbuildings ?

It was given to me in feet i do normally use Meters but yes I guess I am a little older than a 19 year old apprentice. TT wise  am I right in thinking even if you use the suppliers earth but you don’t get the required readings you need to use a earth rod as well ? 

 

[Evans Electric]

You don't have a TT so don't worry about it  .     If you were on a TT  there would be no earth at all ,  you have to create your own , usually in the region of up front 100mA RCD   plus 30mA  on everything else  with a  rod or rods banged in .  ( No RCBOs  as they are only single pole .   

 

[binky]

 TT wise  am I right in thinking even if you use the suppliers earth but you don’t get the required readings you need to use a earth rod as well ? 

if you use TN-s earrh and dont get acceptable Zs readings, you've used too small a cable

 

[Murdoch]

if you use TN-s earrh and dont get acceptable Zs readings, you've used too small a cable

Which brings us neatly back to the original question.

OP - tell us what you calculate the cable size you need (and I would recommend you check the actual Ze on the site before anybody runs off buying the wrong cable)

Hope this helps

 

[Traineeboy]

Which brings us neatly back to the original question.

OP - tell us what you calculate the cable size you need (and I would recommend you check the actual Ze on the site before anybody runs off buying the wrong cable)

Hope this helps

Yeah all my findings will be checked by my boss and he will supervise me testing etc. 
 

just another question if you don’t mind. 
 

If a say a customer wanted a garage unit installed but their current CCU it would come off is a plastic enclosure with a single RCD  and obviously not an 18th Edition compliant is that OK ?  You might recommend they upgrade but do they have to ? 

My friend did this but apparently the CPS ( Think Napit) said the main board should be 18th edition compliant. Your thoughts ?

 

[Murdoch]

If a say a customer wanted a garage unit installed but their current CCU it would come off is a plastic enclosure with a single RCD  and obviously not an 18th Edition compliant is that OK ?  You might recommend they upgrade but do they have to ? 

My friend did this but apparently the CPS ( Think Napit) said the main board should be 18th edition compliant. Your thoughts ?

Napit (if thats who they were) don't know what they are talking about is my opinion - you have to realise that the CPS's don't employ many assessors so they are normally sparks doing assessing as a 2nd income. They run around saying different and conflicting things .......... some are OK though

 

[Traineeboy]

Napit (if thats who they were) don't know what they are talking about is my opinion - you have to realise that the CPS's don't employ many assessors so they are normally sparks doing assessing as a 2nd income. They run around saying different and conflicting things .......... some are OK though

fair. I think he said it’s because the bathroom lights weren’t on an RCD. But from what I understand that wouldn’t  be an issue unless the bathroom lights was the actual circuit you are working on. Would that be right ? 

 

[Murdoch]

fair. I think he said it’s because the bathroom lights weren’t on an RCD. But from what I understand that wouldn’t  be an issue unless the bathroom lights was the actual circuit you are working on. Would that be right ? 

What have bathroom lights got to do with a garage CU?

 

[Traineeboy]

I agree - I think he was meaning because the board powering the Garage CU was only a single RCD it was not covering the bathroom lights and therefore it should have a duel RCD. 
 

I was going to get Napit registered when I have a little more experience but might look else where lol. 
 

 

[Murdoch]

I agree - I think he was meaning because the board powering the Garage CU was only a single RCD it was not covering the bathroom lights and therefore it should have a duel RCD. 
 

That doesn't make sense

If you are a trainee and working for somebody, why would you need CPS membership?

 

[Traineeboy]

I’m just saying for the future if I wanted to start taking on my own domestics jobs or do my own house. I’m not covered by my bosses if I do my own. I’m taking about like 18 months time. My boss is happy for me to take on small jobs on domestic as he is mostly commercial. Im not ready yet I know that. 

 

[Traineeboy]

When you work out Voltdrop I know you are allowed up to 5 % for power and 3% for lighting. 
 

If a distribution circuit after calculation will drop 4.6% by the time it gets to the new distribution board where do you stand on running lighting circuits off the new DB as lighting you can only allow 3% drop ? 

 

[Evans Electric]

It would be designed wrongly then.     I think I said above somewhere,  decide upon the DESIGN load ,  you know the cable length.. you know  the install method  , work that out , forget about TT and all that until you are faced with it .   

 

[Murdoch]

When you work out Voltdrop I know you are allowed up to 5 % for power and 3% for lighting. 
 

If a distribution circuit after calculation will drop 4.6% by the time it gets to the new distribution board where do you stand on running lighting circuits off the new DB as lighting you can only allow 3% drop ? 

Volt drop needs to be calculated using

design load

Ze

R1 + R2 for the distribution circuit

R1 + R2 for the socket circuit

hope this helps