Indeed, and the calcs so far done assume that the same size of cable is used all the way back to the CU (i.e. that any in-house wiring is of the same size as the SWA, assuming that the SWA did not go all the way back to the CU).
Kind Regards, John
Shed wiring
- Thread starter kmb27560
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Kind Regards, John
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No, I really don't think so. There is only one 'installation' and that originates at the cutout/meter.
However, I'm rather confused, since if you actually believed what you've just written, the VD in the 'distribution cable' (SWA) to the shed would be irrelevant, wouldn't it? - so on what basis did you do those calcs above?
Kind Regards, John
I cheated and used TLC VD calculator, and as it stands it seems to be incorrect!
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It's not incorrect, but with the figures you have used you have a 4.1% volt drop from the origin to the end of the supply cable.
This leaves only 0.9% left for your power circuits and you have already exceed the maximum allowable volt drop for a lighting circuit! (as JohnW2 has pointed out already)
Obviously, in reality it will probably be fine.
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Incorrect?
Or did you tell it to do 3-phase calculations and assume 90°C working with XLPE?
No did SWA-PVC. Unless it defaults back to some original settings during inputting.
But TBH was not taking lighting circuit in to consideration, as I assumed origin of installation would be at the CU of shed rather than dwelling.
When you applied for Building Regulations approval, what did you say would be the way that you'd ensure that your work would comply with Part P?
Because it doesn't seem to me that someone who can't do basic cable sizing like that is likely to know all the other things which are necessary to know for safely designing, installing and testing sub-mains, consumer units and final circuits.
If you told them that the work would be done by a qualified electrician, and you then DIY it, you will find yourself horribly disappointed when they find out you misled them.
If your plan is to do it and then find an electrician to "sign it off" then you'll be able to add the disappointment of that not working to the one of LABC refusing you a completion certificate.
So depending on what you told them, and what they are expecting to happen, then it may be that the only advice you should be given is "get an electrician".
If you are just planning to go ahead illegally, then I would strongly urge you to stop now and learn about the work you want to do before carrying on. I can guarantee that there is more to it than you think, and you cannot sensibly carry on on the basis of just asking whatever questions occur to you as you encounter things which you think you should ask about.
Below are the main points you need to cover, but you should also look at the books in the Wiki, and also start working through the online book here: http://www.tlc-direct.co.uk/Book/1.1.htm . Unfortunately it doesn't refer to the current edition of the Wiring Regulations, but it's free, and will still give you a good grounding which you can augment with more up to date publications.
- //www.diynot.com/wiki/electrics:mcbtocable
- http://www.tlc-direct.co.uk/Book/4.3.1.htm (all subsections)
- http://www.tlc-direct.co.uk/Book/4.3.11.htm
- http://web.archive.org/web/20080213151445/http://www.kevinboone.com/cableselection_web.pdf
- http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html
- http://www.tlc-direct.co.uk/Book/5.3.1.htm
- //www.diynot.com/wiki/electrics:mcb2
- http://www.tlc-direct.co.uk/Book/7.13.3.htm
- http://www.tlc-direct.co.uk/Book/8.1.1.htm
- //www.diynot.com/wiki/electrics:swa-gland
- http://electrical.theiet.org/wiring-matters/16/elect-inst-outdoors.cfm?type=pdf
- //www.diynot.com/wiki/electrics:part-p
How many cores?
Maybe I'm being dim, but I'm still confused. If (as you've now repeated) you really believed that 'the origin of the installation' (from which VD is calculated) is in the shed, then the calculation you did (however you did it, and whether you got it right or not) is irrelevant, since the VD in the SWA would not be part of the VD in which you (and the regs) are interested.
The reality is, of course, that the VD from the origin in the house has to be within the limits specified in the regs - which is why we do have tyo do the calcs for the SWA (and any other cable in the distribution circuit), plus VDs in the final circuits (which we've been ignoring, and are probably pretty small).
Kind Regards, John.
In definitions:
Origin of Installation.
The position at which the electrical energy is delivered to an electrical installation.
Where do start or draw the line of the delivery point/installation.
Do you say the origin is at the power station, sub-station, Main CU/FB at property, any sub-boards etc...?
Where do we start to make the calculations from in respect to VD and origin?
Origin of Installation.
The position at which the electrical energy is delivered to an electrical installation.
Where do start or draw the line of the delivery point/installation.
Do you say the origin is at the power station, sub-station, Main CU/FB at property, any sub-boards etc...?
Where do we start to make the calculations from in respect to VD and origin?
It'll do 3-phase calculations if you tell it 3-core.
We've been through this before and, although I agree that the regs are not totally clear (tell me something new!), I think that virtually everyone agrees about the intention - i.e. at least for a domestic installation, the origin is at the cutout/meter - the cruicial point being that this is where the voltage of the supply (230V -6% +10%) is defined.
I have to ask you yet again ... if you do believe that VD (for the purpose of the regs) can be calculated from an 'origin' which is at the end of a (consumer's) distribution cable or sub-main, then why on earth do you think we calculate (as you did, even if with errors) the VD in such a distribution cable/submain, and why do you think that discussion about VD arises so often in relation to lengthy supplies to outbuildings? If you believed that VD in the distribution SWA "didn't count", then the OP could probably have used 4mm² (not 10, 16 or 25 mm²) SWA for his 75m run to his shed.
Kind Regards, John
Oh, now I'm a bit confused! It looks like I can make the run 40m - so does anyone have a definitive answer on the cable size?
While we're here guys, do you know if there's a minimum depth the cable must be buried?
While we're here guys, do you know if there's a minimum depth the cable must be buried?
As has been said, with that length of cable, 10mm² SWA would be more than enough for the loads you mentioned. In fact, if voltage drop within the final circuits in the shed were negligible, 10mm would just about be OK for the 'full load' (32A sockets + 6A lighting).
As TTC pointed out, this is all assuming that the 40m gets all the way back to your consumer unit. Will that be the case?
Kind Regards, John
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