'Clipped direct' to the soil?for 350m with a 3kw rating clipped direct that would be ....
Kind Regards, John
'Clipped direct' to the soil?for 350m with a 3kw rating clipped direct that would be ....
I guess that depends upon what you mean by 'much lower'. The tempersture-resistance coefficient of copper wire is around 0.004 per degree C. Hence, as a rough and ready 'in the head' calculation, if one assumes that witches' tit s are about 20 degrees, the 50 degree difference between that and the temperature (70 degrees) for which VDs are tabulated would correspond to a roughly 20% difference in resistance (hence roughly VD, since resistance is the dominant component of impedance in cables up to about 16mm²). So, one might expect that the 2.8mV/A/m might fall to somewhere around 2.2 mV/A/m at 20 degrees C (a proper calculation would obviously be needed to determine exact figures). For 350m of cable, that would allow about 9A total (i.e. about 2kW) before hitting the maximum permitted VD for lighting.Yes thats correct for a temperature of 70°C, do you live in a particularily hot part of the uk. A 16mm cable carrying 13A will be as cold as a witches tit and therefore the tabulated vd will be much lower.With VD at 2.8mV/A/m
The lower VD limit for lighting specified in Appendix 12 of the regs is a bit of a pain in situations like this, and may tempt one to light one's distamt sheds and workshops with candles! However, I wonder if there is not a way around this ....With VD at 2.8mV/A/m, and (presumably) lighting in the workshop?
Lets see your calcs then Holms....
If I had done calcs I would not have said "something like 3c16mm swa"
BAS did the incorrect calcs because he has no experience in sizing cables.
So instead of standing on the sidelines sniping, why not advise everyone of a suitable cable size.
Actually it appears that you do.Don't need it.
So your claimSo what.
is nonsense.A 16mm cable carrying 13A will be as cold as a witches tit and therefore the tabulated vd will be much lower.
That's nonsense holmslaw claim #2, because the book clearly says "This equation applies only where ... the actual ambient temperature is equal to or greater than 30° C.As you're so in awe of the authors of the BRB the calculation you need is this.
Don't judge everyone by your own standards, holmslaw. It's not your "common sense" which leads you to dismiss that formula, it's your inability to understand it.it is nonsense to anyone with an ounce of common sense,
Actually at 20°C, assuming a resistive load, your 350m of 16mm² will drop 10V.Something else to get your head round, IET say max vd for lighting circuit is 3% of 230v = 6.9v, so for a 240v supply it can drop to 232.1volts.
But ESQCR say my supply voltage could be -6% of 230v = 216.2 volts.
So in the former I'm not allowed a lighting circuit at 232, but in the latter my lighting circuit could be at 216.2v - 6.9v = 209.3v and it complies.
I'm sure you are.So I'm quite happy with the 350 mts of 3c16mm swa for a 3kw load.
Thank heavens for that.Nothing else to say,
There's no need for you to be in any hurry to return.bye, bye.
Would the regs allow the use of a step up transformer to send power over the 350 metre at say 460 volts to reduce the current by half and then step down at the far end ?.
Just to get back to the OP - Bob you can see that from the 'debate' there is some significant variance in the size of the cable needed to accommodate your desire to provide power to the shed.We need to rewire a long outdoor run from a house to a workshop approx 230m away through many trees, and to a further shed another 120m on from that (total run 350m).
We're looking at replacing it with a single run of proper SWA cable. Is 3-core 1.5mm OK or should it be thicker because of the voltage drop? Any thing else we should be doing (like extra RCDs in the workshop/shed?)
All advice gratefully received,
many thanks
That equation is not really applicable in the context of the discussion above, for a couple of reasons:
If you look at the first sentence in Appendix 12, you will see that the 3% permitted drop for lighting is 3% of the nominal voltage of the installation (i.e. 230V), regardless of what supply voltage you are actually getting.Something else to get your head round, IET say max vd for lighting circuit is 3% of 230v = 6.9v, so for a 240v supply it can drop to 233.1volts.
But ESQCR say my supply voltage could be -6% of 230v = 216.2 volts.
So in the former I'm not allowed a lighting circuit at 232, but in the latter my lighting circuit could be at 216.2v - 6.9v = 209.3v and it complies.
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