H
holmslaw
..
joining armoured cable underground
- Thread starter mrcrow
- Start date
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525.1/2 in BS7671 set the minimum voltage required by equipment. The requirement is deemed to be met by complying with the voltage drops allowed by Appendix 12. These voltage drops have necessarily been set to cater for the worst case supply at times of peak demand, i.e. the general case. However, the OP’s case is not general; it is specific, so the volt drop calculations are not necessarily the appropriate way of complying with 525.1/2; the standard calculation may result in unnecessary expense.
The standard calculation allows a worst case voltage at lighting fittings of 209.3V, assuming a consumer’s lowest supply voltage of 216.2V. But this worst case supply implies the consumer is connected at the end of a feeder from the local distribution substation at a peak time of the year and day. For most of the year the voltage will be well above 216.2V. Indeed, the theoretical annual average voltage for such a connection is 243V. All the other connections to the feeder would enjoy a higher minimum voltage, in most cases substantially so. In theory, you could double the lighting volt drop for 80% of connections and still comply with 252.1/2.
It would therefore be reasonable to assess the supply voltage situation before condemning the OP’s proposal because it does not meet the 3% lighting volt drop.
Of course, the fault loop impedance requirement still needs to be met.
The standard calculation allows a worst case voltage at lighting fittings of 209.3V, assuming a consumer’s lowest supply voltage of 216.2V. But this worst case supply implies the consumer is connected at the end of a feeder from the local distribution substation at a peak time of the year and day. For most of the year the voltage will be well above 216.2V. Indeed, the theoretical annual average voltage for such a connection is 243V. All the other connections to the feeder would enjoy a higher minimum voltage, in most cases substantially so. In theory, you could double the lighting volt drop for 80% of connections and still comply with 252.1/2.
It would therefore be reasonable to assess the supply voltage situation before condemning the OP’s proposal because it does not meet the 3% lighting volt drop.
Of course, the fault loop impedance requirement still needs to be met.
A
Alarm
If he needs that, you need a new electrician.all the other electrical information i will pass on to my electrical installer for his benefit..
Then he is the ONLY one who can tell you what to buy, as that counts as design, and I take it you aren't signing part of a multi-signature EIC to attest that your design complies with BS 7671?
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Voltage drop calc for you here;
http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html
What's the total length? Suspect 2.5mm will be too small unless you only plan for a small load at the shed.
Ignore ole misery guts, he just loves to preach the "law" to posters.
thanks yorks
i will i think measure accurately the full run to the shed from the cb in the hallway and do the calc again
much obliged for that link
cheers
geof
If he needs that, you need a new electrician.all the other electrical information i will pass on to my electrical installer for his benefit..
Then he is the ONLY one who can tell you what to buy, as that counts as design, and I take it you aren't signing part of a multi-signature EIC to attest that your design complies with BS 7671?
sorry no offence intended...
thats a brilliant instruction video
the cable looks a bit larger than mine
do you think i could use a large chock block...which is on the bare end just now as it is still exposed in the garden...the garage has gone
and insulating tape which i got from....wait for it....a shed..
its yellow and green tape
or should i get the one 3M are advocating...
a big thanks ticked for this and puts me in the picture just how important this type of exercise is
cheers
geof
thats a brilliant instruction video
the cable looks a bit larger than mine
do you think i could use a large chock block...which is on the bare end just now as it is still exposed in the garden...the garage has gone
and insulating tape which i got from....wait for it....a shed..
its yellow and green tape
or should i get the one 3M are advocating...
a big thanks ticked for this and puts me in the picture just how important this type of exercise is
cheers
geof
thanks again holmslaw...got it done and wired...no smoke yet
God bless
geof
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