Power supply to shed 230m away

larthehar

Hi all,

I need a power supply with a max current draw of 10A in a shed for lights. I intend on using a 25mm^2 swa direct buried @ 900mm with marking tape @ 600mm. My calcs show that the voltage drop is less than 4% which is the law?
Can ye confirm that this would be in spec?

Obviously it would be on a 40A breaker at source and a new dist board with Rcb, Mcbs at shed.

Also can work be completed by competent individual and certified after or does it need to need to be installed by a REC?

2011

I would be surprised if the volt drop will not be excessive with a cable that small, I say this without doing a calculation or having the benifit of having the regulations in front of me).

Make sure you are lying down when you get the quote for the SWA, it will cost more than the national debt.

If you can keep within 4% volt drop it will be compliant.

I would use a far smaller MCB than a 40A if the design current is no more than 10A.

You will need to use a REC for any work on a distribution board.

Boardnashea

Would you not give yourself a little more leeway with a higher Ampage in case you need to use powertools or whatever at some satge down the road?

larthehar

Boardnashea wrote: »

Would you not give yourself a little more leeway with a higher Ampage in case you need to use powertools or whatever at some satge down the road?

Jumping from 25sq to 35sq probably would allow a 20A current draw but 35sq is serious €€€ is the problem...

2011

Boardnashea wrote: »

Would you not give yourself a little more leeway with a higher Ampage in case you need to use powertools or whatever at some satge down the road?

The circuit is designed on the basis that the max current is 10A. Drawing a lager current may result in excessive volt drop and this could have consequences.

foxy farmer

Any harm in asking what supply voltage you have at the point you will be extending from? Monitoring the voltage with a good load on will give you a better idea of what your voltage at far end will be.

Bruthal

larthehar wrote: »

Obviously it would be on a 40A breaker at source and a new dist board with Rcb, Mcbs at shed.

Won't certainly need to be a 40A breaker anyway. Only needs to be big enough for the load, not necessarilly the cable size.

frankmul

4% should cover from the main incoming supply point to the furthermost point in the installation, not just the underground cable.

2011

Bruthal wrote: »

Won't certainly need to be a 40A breaker anyway. Only needs to be big enough for the load, not necessarilly the cable size.

Exactly, this is the point I was making in my earlier post.

Paul_Mc1988

10 Amps=Ib> use this to now pick protective device
Table A61-C1 10 Amp MCB Type B = In
Table A52-E Installation method D > as we are underground
Table A52-H Grouping factor = 1.00 > as its run on its own
Table A52-G2 Temperature factor=1.00 estimating ground temp not to rise above 20 degrees
Iz=(10/(1.00*1.00))=10amps > use this to now pick the cable size

Cable cross sectional area = 1.5mm2 >
Volt Drop=((29*10*230))/1000=66.7 Volts > Not suitable

Cable cross sectional area = 2.5mm2 >
Volt Drop=((18*10*230))/1000=41.4 Volts > Not suitable

Cable cross sectional area = 4mm2 >
Volt Drop=((11*10*230))/1000=25.3 Volts > Not suitable

Cable cross sectional area = 6mm2 >
Volt Drop=((7.3*10*230))/1000=16.79 Volts > Not suitable

Cable cross sectional area = 10mm2 >
Volt Drop=((4.4*10*230))/1000=10.12 Volts > Not suitable

Cable cross sectional area = 16mm2 >
Volt Drop=((2.8*10*230))/1000=6.44Volts > Suitable but would size up

Cable cross sectional area = 25mm2 >
Volt Drop=((1.75*10*230))/1000=4.025 Volts >best fit

Tuco88

I take it we are talking single phase supply.I usually go by the rule of Ib = < In < Iz. If you are drawing 10 amps. I'd have taken (In) for a 16 amp mcb giving a little more flexibility/addition and carry on from there.I'd really take in the advise of extras circuits it's good advise.

Best of luck.

freddyuk

larthehar wrote: »

Hi all,

I need a power supply with a max current draw of 10A in a shed for lights. I intend on using a 25mm^2 swa direct buried @ 900mm with marking tape @ 600mm. My calcs show that the voltage drop is less than 4% which is the law?
Can ye confirm that this would be in spec?

Obviously it would be on a 40A breaker at source and a new dist board with Rcb, Mcbs at shed.

Also can work be completed by competent individual and certified after or does it need to need to be installed by a REC?

Just lights?? What sort of lights?? There may be an easier / cheaper alternative for lighting.

freddyuk

freddyuk wrote: »

Just lights?? What sort of lights?? There may be an easier / cheaper alternative for lighting.

I was waiting for that.
Had to restrain myself tbh.

Carry on.

2011

As already stated the maximum permissible volt drop is 4% of nominal voltage (230VAC), this equates to 9.2 volts.

There are at least 3 places that this volt drop can occur:
● The volt drop from the ESB meter to the distribution board.
● The volt drop from the distribution board to the shed.
● The volt drop from the shed to the furthest point on the final circuit.

That means that the combined total volt drop must not exceed 9.2 volts. Therefore it is not possible to determine that the volt drop will be excessive or not from the information provided.