Hi all.advice please.I am intending to get a log cabin and put it in my garden.I would like to add electric to it so I can add couple of double sockets to run a fridge,hi fi and lamps.I am intending to connect the supply directly to a new circuit.however what cable should I use?the distance is 100m or so.I have been talking to a electrician friend who was advising using armoured core cable (3).I am intending to run approx 15m above ground the rest buried at te correct depth with yellow warning tape attached to it.I have been googeling this and read something about voltage drop this has gone completely over my head.so any advice greatly received.
Long stretch
- Thread starter Talktojake
- Start date
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H
holmslaw
..
Lol.you r properly right.but on what basis?
H
holmslaw
..
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Is the cable Likely to cost more than £200?if I were to move log cabin so I only required 50m would that be just as awkard?
As Holmslaw says, that's a very long way for a cable.
You need an experienced electrician on site to properly measure the distances and assess what the real load is going to be. He/she will then be able to calculate the cable size needed.
The longer the cable is then you lose more volts. If the cable is not thick enough then you will start out at the house with (say) 230v but it may only be 200volts by the time it gets to the cabin. That would mean that your kettle is not ever going to boil to make the tea.
Lets suppose you need 16mm² armoured cable. 100m of that will set you back about £500.
You are going to have to cost in digging a half metre deep trench for the cable for 100metres too....
You need an experienced electrician on site to properly measure the distances and assess what the real load is going to be. He/she will then be able to calculate the cable size needed.
The longer the cable is then you lose more volts. If the cable is not thick enough then you will start out at the house with (say) 230v but it may only be 200volts by the time it gets to the cabin. That would mean that your kettle is not ever going to boil to make the tea.
Lets suppose you need 16mm² armoured cable. 100m of that will set you back about £500.
You are going to have to cost in digging a half metre deep trench for the cable for 100metres too....
H
holmslaw
..
Thanks for info guys.nope all on my land so is ok.my other option is to do a 50m run and connect in a swimming pool filter and pump.what sort of cable would that need?I will do all ground work myself so no cost.I am intending to buy all bits then get my qualified mate to do the job.just awkard to get hold of him to discuss it properly and he lives away away and don't wanna make he come over just to show me what I need.
Talktojake";p="2003734 said:
just looking for advice so can price it up before i waste his time really.
Another question.could I make a 100m extension lead?with atleast a double socket on the end for radio and fridge?what should I use for that?would not be left out in rain or anythin.and would only be used whaen I was out there.
That seems like a silly idea, especially if you are connecting it to a fridge.
How much are you spending on a log cabin? Thousands - then why are you are trying to scrimp and save on the electrics. Either do the job properly and safely or don't do it at all.
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OK fridge, Hi-fi, and lights let me go through them one at a time.
The lights need to be able to work when nothing else is running and when all is running so the only way is to use a device which will accept this. There are two common lamps that will work with volt drop and both use same technology. The HF florescent and the extra low voltage spot light. Both use switch mode power supplies and if selected carefully you can get a HF florescent that will work from 100 to 240vac.
The Hi-fi is similar again looking at switch mode supplies. Or 12v car type with a switch mode power supply external.
The fridge is more of a problem. There are three types of fridges. The type with a motor is going to be a problem two fold. One it will have a problem starting and two it will drip the volts for everything else.
The type used in caravans uses a heater so does not draw a heavy start current these would work a lot better and would likely still work with a heavy volt drop.
The last type uses a French semi-conductor device and runs on DC mainly used with cool boxes and the like. If you were thinking of using 12vdc for Hi-Fi then maybe you can combine the two.
Once you have selected the equipment you will know what volt drop you can cope with. Now comes the calculation time. 2.5mm cable is rated at 18 mV/A/m so for 100 meters with 5 A draw the volt drop will be 9 volt as you go up in size then the volt drop will reduce so 4mm @ 11mV/A/m will be 5.5 volt and 6mm @ 7.3 mV/A/m will be 3.65 volt. Really there is correction factors but these values are close enough. So at 5A with 6mm SWA you are just within the volt drop allowed for lighting.
Since there is also an earthing problem I would say 6mm is really your minimum size. If you want to put more of a load on the circuit then cable sizes must increase.
The problem is safety which is something completely different to volt drop. The idea is should something go wrong and there is a short then some protective device will open. If we look at the 6A MCB these also have a letter and a B6 has a thermal trip current of 6A and a magnetic trip current of 5 x 6 or 30A. For 30A to flow using ohms law then the value of the whole circuit needs to be less than 7.66 ohms. The 6mm cable at 100m is around 7.3 ohms. Just within the value needed to allow this current to flow so open a safety device.
So although one can get around the volt drop one can't do it safely and your smallest cable will be 6mm SWA to comply with just a 6A supply. And I have not included the resistance of the supply which is likely 0.35 ohms in first place.
The problem is all this needs measuring and the results forwarded to the local authority building control (LABC) under Part P so although your electrician may get everything to work he will still need to comply with regulations. So you may be looking at next size up which is 10mm sq.
So you may be looking at £500 for the cable to start with. You may feel this is OK and you may still want to go ahead. I would say you need to think that even with most work DIY by time LABC fees and hire of test equipment etc. is taken into account you are looking at around £1000.
So is it still such a good idea? Yes using active RCD may help with safety but you still need to satisfy safety rules not for LABC but for your own safety!
The lights need to be able to work when nothing else is running and when all is running so the only way is to use a device which will accept this. There are two common lamps that will work with volt drop and both use same technology. The HF florescent and the extra low voltage spot light. Both use switch mode power supplies and if selected carefully you can get a HF florescent that will work from 100 to 240vac.
The Hi-fi is similar again looking at switch mode supplies. Or 12v car type with a switch mode power supply external.
The fridge is more of a problem. There are three types of fridges. The type with a motor is going to be a problem two fold. One it will have a problem starting and two it will drip the volts for everything else.
The type used in caravans uses a heater so does not draw a heavy start current these would work a lot better and would likely still work with a heavy volt drop.
The last type uses a French semi-conductor device and runs on DC mainly used with cool boxes and the like. If you were thinking of using 12vdc for Hi-Fi then maybe you can combine the two.
Once you have selected the equipment you will know what volt drop you can cope with. Now comes the calculation time. 2.5mm cable is rated at 18 mV/A/m so for 100 meters with 5 A draw the volt drop will be 9 volt as you go up in size then the volt drop will reduce so 4mm @ 11mV/A/m will be 5.5 volt and 6mm @ 7.3 mV/A/m will be 3.65 volt. Really there is correction factors but these values are close enough. So at 5A with 6mm SWA you are just within the volt drop allowed for lighting.
Since there is also an earthing problem I would say 6mm is really your minimum size. If you want to put more of a load on the circuit then cable sizes must increase.
The problem is safety which is something completely different to volt drop. The idea is should something go wrong and there is a short then some protective device will open. If we look at the 6A MCB these also have a letter and a B6 has a thermal trip current of 6A and a magnetic trip current of 5 x 6 or 30A. For 30A to flow using ohms law then the value of the whole circuit needs to be less than 7.66 ohms. The 6mm cable at 100m is around 7.3 ohms. Just within the value needed to allow this current to flow so open a safety device.
So although one can get around the volt drop one can't do it safely and your smallest cable will be 6mm SWA to comply with just a 6A supply. And I have not included the resistance of the supply which is likely 0.35 ohms in first place.
The problem is all this needs measuring and the results forwarded to the local authority building control (LABC) under Part P so although your electrician may get everything to work he will still need to comply with regulations. So you may be looking at next size up which is 10mm sq.
So you may be looking at £500 for the cable to start with. You may feel this is OK and you may still want to go ahead. I would say you need to think that even with most work DIY by time LABC fees and hire of test equipment etc. is taken into account you are looking at around £1000.
So is it still such a good idea? Yes using active RCD may help with safety but you still need to satisfy safety rules not for LABC but for your own safety!
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