Hi, I'm after some electrical advice, as I've had three electricians round to quote for running power to my new outbuilding and they are all saying something completely different, so a little extra advice from people without a monetary incentive to influence them, won't hurt. 
A few years ago, when I got a complete new house rewire and before all the plastering and boxing was completed, I asked the sparky to add an extra cable from the consumer unit to an easily accessible area of the house, so that I could run power to a future outbuilding years down the line. I didn't check he did this at the time, but it appears he has done so as looking inside the consumer unit, there is some T+E that isn't connected to a breaker, just coiled up neat with SHED written on it. This cable appears (impossible to check visually as everything is sealed in wall) to run a few meters away to an accessible area, where it terminates with nothing connected, just a few meters coiled up neatly, apparently ready to be connected to SWA for the outside part of the run.
I also have existing power to another shed which is 10m away from the house. It's connected to a breaker in the house consumer unit and has B20 written on it. The T+E cable that it's connected to is much thicker than the spare cable the sparky installed for the future shed, which is concerning.
Now the run to the new outbuilding is 50m from the house, or by spurring off the other shed in which case the run would be 40m. I have some 4core SWA (I know only 3core is needed) that I was given for free and hoped to use, which I explained to the three electricians I've spoken to so far. They asked what I will be using in the new shed, I said 8 LED downlights, an LED security light, and probably a TV, computer and General MAN-cave stuff.
One spark is saying the 4core SWA size is fine (I'm not sure if it's 4mm or 6mm), but it's not long enough to reach the house, so they were going to spur off an existing RCD in a shed only 40m away from the new outbuilding. They seem quite happy this will be fine, and also no earth rod needed.
A second spark says that he is happy spurring off the nearer shed, but the free SWA I have is not big enough to cope with the voltage drop and wants to install a larger one and also put in an earthing rod next to the new shed.
The third spark says the spurring off the RCD in another shed is not acceptable and wants to bring a bigger SWA straight back to the house consumer unit, to allow for voltage drop. Also no additional earth rod needed.
First, how can I determine if a larger SWA is needed as there is split decision on this?
Second, how can I detemine if it will be acceptable to spur from existing shed or if it truly needs to come back to the house consumer unit?
Third, if it does need to come back to the house consumer unit, can it be connected via the future spare cable the original sparky installed, or will it mean removing all the plaster to gain access. I'm concerned as the future cable is much smaller than the cable used for the other shed. Therefore, what's the point in using larger SWA if it's going to terminate to three meters of smaller T+E?
I also wonder why such a massive SWA is needed. I've been running a small TV, and chop saws, radio etc using a 50m extension lead from the existing shed without any issues. I know the Sparks want to do a proper job an using a thick SWA back to the house with eliminate any problems, but I'm the one that has to foot the bill for the cable and the installation and to be honest, the quotes have been horrendous and I can't work out if that's what sparks charge or they are taking the Micky. One of them itemised the supply and clipping of the larger SWA to the fence at £455. A quick Google shows the SWA is £150 so essentially he is trying to charge £300 to clip a cable which is no more than 30mins work. We all have to make a living, and I'm paying for their expertise, but that is insulting in my mind.
A few years ago, when I got a complete new house rewire and before all the plastering and boxing was completed, I asked the sparky to add an extra cable from the consumer unit to an easily accessible area of the house, so that I could run power to a future outbuilding years down the line. I didn't check he did this at the time, but it appears he has done so as looking inside the consumer unit, there is some T+E that isn't connected to a breaker, just coiled up neat with SHED written on it. This cable appears (impossible to check visually as everything is sealed in wall) to run a few meters away to an accessible area, where it terminates with nothing connected, just a few meters coiled up neatly, apparently ready to be connected to SWA for the outside part of the run.
I also have existing power to another shed which is 10m away from the house. It's connected to a breaker in the house consumer unit and has B20 written on it. The T+E cable that it's connected to is much thicker than the spare cable the sparky installed for the future shed, which is concerning.
Now the run to the new outbuilding is 50m from the house, or by spurring off the other shed in which case the run would be 40m. I have some 4core SWA (I know only 3core is needed) that I was given for free and hoped to use, which I explained to the three electricians I've spoken to so far. They asked what I will be using in the new shed, I said 8 LED downlights, an LED security light, and probably a TV, computer and General MAN-cave stuff.
One spark is saying the 4core SWA size is fine (I'm not sure if it's 4mm or 6mm), but it's not long enough to reach the house, so they were going to spur off an existing RCD in a shed only 40m away from the new outbuilding. They seem quite happy this will be fine, and also no earth rod needed.
A second spark says that he is happy spurring off the nearer shed, but the free SWA I have is not big enough to cope with the voltage drop and wants to install a larger one and also put in an earthing rod next to the new shed.
The third spark says the spurring off the RCD in another shed is not acceptable and wants to bring a bigger SWA straight back to the house consumer unit, to allow for voltage drop. Also no additional earth rod needed.
First, how can I determine if a larger SWA is needed as there is split decision on this?
Second, how can I detemine if it will be acceptable to spur from existing shed or if it truly needs to come back to the house consumer unit?
Third, if it does need to come back to the house consumer unit, can it be connected via the future spare cable the original sparky installed, or will it mean removing all the plaster to gain access. I'm concerned as the future cable is much smaller than the cable used for the other shed. Therefore, what's the point in using larger SWA if it's going to terminate to three meters of smaller T+E?
I also wonder why such a massive SWA is needed. I've been running a small TV, and chop saws, radio etc using a 50m extension lead from the existing shed without any issues. I know the Sparks want to do a proper job an using a thick SWA back to the house with eliminate any problems, but I'm the one that has to foot the bill for the cable and the installation and to be honest, the quotes have been horrendous and I can't work out if that's what sparks charge or they are taking the Micky. One of them itemised the supply and clipping of the larger SWA to the fence at £455. A quick Google shows the SWA is £150 so essentially he is trying to charge £300 to clip a cable which is no more than 30mins work. We all have to make a living, and I'm paying for their expertise, but that is insulting in my mind.
