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.
I think you've lost a decimal place - 1 think 100m of 6mm² cable has a resistance (both conductors) of 0.73Ω, not 7.3Ω.
Kind Regards, John.
Yes I have point in wrong place. Which does change a lot. Thank you for pointing out.
Can't anyone else smell a troll? 100m extension, come on.....
Maybe a couple of these plugged in together.
45 meters each and had 4 13 sockets on it
Are
these on the border of illegal?
This has been talked about a lot. And it impacts on the comments on caravans with their supplies.
Where the supply is protected by a RCD likely there is no problem. And today all socket outlets under 20A should be RCD protected.
For caravans the lead set is very exact as to length and size. At least 2.5 mm sq and 721.55.2.6 gives the length at 25 m (±2 m). Which does seem daft as when close to the service outlet I would use a shorter lead. The note after Fig 708 says not more than 25 meters which seems to make more sense unless they are being sure no one tries to stretch a lead really too short for the job.
Due to my mistakes seems a 6mm SWA cable will do the job. Although a smaller cable may also be OK there is an issue with earthing with under 6mm. As to if this is a problem would depend on the installation.
There has been a lot of debate as to earth types with remote out buildings. My personal opinion is where the area is surrounded by other houses and the supply is a TN-C-S to the house then one may as well just use that supply. However where the out building is surrounded by open fields we must consider the voltage gradient and likely using a TT earthing system would be safer especially if there is any earthed metalwork which some one outside the building could touch.
In the real world I have seen 110v extension leads plugged into each other encircling the building. Where some one has seen an unused socket and just plugged into it. Where the supply was from a twin pole B16 MCB there have still been no real problems. Only when those silly yellow brick transformers have been used is there a problem with a fire risk.
So in real terms he may find problems with some fridges which may not start due to start load. He may also have problems with hum on the Hi-Fi if it does not use a switched mode supply. And cheap florescent fittings (Non HF) may not start or my extinguish as fridge starts.
But the only real danger is the fridge malfunctioning due to not starting as it should. As long as a suitable fridge is used i.e. Caravan type with heater rather than motor then there should be no real danger.
The problem arises as one tries to add more and more. There is a 13A socket so people will try to use it. But if the MCB is right size it will just trip so no danger.
