by ericmark »
Sat Apr 30, 2022 8:21 am
Any high powered item needs the power to be there to start with, the domestic supply is limited to 100 amp as we use consumer units which only come as 100 amp units, but we can have multiple consumer units and multiple supplies, this is common in the 80's where one fuse box was for heating from a white meter and one for everything else called economy 7, and farm houses often have a split phase supply, again two supplies, but there is a problem with single phase with motors, in getting them to start turning, so we tend to use three phase for motors.
Today there is no need for a three phase supply to use a three phase motor, my freezer has a three phase motor but a single phase supply and an inverter changes it to three phase for the motor.
In Europe split phase is more common, and often we find cooker hobs designed to use either single phase or split phase, same cooker, just move some links to swap from split to single phase.
So the supply can be increased by using more than one phase, but before we consider that we need to look at what we have.
The old Wylex fuse box was only rated 60 amp, and often our homes have only a 60 or 80 amp supply, not all have a 100 amp supply, and in some cases the supply is split and feeds two homes, so not as simple as fitting a larger fuse.
There is also the supply type, we have TT and TN and the latter is split into TN-S and TN-C-S and the latter needs to be in premises where items are bonded as under fault conditions the earth from the supply can be a different voltage to the true earth.
This has cause problems, so caravans, boats and petrol stations are not permitted a TN-C-S supply, and electric car charging units need special disconnecting systems which will disconnect the point including the earth under fault conditions.
In the main things used in the garden are class II, that means there is no earth, so the lawn mower, etc is no problem, but larger items consideration must be given to how to earth in a safe way.
Some hot tubs are class II, but where not class II then either it needs to be in doors, or supplied with a TT or TN-S supply, TN-C-S or PME as it is also called is not really appropriate.
When a supply is made TT then one has to look at the voltage gradient under fault conditions, items like caravans have to be a set distance from buildings due to fire regulations, so no real problem, but if the hot tub is in the garden looking at least 3 meters from house, or any other PME supply.
So looking at amount of current used, and also earthing arrangements.
Again the EV has seen how you need to inform the DNO if the power used increases, and in some cases you can't have an EV charging point because of bundled supplies (shared with another house) and the cost of getting a new supply can be very high.
Remember we started to build the National grid before the second world war, (1935) but last village to be connected was in 2008, Abergeirw, near Dolgellau, Mid Wales, so to upgrade supplies it is reasonable to expect same time scale, so looking at 70 years to upgrade supplies so all cars can be electric. OK may be a little quicker, but it does take time.
To fit EV charging points electricians need extra training, mainly about the earthing problems, it is not as easy as it looks, the same with your hot tub, it is a lot more complex than one first thinks to put in a supply, and clearly not a DIY job or some thing which can be designed on the internet.
