The whole question of an earth to garden equipment is complex,
this is rather dated and refers to wiring outbuildings, and use of TN or TT supply. The problem with a TN-C-S supply is the earth may not be true earth, and in the garden it is true earth, so touching the appliance earth and true earth could in some situations give one a shock. If the premises are TT or TN-S no real problem, it is the TN-C-S or PME supply that causes the problem.
This has raised its head with charging of electric cars, where special systems are required to disconnect first line and neutral then earth if the voltage goes out of the 207 to 253 volt range. But other than electric cars, either class II equipment is used, or TN-C-S or PME is banned, as with supply to caravans and narrow boats.
I have noted even hot tubs are often class II so no earth required, the odd one out seems to be patio heaters, these are often class I. The typical garden lead connector
is two pin, and as long as the extension it terminated with a two pin socket, and only items which are class II are fitted with 2 pin plugs there is no problem. The problem is you can get a lovely socket
designed it says as a car charging point, so seems great dual purpose unit, however nothing in the advert points out should not be used with a TN-C-S supply,
data sheet here if one reads the data sheet is actually says it should not be used to charge a vehicle, i.e.
A type B RCBO is a combination of two functions, a type B MCB and type AC RCD.
The IET Code of Practice for Electric Vehicle Charging Equipment Installation (3rd Edition) states that mode 2 charging equipment should be protected by a
1) Type A RCD and appropriate equipment that provides disconnection of the supply in case of DC fault current above 6mA or
2) Type B RCD
OK I know your not charging a car, but the problem of using a three core extension in the garden is still there.
So the BIG question which I can't really answer, what is the point of a three core extension lead in the garden when you should not be using class I equipment?
Clearly the problem is the extension may be used else where, where an earth is required, so be it a 5 pin three phase socket where it needs a neutral or a three pin where it needs an earth if the earth or neutral is not connected sods law says it will end up being used where it is required, so if you want to use 2 core for an extension fit a two pin sockets, or 4 core with three phase and no neutral fit a 4 pin socket.
It does I know cause problems the German socket
allows both two and three connections, so my class II battery charger can have a two pin plug, but in the UK my class II battery charger has a three pin plug even though the earth pin is plastic, so I need a three pin socket on my extension lead and a three core cable even when only 2 cores used.
I can't think of anything I have which I may use in the garden which is class I, lawn mower, strimmer, hedge cutter, drill, battery charger, blower/sucker all class II.
As said there is a problem using any class I in the garden with a TN-C-S or PME supply. Maybe a patch lead with
one end and this
the other and keep it locked up so only I can use it? It would actually work out very well as no one borrows the lawn mower lead.
I joke, I will continue using a three core lead, however one must ask is a two core lead really that bad in the garden? Real cure would be ban TN-C-S and PME supplies, would make a lot of sense with the electric car, but instead of banning TN-C-S they have said now 70 volt not 50 volt is allowed to earth. But 25 volt can kill a cow, it really should be reduced not increased.
But what do I know I'm an old fogy at 70, just pay no attention to me.