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1) Ring final needs every outlet to have a 13 amp fuse some where be it in the plug or in a fused connection unit.
2) 16 amp socket does not mean a 16 amp supply.
So there is nothing wrong with a FCU supplying a 16 amp socket so items with a 16 amp plug can be plugged in, be is a caravan or other item which normally has a 16 amp plug.
As a radial nothing wrong with a 16 amp scoket from a 16 amp MCB/RCBO/Fuse, and nothing wrong with multi 16 amp sockets, so you can select each one.
Now moving to welding set, there are two types, the welding transformer and the welding inverter, the transformer has an inrush and normally needs a large supply, and can put spikes on the supply, the inverter is less likely to put spikes on the supply, but the supply likely needs a type B RCD protection due to under fault conditions likely having a DC component. So the welding inverter should not be supplied from a type AC RCD also used to supply other items, as a fault on the inverter could stop it tripping.
So welding output is around 25 volt plus 1 volt per 25 amp, so on a 16 amp supply welding current maximum is around 125 amp, but this does not include in rush, so a welding inverter can run at 125 amp but a welding transformer is more like 90 amp maximum. In the main welding transformers use 32 amp plugs and sockets and normally need around a 20 amp type C MCB.
The problem with a welding inverter is the cost of the type B RCD, what tends to be done is use a type AC or type A which only supplies the welder and nothing else, so if the welder does stop it tripping it will only affect the welder, and not the rest of the house.
The other problem with welding is it can easy cause welding currents to go down earth/bonding cables and burn them out, where I worked the welding bay used 25 mm² cables for all earth wires, mainly as the old Oxford oil filled welders have no insulation on internal wires, and if dropped can have an internal short circuit, so you can get 230 volt output to welding earth or stick, so welding earth was not isolated from supply earth. The newer air cooled models did not have this problem, and welding output was not earthed. But have a regular EICR where welding is done is important.
In the days when I was involved with welding RCD protection was not normal, it started to come in at turn of centenary, so in the main welding outlets were not RCD protected, you no longer have that option, So the old Oxford welder should be well gone, however the oil in them was cancerogenic so needed special disposal, it was often also often fire resistance so could not even burn it, so unscrupulous firms gave them away to anyone that wanted them, so some did arrive in private hands.
Not so long ago where I worked we wanted rid of some machines and it cost a lot of money to dispose of them, due to oil used in them. The fitter who lived on a farm asked if he could have some of the gear to use on farm, and was told no, you can't issue the paperwork to show safe disposal.
So today most welders used in industry are inverters, but the old type transformers are sold for DIY use, with a few exceptions people are allowed in this country to sell things you can't legally use, guns are the odd one out, but I for example can be sold a radio transmitter which I can't use, or an electric bike which I can't legally use on public roads, so the old type welding sets are still sold to unsuspecting DIY people.
It is unlikely you will have a problem with DNO for using an inverter welding set, they don't tend to produce spikes on the supply, problem is cost of type B RCD.
2) 16 amp socket does not mean a 16 amp supply.
So there is nothing wrong with a FCU supplying a 16 amp socket so items with a 16 amp plug can be plugged in, be is a caravan or other item which normally has a 16 amp plug.
As a radial nothing wrong with a 16 amp scoket from a 16 amp MCB/RCBO/Fuse, and nothing wrong with multi 16 amp sockets, so you can select each one.
Now moving to welding set, there are two types, the welding transformer and the welding inverter, the transformer has an inrush and normally needs a large supply, and can put spikes on the supply, the inverter is less likely to put spikes on the supply, but the supply likely needs a type B RCD protection due to under fault conditions likely having a DC component. So the welding inverter should not be supplied from a type AC RCD also used to supply other items, as a fault on the inverter could stop it tripping.
So welding output is around 25 volt plus 1 volt per 25 amp, so on a 16 amp supply welding current maximum is around 125 amp, but this does not include in rush, so a welding inverter can run at 125 amp but a welding transformer is more like 90 amp maximum. In the main welding transformers use 32 amp plugs and sockets and normally need around a 20 amp type C MCB.
The problem with a welding inverter is the cost of the type B RCD, what tends to be done is use a type AC or type A which only supplies the welder and nothing else, so if the welder does stop it tripping it will only affect the welder, and not the rest of the house.
The other problem with welding is it can easy cause welding currents to go down earth/bonding cables and burn them out, where I worked the welding bay used 25 mm² cables for all earth wires, mainly as the old Oxford oil filled welders have no insulation on internal wires, and if dropped can have an internal short circuit, so you can get 230 volt output to welding earth or stick, so welding earth was not isolated from supply earth. The newer air cooled models did not have this problem, and welding output was not earthed. But have a regular EICR where welding is done is important.
In the days when I was involved with welding RCD protection was not normal, it started to come in at turn of centenary, so in the main welding outlets were not RCD protected, you no longer have that option, So the old Oxford welder should be well gone, however the oil in them was cancerogenic so needed special disposal, it was often also often fire resistance so could not even burn it, so unscrupulous firms gave them away to anyone that wanted them, so some did arrive in private hands.
Not so long ago where I worked we wanted rid of some machines and it cost a lot of money to dispose of them, due to oil used in them. The fitter who lived on a farm asked if he could have some of the gear to use on farm, and was told no, you can't issue the paperwork to show safe disposal.
So today most welders used in industry are inverters, but the old type transformers are sold for DIY use, with a few exceptions people are allowed in this country to sell things you can't legally use, guns are the odd one out, but I for example can be sold a radio transmitter which I can't use, or an electric bike which I can't legally use on public roads, so the old type welding sets are still sold to unsuspecting DIY people.
It is unlikely you will have a problem with DNO for using an inverter welding set, they don't tend to produce spikes on the supply, problem is cost of type B RCD.
