I would check the figure's if somebody is telling you a 4mbar drop is okay over a meter.
That would be the Meter manufacturers.
The mains pressure you talk about of 200mbar is of course depending on the sort of main your tapped into High, Medium or Low. We are talking average and that is said to be 75mbar usually. I feel sure no responsible gas supplier would really want 200mbar pressure in a domestic gas service pipe and the higher pressures would seem more appropriate to transport mains not domestic service pipes..
Most services are low pressure, ie <75mb (usually nearer 30) but there are many areas around the country where the domestic service to the regulator is medium pressure ie < or = 2bar
The thing is, if we start accepting lower gas pressures the next step is that people may think they can use under sized piping.
Pipes should always be sized to give max 1mb drop as BS6891, regardless of pressure at meter.
Have a look at British Standards BS 6891 or the copper club Gas pipe sizing PDF based on BS 6891.
I know how to do pipe sizing.
The idea of a gas installation is very much the same as an electrical ring main. You should be able to plug in to it anywhere and get 20 mbar regardless of what you plug in. The electrical ring main works the same way.
Its 13 Amp at the sockets, governed down by the plug top fuse in roughly the same way as a gas appliance can be governed down either by a gas valve, appliance governor or orifice size.
The socket you use should not exceed 13 Amps loading. But you can plug anything below 13 Amp in. Gas is the same idea. In point, in the old days, there where gas points just like electrical sockets in nearly every room of a house as well as gas lighting.
Gas pipe sizing cannot be compared to a ring main. It is a totally different concept.
The pipe is sized for the load with an allowance for further additions if required. Even if a 22mm was run throughout to every appliance, there are occasions where this would be undersized. That is why each pipe has to be sized to suit the load.
However I feel all this confusion over standards could be avoided if they published the Gas Regs, British Standards and Guides to them, like they do the Building Regulations, free for anybody interested to down load.
The British and IGEM standards are available to all, at a price. There is not some big secret from the public. Even registered installers have to buy them.
I wish they would make them free as it would save me a couple of grand every few years updating them but i cannot see that happening in the near future.
The information contained in them is sometimes quite hard to interpret, even for professionals, so they would perhaps be of little use to the layman. The Viper books and suchlike are easier to follow but again, quite rightly as they are a commercial operation, they come at a price.
What people do with that knowledge is up to them. If they decide to break the law and use the knowledge to make money, that is a moral and social value problem, not a gas fitting problem. So free knowledge should not cause anybody any problem, but instead perhaps help many.
