Symbols that stay the same size regardless of the scale factor of the viewport. Symbols that change size dependent on the scale factor of the viewport. If you have all of the symbols together in a Key, a simple solution is that you could just scale the whole lot up or down at once and then simply copy them into place where needed. There's also the option of using annotative blocks but that's likely to open up other cans of worms and is probably best avoided.

If you are working regularly between different scales and need to use the same symbols, it would be worth considering converting them to dynamic blocks and including a number of visibility states which would allow you to simply click through different sizes of each block. By using this method, the symbol should print out at the same size regardless of the output scale of the drawing. If I need to produce a drawing at 1:50, I then halve the scale of the blocks otherwise they would print out at double the intended size when printed at 1:50. I work in metric so I'll give metric examples: all of my electrical blocks are sized for use on drawings to be printed at 1:100. Regarding scaling of symbols your CAD blocks should be scaled up or down depending on the output scale of your drawings. Fortunately, this is still one area that the nannies haven't got their hands on, and it's up to draughtsman to decide the size of symbols. The main intention of any drawing is clear communication and so your primary aim should be legibility. In the old days we used to use stencils which used to regulate the sizes but now there's no convention.

David, there aren't any standards for sizes of symbols.

Cad outlet symbol