Until I started watching Holmes on Homes, I don't recall ever seeing an electrical panel installed horizontally. Of course, virtually every house he works on is in Canada.
Is it a Canadian thing or is there a good reason why they like to install them horizontally?
Vertical installation seems more logical for the door to open.
In fact when looking for an image of one installed horizontally on google images, I was only able to find 1 image in 25 pages of results.