There is an important difference in the use of the two mentioned standards. The 60079-11 standard is to be used for the design of an equipment to be tested an certified / approved as an Exi equipment. The 60079-14 standard is to be used for the installation of certified / approved equipment.

This means that you need to look at what kind of product are you producing (and thus what kind of DOC you are going to deliver: Equipment or Installation) before you decide on what standard you should follow.

Because an installation is not subject to a following examination and test like on an equipment, there are stricter regulations to what can be allowed. This means that the two sections you are referring to are not to be interpreted as equal.In an installation there should always be a separating layer (layer of insulating material) between the non-IS and IS circuits. This does not mean that you need to keep a 50mm distance between the wires. It's only when you have live bare metal (in terminals) it's need for this 50mm separation.You should however not forget that the basic protection consept is to make shure that the energy level in the IS loop is kept low, and that this means there could be need for a greater distance between the IS and non-IS wires to minimize electro-magnetical interferrence.