Armour, weapons, shields will encumber a wizard and cause spell failure. Light equipment causes no failure at all whereas heavy equipment causes mondo failures. The reasoning is that the bulkiness of objects, not their weight exactly, is what causes failures. So the basic idea of encumbrance is that items get in the way more than they weigh down. Unfortunately, our only measure of 'getting in the way' was the weight.
Encumbrance points are tallied only from applied objects. Weapons give 3x their weight in kg in encumbrance points. Shields give 1/2 their weight in kg in encumbrance points. Armour gives its weight in encumbrance points.
There's an allowance of encumbrance points which all players get before they start losing incantations, this was about 35-45, not too much.
The formula works like this: You make a roll of 1-200. You compare it to a failure threshold. This threshold is: encumbrance + incantation level - caster level - 35
For example, lets say a 4th level wizard is casting a 5th level incantation . The wizard is wearing plate mail (100 kg), a 20 kg shield and wielding a 15 kg weapon. His encumbrance is 100 + 10 + 45 = 155. Thus, his threshold for failure is 155 + 5 - 4 - 35 = 121 or over 50% failure rate.
Some examples of encumbrance are:
|Character Level||Incantation Level||Weapon Weight||Shield Weight||Combined other armour weight||Encumbrance||Offset constant||combined score||probability of failure|
There is no special bonuses for using magical equipment, although, it is clear that magical armour and weapons make things better through their weight.