Each gear piece has its own hidden Enchantment Charges Capacity (ECC) based on its level, quality, value and gear slot used e.g. a 2H sword occupies two slots and thus can bear more enchantments than a one-hander, plus their effects are doubled (as being given for each slot occupied). A chest armor piece can bear more enchantments than boots or gloves due to its increased value.
Enchantments in turn use up amounts of ECC based on the enchantment's type and tier e.g. proc uses up more ECC than suffix of the same tier due to the greater parameters' increase.