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Channeling or channeled abilities are abilities which require the caster to remain stationary for the channeling duration, while regularly causing an effect. A time bar will appear and it goes from full (with green) to empty. Generally, channeling spells also have a casting time, although it is zero (hence instant). However, some exceptions with a casting time above zero do exist, as mentioned below.

Additional notes:

• Usually attacks that hit the caster will put the channeling time bar closer to being empty, reducing the ability's duration.
• Some attacks will interrupt the spell-casting completely and the time bar will fill completely with red and say "Interrupted".
• Some abilities, powers, or talents can prevent interruption.
• Mana is consumed before the channeling starts.
• The player can interrupt their own spell at any time during the channeling by either moving, jumping, or pressing the Escape key.

Currently, all channeled spells, with the exception of [Arcane Missiles], are calculated as periodic effects (Damage over Time, Heal over Time).

Using bandages is a channeled ability.

Channeled Abilities with a Casting Time

Some channeled abilities still have a Casting Time, such as [Mind Control]. Their behaviour at the beginning is that of a normally cast spell (see Casting Time), and after finishing to cast, they function like channeled spells (as above). So the mana is consumed after finishing normal casting, but before starting to channel.

Differences to spells with cast time

Currently, all channeling spells (except [Arcane Missiles]) technically cause periodic damage, which means that they behave like damage over time spells for the most part. As a result, do not cause interruption. In addition, they have only one line of sight check at the cast of the spell; as soon as the spell hits the target, the caster does not need to maintain LoS in order to keep the channel active.

There are some characteristics that make channeled spells more or less desirable in specific situations. These are:

• DPS while being attacked: If you are attacked while channeling a spell, it will not lower your DPS as much as for a normally cast spell, as your damage is still applied regularly (every tick), regardless of where your channeling bar is. The only case where your DPS is lowered is when you are interrupted at the end so that you lose one tick of damage.
• DPM while being attacked: As your mana is consumed before the spell is cast, your DPM is lowered if you are being attacked, as your channeling time and consequently the damage are reduced.
• Regular Damage: Channeled spells regularly cause damage, therefore if you are interrupted while mid-channeling, you will have caused damage proportional to your channeling time. Any normally cast spell will not do any damage until the cast is complete. For example, [Shadow Bolt] has a 3.0 second casting time. Consider casting [Shadow Bolt] versus [Drain Life]. If a warlock is interrupted after 2.1 seconds Drain Life would have done damage twice, while Shadow Bolt would have done none. However, the Drain Life spell would have cost full mana while the Shadow Bolt would have cost nothing since it was never cast.
• Line of Sight Check: For a channeled spell, the LoS check is done before the spell is channeled. So if you passed the check and you hit your target, your damage will be applied and your target cannot run out of your LoS anymore (apart from running out of range). This can be very handy against skilled players, as your normally cast spells can easily be "dodged" (by running out of your LoS), whereas for channeled spells you just need to keep pressing the button until the animation appears and the damage will go through. If you find yourself having trouble with such players, it may be more helpful to abstain from using normally cast spells.
• Resists: Due to most channeled spells being binary effects (with the exception of [Arcane Missiles]), such spells can only hit or miss; partial resists are not possible. This and the fact that those spells are cast instantly means that a resist will only cost the time of the Universal Cooldown instead of the whole channeling time. Therefore, channeled spells, particularly ones with especially long time channel times, are only affected by resists by a minor amount.

Conclusion

If in a situation in which incoming spell pushback, interrupts, or movement is likely, you must decide whether time or mana is of more concern. If mana is more important, you will want to use non-channeled spells. If time is more important, you will want to use channeled spells to do as much damage or healing as you can. Note also that if a channeled spell is fully interrupted (such as with a knockback or a type of stun perhaps) after a couple seconds, you're better off than if you had been casting a non-channeled spell for a couple seconds and then got an interrupt.

Different classes and situations call for different tactics, however; For example, in melee PvE, a shadow priest who is low on mana but has [Power Word: Shield] up will often focus on using the mana-efficient, channeled spell [Mind Flay], but when the shield falls they will often switch to using a combination of [Mind Blast], [Mind Spike], or even their wand to deal damage.

Patch changes

• Patch 1.7.0 (2005-09-13): Fixed a bug where mana was being regenerated while channeling spells that use mana.