Elemental Equilibrium

I read thread about EE in keystone feedback but it's 1 year old so I don't know if it's still valid.

My question is:
I use arc totem as EE trigger before I cast fire traps. I know it works because monsters get vulnerable to fire and cold status. Then I throw fire trap at them and their status is still vulnerable to cold and fire. So does trap affect only the monster that triggers it (and most likely dies in one hit) and the burn damage doesn't trigger EE for all the other?
Or why if I throw my fire trap first they get fire resist and then they're hit by totem thair status is still fire resist. Shouldn't that change to resist lightning?

Or am I missing something obvious?

Their resistance gain/loss is based on the first hit they take.
If you want to be doing a large damage with fire trap you must hit them with another element first, such as your arc totem.

The arc totem triggers EE -> anything hit gets vulnerable to cold an fire.
The fire trap therefore causes more damage. It also triggers EE: anything hit by the fire trap gets vulnerable to cold and lightning and resist to fire. The burning damage on the ground doesn't trigger EE as it is not a hit but dot. Anything that is affected by the initial arc totem EE and wasn't hit by the trap but is standing on the burning ground is still vulnerable to fire.

If something is hit first by your fire trap it gains fire resist and light/cold vulnerability. When hit by your arc totem it will take extra lightning damage. The arc will also trigger EE giving the monster now lightning resist. It will therefore take less lightning damage on the following arc hits.

That's how I understand it works but I've seen it like this:
Arc first causes fire and cold vulnerability, fire trap doesn't change that to lightning and cold.
Or fire trap first causing cold and lighting vulnerability followed by arc which doesn't change it to fire and cold. Basically monster standing in fire trap burning ground getting hit by arc and it's still resistant to fire and vulnerable to lightning and cold.

- i thought that EE makes mobs permanently vulnerable to 2 of 3 elements or: i need to throw only 1 fire trap to make mobs vulnerable to cold /and lighting/ and then i can cast ice spear until i kill them and to throw another fire trap only if there are not-affected by first fire trap mobs and then to cast again ice spear until i kill them...

let's say i'm using ice spear for main attack of my cold magician and fire trap for EE trigger, so i have to use them by this way:
1) throw fire trap
2) cast ice spear
3) throw another fire trap
4) cast another ice spear
???
if this ^ is true, then it's stupid -> it's like to have to curse enemies on every hit/spell :X
please explain /again/ which is correct, thank you

thank you for the fast answer and...this sucks :D maybe only in party game with lighting/fire mage could be useful enough -_-