EC3 can accept up to 12 gauge. Thats a bit of a tight fit.
There is no real relationship of cell count to wire size. You are more likely to find a relationship between capacity and wire size.
The Sky LiPo 3S and 4S I have between 1800 mah and 3300 mah have wire that would fit the EC3. The 3S 4000 mah through 5000 mah packs have wire that barely fits in the 4mm bullets that come on them. But other brands might use different gauge wire...