Precaution of water prevention and moisture to enter the lamp through power cable IP65 / IP66 Ip68, According to the research and test. The water infiltration is one of the biggest damage to the outdoors fixture. The bellowing pictures are those typical circumstances will take place:

Why use the water-proof connector?
When the fixture is turned on, the inside temperature will increase as the operating time goes. Conversely when the lamp stops working, the temperature will slowly drop. This phenomenon will cause “The Siphon effect”. Thermal expansion and contraction make the inside and outside air pressure differences. The vapor will infiltrate to the housing through the wire entry as soon as the internal air pressure is smaller than the external. The infiltration is caused by several incorrect connections like the picture below:

The best and easiest ways to prevent the water filtration are by isolating directly
We recommend using the water-proof connector like the following pictures. The connector was developed especially for outdoors lightings to make sure the fixture is protected. (For more accessories about waterproof connector for outdoor lighting installation, please click here> Outdoor lighting accessories--Waterproof connectors.)

For more information & Products of IP67 or IP68 connector or connection box, please click below link>>

Outdoor Lighting Accessories-COMI Lighting Limited (comilandscapelighting.com)