At the moment on the market is few fan what is suitable to fixing in the shower.
You should looking for shower light ans extractor fan kit.
This is generally rules regarding electrical items.
BS7671:2008 requires all electrical items in the bathroom to be RCD protected. A lot of the 230V fans are suitable for use in Zone 1 if they are RCD protected. Its unclear if your saying that the casing has been cut in some way at the top to allow the cable to enter the fan? if so then this will need to be sealed with silicone or similar if there is a gap of 1mm or bigger. IP45 is not a splashproof rating so the casing only needs to prevent access to live parts from human fingers and small diameter objects being pushed through small gaps.
briefly explained, as can their effect on the type of extractor fans which can be used.
Zone 0 for a bathroom is the area inside the bath.
Zone 0 for a shower room is the area inside the shower basin. If there is no shower basin, zone 0 is 10cm high from the finished floor level and extends to 1.2m around the fixed shower head.
It is not practical to mount extractor fans in zone 0.
Zone 1 for a bathroom is the same width as zone 0 (the width of the bath) extending to 2.25m above the finished floor level.
Zone 1 for a shower room is 2.25m from the finished floor level or the height of the fixed shower head from the finished floor level if more than 2.25m, and the width of the shower basin. If the shower has no basin then zone 1 extends to 1.2m around the fixed shower head.
Zone 1 does not include zone 0.
The space under the bath tub or shower basin is considered to be zone 1. However, if the space under the bath or shower basin is only accessible with a tool, it is considered to be outside the zones.
Extractor fans installed within zone 1 must be at least IPX4.
Extractor fans installed within zone 1 must be fitted with 12v SELV motors with the SELV transformers and isolators fitted outside of zone 0, 1 & 2.
Zone 2 for a bathroom is the same height as zone 1 (2.25m) extended to 0.6m around the bath.
Zone 2 for a shower room is the same height as zone 1 extended to 0.6m around the shower basin. If there is no shower basin zone 2 is replaced by zone 1 extended to 1.2m around the fixed shower head.
Extractor fans installed within zone 2 must be at least IPX4.
Extractor fans installed within zone 2 must be fitted with 12v SELV motors with the SELV transformers and isolators fitted outside of zone 0, 1 & 2.
The extent of the zones in a bath or shower room can be limited by floors, ceilings and walls. For more detailed information see BS 7671 diagrams 701.1 & 701.2. Any electrical equipment installed on the surface of floors, ceilings and walls that limit a zone is subject to the requirements of that zone.
RCDs are required for all circuits in locations that contain a bath or shower. The requirements for local supplementary bonding have been relaxed if certain conditions are met
Hey, Fan must be 2.4mtrs above the floor and should be out of reach of splashes. Make sure the fan is rated for a bathroom (IP44 min on the unit / box). It must be fitted with an isolator switch for safety and best linked to lights if fitted with a time delay. Cheers. Good Luck