Your cable is not rated for the current you want it to cary.
STOP USING IT! You have a very serious fire hasard as it is now!
Check the amp load of your shower. Compare it to the amp rating of your cable.
The cable's rating must be LARGER than it's load.
A longer the cable, require a larger caliber.
if your shower need 20A, a 20~25A cable is good up to around 3m.
You need at least a 30A for a 5m lenght, and a 40A cable is recomended for anything longer than that.
Electro
September 2011