Question: How do I install the underwater cable for submersibles?


Cable splice/connection of motor cable and drop cable Faulty or unapproved cable joints are frequent causes of burned-out motors. Grundfos-recommended products or products of similar quality should be chosen and the manufacturer’s guidelines followed. Any cable joint must be watertight and have an insulation resistance of minimum 10 megaohms, measured in a submerged state after 24 hours in water.

In order to obtain this, all cable parts must be 100 % clean and all other requirements indicated in the service manual and in service video programs observed. There are three ways of making a cable joint.

  1. Heat shrink Heat shrink uses a plastic tube with the inside covered with glue. When exposed to heat, it will shrink and the glue melts, and this makes a watertight cable splice. The advantage of this principle is that it is easy to do, no drying time is required, it is ready immediately after fitting, and is a safe connection. Grundfos recommends this kind of cable termination. The Grundfos heat shrink series “KM” covers all types of motor cable connected to drop cable. 
  2. Resin Sealing with resin is an old type of joint. This type of joint is difficult to make correctly for installations in warm water and liquids with high conductivity. Grundfos recommends therefore using heat shrink. 
  3. Plug connection It is important not to use cable joint kits or tape which are more than three years old. This age limit should be reduced to one year if stored above 15 °C. Always test the cable joint during maintenance. 

Motor cable plug

The motor cable plug must always be fitted at the torque stated in the documentation. In case of lubrication of the cable plug, a non-conductive material should be used (e.g. silicone paste). Motor cable plugs that are more than three years old should not be reused, as they may have lost the ability to make a safe, water tight connection.

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