The power cable is the only physical interface between the surface electrical supply and the submerged motor — and it operates in one of the most demanding environments of any electrical component in industrial use. Mechanical stress, chemical attack, temperature cycling, ultraviolet exposure above the waterline, and sustained hydrostatic pressure below it act simultaneously on a cable that may be in service for 10–15 years without replacement. Understanding what the SUBCAB specification provides — and what happens when non-specified cables are used — protects both the motor and the installation.
What SUBCAB Is Designed to Do
Flygt's SUBCAB cable is engineered for submersible duty — which is a fundamentally different operating environment from standard power cables. The specification addresses six distinct performance requirements that standard cables do not meet:
- Water absorption — SUBCAB uses insulation compounds with extremely low water absorption rates. Standard PVC and even standard rubber compounds absorb moisture over time, reducing insulation resistance and eventually causing tracking failure
- Mechanical strength — the cable must withstand tensile loads during installation and removal, bending over the cable guide, and sustained tension from its own weight in deep submergence applications
- Chemical resistance — wastewater, industrial effluents, and marine environments contain chemicals that attack standard cable insulation. SUBCAB compounds are selected for resistance to the chemical environment of Flygt pump applications
- Temperature range — the cable operates from below-freezing conditions in outdoor drainage applications to elevated temperatures near the motor housing
- Outer diameter tolerance — the cable must pass through the Flygt cable entry sleeve with a specific interference fit that provides the primary seal between the motor housing and the outside environment. SUBCAB outer diameter tolerances are specified tightly to ensure this seal is consistently achieved
- Screened control cores — SUBCAB integrates screened monitoring conductors for thermal protection, moisture detection, and other pump sensors within the same cable assembly — eliminating separate control cable routing and reducing connection complexity
The Cable Entry Seal — Why Outer Diameter Matters
The Flygt cable entry sleeve creates a compression seal around the outer jacket of the SUBCAB cable. This seal is the last line of defence against water ingress into the motor housing along the cable route. The sealing force and integrity of this compression seal depend directly on the outer diameter of the cable falling within the specified tolerance range.
A cable with an outer diameter slightly below the SUBCAB tolerance — even by 0.5mm — will not generate sufficient compression in the cable entry sleeve to create a reliable seal. This failure mode is invisible at installation and may not manifest for months, particularly in intermittent submergence applications. When it does manifest, moisture reaches the stator housing and motor winding failure follows.
Non-Specified Cable Risks
The most common alternative to SUBCAB is standard rubber or thermoplastic elastomer (TPE) submersible cable sold as "equivalent." These cables may meet standard cable specifications for submersible use in general applications — but they are not manufactured to the Flygt-specific tolerances for outer diameter, conductor arrangement, and screening configuration.
The risks of non-specified cable:
- Cable entry seal failure from non-compliant outer diameter — allowing moisture ingress along the cable route
- Loss of monitoring capability if the control core screening configuration differs from the Flygt specification — masking thermal or moisture alarms
- Accelerated insulation degradation if the water absorption rate of the alternative compound is higher than SUBCAB specification
- Voiding of the motor warranty — non-genuine cable is considered a non-genuine part for warranty purposes
Installation Note
SUBCAB cable length should always be specified with sufficient slack to allow the pump to be raised to the surface for service without disconnecting the cable at the junction box. A cable that is too short forces the installation engineer to disconnect at the surface, creating a potential connection quality issue at each reconnection. Over-length is preferable to under-length.
Key Points
- SUBCAB outer diameter tolerance is specified for the Flygt cable entry seal — standard cables may not meet this tolerance
- Cable entry seal failure from non-compliant cable allows moisture ingress — leading to motor winding failure
- SUBCAB integrates control cores for pump monitoring — non-standard cable may not provide equivalent screening
- Always specify SUBCAB by pump model — different Flygt models require different cable cross-sections and core configurations
- Non-genuine cable voids the Flygt motor warranty — the cable is part of the sealed motor assembly