Solid-State Decouplers
A solid-state decoupler, or SSD, is an advanced isolation and grounding device. It is used when a CP system needs DC isolation but also needs an AC, fault-current, or lightning path.
Quick Definition
A solid-state decoupler blocks DC cathodic protection current below its threshold while allowing AC current to pass. When voltage exceeds the selected threshold, it switches to a conductive state to limit voltage between its terminals.
Why SSDs Are More Advanced Than OVPs
An OVP is easiest to understand as normal isolation plus over-voltage bypass. An SSD adds another important behavior: it can allow induced AC current to flow while still blocking DC CP current. That makes SSDs important for AC mitigation, gradient control mats, equipment grounding, and isolation-joint protection where AC exposure is present.
blocked below threshold
allowed to pass to grounding path
device clamps and conducts
Common Applications
- isolation joint protection
- AC voltage mitigation
- decoupled gradient control mats
- decoupling electrical equipment grounding systems from CP systems
- maintaining DC isolation while providing AC continuity
Field Interpretation
If an SSD is present, the question is not simply whether two structures are isolated. The question becomes: isolated for DC, coupled for AC, or conducting because the threshold has been exceeded? A technician must understand which current type is being measured and which state the device is in.
Safety and Design Caution
Decoupling devices are part of both corrosion-control behavior and electrical safety behavior. Device selection, threshold selection, fault-current rating, hazardous-location classification, installation details, and grounding requirements must be handled by qualified personnel using applicable standards and manufacturer instructions.