Sub-distribution boards (often abbreviated as SDBs) are electrical distribution panels that receive power from a main distribution point (such as main LV panels or a main switchboard) and distribute it to multiple downstream circuits. In EV charging projects, SDBs are typically used to supply groups of chargers in a car park, depot, basement, or outdoor charging zone, keeping distribution local, organized, and scalable.
SDBs may also be called sub-boards, secondary distribution boards, or local distribution panels depending on regional terminology.
Why Sub-distribution Boards Matter in EV Charging Infrastructure
As EV charging sites scale, running every circuit back to the main switchboard becomes costly and complex. SDBs help by:
– Reducing long cable runs and simplifying cable management
– Creating a clean expansion point for adding new charger circuits
– Improving fault isolation so one charger issue doesn’t affect the whole site
– Supporting phased rollout for multi-tenant charging and fleet depots
– Providing a convenient location for metering and load management hardware
They are a common building block in EV-ready parking designs.
How Sub-distribution Boards Are Typically Used
A common layout looks like:
– Main switchboard / main LV panel supplies a feeder to an SDB
– The SDB supplies multiple outgoing circuits (often one per charger)
– Protective devices are coordinated at SDB level
– Optional monitoring/metering is installed on the feeder and/or circuits
– The charger group is controlled under a shared site limit via load balancing
Large sites may use multiple SDBs, each serving a charger cluster (for example, one per parking level or zone).
What Sub-distribution Boards Typically Include
Depending on site requirements and local electrical rules, an SDB may include:
– Incoming isolator and main protection
– Overcurrent protection devices (OCPD) for outgoing charger circuits
– RCDs or EV-specific fault protection devices where required
– Surge protection (SPD), especially for exposed outdoor runs
– Terminal blocks, neutral/earth bars, and clear circuit labeling
– Lockable isolation for safe maintenance
– Optional energy metering (including MID metering when billing requires it)
– Spare ways for future expansion (an important scalability feature)
Key Benefits for Installation and Operations
– Lower installation cost by avoiding excessive home-run cabling
– Faster expansion by adding breakers and circuits locally
– Improved troubleshooting and service speed through better fault segmentation
– Cleaner commissioning and documentation of charger groups
– Easier integration of maximum site demand limit control and monitoring
Design Considerations and Common Pitfalls
– Feeder sizing must reflect real demand, diversity, and future expansion
– Protection coordination should prevent nuisance tripping across multiple chargers
– Enclosure rating (IP/IK) must match the environment (outdoor, public, industrial)
– Ensure space for CT clamps, gateways, and control wiring if using load management
– Poor labeling and missing as-builts can make later maintenance slow and risky
– Lack of spare ways can force expensive board replacement during expansion
Relationship to Load Management and Site Scaling
SDBs are often the physical hub where site power control is implemented:
– CT clamps measure feeder load in real time
– A controller enforces a maximum site demand limit
– Power is allocated across chargers using load balancing
– Additional chargers can be added later without redesigning the entire distribution architecture
Related Glossary Terms
Sub-distribution Board (SDB)
Main LV Panels
Distribution Board
Feeder Circuit
Overcurrent Protection Device (OCPD)
Residual Current Device (RCD)
Load Management
Load Balancing
Maximum Site Demand Limit
MID Metering