Solid State Relay Panel  

One panel is located in basement with a second planned for the third floor. It was inspected and approved by the local wiring inspector as being compliant with the 1999 U.S. National Electrical Code (NEC).

The panel uses 16 standard, RU/UL/CSA-approved, random-phase, 25-amp Crouzet Solid-State Relays (SSR’s) and a 24”x18”x6” enclosure (Hoffman J&P Box 431A catalog A-SE 24x18x6).

Solid State Relays used for dimming need to be designed to be turned on at any time (angle) during the 60-cycle (North America ; 50-cycle in other parts of the world). These are called "random phase". "Zero-crossing" SSR's are preferable for on-off switching because they turn on and off when the voltage is at a minimum which minimizes noise put on the powerline and radiated through space. These need additional circuitry to be used as dimmers.

The large (18”x4-3/4”x4-3/4”, 16 lbs), black, extruded-aluminum heat sink in the middle provides for both passive and active (fan) cooling of the SSR’s.  Passive cooling from enclosure sides and cover is ample for the actual lighting load. Two 4-3/4” fans (top and bottom) are built in should additional cooling ever be required.

There were an insufficient number of available circuit breakers in the existing main entrance panel, so another load center with breakers for each pair of SSR’s was added near the main entrance panel (not shown). A Cutler Hammer panel provides flexibility.

The zero-crossing for the dimmer comparator circuits are derived  from both phases.

There is ample room to add chokes as required or capacitor-based controls for ceiling fans.

The lower compartment is intended to accommodate low voltage circuitry including power monitoring components.