DDC Panel Device Sizing: P-40 and IO-40 Quantities from the Point List (Calculator)
10/20/2026
Calculate how many EPL-P-40 and EPL-IO-40 each DDC panel needs from its DI/DO/UI/AO points, plus relays and transformer sizing, and export to Excel.
The first concrete step in a building automation project is deriving, from the point list, how many controllers and expansion modules each panel needs. This tool takes each DDC panel as a row, adds spare points and calculates the EPL-P-40 and EPL-IO-40 quantities along with relay and transformer requirements.
Channel layout
The EPL-P-40 controller and the EPL-IO-40 expansion module share the same channel layout: 16 DI · 8 UI · 8 AO · 8 DO.
Sizing rules
- UI and AO channels are used as DI when needed. Once DI channels are full, extra DIs go to free UIs first, then to free AOs.
- An AO channel is used as DO via a relay. If DO channels run out, extra DOs are wired to free AOs through relays; each one means one relay. The relay coil must be 5 VDC / 10 mA; the AO output cannot drive a coil that draws more current.
- Up to 4 IO-40 can be connected under one P-40. If more are needed an extra P-40 is added, and its own channels are counted too.
- Spare points are added per panel as a percentage of each point type and rounded up.
- If a panel has no controller, its IO-40s connect to free slots of P-40s in other panels; if there are not enough slots, an extra P-40 is calculated.
Integration
The number of Modbus and BACnet devices to integrate is entered per panel. Modbus devices connect through EPL-MBC-100 (Modbus TCP-RTU converter) and BACnet devices through EPL-BAC-100 (BACnet IP router). Each gateway has 2 ports with up to 30 devices per port; sizing is done per panel. The point count read from those devices is entered separately; the tool adds I/O, Modbus and BACnet points to give the project's SCADA point count.
Bulk entry with the template
For multi-panel projects, get the Excel template with the tool's Download template button, fill in one row per panel and load it back with Load from template.
Transformer
Panel consumption is the sum of the P-40, IO-40 and relay consumption plus the VA of other equipment in the panel. After adding the safety margin, the next standard transformer size is selected per panel, and a project total is shown as well.
Calculator
DDC Panel Device Sizing (P-40 / IO-40)
EPL-P-40 and EPL-IO-40 quantities, relays and transformer from the point list
Parameters
P-40 and IO-40: 16 DI · 8 UI · 8 AO · 8 DO. UI and AO are used as DI when needed; AO is used as DO via a relay. Up to 4 IO-40 per P-40; beyond that an extra P-40 is added and its channels are counted too. Integration per panel: Modbus devices connect to EPL-MBC-100 (Modbus TCP-RTU), BACnet devices to EPL-BAC-100 (BACnet IP router); 2 ports per unit, up to 30 devices per port.
| Point summary | DI | DO | UI | AO |
|---|---|---|---|---|
| Point list | 0 | 0 | 0 | 0 |
| Required incl. spare | 0 | 0 | 0 | 0 |
| Total channels (P-40 + IO-40) | 16 | 8 | 8 | 8 |
| Used channels | 0 | 0 | 0 | 0 |
| Free channels | 16 | 8 | 8 | 8 |
Used channels include shifted points: DI→UI 0 · DI→AO 0 · DO→AO (relay) 0. Free channels are those still free after adding spare.
| SCADA point count | Point list | Required incl. spare |
|---|---|---|
| I/O (DI+DO+UI+AO) | 0 | 0 |
| Modbus point count | 0 | 0 |
| BACnet point count | 0 | 0 |
| Total | 0 | 0 |
⚠ Preliminary sizing
- Results are for preliminary design; the final selection must be approved by the project engineer.
- Consumption (VA) values are the ones you enter; verify them against the device datasheet.
- Field devices (sensors, actuators, valves) are included only if entered in 'Equipment (VA)'.