Engineering tools
Control Panel Load Calculator
Calculate control panel electrical loads, assess individual AC and DC supply rails, and produce a traceable load schedule for engineering review.
This free online calculator helps electrical, control and instrumentation engineers calculate connected, diversified and design loads; assess 24 V DC power-supply requirements; estimate upstream AC input demand; and keep different voltages and supply rails separate.
All calculations run locally in your browser. Calculation data is not uploaded to a server.
Control panel load calculation
Calculation engine: CP-load v1.3
Supply sources
Every load must be assigned to a defined electrical source.
Calculation settings
Choose how design allowance and practical supply selection are applied.
Load schedule
Enter manufacturer input current in amps. Diversity defaults to 1.00 (100%).
| ID | Qty | Part Number | Description | Supply | Rated current (A) | Power Factor | Efficiency (%) | Diversity | Calculated current (A) | Manufacturer | Notes / Remarks | Actions |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0.5 | ... | |||||||||||
| 0.185 | ... | |||||||||||
| 0.04 | ... | |||||||||||
| 0.03 | ... | |||||||||||
| 0.02 | ... |
Results by supply
Output sizing and upstream input demand are reported separately.
| Supply | Running | Design | Installed | Suggested | Operating utilisation | Design utilisation | Remaining | Estimated supply input | Status |
|---|---|---|---|---|---|---|---|---|---|
| PSU-01, 24 V DC | 0.78 A 18.6 W | 0.97 A 23.25 W | 4 A | 1.3 A | 19.38% | 24.22% | 3.03 A | 0.12 A 25.27 W | pass |
Warnings and unresolved assumptions
Invalid rows are excluded from trusted totals until corrected.
No unresolved validation issues.
Calculation method and limitations
Traceability information included in printed reports.
Method
DC and single-phase loads use V × I; balanced three-phase loads use √3 × VLL × I. AC active power applies power factor. Design allowance uses the selected added-margin or minimum-reserve method.
Limitations
This early-stage tool does not perform protective-device coordination, voltage-drop, fault-level, harmonics, full thermal, battery-autonomy or manufacturer derating studies. Final design requires competent review and current manufacturer data.
Using the control panel load calculation
Enter the project information, define every electrical supply and assign each load to the correct source. The calculator evaluates each supply independently; loads connected to different voltages or power supplies are not combined into a single suggested rating.
Project information
Record the calculation title, project, panel reference, document number, revision, design stage, preparer, checker and supporting notes so saved and printed results remain traceable.
Supply sources
Add every source used by the panel, including 24 V DC power supplies, single-phase supplies, balanced three-phase supplies, UPS-backed sources and separately protected auxiliary circuits. Record the input arrangement, input and output voltages, installed capacity, efficiency, power factor and operating arrangement.
Calculation settings
Add design margin increases the calculated running load by the selected percentage. A 25% margin produces a design load equal to 125% of running load.
Maintain minimum reserve requires the selected percentage to remain unused after a supply is selected. A 25% minimum reserve therefore requires more installed capacity than adding a 25% design margin.
Load schedule
Enter each connected device using the maximum continuous current or power stated by its manufacturer. Record the tag, quantity, manufacturer, part number, description, assigned supply, rating, power factor, efficiency, diversity and relevant assumptions.
Use diversity below 1.00 only where maximum simultaneous demand can be technically justified. Invalid or incomplete rows are excluded from trusted totals until corrected.
Results by electrical supply
Each source is reported separately with running and design demand, installed capacity, a suggested nominal size, running and design utilisation, remaining capacity, estimated supply input and validation status.
DC output current assesses the required power-supply output capacity. Estimated upstream AC current is calculated separately from output demand, efficiency, input voltage, input power factor and phase arrangement.
Worked control panel load calculation
The loaded example contains one Siemens SIMATIC S7-1200 CPU, one Siemens digital I/O module and nine 24 V DC panel indicators.
The running demand is 0.775 A at 24 V DC, equivalent to 18.6 W. With a 25% design margin, the requirement becomes 0.969 A or 23.25 W.
A selected 4 A power supply therefore operates at 19.38% running utilisation and 24.22% design utilisation. Estimated supply input is not a complete panel incomer, protective-device or cable-sizing calculation.
Calculation method
DC electrical loads
Single-phase AC loads
Balanced three-phase AC loads
Power-supply input demand
Added design margin
Minimum reserve capacity
Selecting a control panel power supply
Use maximum continuous ratings from current manufacturer datasheets and consider the credible maximum number of devices operating simultaneously. The calculator determines a required capacity and suggests a nominal size; it does not make a final equipment selection.
Before selection, check ambient and orientation derating, boost capability, starting and inrush currents, transients, cable voltage drop, redundancy losses, failure-state loading, current sharing and protective-device compatibility.
External equipment such as solenoids contributes to electrical load even where its heat is dissipated outside the enclosure. Electrical demand and panel thermal load must be assessed separately.
Mixed-voltage control panels
A 24 V DC load contributes to its assigned DC source. A 230 V AC load contributes to its assigned AC circuit. The calculator reports each rail independently and identifies incompatible assignments.
Frequently asked questions
Which equipment rating should I enter?
Use the maximum continuous current or power stated in the current manufacturer datasheet unless the approved project design basis permits another value. Typical or nominal consumption may understate the electrical capacity needed under maximum operating conditions.
What is the difference between connected, diversified and design load?
Connected load is the total of all included equipment ratings. Diversified load applies justified assumptions about which loads can operate simultaneously. Design load applies the selected margin or reserve requirement to the diversified load.
Why does duty cycle not automatically reduce maximum demand?
Equipment operating intermittently may still be energised at the same time as other loads. Use maximum credible simultaneous demand when assessing the electrical supply and treat average thermal duty separately.
What is the difference between PSU output current and AC input current?
Output current determines the required DC power-supply capacity. Upstream AC input current also depends on output power, power-supply efficiency, input voltage, input power factor and phase arrangement.
How should redundant power supplies be selected?
The remaining healthy power supply normally has to support the required load after one supply fails. The design must also consider module losses, voltage drop, current sharing, overload behaviour and manufacturer requirements. This calculator does not perform a complete failure-state assessment.
Can the calculator be used for final design?
The calculator supports preliminary design, checking and design review. It does not replace project-specific calculations, approved requirements, current manufacturer data, applicable standards or competent electrical design verification.
Scope and limitations
This calculation does not include:
- Protective-device selection or coordination
- Prospective fault-current assessment
- Cable sizing or voltage-drop assessment
- Discrimination studies
- Harmonic assessment
- Enclosure thermal modelling
- Transformer sizing
- UPS autonomy or battery sizing
- Hazardous-area verification
- Functional-safety verification
- EMC assessment
- Manufacturer-specific derating
- Complete redundant-supply failure analysis
Peak-load and redundancy information may be retained in saved data but is not used to claim design compliance.
Engineering disclaimer
This report supports engineering estimation, design review and independent checking. The results depend on the accuracy and completeness of the entered data and stated assumptions. Before equipment is specified, purchased, installed or energised, the calculation shall be verified against current manufacturer data, approved project requirements, applicable standards, environmental conditions and foreseeable operating and failure states. This report does not constitute design approval, equipment certification or confirmation of compliance by itself.