How to use this calculator
- Enter nameplate FLA. Use the motor nameplate full-load current or the required project current basis.
- Enter the multiplier. Type the overload multiplier required by the equipment instructions or governing code basis.
- Compare the selected setting. Enter the selected relay setting or heater value to see its percent of target and deviation.
- Check running headroom. Enter measured running current to see margin against the selected overload setting.
How it works
Motor overload sizing starts with a current basis, usually motor nameplate FLA for actual protection work. This screen applies your entered multiplier:
I_OL = FLA × M_OL / 100
Motor Overload Setting Worksheet
Use this worksheet to keep overload protection separate from breaker, conductor, disconnect and grounding checks. The calculator applies the multiplier you enter; it does not hide a code or relay manufacturer table.
| Sizing question | Calculator input | Design read |
|---|---|---|
| What current basis controls? | Nameplate FLA | Use the motor nameplate or required project basis for actual overload protection. |
| What overload percentage applies? | Overload multiplier | Enter the value required by equipment instructions, relay data and adopted code basis. |
| Only know service amps or breaker size? | Nameplate FLA, not service amps | Service or feeder ampacity is a separate circuit-sizing input; overload setting starts from the motor current basis. |
| What is the target setting? | I_OL = FLA x M_OL / 100 | Calculates the target relay, heater or overload setting in amps. |
| Does the selected device match? | Selected overload setting | Compares the chosen setting with target and reports percent/deviation. |
| Is steady running current reasonable? | Measured running current | Shows running utilization and margin, not startup or nuisance-trip behavior. |
| What else must be checked? | FLA, ampacity, voltage drop and EGC tools | Branch protection, conductors, disconnects, VFDs and grounding are separate checks. |
Motor Overload Heater Size Chart
People often search for a motor overload heater chart when they really need
the target current before choosing a listed heater element or relay dial.
This chart shows the workflow with the page's default 14 A
nameplate FLA. For the real motor, enter its nameplate FLA above and use
the heater or relay manufacturer's actual table for the final selected part.
| Entered multiplier | Example nameplate FLA | Target overload setting | How to use it |
|---|---|---|---|
| 100% | 14 A | 14 A | Use when the selected rule or device instructions call for a 100% nameplate-FLA target. |
| 115% | 14 A | 16.1 A | A common entered screening value for some service-factor or temperature-rise cases; verify before installing. |
| 125% | 14 A | 17.5 A | A common entered upper screening value where the governing rule and relay instructions allow it. |
Do not size the heater from service amps, feeder ampacity or breaker size. The live calculator gives the target setting and selected-setting deviation; the installed heater element or electronic relay setting still has to come from the device instructions.
It then compares the selected relay setting with that target, reports the setting deviation, and checks measured running current against the selected setting. If you only know horsepower, voltage and power factor, use the motor full-load amps calculator first for an early estimate, then check conductor runs with voltage drop, ampacity derating, conduit fill and pull tension.
Worked example
Verified against the live calculator
A motor with 14 A nameplate FLA and an entered overload multiplier
of 115% has a target setting of 16.1 A. If the selected
setting is 16 A, it is about 99.4% of target. With
12 A measured running current, the running current uses
75% of the selected setting and leaves about 4 A of
headroom.
Frequently asked questions
How do I size a motor overload setting?
Start with nameplate full-load current, then multiply by the overload percentage that applies to the motor, controller and adopted code or manufacturer instructions: I_OL = FLA x multiplier / 100.
Why does the calculator ask for the overload multiplier?
The correct multiplier depends on motor details, equipment instructions and the governing code edition. This screen keeps that value explicit instead of hiding a one-size-fits-all table.
Can I use this as a motor overload heater chart?
Use it as a calculation worksheet only. Heater elements and electronic relay settings are manufacturer-specific; start from motor nameplate FLA, apply the permitted multiplier, then choose the nearest listed heater or dial setting from the actual device instructions.
Should I use formula motor FLA or nameplate FLA?
Use nameplate FLA when sizing actual overload protection. The motor full-load amps calculator is useful for early current estimates, but overload protection should be checked against the required nameplate or code basis.
Can I size motor overload by service amps?
No. Service amps, feeder amps or breaker size do not set the motor overload setting by themselves. Use the motor nameplate FLA and the required overload multiplier; use service or feeder current only for separate conductor, breaker and voltage-drop checks.
What does selected setting vs target mean?
It is the selected relay dial, heater or setting divided by the calculated target setting. Values near 100% match the target; large differences should be reviewed before installation.
Does this size breaker or short-circuit protection?
No. Motor overload protection, branch-circuit short-circuit protection, conductor ampacity, disconnects, starters, VFDs and grounding are separate checks.
Method & assumptions
- Uses an explicit user-entered overload multiplier rather than an embedded code table.
- Compares selected setting with target setting using a practical tolerance band.
- Running-current margin is a steady-state screen, not a startup or nuisance-trip model.
- Does not size conductors, short-circuit protection, disconnects, starters, VFD parameters, grounding or control gear.
- Final work still needs motor nameplate data, equipment instructions and the adopted local code edition.