Voltage Present But No Load: Decision Tree
Why this matters
"There's voltage, but nothing runs" is one of the most common and most misleading situations in the field. Voltage at a terminal feels like proof the circuit is good, so techs assume the load is bad and start swapping parts. Often the voltage is real but cannot do any work, because there is no complete path for current to flow. Voltage is potential; current is what does the job. Knowing the difference saves you from condemning a healthy motor, coil, or board.
Safety: every test below is on a live circuit. Verify your meter on a known live source first, use proper PPE, and keep one hand free.
Start here: voltage is not the same as a working circuit
A voltmeter reads the difference in potential between two points. It draws almost no current to do that. So a meter can show full voltage across a path that current cannot actually flow through. Voltage present + load dead means one of three things: the voltage is real but the return path is broken, the load is open internally, or the voltage you are reading is not real (phantom voltage). Walk it in that order.
Step 1: Confirm the voltage is real (under load)
A high-impedance meter can read voltage that collapses the instant any load tries to use it. This is phantom voltage from capacitive coupling on a run of wire, and it is the number one false lead here.
- Re-read with a load on the meter. Use a low-impedance meter setting or a solenoid-style tester, or briefly apply a known small load.
- If the voltage holds under load: the voltage is real, move to Step 2.
- If the voltage collapses toward zero the moment a load is applied: it was phantom voltage. The "source" you are reading is not actually feeding the circuit. Treat it as no voltage and go upstream to find where the real feed is open. (See the backfeed and phantom-voltage material.)
Do this first. It costs ten seconds and prevents the most common wrong diagnosis.
Step 2: Check for a broken return path
If voltage is real and present at the load but nothing runs, suspect an open neutral or open return. The hot side is fine; the current cannot get back.
- Measure across the load itself (both load terminals), not hot-to-ground. If you read full voltage across the load but it does nothing, current is not flowing through it.
- Check the neutral/return. A loose, corroded, or open neutral leaves full voltage at the hot terminal and a dead load. The voltage "stacks up" across the open because no current flows.
- If the return is open: that is your fault. Restore the neutral or common connection. Many no-load-with-voltage calls end right here.
Step 3: Test the load for an internal open
If voltage is real and the return is good, the load itself may be open internally - a burnt-open coil, a blown internal element, a motor with an open winding.
- De-energize and verify dead.
- Ring out the load for continuity. A coil, element, or winding should show a real resistance value. Infinite resistance (OL) means it is open internally and that is your bad part.
- Compare to spec where you have one. A reading far off the nameplate (open, or wildly high) condemns the component.
An open load is the legitimate "part is bad" case. But you only reach it after ruling out phantom voltage and an open return, because both of those mimic a bad load.
Step 4: Check what enables the load
Some loads have voltage present but are being held off by a control, interlock, or missing enable signal. The power is there; the permission is not.
- A safety or interlock is open. A limit, float, pressure switch, or door interlock in the control path is preventing the load from running even though line voltage is present at it.
- A control signal is missing. A relay coil that is not energized, a thermostat not calling, a board output not commanded. The load has power and a path but is waiting for a command it never receives.
- Trace the control circuit (the ladder logic) to find which gate is open. The fix is upstream in the control rung, not in the load.
The ordered path
- Is the voltage real under load? No -> phantom voltage, go upstream.
- Is the return path complete? No -> open neutral/common, restore it.
- Does the load read continuity in spec? No -> load is open internally, replace it.
- Is the load enabled by its controls? No -> find the open gate in the control circuit.
Work it top to bottom. Each step rules out a cause that looks exactly like a bad load but is not.
References
- NFPA 70 (National Electrical Code) on circuit conductors and continuity
- Manufacturer component resistance and control specifications
- OSHA electrical safety and lockout/tagout standards
- Trade-standard live and dead diagnostic practice
- See related: Open vs Short vs Ground (The Three Faults), Backfeed and Phantom Voltage