GFCI Trips at 5 mA of Imbalance: Why Yours Keeps Tripping
The imbalance that trips a GFCI is about 5 mA: UL 943 Class A must trip at 6 mA and must not trip below 4 mA. Plus why yours keeps tripping and when to stop.
Short answer: about 5 milliamps (mA). Under UL 943, a Class A GFCI must trip at 6 mA of imbalance between hot and neutral and must not trip below 4 mA — 5 mA is shorthand for the middle of that window. It measures imbalance, not load: a 15 A circuit carries 15,000 mA.
Start here: it is not a load problem
The most common mistake in GFCI troubleshooting is treating it like a breaker trip. It is not one, and that difference matters more than anything else here.
A circuit breaker measures how much current flows and opens when it exceeds what the wire behind it can carry. A GFCI measures the difference between current leaving on the hot conductor and current returning on the neutral, using a current transformer that watches both. In a healthy circuit they are equal. When they are not, the missing current is going somewhere it should not — through a wet enclosure, through failing insulation, or through a person.
So the usual reflexes fail. A bigger breaker moves the overcurrent threshold and leaves the imbalance sensing untouched; unplugging half the room reduces a load that was never the trigger. A 15A circuit carries 15,000 milliamps; the GFCI is hunting a mismatch of roughly five.
The actual number, and where it comes from
Residential GFCIs in the US are Class A devices under UL 943. The requirement is a window, not a single figure: a Class A GFCI must trip at 6 mA of imbalance and must not trip below 4 mA. “5 mA” is shorthand for the middle of that window.
The trip is not instantaneous either. UL 943 specifies an inverse time-current curve — the bigger the fault, the faster the interruption:
t = (20 / I)1.43
where I is fault current in milliamps and t the maximum permitted trip time in seconds. At 20 mA that is exactly one second; at 100 mA, about a tenth of a second. Near the bottom of the range the device is deliberately allowed several seconds, so brief transients do not nuisance-trip the outlet. Hence a marginal fault — a damp cord end, an aging heating element — can sit just under threshold for hours, then trip when conditions shift a fraction.
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Where code requires GFCI protection
NEC 210.8 drives this. In a dwelling unit, 210.8(A) requires GFCI protection for receptacles in bathrooms, kitchens, garages and accessory buildings, outdoors, in laundry areas, in basements (finished or not, in current editions), near sinks and in crawl spaces. The list has grown at nearly every code cycle.
One caveat most articles skip, and it decides the whole of the next section: the NEC is a model code, not federal law. Each state — and in many places each county or city — decides which edition to adopt and what to amend on the way in, and the spread is wider than most guides admit. NFPA’s own enforcement maps, dated 3 August 2026, state that the 2026 NEC is in effect in six states, the 2023 in 20 states, the 2020 in 15, the 2017 in three, and the 2008 edition in two — Illinois commercial work and Kansas. Michigan still governs one- and two-family dwellings under the 2014 edition, and Arizona, Mississippi and Missouri have no statewide electrical code at all. Around 21 states adopt with amendments. Chicago is routinely described as rejecting the NEC in favour of its own code; that is wrong. Chicago Municipal Code §14E-1-010 adopts NFPA 70, 2017 edition, by reference and then amends it heavily — and New York City’s electrical code is the 2020 NEC with NYC amendments. Your authority having jurisdiction — normally the city or county building department — is the only authority on what applies to you.
The 240-volt appliance problem, which is real and unresolved
GFCI rules historically applied to 15- and 20-ampere, 125-volt receptacles. The 2020 NEC deleted “15- and 20-ampere” from 210.8(A) and extended protection up to 250 volts, sweeping in the ordinary range and dryer receptacle for the first time. The 2023 NEC then rewrote 210.8(D). That subsection was not new — it had required GFCI protection for dwelling-unit dishwasher outlets since the 2014 edition — but 2023 expanded it into a list of specific appliances requiring protection on the branch circuit or outlet, rated 150 volts or less to ground and 60 amperes or less: dishwashers, electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers and microwave ovens — cord-and-plug connected or hardwired, closing the loophole that had exempted hardwired units.
Whether that is a requirement where you live depends entirely on adoption. There is no date on which this took effect across the US. Under the 2017 NEC, still enforced in three states, 210.8(D) covers dishwashers only — that requirement has existed since 2014, but there is no range, dryer, oven or microwave list and no 250-volt extension. Under 2020 you get 240-volt receptacles in 210.8(A) locations but not the appliance list. Only from 2023 does the full list apply, and some states amended or deferred 210.8(D) on the way in, precisely because of the problem described next. If your new range trips and an identical one in the next state does not, the code edition each of you lives under may be the whole explanation.
Widespread nuisance tripping followed, and the cause is a standards gap rather than bad wiring. UL 858, the standard for household electric ranges, has not required leakage assessment above 125 volts or GFCI compatibility, and UL 1030 excepts range heating elements from leakage testing. Sheathed (“Calrod”-type) elements use compacted mineral insulation that absorbs moisture; if it is not fully driven out in manufacturing, the element leaks past 6 mA while remaining entirely normal by its own product standard.
In April 2021, AHAM and range manufacturers submitted a technical update to UL 858 aimed at GFCI compatibility, advising builders meanwhile to move the outlet more than six feet from the sink or ask the local authority to invoke NEC 90.4 to permit an earlier edition.
The 2026 NEC shows the code adapting rather than retreating. 210.8(D) keeps the appliance list, but 210.8(F) for outdoor outlets raised its single-phase threshold from 50 to 60 amperes and added an exception permitting a listed Class C SPGFCI for listed HVAC equipment — a special-purpose device that trips at roughly 20 mA rather than the Class A 6 mA (UL’s own published figures for Class C are not entirely consistent, so treat the exact threshold as approximate).
Practical upshot: if a brand-new range, dryer or dishwasher trips a correctly installed GFCI, suspect the appliance before your wiring. Call the manufacturer while it is under warranty. Do not “solve” it by removing the protection.
The real causes, sorted
There is a genuine distinction between a ground fault (current is escaping the intended path — the GFCI is right) and nuisance tripping (accumulated normal leakage crosses the threshold with no single fault). From the hallway they look identical.
| Symptom | Likely cause | What to do |
|---|---|---|
| Trips after rain, or after washing the car | Moisture in the box, the in-use cover, or a cord end | Kill power at the breaker, let it dry completely, replace a cracked or missing weatherproof cover |
| Trips the instant one specific appliance starts | That appliance’s insulation, motor windings or heating element are leaking | Try it on a different GFCI-protected outlet; if it trips there too, the appliance is the fault |
| Brand-new 240V range, dryer or dishwasher trips | Appliance leakage legal under its own product standard but above 6 mA | Contact the manufacturer under warranty — a known, documented industry issue |
| Trips intermittently hours after reset, no pattern | Marginal accumulated leakage — long run, many devices, or an intermittent fault | Electrician: needs measurement, not guesswork |
| Trips together with an unrelated circuit | Shared or crossed neutral (multiwire branch circuit) | Electrician — do not attempt |
| Will not reset with nothing plugged in | Real downstream fault, wiring error, or end-of-life device | Stop. Licensed electrician |
| TEST button does nothing | Device is dead, unpowered, or line/load reversed | You have no protection right now — replace or have it verified |
| Solid or blinking red indicator, will not reset | Self-test has detected end of life | Replace the device |
Two rows deserve expansion. Long circuit runs matter because every conductor has small distributed capacitance to ground; over a long run with many devices, that plus each appliance’s own legal leakage can sum toward the threshold with nothing broken. Shared neutrals trip a GFCI reliably, because the return current genuinely does not match the outgoing current at that device — squarely electrician territory.
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Your GFCI may simply be worn out
Effective June 29, 2015, UL 943 required newly manufactured GFCI receptacles and breakers to include an auto-monitoring (self-test) function: an automatic test within five seconds of power being available, repeated at least every three hours. If that self-test fails, the standard requires power denial — the device shuts off rather than silently pretending to protect you, with a narrow exception permitting an audible or visual indication for two specific failure modes.
It was added because GFCIs fail, and they used to fail silently. A 1999 American Society of Home Inspectors study found 21% of GFCI breakers and 19% of GFCI receptacles inspected were no longer protecting, usually from damage to the internal surge-suppression components shielding the sensing circuit; in high-lightning regions such as southwest Florida the failure rate exceeded 50%. The failure mode left the contacts closed: the outlet kept delivering power, looked normal, and protected nobody.
So a device predating mid-2015 has no self-test, and its outward normality proves nothing.
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Testing it correctly
Monthly, press the TEST button on the device itself. It should snap audibly, and power to that outlet and anything downstream should die. Then press RESET. That is the whole procedure, and it is what manufacturers actually specify. If TEST does nothing, treat that outlet as unprotected until it is replaced or verified. If TEST works but RESET will not hold, a fault is likely still present — do not keep hammering RESET.
One nuance about plug-in testers with a GFCI test button: they work by leaking current from hot to the equipment ground. On a two-wire circuit with no equipment ground — common in older homes, where a GFCI is the code-recognized way to update an ungrounded receptacle — that tester cannot trip a perfectly healthy GFCI, and a failed test there proves nothing. The device’s own TEST button routes its test current internally and works either way. Use the button.
If TEST fails and you go on to swap the receptacle, the screws are the next trap: cross-head fasteners on imported devices are often cammed out by the wrong driver, and the fix is bit fit rather than force — see the JIS vs Phillips screwdriver difference.
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Where this article stops
Everything above is diagnosis. Below this line, stop — and note that who may legally do the repair, and whether a permit is required, is set by state and local rules rather than nationally. Call a licensed electrician if the GFCI will not reset with nothing plugged in (treat that as a positive result, not a malfunction), if you suspect a shared or crossed neutral, if anything nearby shows scorching, melting, a burning smell or buzzing, if a second new GFCI behaves identically, or if the work involves a 240V appliance circuit or opening the panel.
The non-negotiable part: persistent tripping is information, not an inconvenience to engineer around. Removing the device, swapping in a standard receptacle, or feeding the load from an unprotected circuit defeats the one thing in your house designed to interrupt current flowing through a person.
Summary
A GFCI trips on an imbalance of roughly five milliamps between hot and neutral, not on load — UL 943 Class A requires it to trip at 6 mA and not below 4 mA. That is why bigger breakers and unplugging things accomplish nothing. Check moisture first, isolate suspect appliances second, press TEST monthly. If it will not reset with nothing plugged in, it may be doing precisely its job: stop and call a licensed electrician.
For the other half of the household electrical picture — the one that genuinely is about load — see the 1,800-watt ceiling on US 15A circuits. More home and gadget guides at GadgetHub English.
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Frequently Asked Questions
- Q: Is my GFCI tripping because I have too much plugged in?
- A: Almost certainly not. A GFCI does not measure total load at all — it measures the difference between the current going out on the hot conductor and the current coming back on the neutral. A 15A circuit carries 15,000 milliamps; the GFCI is looking for a mismatch of about five. You can overload a GFCI outlet badly enough to trip the breaker behind it without ever tripping the GFCI itself.
- Q: Will a bigger breaker stop my GFCI from tripping?
- A: No, and it is dangerous to try. The breaker protects the wire in the wall from overheating and has nothing to do with the ground-fault sensing circuit inside the GFCI. Fitting a larger breaker on existing conductors removes the wire's protection while leaving the actual cause of the tripping completely untouched.
- Q: Why did my new electric range start tripping when the old one never did?
- A: Because your jurisdiction adopted a newer NEC edition in between. The 2020 and 2023 editions extended GFCI protection to 240-volt appliance circuits — ranges, wall ovens, cooktops, dryers — whether cord-connected or hardwired. The NEC is a model code, so this took effect on different dates in different states and does not apply at all where the 2017 edition is still enforced. Range heating elements have historically been allowed to leak more current to ground than a Class A GFCI tolerates, because the appliance standards were never aligned with the electrical code. If the appliance is new and under warranty, contact the manufacturer before you touch the wiring.
- Q: How often should I press the TEST button?
- A: Monthly, which is what essentially every manufacturer's instruction sheet says. Press TEST — the device should snap off and power to the outlet should die — then press RESET to restore it. If pressing TEST does nothing at all, the device is not protecting you and needs to be replaced regardless of how normal it looks.
- Q: Which of the following is the amount of electricity imbalance required to trip a GFCI and stop the flow of electricity to the circuit?
- A: Roughly 5 milliamps. UL 943 defines residential GFCIs as Class A devices and sets a window rather than a single number: the device must trip at 6 mA of imbalance between the hot and neutral conductors, and must not trip below 4 mA. "5 mA" is the shorthand for the middle of that window, which is why it is the answer given on most exams. Note that this is an imbalance figure, not a load figure — a 15 A circuit carries 15,000 mA.
- Q: When does a GFCI trip, and how fast?
- A: It trips when the current leaving on the hot conductor and the current returning on the neutral differ by roughly 5 mA. The trip is not instantaneous: UL 943 specifies an inverse time-current curve, t = (20 / I)^1.43, where I is fault current in milliamps and t is the maximum permitted trip time in seconds. That works out to exactly one second at 20 mA and about a tenth of a second at 100 mA, with several seconds deliberately allowed near the bottom of the range so brief transients do not nuisance-trip the outlet.
- Q: My GFCI will not reset no matter what I do. Is it broken?
- A: Maybe, but consider the alternative first: a GFCI that refuses to reset may be doing exactly its job, holding open because a genuine fault is still present downstream. It could also be at end of life — devices made since mid-2015 are required to self-test and to deny power when that self-test fails. Either way, a GFCI that will not hold with nothing plugged in is a stop-and-call-a-licensed-electrician situation, not a DIY one.