What the two types do after the power blinks
Both types trip the same way on a ground fault. They differ in what happens when power is removed and restored, whether that was a trip, a breaker, or the utility.
A manual-reset GFCI opens on loss of power and stays open. The load is dead until a person presses RESET. Nothing downstream can restart on its own.
An automatic-reset GFCI re-closes when power returns. After a genuine ground-fault trip, most designs also reconnect once the fault current is gone. The load comes back with nobody there.
Manual reset, when a restart is the hazard
Power tools, saws, grinders, drills, pressure washers, portable heaters, mixers, anything with a blade or a hot surface. If the power blinks while the operator has walked away or is clearing a jam, an automatic restart is the accident. Manual reset is the safe default for handheld and portable tools. It is what OSHA's construction rule (29 CFR 1926.404) and most tool makers' instructions expect. It also makes a trip visible: somebody has to walk to the device and press RESET, and that is usually the moment they notice the cord was lying in a puddle.
Automatic reset, when a stopped load is the hazard
Refrigerators, freezers, sump pumps, aquarium pumps, vending machines, medical refrigerators, heat tape, livestock waterers. Here the failure that costs money or lives is the load staying off after a two-second outage nobody witnessed. Automatic reset restores it. The NEC lived with this tension for years: it exempted dedicated refrigerator and freezer receptacles in garages and basements from GFCI protection precisely because trips went unnoticed. Recent editions have removed most of those exemptions, and an automatic-reset GFCI cord is how you protect those loads without losing them.
Four questions that settle it
- If this restarted by itself with nobody there, what happens? Injury or fire: manual. Nothing: automatic is allowed.
- If this stayed off for a weekend, what happens? Spoiled goods, a flooded basement, dead fish: automatic. Nothing: manual is fine.
- Can anyone reach the outlet? A manual-reset device behind a machine nobody can get to becomes a maintenance call after every outage. Put the device in-line where it can be reached, or use automatic reset.
- Does a specification already say? Rental fleets, schools and hospitals often mandate manual reset on portable tools. Food service and pharma often mandate automatic on refrigeration. Follow the spec.
What we see in the field
The order that comes in most often is a manual-reset cord for a walk-in cooler, because "manual" sounded safer to whoever wrote the purchase order. It is safer for the operator and worse for the food. The cooler trips on a brief outage at 2 a.m., nobody is there to press RESET, and the loss is found at 6. The other mistake runs the other way: automatic-reset cords bought for a rental fleet of pressure washers because they "come back on their own". They do, sometimes with the wand pointed at someone. We ask what is on the end of the cord before we quote either one, and we suggest you do the same before you specify.
The same choice on an RCD
Portable RCDs to IEC 61540 (PRCDs) split the same way. A PRCD-S ("switched") is the manual-reset type. It will not re-close on power return, and it checks the protective conductor before it will switch on at all. The ordinary PRCD re-closes. Tools versus refrigeration works out the same at 230 V.
What the choice does not change
Trip level, trip time and the TEST button are identical on both. Neither type protects against overload. Neither should be used as the on/off switch for the equipment. Both need the button test, monthly and after any drop or soaking.