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The plug on my pressure washer has a built-in GFCI. When I plug it into a GFCI protected (at breaker or at outlet) wall outlet at home, is the protection redundant (I'm asking about my safety while using the pressure washer), or are there any safety aspects uniquely provided by each?

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4 Answers 4

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Yes, it is redundant. But the problem is that products used with water (e.g., pressure washers) and products used near water (e.g., hair dryers) are extremely dangerous if there is a ground fault. This is being resolved from two different directions:

  • Location

Over the past few decades, GFCI requirements have been rolled out to kitchens, bathrooms, outdoor receptacles, laundry rooms, unfinished basements and other specific locations. However, many people never replace/upgrade their receptacles unless something fails. Kitchens and bathrooms tend to be more frequently upgraded (with GFCI coming along with the other upgrades) for functional and/or aesthetic reasons. But outdoor receptacles are rarely changed.

Which means that outdoor receptacles on houses from the 20th century have a very high chance of not being GFCI protected. But appliance and tool manufacturers can only specify the type of plug (e.g., NEMA 5-15) and can't force a user to plug it into a GFCI-protected receptacle.

  • Device

Devices are a different situation. It is not practical (for both cost and political reasons) to mandate adding GFCI protection to existing products. However, new products can have these requirements enforced by UL, ETL or other certifying organizations. The cost is far from $0, so this is again a cost-benefit issue. Most people don't use their vacuum cleaner near water. Most people don't plug in their lamps near water (bathrooms and kitchens almost always have permanently wired ceiling fixtures, unlike bedrooms). So this is required on the most likely problem devices - those used near water (hair dryers, etc.) or with water (pressure washers). Since small appliances don't last forever - figure anywhere from 5 to 15 years for most of these things before something breaks - this is an effective way to provide GFCI protection for the most critical devices.

But the device manufacturers can't sell you two different devices - one for "I have GFCI" and one for "I don't have GFCI". Even if you signed a form saying you have GFCI on every bathroom receptacle, what happens if you give the hair dryer to one of your kids to take to a dorm room or apartment that has not had GFCI added to the circuits?

The safety provided by the two types of GFCI is essentially identical. In most cases there will be no problem, except that if you have an actual ground fault then you can't predict which GFCI will trip or if both will trip. But if that happens, unplug the device, figure out the problem (it may be really obvious), reset both GFCIs and then plug the device back in.

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  • Wet/Dry shop vacs. Doesn't a non-GFCI circuit breaker provide the same protection in the case of an appliance/tool dropped into water?
    – user158587
    Commented Nov 4, 2022 at 20:03
  • I don't know whether wet/dry vacs require a built-in GFCI - logically they should. But in any case, a non-GFCI breaker absolutely does NOT provide the same protection as GFCI (whether in the plug/cord or receptacle or breaker). It takes a large overload to trip a regular breaker. But just a little bit of the regular current (not even an overload) going the wrong place can be deadly but will trip a GFCI in time. Commented Nov 4, 2022 at 20:49
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    Thanks, one last line of question. GFCI works by comparing the currents in the black and white wires, and if it detects too much of a difference, it trips -- is that correct? so the GFCI provides protection even if the appliance comes without grounding and just a two-wire cord? What are the safety concerns with using a 3-wire tool (e.g. power saw) on a GFCI circuit IF the power cord plug has a broken off ground terminal?
    – user158587
    Commented Nov 4, 2022 at 22:00
  • Not between black and white wires. Between hot wire(s) and neutral. Which is normally black/white on a 120V circuit, can be black/white or black/red (or other colors) on a 240V circuit and black/white/red on a combination 120V/240V circuit (e.g., dryer) - GFCI is color-blind. But real question is grounding: Correct, GFCI will work with (a) a 2-wire appliance (e.g., lamp, radio, etc.) (b) a 3-wire appliance (power saw with a ground pin) and (c) a 3-wire appliance with a broken ground pin. The ground pin has two primary uses - enable a circuit breaker trip in a hot-to-case fault, Commented Nov 5, 2022 at 23:34
  • which a GFCI will take care of quite well in most cases, ground wire or not (but see below) and dissipating noise/surges/etc. As a result, GFCI is permitted as a way to protect 2-wire circuits that don't have a ground available, turning them into 3-wire circuits but with a non-functional ground wire, but providing almost all the same protection. There is one catch: If you try a GFCI tester on a GFCI which has no ground connected, the tester will usually not work! That's because it is trying to send a little current to ground and can't, so the current doesn't "disappear" and the GFCI Commented Nov 5, 2022 at 23:36
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The built in GFCI is a safety feature mandated by governmental and insurance entities on any tool or small device that uses electric and water. It is for your safety if the outlet you plug it into does not have GFCI protection. There should be no problem with the redundancy.

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"lump on cord" GFCIs might not just be a GFCI. It might be an LDCI. (Leak Current Detection and Interruption) or a combo LDCI-GFCI.

Some of them have a mesh along the cord that they're also measuring, and some even have a pilot wire going to the device, so the device's internal microcontroller can trip the LDCI if it sees a problem.

They all use the same conspicuous "Test" button / "Reset" button user interface people are familiar with from GFCIs, so they tend to be all labeled GFCIs by the public.

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  • I'll look more closely, thanks, but what are the differences in safety between the LDCI / LCDI and GFCI?
    – user158587
    Commented Nov 4, 2022 at 20:33
  • @user158587 It depends what they put in it. I would expect a water appliance to have full GFCI protection. Commented Nov 4, 2022 at 20:33
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(I'm asking about my safety while using the pressure washer

Redundant is good

Just in case one of the GFCI goes bad (and they do that)

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  • They usually fail to off, which is another pain.
    – crip659
    Commented Nov 4, 2022 at 18:32

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