Speaker: Mike Sokol, RV Electricity

Hey, everybody. I’m Mike Sokol from RV Electricity, and welcome.

First, thank you all for taking the time to watch this. We’ll keep this to about an hour, and you’ll also be able to watch it again later as many times as you want. There’s a bonus section at the end. If we don’t get to all of it today, it will still be included in the PowerPoint presentation, which you can sign up to receive.

I’m Mike Sokol from RV Electricity. I’ve been doing electrical work for 68 years, if you can believe that. I also have a long background as a rock-and-roll sound engineer. I’ve worked with everyone from AC/DC to Frank Zappa and plenty in between. One of my responsibilities has always been making sure everything is properly grounded so nobody gets electrocuted on stage and we don’t introduce hum into the sound system.

That gives me a deep background in grounding and bonding going back about 50 years, and all of that applies to camping and to the GMI structure. I also have a close association with the National Electrical Code committees.

Today we’re going through GMI 101. Bobby sent me your top 10 questions a couple of weeks ago, and we’re going to work through them, starting with the basics and getting into some of the more technical questions, including the difference between grounding and bonding.

What Is a Grounding Monitor Interrupter?

The first question is: What is a Grounding Monitor Interrupter, or GMI?

A GMI is required on all new RVs with 30- or 50-amp shore power beginning with the 2028 model year. That should begin showing up around the middle of 2027.

The GMI is basically a box permanently installed inside the RV, similar in some ways to an automatic transfer switch. Its job is to check the incoming electrical system and make sure the grounding is correct and the RV is safe from shock hazards before allowing shore power into the RV.

There was an incorrect press release a few months ago suggesting that GMI devices would be installed in campground pedestals. That is incorrect. Installing them in every campground pedestal would require millions of units. GMIs will exist inside the RV.

The GMI tests the pedestal power and, really, the entire power path all the way into the RV. It checks for correct hot-neutral polarity, proper grounding, and the absence of a hot-skin voltage before it allows shore power to flow into the RV.

It is permanently installed directly at the RV’s shore power inlet during manufacturing.

The GMI controls the 120- or 240-volt AC shore power entering the RV. It does not control the RV’s 12-volt battery system. If the RV has an onboard 120-volt inverter, it does not control that either.

So if someone’s battery system isn’t working, that isn’t the campground pedestal’s fault. The RV can still potentially operate from its battery, generator, or inverter. But if the GMI decides that the shore power coming in is unsafe, it will not allow that shore power into the RV.

When Will GMIs Begin Showing Up?

This requirement has been pushed back a couple of times, but as of August 2026, I don’t expect it to move again.

This is an RVIA requirement. All new 2028 model-year RVs with 30- or 50-amp shore power connections will need to have a factory-installed GMI.

Another incorrect press release suggested that the requirement applied only to towable RVs. At this point, it applies across RV types, including Class A, Class B, and other motorized and towable RVs.

Industry predictions are that GMIs will begin appearing in new RVs around July or August 2027 as manufacturers begin producing 2028 models.

There currently are no production GMI units available to consumers and no aftermarket GMI units you can simply buy and install. There are also no portable plug-in versions currently being offered that I know of.

UL 2299 does allow for portable designs, so portable versions could eventually exist. But at this point, GMI devices are still in the prototype and testing stage.

I wrote one of the original white papers on how this technology was supposed to work, so I know what these devices are intended to do. A number of manufacturers will probably send me prototype units for evaluation. Once I have several of them, I’ll test and compare them in my Funk Works lab.

For those who don’t know me, I live outside Funkstown, Maryland, so I named my lab the Funk Works. I do a lot of destructive testing for manufacturers there. That’s become my retirement gig.

Once I know more about the production units, I’ll publish the results.

Do Campground Pedestals Need Special GMI Wiring?

Another big question is: Will campground pedestals require special wiring to be GMI compliant?

No.

If your pedestal is miswired and someone with a GMI-equipped RV plugs into it, the RV may not receive power. But a properly wired campground pedestal that complies with NEC Article 551 standards should work perfectly with a GMI-equipped RV.

That also means the entire connection needs to be correct—the shore power cord, extension cord, dog-bone adapter, and other components between the pedestal and RV.

Every campground pedestal needs correct hot-neutral polarity, low ground-bonding impedance, and no hot-skin voltage condition.

Those requirements don’t just make a pedestal compatible with GMI-equipped RVs. They make the electrical hookup safer for every RV, whether it has a GMI or not.

The relevant pedestal standards go back to approximately the 1970–1971 code era. If your campground wiring was installed after that and has been properly maintained, it should generally be fine.

Any campground pedestal wired to the 1971 code or later should be GMI compatible if it remains correctly wired and maintained.

For 120/240-volt split-phase service, a four-wire configuration is required. The code also permits 208/120-volt three-phase wye configurations in the appropriate applications.

What About Worn 30- and 50-Amp Receptacles?

Will pedestals with worn 30- or 50-amp receptacles need to be replaced?

Possibly, yes.

GMI devices perform proactive testing of the electrical system. If a pedestal receptacle is loose, worn, or has an intermittent connection, it can potentially create a shutdown condition.

For example, if a 30-amp plug is hanging loosely in a worn receptacle and moving around, the GMI could detect an unacceptable condition and refuse to energize the RV.

The same thing can happen if the RV owner has a damaged dog-bone adapter, extension cord, reverse-polarity connection, broken grounding conductor, or loose connection at the RV.

If the GMI doesn’t like what it sees, it will refuse to provide shore power.

I’ve been running the RV Electricity blog and doing No Shock Zone training for about 15 years, and I have hundreds of examples of burned-up dog-bone adapters, damaged twist-lock connectors, and dangerous campground pedestals.

Some pedestals simply live a hard life.

Those receptacles or complete pedestals may need to be repaired or replaced.

I’m also working on a training video series covering campground pedestal maintenance. If a campground doesn’t want to perform that maintenance internally, it should use a technician who is specifically trained to work on RV campground electrical systems.

I’m working toward a certification program because campground pedestal wiring may not be obvious to someone whose experience is limited to residential electrical work.

Any of these poor electrical conditions can result in a GMI shutdown.

Will GMIs Be Solid State?

One question is whether these GMI units will be solid state or whether they will be prone to failure like some surge protectors.

They will be solid-state devices.

They are not required to include surge protection. Surge protectors are typically sacrificial devices. After enough surge events, they can eventually fail.

The GMI is doing something different.

Manufacturers and code organizations are still working through some of the voltage requirements and other parameters, and I’m trying to help make sure these units don’t create unnecessary nuisance trips.

This is new technology, so there will be things we learn as it rolls out.

One reason I like having a central place where campground owners can submit their questions is that I can investigate those issues, determine what’s actually happening, and provide feedback to manufacturers.

What About Older Campgrounds With Three-Wire Distribution?

If you have an older campground, you may have a three-wire 120/240-volt distribution system. In that case, you may need to install new grounding conductors.

Grounded and bonded campground pedestals have been required under the NEC Article 551 code structure for many decades.

But if your campground was built before approximately 1970, you could have an older ungrounded three-wire 120/240-volt power system. That would be a code violation under modern standards.

To maintain GMI compatibility, you may need to install new equipment grounding conductors and pedestals with properly separated neutrals and grounds.

The important point is that you need four wires for a modern 120/240-volt split-phase system.

You cannot use a bootleg ground.

If you have an existing three-wire 120/240-volt or two-wire 120-volt distribution system from the 1960s, for example, you may need to run new equipment grounding conductors to each pedestal.

There really isn’t another good way around it.

That may mean trenching and installing new conductors.

What Could Campground Upgrades Cost?

A question came in about cost.

The campground isn’t paying for the actual GMI inside the RV. That device will be installed by the RV manufacturer and ultimately paid for as part of the RV.

The campground’s cost comes into play if its electrical infrastructure needs upgrading.

If you need to run new grounding conductors, the cost will depend on the campground.

You may be dealing with conductor costs, trenching, site conditions, labor, and other factors. The grounding conductor could need to be 8-gauge copper or heavier depending on the installation.

It’s difficult to give a universal cost-per-foot estimate without knowing the site.

I know several campgrounds in Pennsylvania near me—I’m in Maryland near the Pennsylvania border—that still have three-wire connections. They’ve asked me to come out and look at their systems.

One thing I can do is talk with some of the companies that specialize in campground pedestal work and develop some representative costs for campgrounds with 50, 200, 500, or however many sites.

And remember: you don’t necessarily have to update the entire campground at the same time.

You might update one section first—maybe a dozen or 20 sites—and continue working your way through the campground.

One idea we’ve discussed is having GMI-equipped RVs carry a large, visible sticker near the shore power inlet identifying them as GMI equipped. That would allow a campground with only part of its property upgraded to direct those RVs into a GMI-ready section.

The cost of underground work also depends heavily on site conditions: required depth, rocks, soil type, roots, labor costs, road crossings, and local code requirements.

Older campgrounds with mature trees present another problem because trenching can severely affect tree roots.

So there’s no single inexpensive solution. But campground associations and qualified utility contractors should be able to help owners evaluate the infrastructure and determine what’s actually necessary.

Can Campgrounds Test Their Own Pedestals?

Another question is: Is there a test a campground can perform if a GMI-equipped RV can’t get power?

At this point, you can’t fully perform the necessary test with a basic multimeter.

You also can’t do it with one of the simple three- or four-light outlet testers.

In addition to voltage and polarity, you need to test the grounding conductor’s bonding impedance and confirm that there isn’t an excessive neutral-to-ground potential.

At this point, there are no widely available, approved meters and methods specifically designed to give campground staff a simple GMI-compliance test.

However, I’m already evaluating prototypes.

What I would like to see is a simple tester that a campground could keep behind the front desk. If there’s a question about a pedestal, someone could plug in the tester and get a straightforward indication of whether the pedestal passes or fails the relevant requirements.

I expect more developments on that front soon.

I’ve been doing ground-loop impedance testing on rock-and-roll sound systems for approximately 50 years.

There are existing analyzers that can perform some of these measurements. Some are no longer manufactured. Others are much more complicated than a campground needs.

What I’m looking for is something much simpler: essentially a pass/fail, go/no-go tester that campground staff can easily understand.

I believe I’m well positioned to help create the SOP, training class, testing procedures, and compliance education around this because, in addition to my electrical work, I’ve also been an adjunct college professor for more than 10 years.

How Will You Identify a GMI-Equipped RV?

How can you identify which RVs already have a GMI installed?

We’re proposing that new RVs with onboard GMIs have a plainly visible sticker near the shore power inlet stating that the RV is GMI equipped.

I’ve also proposed creating a one-page handout for every buyer who purchases a GMI-equipped RV.

It would simply explain: What is a GMI, and what does it mean to me as an RV owner?

The information could be distributed as a printed handout, a sticker, or through a QR code linking to an online explanation.

RV owners are going to ask what this new device means, so we need to make the answer easy for them to find.

Will Campgrounds Need Ground-Rod Impedance Testing?

I’ve been reading some of the information RVIA has distributed to campgrounds, and I have concerns about one recommendation involving a fall-of-potential ground-rod impedance test.

I’m currently discussing this with National Electrical Code Code-Making Panel 7 and RVIA.

A fall-of-potential test is specialized, complicated, and relatively expensive.

In many situations, there is an allowance in the code to install a second grounding electrode instead of performing this test. That can mean installing two ground rods spaced appropriately apart.

But you cannot simply start pounding ground rods into the ground anywhere you want.

Below the surface of a campground you may have electrical conductors, water lines, sewer lines, and all kinds of other infrastructure.

I’m going to continue discussing this with the code experts because I don’t want campground owners being unnecessarily confused or frightened into thinking they need an expensive ground-rod testing program if the code allows a much simpler compliant solution.

To understand why this test is complicated, a fall-of-potential test involves installing temporary test electrodes significant distances from the main ground electrode, connecting a specialized meter, taking multiple measurements at different positions, and plotting the resulting values.

I’ve done this type of work for government facilities and radio stations. When you’re dealing with nuclear missile guidance systems or large radio antennas, grounding measurements can be extremely important.

I’m not convinced we need to impose that same kind of testing burden on campgrounds when there may be a simpler code-compliant alternative.

Grounding vs. Bonding

Now let’s get into an important subject: What is the difference between grounding and bonding?

This can get technically complicated because we’re dealing with both resistance and impedance, but I’ll give you the basics.

A typical ground rod can have an impedance of around 100 ohms.

Contrary to what many people have been told, a ground rod is not what grounds your RV in the sense of clearing an electrical fault.

The primary purpose of an earth-grounding electrode is to help divert events such as lightning into the earth and reduce dangerous surface voltage effects.

It is not a substitute for a properly bonded electrical distribution system.

Inside the main service equipment is a low-resistance neutral-to-ground bond.

That bond belongs at the service equipment. It does not belong at campground pedestals, downstream subpanels, or inside the RV.

The low-impedance bonding path allows a very high fault current to flow when a hot conductor contacts grounded metal. That high fault current causes the circuit breaker to open quickly.

A ground rod by itself has far too much impedance to do that.

I’ve performed demonstrations where a ground rod connected to 120 volts drew only about 1.3 amps.

That is nowhere near enough current to trip a typical circuit breaker.

That can create an extremely dangerous energized area around the ground rod.

By comparison, the neutral-ground bond in the service equipment creates the low-impedance fault path that can produce hundreds of amps for a brief period and cause the breaker to trip almost immediately.

So a ground rod alone does not provide the fault-clearing safety path for your RV.

The bonding connection at the service equipment does that, provided all of the equipment grounding conductors between the RV and that bonding point are correctly connected.

And that is one of the things the GMI is evaluating.

It is effectively looking at the grounding path from the RV all the way back to the service equipment’s neutral-ground bonding point.

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Bonus Round: Things You Thought You Knew About GMIs

Let’s go through some common statements about GMIs and determine whether they’re true or false.

1. A GMI Is the Same as an EMS Surge Protector

False.

An EMS surge protector may shut down power if it detects high voltage, low voltage, reverse polarity, or an open ground.

But it does not perform the same proactive low-impedance test of the equipment grounding conductor back to the service equipment’s neutral-ground bonding point.

A GMI proactively tests that grounding path.

If the measured grounding impedance is too high, it shuts off power to the RV.

That is designed to help protect against a hot-skin voltage shock hazard.

2. GMI Devices Can Be Portable or Built Into an RV

True.

UL 2299 provides listing requirements for both portable and permanently installed devices.

However, the 2026 edition of the National Electrical Code, Article 551.40(D), requires the GMI to be permanently installed in newly manufactured RVs covered by the requirement.

Portable plug-in versions may eventually become available, but manufacturers first have to satisfy the enormous demand for factory-installed units.

Roughly 400,000 RVs are produced annually, and manufacturers will also need additional replacement inventory. I estimate that GMI manufacturers could need on the order of half a million units as the requirement takes effect.

3. GMIs Must Be Installed in All Campground Pedestals by Late 2027

False.

That misconception came from an inaccurate press release issued in 2025, which was later corrected.

There is no requirement to install GMI devices in campground pedestals.

The GMI is installed inside the RV.

Eventually, there may be aftermarket GMIs that can be retrofitted into older RVs, and someone may eventually develop a portable plug-and-play version.

But I don’t currently have direct knowledge of a production portable unit.

4. Older RVs Will Soon Be Required to Have GMIs Retrofitted

False.

At this point, the requirement is expected to apply to new RVs manufactured for the 2028 model year.

There is currently no requirement to retrofit GMI devices into older RVs.

Aftermarket products may become available later, but that is different from a retrofit requirement.

This is still a moving target, so if anything changes, I’ll keep everyone updated.

5. If a GMI Fails, a Technician Can Simply Bypass It

There is no bypass button on the GMI.

An RV owner can’t simply push a button and decide to ignore the GMI because the campground power isn’t passing the test.

While an owner may physically be capable of modifying their own electrical system, I would never advise a technician or dealer to bypass or defeat a safety device.

If you bypass a GMI and somebody is later electrocuted, that could create serious liability.

I’m not going to teach people how to bypass one.

There is a related question about camping in locations such as Mexico where properly grounded electrical hookups may not always be available.

That’s a legitimate technical issue we’re going to have to think through carefully.

At this point, I don’t have a simple answer.

6. GMI-Equipped RVs Won’t Work With Portable Generators

False, with a caveat.

You should be able to use a portable generator with a GMI-equipped RV by using the appropriate neutral-ground bonding configuration.

Years ago, I developed what I call a generator bonding plug. It’s essentially a plug inserted into an unused 15- or 20-amp receptacle on the generator to create the voltage reference needed for systems that are expecting a neutral-ground bond.

A ground rod is not required for a typical portable or onboard generator supplying a single RV.

That’s another misconception I frequently see.

If you were installing a large generator in a campground and using it as a distribution source to power dozens of RVs for a special event, then grounding-electrode requirements can be different and become important.

But for a portable generator dedicated to one RV, a ground rod is generally not required simply to make the GMI work.

You may, however, need the proper neutral-ground bonding plug.

7. You Can Fix an Ungrounded Campground Pedestal by Adding a Ground Rod

False.

A grounding rod is not a substitute for a proper equipment grounding conductor and bonding path.

You cannot correct an improperly grounded pedestal simply by pounding a ground rod into the earth next to it.

The safety system depends on the low-impedance equipment grounding path back to the service equipment’s neutral-ground bonding point.

That is fundamentally different from an earth-grounding electrode.

One attendee suggested that GMIs should have a manual override.

I understand the reasoning.

However, the NEC process has solicited input over multiple code cycles, and at this point the decision has been made not to include a manual override.

The thinking appears similar to a GFCI in a bathroom: you’re not supposed to simply override the safety function when it becomes inconvenient.

At this point, there is no manual override.

Could there eventually be some other approved workaround for unusual situations? I don’t know yet.

This technology is still developing, and I’ll continue testing, working with manufacturers and code organizations, and sharing what we learn as GMI-equipped RVs begin reaching the market.