If you touch a metal part on the outside of your RV and get shocked, is that a problem? What if it’s only a tingle?
Yes, any stray voltage condition is potentially dangerous – even life-threatening! This is commonly known in the RV industry as a “hot skin” condition. It occurs when the RV is improperly grounded and stray currents have energized the chassis.
Understanding a hot skin condition takes a little mental effort. But it’s worth your while. Teeny amounts of current at very low voltages are sufficient to kill a human. Hot skins can be fixed, and often fixed quickly. Keep you, your family, your pets, and your neighbors safe!
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What Is an RV Hot Skin?
Ever stepped on the metal threshold or step into your RV and felt a shock? Ever grabbed an RV door handle (especially during a rainstorm) and felt a tingle? Then you’ve experienced a hot skin condition!
The term “RV hot skin” can be misleading. It’s more accurately called a stray voltage condition or a “hot chassis” condition.
A hot skin happens because:
- The RV has a disconnected ground connection …
- …AND the RV has a fault current source.
A hot skin occurs because the chassis and exterior of your RV is at a different voltage than the earth. When this happens, all the conductive components of your RV – the metal frame, aluminum skin, axles, rims, metal fasteners, etc. can be energized.
Whenever two points have a difference in voltage, electricity can flow. When you touch the RV and feel a shock, that’s because electricity is passing through you. You become the conductor between the RV and the earth.
A few volts difference between the earth and the RV is normal. But if you see more than 5 volts AC, take heed!
- 0-5 volts: Normal fluctuations. Anything above 5-10 volts indicates a hot skin condition!
- 10-30 volts: Usually caused by small leakage currents from plugged-in appliances.
- 30-60 volts: Usually caused by many small leakage currents or a burned-out water heater element.
- 60-120 volts: Usually caused by a short circuit, such as a pinched cable, stray wire, a screw through a wire, or a loose wire connection. Should trip a circuit breaker or blow a fuse!
30 volts is usually taken as a conservative minimum for potentially hazardous electrical currents. But people have been electrocuted at levels as low as 42 volts! And anything over 50-60 volts is considered universally dangerous.
The problem usually lies outside the RV: Either in the power pedestal or the power cord. We’ll talk about how to fix that in a minute.
What Causes an RV Hot Skin?
Unlike a house, an RV doesn’t have a grounding rod. There’s no direct low-impedance connection to the earth. Plus, an RV essentially sits on a bunch of insulators (rubber tires), plus further insulation thanks to wooden or plastic leveling blocks, plastic jack spacers, painted metal components, etc.
Instead, an RV is primarily grounded through the power cord. That’s why your RV extension cord has three or four contacts – one of them is a ground! The RV’s electrical system is bonded only when it’s plugged into the power pedestal; there’s an earth ground somewhere upstream in the power distribution system.
In fact, every appliance and outlet in your RV has a ground wire (usually green) that runs from the appliance back to the converter/breaker box. Inside the breaker box compartment, all the circuit neutral wires are landed on a buss bar, and all the ground wires are landed on a separate buss bar. There is no bond between the two. In fact, there’s no bond between the ground and the neutral lines until the G-N-E bonding point at main service panel.
But electricity is like water: It always takes the path of least resistance. In a properly wired RV, any stray fault currents should be harmlessly conducted through the ground wire in the power cord. But in a hot skin situation, stray voltage can build up on any connected conductive parts – there’s nowhere for the current to go!
Is an RV Hot Skin Dangerous?
Yes, it certainly is. In fact, it can be fatal!
Never allow a hot skin condition to exist. You don’t know what’s causing the problem. Even if you measure the potential difference at “only” 20 volts, there’s no guarantee it won’t jump up to 50, 60, or even the full 120! And an electrical current you can’t even feel on a dry, sunny day standing in construction boots could easily kill your dog tomorrow, a drenched Labrador standing in a puddle who touches his curious nose to the frame.
There’s no such thing as a “safe” hot skin. And if you’re still wondering, “Just how many volts can kill a human?”, then here’s the answer: There isn’t an answer. There’s not a single number for voltage or current above which you’re in danger, and below which you’re safe. That’s because electrocution … is actually really complicated.
- For one, the electrical resistance of human skin varies by person, hydration, time of day, moisture, etc. It can be as high as 100,000 Ohms or as low as 500 Ohms! And if you touch a conductor with jewelry rather than dry, bare skin, a hundred times more current could pass through you! The condition of your skin has a huge impact on your risk of electrocution. About 70 percent of your body is water – once electricity can pass through your skin, the hard work is over!
- Secondly, electricity passes differently through the body depending on where the ground and hot connections are. If electricity passes from arm to leg, for instance, it will pass through the heart (in the center of the body), increasing the risk of fibrillation and cardiac arrest. If electricity passes from, say, head to hand, it will pass through the brain, which can immediately knock someone unconscious.
- Thirdly, there’s an old saying that “it’s not the volts that kill you, it’s the amps.” That’s not strictly true, however. Electrocution is a function of both volts and amps, alternatively measured as watts and seconds. A shock lasting 0.08 seconds might not kill you; that same shock for 2.4 seconds might just do you in!
- And if you’re thinking, “There’s no way anyone would be foolish enough to touch a hot conductor for 2.4 seconds” – well, you might not have a choice! Currents as low as 10 milliamps can cause your muscles to contract and freeze; you can’t let go!
Why Do I Only Feel a Shock When Wet?
If you have a hot skin condition, you might not notice it all the time.
Electricity is always looking for the easiest path to ground. That may or may not be you. That depends on what you’re wearing, what you’re touching, the atmospheric humidity, etc.
So you might only notice a shock when it’s damp or raining outside. You might not notice even a tingle if you’re wearing rubber-soled shoes. But if you’re standing in a wet puddle with your bare feet – watch out!
So don’t assume “it’s just a tingle.” It’s not harmless. In a different situation, that tingle could become a powerful jolt that shuts down your heart!
Can I Just Make My Own Ground Connection?
There’s a popular misconception that lowering your stabilizer jacks until they touch the ground will ground your RV. Unfortunately, that is usually not true. There’s a reason a residential grounding rod must be ⅝” diameter in buried 8 feet deep! Just touching a bit of metal to the top of the soil (especially dry, sandy dirt) doesn’t establish a true grounding connection.
How Do I Fix or Prevent an RV Hot Skin?
Fixing a hot skin condition requires knowing what’s wrong. You might need to do some sleuthing.
- The solution might be as simple as a new power cord or dogbone adapter. If you have a blown ground contact or a broken wire inside the cable, a new power cord should fix the problem.
- The solution also might be as simple as contacting the campground. If the power pedestal is improperly wired, then it’s not your fault! Alert the campground and request a new site. Don’t use the bad pedestal until a qualified electrician has rewired and tested the pedestal.
- But if there’s no problem with the power source or power cord … then your RV likely has a loose ground connection. This can be difficult to find. If you’re lucky, the loose connection will be between the converter and the chassis: usually an #8 or #4 bare copper wire into a tinned copper or aluminum lug.
If you’re measuring low voltage levels, say, under 20, then the potential difference could be caused by the normal operation of your appliances. But if you’re measuring 60, 80, or even the full-circuit 120 volts, then that indicates a burned-out water heater element or short circuit. You will need to trace the source of the fault current. Start by looking at the breaker box and fuse panel for any blown fuses or tripped breakers.
Follow these rules when investigating for your loose ground connection:
- Use only one hand to plug or unplug cords and cables.
- Turn off the breaker in the power pedestal before plugging or unplugging.
- Do not wear metal jewelry. Put up long hair.
- Keep everything dry!
- Use a multimer or non-contact voltage tester (NCVT) to test for a hot skin on your RV.
- Protect your RV (and yourself!) with an EMS surge protector.
I’ve written about advanced EMS surge protectors before. I can’t recommend one enough. They’re cheap insurance against all sorts of problems.
- Psst . . . if you’re reading this content anywhere besides Ask The RV Engineer, it’s been illegally “scraped,” and you’re probably on a spam website. So please be careful! Don’t share any private information, and come back to us at www.askthervengineer.com!
A Non-Contact Voltage Tester: Your Secret Weapon
Full disclosure: I am a mechanical engineer, not an electrician or electrical engineer. While I bring some technical knowledge to the table, much of what I’ve learned is thanks to the free education from Mike Sokol, master electrician and electrical engineer, author of the book RV Electrical Safety, and guest tech writer for RV Travel, No Shock Zone, and other publications. The RV industry owes this man a debt of gratitude for teaching us how to keep ourselves safe!
Mike is a big proponent of using a Non-Contact Voltage Tester to safely, quickly check for a hot skin/stray voltage condition. Mike wrote a whole article about how to use a NCVT here, or you can watch the video below.
To learn more about RV hot skin conditions, I invite you to visit Mike’s website here. He also recommends an affordable NCVT like this Southwire 40136N tester, which costs less a dinner out. I highly recommend you pick one up as part of your RV tool kit!
- You can purchase that Southwire NCVT here. Most RV dealerships don’t carry them.
Camp safely out there!
