By Mike Sokol
Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) noshockzone.org with the subject line – JAM.
Dear Mike,
People are always talking about how a bad ground on an RV can cause problems such as a hot-skin condition. So how exactly is an RV grounded? I don’t see a ground rod anywhere. I’m pretty stupid when it comes to electricity, so can you please explain? —Sam (the Sham)
Dear Sammy,
You don’t mind if I call you Sammy, do you???? [From the editor: You can call him Sammy if he can call you Mikey.] This is a great question that confuses a lot of electricians and even electrical engineers at times, so don’t feel stupid. I’ll show you how your RV is supposed to get its ground connection if it’s properly wired. But since this is a J.A.M. session I’ll save the in-depth explanation for another time.
Just the basics
The ground wire of your RV’s shore power cordset is connected (bonded) to your RV’s chassis on the one side, and the power company’s service panel Neutral/Ground bonding point on the other side.
Yup, your RV doesn’t have to have any sort of ground rod to be “grounded” since the green conductor in your power cord (technically called the EGC for Equipment Grounding Conductor) provides that grounding path.
In fact, a ground rod is a pretty poor ground since the dirt beneath our feet isn’t a great conductor of electricity. Certainly it’s conductive enough to get shocked, but it’s not enough of a conductor to trip a circuit breaker.
How do I know this? Well, first of all it’s written right into the electrical code and all my engineering textbooks. But I recently did an experiment where I confirmed just how much fault current an 8-foot ground rod could get rid of, and it’s not much more than a few amperes. So if a ground rod doesn’t actually ground your RV, what does?
Your RV’s electrical ground is dependent on the aforementioned green ground conductor in your shore power cord being properly connected to the service panel’s neutral/ground bonding point either at your house or the main electrical service panel of the campground your RV is plugged into.
Note that the campsite power pedestal doesn’t require a ground rod, nor should it have a ground/neutral bond (that green screw). That neutral bond is only allowed to occur at one place, which is inside of the main service panel. Note in the diagram that this connection is also where the bare copper wire from the power company service panel’s ground rod is connected to. So it’s actually a Ground/Neutral/Earth bonding point where they all come together. And that’s what your RV chassis is eventually connected to.
So this is a great reason to maintain your shore power cords properly, including any dogbone adapters or extension cords. Never use a damaged electrical cord or connector since it can cause all kinds of problems.
OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.
Let’s play safe out there….
Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.
Join Mike’s popular and informative Facebook group.
And you don’t want to miss Mike’s webcasts on his YouTube channel.
For information on how to support RVelectricity and No~Shock~Zone articles, seminars and videos, please click the I Like Mike Campaign
##RVDT1482;RVT977m
Hi Mike, I just started maintenance at an old RV park built 60 years ago. Taking a look at the power pedestals I noticed that only three wires were pulled to each pedestal, Hot 1, Hot 2, and Neutral (I say “pulled,” but the conductors are directly buried). Each pedestal has its own ground rod, and Ground is bonded to Neutral in each pedestal! Is this the way RV parks used to supply power? I’m assuming this wiring scheme is “grandfathered” in, but it just doesn’t seem safe. There is one section of newer sites, where a competent electrician pulled Hot 1, Hot 2, Neutral, and Ground from the campgrounds main panel to each pedestal.
Other than pulling a Ground conductor to all of the old pedestals, the only way I see to make them safe is to disconnect Hot 2 at the main panel, bond it there to neutral, and make this conductor the ground. That would limit all of the older sites to 120V. I would also need to rewire the old 240V Sangamo meters to properly read kWh at 120V.
Jason, we need to talk. Yes, that old 3-wire run isn’t code compliant anymore, so it would need an additional Ground wire (EGC for Equipment Grounding Conductor), to be pulled from each pedestal back to the service panel, which could be a daisy chained connection. Shoot an email to mike@noshockzone.org and let’s discuss.
As I understand it, you can’t have a hot skin condition if you are not plugged in to shore power (or some other grounded system.) If you do have a hot skin condition, you have two things wrong – a live wire with worn insulation or some other problem connected to the vehicle frame/skin allowing the electricity to stray to where it shouldn’t be, and a broken “ground” wire so that the stray electricity can’t get back to its’ source. Then if you touch the frame/skin while standing on the ground, your body becomes the path for the stray electricity to go home. The word “ground” above has two very different meanings, in one case it is the wire which allows stray current to go home which is a very good and safe way for it to go, the other is the earth which is a very poor and dangerous way.
Yes, you are correct as far as dangerous fault currents are involved. However, parking your “ungrounded” RV underneath high-voltage power lines will allow it to become energized up to 10,000 volts or so, but at very low currents (less than 1 mA). This can create a non-dangerous shock that can startle you. I’ve posted about this strange event before, so it’s time to reprint that article once again.
So, when we’re boondocking (which is most of the time), how is our trailer grounded then? I’m pretty sure it is because everything works fine, but . . .
When you’re running from generator or inverter power, your RV wiring creates its own “ground plane”, that is – all of the metal surfaces in your RV are bonded together. So there’s no need to connect your local “ground plane” with the earth ground. Read this: https://www.rvtravel.com/rv-electricity-jam-generator-grounding-rod/
Thanks Mike. I was curious about that.