RV Electrical Safety: Part V – Amperage

Sep 2nd, 2010 | By | Category: RV Safety

The No~Shock~Zone: Part V -Amperage

Understanding and Preventing RV Electrical Damage

Copyright Mike Sokol 2010 – All Rights Reserved

If you’ve read the survey we did July 2010 in www.RVtravel.com, you know that 21% of RV owners who responded have been shocked by their vehicle. Review the 21% report at http://new.noshockzone.org/15/.  What follows is #5 in a 12-part series about basic electricity for RV users and how to protect yourself and your family from shocks and possible electrocution.

This series of articles is provided as a helpful educational assist in your RV travels, and is not intended to have you circumvent an electrician. The author and the HOW-TO Sound Workshops will not be held liable or responsible for any injury resulting from reader error or misuse of the information contained in these articles. If you feel you have a dangerous electrical condition in your RV or at a campground, make sure to contact a qualified, licensed electrician.

What’s an Ampere?

Besides being the name of the guy  (Andre Ampere) who discovered that current flow caused electromagnetism,  it’s the measure of how many electrons are flowing through a wire or conductor per second. For those who are counting that would be exactly  6.24151 × 1,000,000,000,000,000,000 (10 to the 18th power) electrons per second per ampere of current.  However, the actual electron count isn’t important, so you can just think of it as gallons of electrons per minute, using our water tank model [illustrated in earlier articles in this series].  And, yes, we call this effect “current” both when talking about the flow of water in a river as well as the flow of electrons in a wire. Pretty cool, eh?  It’s often abbreviated as “amps” and you’ll sometimes see it listed in milliamps (1/1,000 of an amp) on voltmeters. It takes 1,000 milliamps to equal 1 amp of current.

Pumps and Hoses

If you look at the illustration to the left, you’ll see a turbine pump pushing water counterclockwise around in a circle.

And depending on the pressure produced by the pump and the size of the water pipes connecting around in the circle, you’ll either pump a lot of Gallons Per Minute (GPM) or a few Gallons per minute.

In this case we’re using a pump that can produce 120 PSI (Pounds per Square Inch) of pressure to move water around a pathway or circuit. And because we have a large diameter pipe all around, this circuit can support a lot of current flow without losing much energy or pressure in the process.

Small Hoses

As you can see from the next illustration, if you use a very narrow pipe for part of this circuit, your gallons per minute (GPM) flow will be very low.

So if you have a pump that might be able to push 10 Gallons Per Minute through a big pipe, it could be restricted to perhaps 1 GPM flow if you use too narrow of a pipe for any part of the circuit.

And just like the garden hose you use to water the plants in the back yard, it won’t be able to deliver enough water flow if it’s too small in diameter or too long in length.

The exact same thing happens to electricity as it flows through a wire like an extension cord.  Just like pipes, thick extension cords can support lots of current flow, while skinny extension cords can only support a small current flow.

Big Wires

Take a look at the illustration of the electrical circuit on the left. Instead of a pump let’s substitute a battery or AC generator, and instead of a pipe let’s use a wire going around in a circle, which we’ll call a circuit (just like a horse racing circuit).

If the wire being used is large enough in diameter, then the generator or battery can push the full 10 amperes around through the circuit without any loss, which is the typical amount of current your coffee pot might require to heat up water.

And as long as you don’t try to push more amperes of current through a wire than its rated for, then all should be fine.

Little Wires

However, the exact same generator or battery could be in trouble when attempting to push those 10 amperes of current through a skinny wire or extension cord.  Now your generator might only be able to push 2 amps of current through the circuit since there’s so much resistance to flow built into the smaller wires (think pipes).

And while you will certainly notice a significant drop in water flow from your garden hose if it’s a bit too skinny for the job, you may not notice the problem you’ll have from a small extension cord when it’s supporting a lot of current flow.  And that can cause all sorts of problems with your RV.

That’s because, instead of just restricting the water flow in a hose, electrical wires can heat up to the point of catching on fire if you try to push more current through them than they’re rated for. Ever lay your hand on an extension cord and felt it was hot? That’s the problem with too much current, it causes heat. How much current is OK to run through an extension cord? Well, glad you asked.

Size Me Up

For those of you unfamiliar with extension cord and wire specifications, the lower the number of the gauge, the thicker the wire and the more current (amperage) that can flow through it without overheating. Sort of like shotgun gauges.

For example, a 14-gauge extension cord might be rated for only 15 amperes of current flow, while a 10-gauge extension cord could be rated for 30 amperes of current, depending on total length of the cable and type of insulation. And if you exceed the rated amperage capacity of an extension cord, then you’re asking for trouble.

(FYI: If you want a gauge tester for yourself, you’ll need to order one from Amazon for $19 since the big box stores won’t know what you’re talking about. Here’s what I use:  Just search on Amazon for – General Tools 20 American Standard Wire Round Gauge )

Flow Capacity

More on this in a future article, but here’s the basic AC amperage capacities of AWG [American Wire Gauge; standardized U.S. wire gauge system] standard wire sizes. As you can see from the chart, the lower the gauge, the larger the diameter of the wire and the more current it can carry without overheating. Also, it’s often noted that you should make the wire one size larger than called for in the chart if you’ll be running a long distance. NOTE: 50 or 100 ft of extension cord from the campsite pedestal to your RV is a very long distance. Do not expect a 12-gauge extension cord to carry a full 20 amps of current over 50 feet or more. In that case, go to a 10-gauge cable to handle the current over that distance. And you can see that if you want to hookup to  a 240-volt receptacle with a 50 amp circuit breaker, you’ll need a 6-gauge extension cord if you’ll be drawing current from the outlet at maximum capacity. And you know you will because RVs are power hungry with microwaves, air conditioners, flat screen televisions, coffee makers, and all sorts of other electrical appliances. Using a cable with sufficient amperage capacity will also minimize your voltage drop which can cause some electronic devices to misbehave.

Did I say “voltage drop”? I’m sure you’ve heard of it, but how many of you know what it really means? Well, that sounds like a good subject for the next article. So stick around while we continue learing about RV electricity and how to stay safe while using it. See you all next week.

Quick Tips

  • Extension cords can heat up and catch on fire if you exceed their amperage rating by drawing too much current.
  • The lower the gauge number (AWG) on an extension cord or wire, the more current it can safely carry without overheating.
  • Electricity needs a complete circuit for current to flow from the high voltage side to the low voltage side of the generator or battery. That current is measured in amperes.

Future Shock

Part VI of this series will cover how amperage draw causes voltage drop, which is why your coffee pot can cause your lights to dim in your RV. Stay tuned.


After you’ve read this article, please leave us any comments or suggestions for future topics. We’d love to know how we’re doing with this important project. And while you’re at it visit www.RVtravel.com for all things related to RV travel and lifestyle.

Mike Sokol is the chief instructor for the HOW-TO Sound Workshops (www.howtosound.com) and the HOW-TO Church Sound Workshops.  He is also an electrical and professional sound expert with 40 years in the industry. Visit www.NoShockZone.org for more electrical safety tips for both RVers and musicians. Contact him at mike@noshockzone.org.


12 Comments to “RV Electrical Safety: Part V – Amperage”

  1. Larry says:

    Question–You state that for a 50 amp 240v that you need a #6wire but aren’t you really just pulling either 20 or 30amps off of two different 120v circuits for most applications? Thanks for the good articles.

    • Mike Sokol says:

      Well, first here’s the legal answer. If your RV has a 50 amp master circuit breaker, then legally you need to run a extension cord rated to carry that much amperage, assuming that the pedestal’s breaker is also 50 amps. However, if you’re running a 120 volt / 30 amp service into your RV that has a 30 amp master disconnect, and tapping into a 120/240V 50 Amp CB on the pedestal with a dogbone that pulls only one 120-volt hot leg from the 120/240 volt outlet, then an extension cord rated for the 30 Amp max that your RV could pull would be sufficient. That’s how the NEC defines wire size selection, and that mindset is designed to keep you safe no matter how you attempt to load the electrical system. If you overload anything the circuit breaker is supposed to trip before a fire can start.

      Of course, some RV owners will justify using a lighter-weight extension cord than called for saying they don’t turn on all their appliances at once. But I would guess that very few (if any) of them have any sort of ammeter on the incoming line(s) or any idea how much current a coffee maker or microwave really uses. In those cases, they’re risking their expensive RVs and the lives of their family members to a potential fire because they’ve cheaped out on the extension cord. To me, that’s unconscionable since an RV fire is about as scary as it gets. I do electrical tech for a lot of big rock concerts, and the safety of the performers and audience is my primary duty. I would hope that RV owners would have the very same attitude about their own family and friends.

      So the legal definition is this: You need to use an extension cord capable of carrying the maximum amperage of your RV’s incoming Circuit Breaker disconnect. If it’s a 20 disconnect, you need a 20 amp extension cord. If it’s a 30 amp disconnect, you need a 30 amp extension cord. If it’s a 50 amp disconnect, you need a 50 amp extension cord, no matter how few appliance you plan to turn on. And that’s because you never know when your daughter will be running a 1200 watt hair dryer (10 amps) while you’re heating up your coffee in a microwave (11 amps) and maybe your wife is making pancakes on a 1500 watt griddle (12.5 amps), plus you’ve got a bunch of lights and a battery charger all running on the same leg. Sizing your extension cord to anything less than the maximum amperage of your RV’s Circuit Breaker disconnect is illegal and what I consider immoral. Spending $100 or so on a heavy enough extension cord to do the job under all situations is cheap insurance.


  2. Thomas Wilds says:


    One question and possible idea for another section: How do it know? I understand basic electrical connections, amps, etc (and these articles have help a lot) but what I have never really known is how does your coffee pot “know” to draw 1500 watts but no more? How does a 50 watt light bulb only draw 50 watts or better yet what causes it to use 50 vs. 25? Using your metaphore I can understand a valve being used to control the flow of water. But what prevents all available amps from flowing into my TV when I plug it in? Thanks for any reply.


    • Mike Sokol says:


      Glad you’re getting something out of the NSZ series. And the full answers to your question will come in the next installment when we discuss appliance wattage. But the short answer is that every electrical appliance has a built-in resistance, sort of like a little restricter plate inside of the “pipe”. So a coffee pot that needs to draw 1,500 watts to heat up your water has a large orifice in its restricter plate with a low resistance that lets a lot of water flow (amperage), while a 50 watt bulb is designed with a much smaller orifice in its restricter plate with a lot more resistance which limits the flow to much less. Now when you multiply the flow (amperage) of a circuit by the voltage (pressure), you get work . And that work is measured in something we call “watts”. That’s how each appliance “knows” how much to draw. It has its own “restricter plate” that’s been designed up let just the right amount of current flow though itself. Don’t worry if your head hurts right now, all will be revealed soon.


  3. robert uhlich says:

    What do you do when an RV Park advertises 50 amps and upon arrival they don’t even have 30. Big weekend no other place to go. The park laughed when we questioned them. Are they liable for any damage to my coach? Also is there a means via the internet to expose these charlatans?

    • Mike Sokol says:

      I’m working with a few RV owners who have indeed had their vehicle electrical systems damaged by improper wiring at campgrounds. The campgrounds insists it’s the RV owners’ fault and expects their insurance companies to pay (with a $500 deductible), but we’re asking the RV owner’s insurance companies to go after the campground’s insurance companies. Yes, it’s a battle of the lawyers, but this is where the battle lines will be drawn, I believe.

      I do wish there was some rating service for RV campgrounds that included power hookups and such. I’m more on the technical side of things, but if anybody knows and uses such a service, please let me know about it.

  4. Lou Sills says:

    I, too, wish there were a way to expose the shoddy campground wiring. I am at one now that the Progessive Wiring Monitor said “P01” Reverse Polarity. The campground manager says someone was just there a month and it was okay. After a 2nd complaint, she said her ‘electrician’ checked it out and there wasn’t a problem. Then the next day a woman came in, did the wiring check, went up to the office and told her she had the reverse polarity problem and she again denied there was a problem. Of course, the Progressive will not allow power thru. Her comment, pull the dang thing out it isn’t working and my plug is okay. Certainly will show this as a don’t plug in here unless you check the wiring in my campground review. Gives it a low rating.

    • Mike Sokol says:

      I also wish there was a way to address this problem. I’ve spent the last two years looking for any kind of support from the RV industry, but nobody wants to talk about or address the issue of unsafe power in campgrounds. All the RV building industry wants to do is sell RV’s, and all the campground providers want to do is rent spaces, not repair anything that costs money.
      And sadly, when it comes to polarity, grounding and hot-skin issues, even a lot of electricians and inspectors don’t seem to understand the problems associated with campground power. If there are any grants available to support this RV electrical safety training, please let us know.

      Mike Sokol

  5. Bubba says:

    So a 10A 12v fuse gets hot. should any fuse get hot? Is it ok to clean the fuse tabs and/or bend then so they make better contact?

    • Mike Sokol says:

      A fuse will only get hot when one of two conditions exist. Either it’s passing close to its rated capacity for an extended period of time. Or there’s a poor connection in the fuse holder. The poor connection can be the result of low-tension of the spring tabs, or perhaps simply corrosion (rust) on these same connections. So cleaning the connections with fine sandpaper and bending them a bit for better contact is a good idea.

  6. Jerry g says:

    Plugged into a 50 amp Progressive monitor. Have a quality MH with proper size cord. 8 years across the country, no problems with 50 amp service. Currently volunteering for US Army COE. Plug in and get a PE 6( low voltage line 2). COE electrician trying to blame our equipment. Since we’ve not had this problem anywhere else, what could be causing their pedestal to supply insufficient power.

    • Mike Sokol says:

      You need to meter the outlet with a digital multimeter to see just how much voltage it’s supplying. The PI monitor is pretty smart, so it’s telling you that’s something is wrong. Unless you have a damaged extension or shore power cord, the problem is likely in the pedestal. So measure the pedestal and I can help you figure out what’s causing the problem

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