Issue 5 • March 25, 2017
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Dear Readers …
Lots of things happening this month including my debut on the syndicated radio program The RV USA USA last week. Did you hear me? If not, listen to the rebroadcast on YouTube here. If all goes well I’ll being doing a monthly half-hour radio broadcast discussing all sorts of electrical topics. So, as they used to say … Don’t turn that dial.
Also, our new RV Daily Tips newsletter is getting lots of views and comments, so keep up the good work. As you’ve probably figured out, I’m doing a “Short (Quick) Tip” every Monday through Thursday, plus a “Tall Tip” every Wednesday that’s the lead article for that issue. Last Tuesday’s RVDT issue included my latest “Short Tip” that shows you how to avoid getting shocked by something you can’t let go of – no matter how hard you try. Read it here.
I’m working hard to keep my “Short Tips” short enough since my editors have told me that I can’t even write my own name in less than 250 words, so please bear with me if I get too verbose.
Let’s play safe out there…
P.S. And just a quick note that this newsletter is made possible by the voluntary pledges of the readers of RVtravel.com. We could not bring this to you without their support. If you deem what we provide to you here and at RVtravel.com to be of special value and would like to be a part of our effort, please consider pledging a voluntary subscription. More information is here. We will include you in special emails, articles and videos exclusively for our supporters.
Truma AquaGo®: Instant, Constant and Endless Hot Water
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What is Amperage?
I covered Volts a few issues ago, and now it’s time to cover Amperage. Otherwise known as current or amps, amperage is the actual flow of electrons in a conductor. So put on your learning caps and let’s get studying. The professor is in…. [All images can be enlarged by clicking on them.]
Page Contents
What’s an Ampere?
Besides being the name of the guy (André Ampère) 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. 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 right, 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 right. 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 about $22 since the big box stores probably won’t know what you’re talking about.
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 it a long distance.
NOTE: 50 or 100 feet 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 hook up 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 learning about RV electricity and how to stay safe while using it. See you all next week.
Quick (Amperage) Tips
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Extension cords can heat up and catch on fire if you exceed their amperage rating by drawing too much current.
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The lower the gauge number (AWG) on an extension cord or wire, the more current it can safely carry without overheating.
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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.
Klein Tools Electrical Test Kit — Essential!
Every RVer should have this aboard their RV. The highly-rated, updated electrical test kit contains MM300 (manual-ranging digital multimeter), ncvt-1 (non-contact voltage tester) and the RT105 (receptacle tester). The ncvt-1 automatically detects standard voltage in cables, cords, circuit breakers, lighting fixtures, switches, outlets, and wires. The RT105 detects the most common wiring problems in standard receptacles. Learn more at Amazon.
Industry Updates
Ford Expedition and Navigator get trailer backup assist system that debuted on F-150
I wrote about this trailer backup assist system a couple of issues back, and had lots of inquiries from you about adapting it to bigger tow vehicles. No word on that just yet, but Ford is introducing this same system on their 2018 Expedition and Navigator. So it’s probably just a matter of time before this system is available on other trucks. I did find the company that designed the software and I’ve asked their marketing department for an update on an aftermarket version, but no word back yet. But if you’re towing a small camper or boat trailer occasionally, this could be a useful option. See the full Motor Trend report here.
Let’s tow safe out there… — Mike
Survey Question
Have you found or plugged your 30-amp/120-volt shore power cord into a pedestal that was miswired with 240 volts?
I’ve recently received more comments and emails about 30-amp/120-volt pedestal outlets being miswired by electricians and technicians with 240 volts since it resembles a dryer outlet. Read my full No~Shock~Zone article about it here. Please take the survey below and include any comments about how you found it and if your RV’s electrical system was damaged. Also let us know who paid for the damages.
Please take the 30-second survey:
Tools and Other Devices
Extech CT70 – Ground Loop Impedance Tester
Now, at $170 this isn’t cheap enough for the casual user to purchase, but the Extech CT70 is the least expensive version of the Ground Loop Impedance Testers I use to check the ground/chassis bond of an RV via its shore power ground connection. It works by applying a single-cycle/5-amp fault current between the incoming hot line and the ground pin. Then it calculates the impedance of this connection all the way back to the campground’s incoming service panel. Anything less than 1 ohm is considered code compliant, while anything more than 1 ohm is suspect and needs to be inspected. However, anything less than 0.1 ohm is likely a bootleg ground (neutral to ground jumper), which is definitely a code violation. While I don’t think that many of you will rush out to buy one of these, every RV or campground technician should have one for troubleshooting electrical problems. So instead of wasting hours second-guessing why you’re feeling a hot-skin electrical shock, they can narrow down the cause in minutes. I’ll do a video on using one of these in a future article. Learn more or order at Amazon
Last Month’s RVtravel.com Posts
RV Electricity posts in last month’s RV Travel Newsletters:
• Exercising your generator with a load.
• What’s “the Code”? Find out here.
• Reducing hot-skin shocks – Are we there yet?
• Generator ground rod confusion and clarification.
Last month’s RV Daily Tips Newsletter RV Electricity Tip of the Day:
• Quick Voltage Reference Chart.
• Care and feeding of your shore power connection – Part 3.
• 12-volts DC can be dangerous too!
• Getting all the watts from your generator.
Last month’s survey results:
Don’t come up short!
Sometimes your 50-amp power cord is not quite long enough! That’s when this 15-foot extension cord will come in very handy. Sure, you can use a wimpy orange extension cord with an adapter — and risk burning up the cord, ruining appliances, or maybe even burn up your rig! With this cord along you’ll be all set. Learn more or order.
Q&A’s from Forums
I spend a lot of time on dozens of RV forums answering questions about electricity. Here’s a really good one that will allow me explain the differences between grounding and bonding:
From The No~Shock~Zone:
Mike,
Is it possible to use normal measurement tools such as a multi-meter, surge protector or Klein dual voltage no-contact tester to simply measure the effectiveness of a “ground”? I know that not all soil conditions will ground the same. I try to be very thorough prior to connecting to shore power to prevent damage to my motorhome electronics. Because of the information you have provided in your articles, I have learned how to use my electrical tools with greater confidence. Thank you for sharing the information that you do! Sometimes I get lost in the narrative, and read s-l-o-w-e-r! —RAY
Read Mike’s answer here.
Email me at mike (at) noshockzone.org with your questions.
Camco Store at Amazon.com
There isn’t much you need for your RV that Camco doesn’t have. If you think we’re kidding, then click through to the Camco store on Amazon where you’ll find some of their best-selling products — all for your RV or for you to make your RVing better. Click here and you’ll feel like a kid in a candy store.
Safety Alert
Sadly, Mary Pinney, 40, of Mont Belvieu,Texas, was killed at an east Texas campground on March 10, when a severe storm knocked a tree on top of her family’s tent. Read the full story here. This is a good reminder to look overhead when picking your camping spot and be aware of any tree branches, electrical wires or other objects that could injure or even kill you if they fell. Of course, tents and pop-up campers offer zero protection from falling objects, but don’t think that even a full metal RV can protect you from a big tree branch.
Two years ago my pickup truck was flattened by a large branch that fell maybe 15 feet. Luckily my family was safe inside our house when the branch fell. My son discovered the smashed truck when he was the first one leaving in the morning. Of course the insurance company totaled the truck, but no amount of insurance would cover the loss of a family member being injured in a storm.
So if there’s any question of a falling object possibly hitting your campsite during a windstorm, best to get to the campground main building and hang out until it’s over. Yes, that’s an actual picture of my flattened truck. The cab was smashed down so low that I couldn’t get into it, the frame was bent, and one of the axles was broken. And that was just a big branch, not an entire tree. Ouch!
The best book on RV electricity, hands down!
RV Travel contributor Mike Sokol is America’s leading expert on RV electricity. Mike has taken his 40+ years of experience to write this book about RV electricity that nearly anyone can understand. Covers the basics of Voltage, Amperage, Wattage and Grounding, with additional chapters on RV Hot-Skin testing, GFCI operation, portable generator hookups and troubleshooting RV electrical systems. This should be essential reading for all RVers. Learn more or order.
Videos by Mike about RV Electricity
Chuck Woodbury hosted an RVtravel.com Meetup a few weeks ago and asked how many attendees were familiar with the term “RV hot-skin condition.” To his amazement (and mine) only 2 out of a group of 40+ had ever heard of the term, much less what it meant. So here’s a video I did a few years ago on the condition and how to find it with a basic NCVT (Non Contact Voltage Tester). Watch the video here.
This adapter might save the day
You’ll be glad you have this along if you need to plug your 30-amp cord into an ordinary 110 outlet. Just use this adapter. You’ll need to watch your energy usage carefully, of course, but at least you’ll have enough power for basic needs. Learn more or order.
My Other Life
My interaction(s) with Dave Barry
I don’t just write for the RV world. I sometimes interact with celebrities (well, sort of…). Here’s what I sent to humor columnist Dave Barry in early January, 2000. Yes, that was 18 years ago.
December 31, 1999: Literally hours before Y2K takes out my word processor…
Read the rest of my riveting correspondence with Dave Barry here.
Road Signs 
Get ready …
By Mike Sokol
As many of you already know, I’m an adjunct professor at Shenandoah Conservatory, where I teach live and recorded sound production. Classes begin again next week after spring break and an interlude from the blizzard, and I’m busy working on syllabi and schedules, as well as doing sound system installations for my own business. While I’ll mostly have seniors this semester, I’ll have at least a few sophomores for the first time, and they’ll need an attitude adjustment when it comes to how early they need to show up for a gig. Read more.
STAFF
Editor: Mike Sokol. RVtravel.com publisher: Chuck Woodbury. Managing editor: Diane McGovern. Staff writer: Emily Woodbury.
Everything in this newsletter is true to the best of our knowledge. But we may occasionally get something wrong. So always double check with your own technician, electrician or other professional first before undertaking projects that could involve danger if not done properly. Tips and/or comments in this newsletter are those of the authors and may not reflect the views of RVtravel.com..
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How do I get and read back issue 1, 2, 3, 4
Hi, Henry. Here’s the link to go to the RV Electricity Newsletter “category” — which lists all of the issues: https://www.rvtravel.com/category/rv-news/rv-electricity/ Have a great day! 😀 —Diane at RVtravel.com
Henry — you can read all the issues at https://www.rvtravel.com/category/rv-electricity
mike ,just in case the electricity goes off at our house ,how can my mtr. home generator be hooked up to the house elec. to maybe suppy power for our furnace , which is powered by propane , tv ,lights, and especially our water well, which is 240. our electric company does electric work for its customers ,but not sure if theyve ever done this. i have a 2009 winebago adventurer with a 50 amp generator.
Mike what is the purpose of the battery disconnect on my TT.
They’re generally used to disconnect your RV’s house batteries when it won’t be used for an extended period of time, say a week or more. Its job is to limit the parasitic power draw from all your gadgets and appliances. For instance even if you shut off your inverter it’s probably still drawing a few watts to keep the CPU up and running. Same goes for your 12-volt DC TV on the wall. Even when you shut it off with the remote, its internal computer is still running, waiting for your command to turn fully ON. These sleeping gadgets and appliances can drain an otherwise healthy battery in a month or so, and few things are harder on a battery than leaving it flat for months (except for letting the water get low). So if you won’t be using your RV this month, then disconnect the battery and it will hold its charge much longer. A secondary function of these switches on race cars is that if you crash and sitting in a puddle of high octane fuel, you don’t want any sparks setting the whole works on fire. So the first thing the emergency crew does when they get to a race car wreck is disconnect the battery. Oh yes, you should probably hook up a battery tender directly to your house batteries if you’re going into storage, but that’s another story…
Mike, Is it possible to add several 12 volt LI batteries to a bank of 6 volt AGP batteries inline. I want to expand my capacity as I’m adding Solar Panels to my system. I’m rather limited on space but can fit 2 12 volt batteries and not have to move the entire bank to a different and larger bay.
No, that won’t work. Lithium batteries have a completely different voltage, discharge rate, and internal impedance compared to lead-acid/AGP batteries. There’s just no good way to mix battery chemistries that will work.
Thank you for giving us a lot of information that some of us don’t think about
You’re welcome. Electricity is one of those things we usually don’t think about until something goes wrong. But since electrical design and troubleshooting is my primary business, I think about it a lot. Glad you’re getting something out of my articles.
Hi Mike, I have a 2007 motorhome on a Ford E-350. When replacing the front running/blinker bulbs with LED bulb I needed a load resistor. The load resistor (6 ohm, 50 watt) gets quite warm when bulb is turned on. Am I wasting more power with this set up versus standard factory element bulb?
Thanks Pete
Keep reading Dummy….You are an associate Professor!
What does that mean, Teresa? I don’t understand your comment — maybe because I’m not a professor 😕 –Diane at RVtravel.com
I was calling myself a dummy as I had only partially read the article before adding a comment that Mike should be a professor because for the first time in my life I finally “get it”! Had I read on…I would have learned he is an associate professor.
Oh, good! Thanks for the explanation, Teresa. Mike phoned me yesterday concerned that he had said something to offend you, and I told him I didn’t understand your second comment either. I feel better now, and I’m very sure he will, as well. (BTW — Mike’s not only super smart, he’s also super nice.) Have a great day! 😀 —Diane at RVtravel.com
Hi Mike
I’ve noticed that there seems to be different size switches used for 120VAC & 12VDC, meaning that the contacts in the 12VDC are of heavier thickness, also the wire used for DC verses AC seems like its a heavier gage! I have some old (NEW) toggle switches that I got when I worked for NCR in the early 70’s & their rating in amps is higher for AC than DC. Is their a difference & if so would you be kind enough to explain it. As I’m writing this I kinda remember that the way older cars used 6VDC & the battery cables seemed like twice the size as our current 12VDC systems.
Thanks
Dave
Any switch has to be derated for DC current compared to AC current because of the arc that occurs when you open the switch. In 60 Hz AC the current goes to zero 120 times a second, so any arc is quickly extinguished. But in DC power the same arc will go on and on, quickly melting and destroying the contacts. So the same switch will have different voltage and current ratings for DC vs. AC usage. And yes, 6-volt electrical systems in old cars had very thick wiring compared to 12-volt systems because half the voltage needs twice the current for the same amount of wattage. That means the cross-sectional area of a wire would have to be doubled if it had half the voltage potential. That’s an entirely different situation of AC vs DC though, since wires really don’t care if they’re carrying Direct Current or Alternating Current until you get into really high frequencies and voltages.
Mike, its interesting that you mention derated for DC current & switches! Is their a calculation or a chart for them?
Dave
I think that every switch manufacturer has both AC and DC ratings for their products. I don’t know that there’s a standard calculation that works for everything.
Many years ago, my husband was moving to a new job and stayed in the RV while I stayed back and sold the house. He’d rented a spot in a mobile home/RV park. The prior resident of that spot had modified the power on the post to supply more than the specified 30 amps.He didn’t bother to mention it to the management. Fortunately, it didn’t fry everything in the coach. Had it worked on a few times to fix it, but since the manufacturer had no wiring specs, it never was completely right after that.
The problem with over-voltage on an RV is that so many of its electrical systems can be stressed just enough that they don’t die immediately, but can bite the bullet months later. And most of the time it’s the big ticket items like the fridge, converter and air conditioner that take the hit.
One more warning re: extension cords. Don’t use them if they are partly wound up on a reel. Even if the cord doesn’t feel warm, it may be putting off enough heat to melt the insulation if several layers of cord are wrapped around a reel. (I know this from experience.)
True that. I covered that problem a while ago at: https://www.rvtravel.com/does-coiled-extension-cord-heat-up-in-storage-bucket/
Yes and no on the reel: I wouldn’t be paranoid but you need to understand the issue. The problem is not the coiling, air-core induction or even eddy currents If the reel happens to be metal, but simply air flow. Any wire carrying current will heat just a bit and the more current and smaller wire, the more heating there is. Spread out the heat dissipates, but wound up with almost no air flow to the inner strands, the middle of the bundle has trouble dissipating heat. Remember you could heat your house with a candle if it were perfectly insulated?
The takeaway here is don’t put a lot of wire carrying significant current into a closed bucket, cardboard box, or the cabinet of your RV where the shore power cord retracts into IF there isn’t enough airflow to remove the heat. Mesh basket, big wires, loosely jumbled, low current… don’t worry so much!
As I said inductance is not really the problem anyway, but one funny solution I’ve seen thinking it was is wrapping the extension cord double on the reel to cancel out the field. Since an extension cord is not a single wire coil, thiis would have absolutely no effect since there are already two opposed conductors in the extension cord – the supply and return wires are already spooling together opposed.
I DO spool my standard cords from the middle on simple reels, just to make them conveniently adjustable in length, not for heating issues.
Only if you are drawing near or at the max capacity of the cord. Drawing 5 amps through a coiled or roll wound 15 amp max extension cord will not cause any problems.
Mike, I am not a genius. However, I do consider myself somewhat intelligent. I have never had anyone explain this stuff so that I could grasp it. It was all just new jargon being thrown at me. (Math is not my strong suit…) Are you a professor? If not, you should be! At 57 years of age, I finally get it! Thank you for explaining it in such a way that it can be easily understood.
You’re very welcome. And yes, I am indeed an adjunct professor at a big university teaching advanced live sound mixing. I really enjoy teaching technology to anyone who wants to learn. Thanks for reading my articles.