Fight The Power!

By , December 14, 2009 6:21 pm


Photo from Kuzeytac on flickr, under Creative Commons license

A soon-to-be RV’er posted on her blog about a couple of RVs she is considering and an issue came up about the power.  One RV is 30 amp, the other is 50 amp.  There’s some confusion about which is better and why.  I don’t have an answer for that particular question, but I can shed some light on the differences between the two and how RV electrical systems work in general.

Warning: This is going to be long and somewhat technical… proceed at your own risk! 😛

RV electrical systems

Let’s start with how RVs are wired.  As far as I know, almost all RVs have two distinct electrical systems:  AC and DC.  This pretty much applies to just about any RV, whether it’s a tow-behind, fifth-wheel, or motorhome.  Some of the real small ones may only use one type, but that’s the exception, not the rule. 

AC (alternating current) is what your house has.  If you plug a toaster into a three prong socket, it’s using AC.  Normally the AC sockets in your house put out somewhere between 110 and 120 volts.  We’ll just say 110 to keep it simple. 

DC (direct current) is what your car has.  If you plug a cell phone charger into your cigarette lighter socket in your car, it’s expecting to get around 12 volts (although it can actually be anywhere from 11 to 15 volts).

An RV is a house and a car, so it has both.  All the engine stuff is 12 volts DC.  If it comes in a car, it’s probably 12 volt DC.  This includes a majority of the overhead lights (just like a car dome light), the headlights, turn signals, radio, cigarette lighter socket, power seats, etc.  All the house stuff is AC… microwave, washer/dryer, air conditioner (the one with the thermostat… the one on the dashboard isn’t really electric and only works when the engine is running, so it doesn’t count in this discussion). 

When you’re actually staying in an RV at a campground, you’re probably using some odd mix of both AC and DC stuff.  We use our air conditioners (AC), our microwave (AC), our coffee maker (AC), our radio (DC), and our overhead lights (DC) a lot.  So, we really need both AC and DC power to be comfortable.

I’ll address DC stuff in a separate post some day, for now, we’re dealing with AC.  I just needed to make sure everyone understood what I was talking about first.

Amps and plugs

So, what’s the deal with AC and what types are there?

That’s where the “amps” come in.  IMG_0177Saying an RV is 30 amp or 50 amp isn’t technically accurate (so don’t flame me about it). It doesn’t mean that an RV needs 30 or 50 amp, that’s just what it’s set up to use.  It’s also generally used to describe the type of socket that it uses when plugged into “shore power”.    Shore power is simply what you plug it in to when your parked at a campground and need power for your appliances.  It’s normally a collection of sockets and breakers on a post right next to your parking pad (picture to the right).  We’re going to call that a pedestal.

Here’s a short table with the different plugs and sockets that are generally used:

Amperage (Amps)

Plug (male)

Socket (female)











You should notice right off the bat that the 10/15 amp looks like your normal house appliance plug.  10 and 15 amp plugs are pretty much the same, although there are some subtle differences we aren’t going to worry about right now.  I’ll also mention the odd-ball, a 20 amp plug.  I don’t have a picture of one because they’re not normally used around a house or RV and you should have to worry about them unless you’re trying to run a drill press or something.

The 30 amp plug looks kinda like your normal house plug, but has bigger prongs and they’re “tilted”.  This is to make sure you don’t accidentally put it in a 10 amp socket. 😉

The 50 amp has even bigger prongs… and there are more of them. :S

Your RV is going to come with one of those plugs, probably the 30 or 50.  So what’s the difference?  Power!  …How much you get and how much you can use.

Feel Da Powah!

Almost everything that uses electricity can be measured in amps.  Amps is simply a rating that describes how much power something can or does use.  Different appliances use different amps.  A regular 40 watt light bulb in your house draws less than half an amp.  A 1000W microwave oven can draw almost 9 amps.  A car headlight is generally between 4 – 5 amps.

So, if you’re plugged into a 50 amp outlet and you’ve got a 50 amp RV, you can use a great big air conditioner (cools quickly even when it’s real hot out), your big microwave (cooks evenly and fast), a great big TV and a sweet treadmill for working off the microwave burritos. 🙂

But, if you’re on a 30 amp circuit, you can run a smaller air conditioner (takes longer, doesn’t work as well when it’s really hot outside), use a smaller microwave (takes longer, may not cook evenly), get a smaller LCD TV (LCDs use a lot less power than tube types)… and, uh, go jogging. 😉

I mention the treadmill because I remember some RVer somewhere wanting one or having one…  Normal treadmills can draw about 15 amps… 20 if you’re “husky” and run fast (I know, but it’s the best I could come up with).  Oh, ladies… your amazing 1800 watt hairdryer can draw about 16 amps on a bad day!

So, your 30 amp RV is parked and plugged in.  You’re running on your treadmill, while drying your hair and the air conditioner comes on…  For a split second, then everything stops!  Why?  Well, you exceeded your amperage.  Treadmill, 15 amps…  hair dryer, 15ish… You’re already at 30 amps.  The air conditioner is just the straw that broke the camel’s back. 

Actually, it should have only broken a breaker.  What’s a breaker?  One of these switchy things:


Those are meant to stop you from using more electricity than the circuit can handle.  Generally they’ll save you from bad things happening.  What happens when you bypass them or when they don’t work right?  Something starts melting or burning.  Different wires can handle different amounts of electricity.  If you try to get too much electricity on one wire, it gets hot and will start burning stuff.  Fire is generally not a good thing to introduce to your RV.

“So, Jonathan… if I want to use lots of electricity, I just need more amps for my RV, right?”

I’m glad you asked!  The short version is “yes”.  The long version is not so easy.  Since we’re already way into the long version, I might as well just give it to you.  Go take a look at the picture of the 50 amp plug again.  What’s different about it when you compare it to the 30 and the 10/15/20?  Here’s a hint… start counting.

It’s got FOUR prongs!!!  The others only have three.  Well, if you’ve got only three prong sockets on your pedestal, there’s not really a good way to get another prong on there.  This is where we start messing with adaptors and stuff.

I’m tired of typing, so I’ll try to wrap this up and I might explain some more later…

Adapters and Cheating

The best pedestal you can find should have a bunch of sockets and breakers…  it’ll have a 50 amp socket and breaker, a 30 amp socket and breaker, and probably a couple of 20 amp sockets and breakers.  That there is electrical gold! (Well, assuming it’s actually wired right and putting out the amperage its supposed to).  You can plug in anything into the right socket and it’ll work!  Most excellent!

But what happens if you have a 30 amp plug and only have a pedestal with a 50 amp socket?  Easy, you get an adapter.  50 amps is more than you’ll need, so the adaptor just kind of ignores the extra prong on the 50 and lets you use half of it.  But, the circuit wasn’t designed to be used like that, so go easy on what you use…  Air conditioner and microwave at the same time are probably ok, just don’t fire up the hairdryer too. 

Ok, so what happens if I have a 50 amp plug and I only have a 30 amp socket?  Err…  things just got complicated again.  What you basically have is an RV that wants 4 wires (prongs) but you’ve only got three.  You can get a single adaptor that will allow you to physically plug the 50 amp plug into the socket, but there just aint enough wires available.  One of your 50 amp wires isn’t connected.  That can cause one of two things to happen.  If you have a fairly simple electric system, you can probably run half your appliances.  Maybe the air conditioner will work and nothing else does.  Maybe it’s the other way around.  Chances are pretty good that something important isn’t going to work…

…Or, nothing works at all.  That’s what happens with our RV now.  IMG_0167It’s got some smarts and knows what you’re trying to do.  It doesn’t like it and simple refuses to do anything.  I’m pretty sure our “transfer station” is the brain behind this (picture should be over there on the right).   While it’s annoying when we don’t have a 50 amp connection, it does save us from blowing up the microwave or air conditioner, so I guess I can’t whine too much.

There is one more option for tricking the system if you really need to.  I have no idea what this thing is called, but it can work in a pinch.  It’s a weird adaptor that has two 30 amp plugs connected to a 50 amp socket.  The theory is that you can take two 30 amp circuits and combine them into a 50 amp.  It’s risky.  You HAVE to be sure that they are different circuits first.  When you pull up to the power pedestal in Uncle Bob’s Wonderful Campgroundland, do you have any idea what kind of monkey wired that pedestal?  Nope, neither do I.  Did he use one circuit and just wire each plug into it?  Maybe… it’s cheaper that way. He only had to run one wire and it works if you’re only using one plug at a time.  What happens when you use one of these funky adapter things if the pedestal isn’t wired with individual circuits?  IMG_0174I have no idea, but I’d bet that it’s not good and I don’t want to be the one to find out.  Oh… campground employees tend to get real torqued up if you use one of these “combiner” things and they find out about it.  Just for reference, there’s a picture of one over there to the left.

Shutting Down

Ok, I have more to talk about, but I’m tired of typing and you probably didn’t make it this far anyway.  Maybe I’ll go into the adaptors and stuff and how they all work in a future post.

Not An Elektrishun

Ok, I hate to say it, but I know I have to… I’m not an electrician.  I don’t play one on TV.  I didn’t sleep at a Holiday Inn last night.  Any of the above is based on my limited understanding and research.  None of it is guaranteed to be accurate and I’m not responsible for anything you do or anything that happens.  I’m sure I have some bits in there that some electrician-type friend (that would be Rob) will ping me on.  I’ve probably got some of the jargon a bit whacked and I may have used amp as a verb when it should have been a noun or some such nonsense.  I’m just trying to present an idea of why this stuff matters and how to deal with it.  Don’t beat me up over it.  Oh, if anyone of our readers does have a link to a better description of this stuff, feel free to post it.  If you’re shy, just email me (addy on the About Us page) and I’ll post it up with this entry.

If you’re in an RV (or going to be), there will come a day when your plug don’t fit someone’s socket.  All I’m trying to do is stop my peeps from freaking out about it. 😉

Note from the editor: Much of the 50 amp stuff I figured out thanks to my awesome family who wired up a 30 amp connection before we got here, then had to call an electrician back a few weeks later to wire up a 50 amp when we got the Dutch Star.  You guys rock! 🙂

Additional note from the editor: If you’re the one with the treadmill, email or comment with the following information from the tag near the plug on the treadmill – Volt (V), Watts (W) and/or Amps (A).  At least two of those should be listed.  If (A) is listed, that tells you how much they expect it to use.  If the other two are listed (V and W) I can tell you how to figure out the amperage.

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5 Responses to “Fight The Power!”

  1. Eric says:

    Hi guys!
    Wow, now you really have a land yacht! Interesting for me to read about your experiences and see how many parallels there are between boats and RVs. I am surprised to see that your “Shore Power” connections do not use twist lock plugs and sockets – that’s a difference – on boats they are all twist locks. Otherwise the same – 30 amp and 50 amp are the normal varieties found at marinas. most boats have both AC and DC systems too.

    Having fun reading about your adventure – enjoy!


  2. Karl P says:

    I think it will work if you plug a 50A > dual-30A adapter into a circuit that is wired with only one 30A main, but if you pull more than 30A, you risk blowing a breaker in the campground’s circuit box, or worse, if the circuit isn’t properly protected with the right size breaker, you can start a fire and/or damage the ground’s wiring. I assume this is why they get angry when they find out someone is using one of these adapters. Imagine how unpopular you would be if you caused the groundskeeper to run around resetting a popped breaker at 2am because you decided to use a 50A “cheater” adapter. Yikes!

    Regarding normal household voltage, in the U.S., national standards specify that the nominal voltage should be 120 V, but allow a range of 114 to 126 V (-5% to +5%). Historically 110, 115 and 117 volts were used at different times and places in this country. Main power is sometimes spoken of as 110, but 120 is the actual modern voltage. Right now the UPS running my computer is showing 121.8 V from the mains, but I’ve seen that dip as low as 114.2 V on a hot summer day here in southwest Florida when everyone has their A/C running. If it fell much below that, it would be out of spec, and bad things could start happening to sensitive modern devices. Even worse is if the voltage spikes too high. That’s why it’s a good idea to plug your electronics into a voltage-regulating UPS. I would be especially concerned about this in an RV where your mains power comes from all kinds of different sources. In practice, do many RV owners use UPS units to protect electronics like computers and TVs? Or do many RVs have built-in voltage regulators? If not, it’s something that would worry me.

  3. Dasy says:

    You got through that novel, er post!?! What a trooper!

  4. Jonathan says:

    Eric, a lot of the systems are the same as marine systems. I even check boat stores when I’m hunting for odd parts. I’m not sure why the RV industry doesn’t use twist-locks… My guess is that it just kind of “evolved” into using utility outlets… garage 30 amp sockets and stuff like that.

    Karl, unfortunately, not many use any kind of voltage regulators. Plenty of people have learned the hard way that it’s not a good way to go. Some of us use something like a Surge Guard for protecting the whole RV system, as the RV has several sensitive parts of it’s own. Here’s an inline plug-in one on Amazon:

    I actually prefer to have them wired in, that way I can make sure it’s securely in a storage bay, instead of being advertised and easily swiped hanging off a pedestal. :S

    At campgrounds, I’ll also use a UPS for my big desktop machine, once it works. But that’s a story for another time.

  5. Eric says:

    One tip, when you are shopping for plugs and receptacles (scokets) – the “universal” identification system is from NEMA (National Electrical Manufacturers Association). Each plug or receptacle should have a NEMA number. The locking ones, like we use on the boats, start with an “L”, next is the NEMA number, 5 is very common because that defines a 3-wire (hot-neutral-ground) device for normal “house current” (120V), then a dash, followed by the current carrying rating. As I recall my boat’s shore power cord has a NEMA L5-30 plug and socket. The NEMA numbers are normally molded into the plug or socket.


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