Sunday, September 19, 2021
Sunday, September 19, 2021

RVelectricity: Power-hungry RVs, and appliances

Dear Mike,
I would love to see an article about exactly what you can run on a 30-amp breaker. We have a COE campground with a lot of people coming into it dragging the most beautiful mansions on wheels. They have electric hot water tanks, fridge, microwave, electric cooktops, air fryer, electric skillet, electric grill, two ACs, washer and dryer – and complain every 10 minutes because they keep tripping the 30-amp breakers.

They are ALWAYS only running one AC. Nothing else. They burn out the breakers the first two hours they are there and we have only 3 maintenance guys on the entire lake. These older campgrounds were not set up to run all of the electronic gear they bring, let alone almost an entire house. —Cheryl K. 

Dear Cheryl,
You’re in luck because I’ve been researching that exact topic lately, so I have a lot of info at my fingertips. Now, what I’m going to say won’t make me very popular with my readers. But, as you all know, I publish the unvarnished truth.

How much power do I have?

An RV electrical system will never be able to supply the same amount of power as your sticks-and-bricks house. There’s just no way! Here’s a quick list of just how many watts are available from shore power at a campground or your stationary home:

  • 20 amps at 120 volts = 2,400 watts (pedestal or home outlet)
  • 30 amps at 120 volts = 3,600 watts (campground pedestal)
  • 50 amps at 240 volts (100 amps at 120 volts) = 12,000 watts (campground pedestal)
  • 200 amps at 240 volts (400 amps at 120 volts) = 48,000 watts (residential service panel)

Let’s start with the watts!

Yes, the only thing that really counts is watts of power. And, as you can see, a 30-amp pedestal outlet can only supply 3,600 watts of power for your entire RV. Compare this to the 48,000 watts of power your residential service panel can supply.

A little quick division shows us that your home service panel can supply more than 13 times the amount of wattage available from a 30-amp shore power outlet. And it can supply 4 times the amount of wattage of even a 50-amp/240-volt shore power outlet.

Okay, let’s convert watts to amps…

So if we know how many watts a particular appliance draws, it’s pretty simple to convert watts into amps at any particular voltage. In this case we’re only thinking about 120-volts AC, so let’s take a look at Ohm’s Law to figure it out.

Looking at the Ohm’s law chart, if we know the watts (P) and the volts (V) all you have to do in order to calculate Amps (I) is perform this simple equation of P/V=I (Power / Voltage = Amperes). For example, a 1,200 watt heater at 120 volts would draw 10 amperes of current. That’s because 1,200 watts /120 volts =10 amps. Pretty easy, right?

How many amps do different appliances use?

Glad you asked, because that’s the second part of the equation. Some things that are big use a little power, while other things that are small use a lot more power.

Consider your big screen television set. This looks like it should take a LOT of power to run, but actually they are very efficient and don’t require a lot of wattage to run.

Here’s a chart comparing the wattage of various television technologies and screen sizes. As you can see, your flat screen television is likely drawing less than 100 watts of power. So 100 watts / 120 volts = 0.8 amps.  Yup, that’s less than 1 ampere of current at 120 volts.

What about my Instant Pot?

Well, according to the literature, your Instant Pot uses 1,000 watts of power. That’s only during the heat-up cycle, and it may only come on 10% of the time after that while cooking. (I don’t know for sure because I don’t have one, nor have I ever metered one.) Let’s calculate the amps – 1,000 watts / 120 volts = 8.33 amperes of current.

But while it’s running for the first 5 or 10 minutes to come up to temperature, it will be pulling around 8 to 9 amperes at 120 volts. That’s like 1/3 of the available amperage from your 30-amp shore power outlet.

Anything with a heating element is going to draw a LOT of amps!

Your convection microwave oven will likely draw around 1,800 watts, which is 15 amps or 1/2 of your available power. (1,800 watts / 120 volts = 15 amps). Even on microwave mode only it’s still drawing around 1,100 watts, or close to 10 amperes of current.

The same goes for your daughter’s 1,800-watt hair dryer or your electric griddle. And don’t even think about running a 1,500-watt portable space heater from a 30-amp shore power outlet if anything else is running. It will use at least 12.5 amps of your available 30 amps (1,500 watts / 120 volts = 12.5 amps). If your battery charger and water heater are on, then the 30-amp breaker will certainly trip.

In hot water!!!!

If you have the water heater turned to electric mode, it’s probably using its 1,500-watt heating element that draws around 12.5 amperes of current (1,500 watts / 120 volts = 12.5 amps). Again, 12.5 amps of your 30-amp shore power connection is going to use 40% of available power. So switching your water heater to propane helps reduce current draw considerably.

What about battery charging?

Well, old-school FLA (flooded lead-acid) batteries only like to charge with around 20 amps of current at 13 volts, so that’s maybe 2 or 3 amperes of current at 120 volts.

However, a modern lithium battery can be charged with 100 amps of 12 volts DC or more, which equates to 10 or 12 amps of 120-volt current from your shore power. If you add a second lithium battery with the appropriate charger it can draw up to 20 amps at 120 volts. That’s 2/3 of your available current from a 30-amp shore power outlet!

Oh, no, it’s the air conditioner…

Yes, indeed it is. That air conditioner on the roof of your RV will use around 14 amperes of 120-volt current while running (even more in hot weather or with low campground voltage). And there’s a big startup surge when the compressor kicks on that can be 400% more current from 1/3 of a second.

So an A/C can easily draw in excess of 50 amps of current for a few hundred milliseconds during compressor startup. That’s enough to trip circuit breakers that are already close to the edge.

What about the 80% current rule?

More on that later, but according to NEC, that only applies to continuous loads over 3 hours. And note that TT-30 plugs and receptacles are supposed to handle 125% of their rated load without overheating. However, tightly packed circuit breakers in a panel without air circulation may need to be derated to 80% of their amperage rating for near continuous loads. That’s an entire white paper worth of discussion which I may cover in an advanced article.

You need to manually load shed

Well, Lisa Douglas from “Green Acres” had the right idea. Since their farm house also had limited power, you couldn’t plug in the hair dryer and waffle iron at the same time.

Oliver created a plug-board and extension cords from each appliance with various numbers, and Lisa knew what combinations worked, and which would blow the fuses. I’m afraid that’s what you need to do with a 30-amp shore power service.

I’ll try to make a simple amp chart with various appliances that you can print out for your own use. But note that many modern EMS Surge Protectors give you an instant readout of current draw, so it’s pretty easy to make your own chart.

Is there another solution?

Well, yes, there is – But it ain’t cheap. It’s called a hybrid inverter, and the one I have is rated for 3,000 watts total. But you can set the maximum incoming amperage draw down to 25, 20, 15, 10 or even 5 amps of current. You could power your air conditioner separately from the pedestal and everything else on the 3,000-watt hybrid inverter.

But this isn’t a simple or easy install. However, it may be the only way to get more things running from a 30-amp service since it could double the available amperage until your battery runs down supplying the extra power needed. More on this in a future discussion.

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.

For information on how to support RVelectricity and No~Shock~Zone articles, seminars and videos, please click the I Like Mike Campaign.

##RVT1014

Comments

Subscribe
Notify of

This site uses Akismet to reduce spam. Learn how your comment data is processed.

15 Comments
Newest
Oldest
Inline Feedbacks
View all comments
pursuits712
27 days ago

Great article! Here is a site that provides some charts that may be helpful. I think I am going to just label all my appliances in nice, clear numbers so I can easily see what’s going on at any one time!

Wolfe Rose
26 days ago
Reply to  pursuits712

I have a cheap 6way AC meter on my shore feed, and mounted next to my thermostat since it’s the worst offender. With live wattage in front of them, I then have a chart for family to consult before turning things on.

I just got a new trailer, so i’ll probably redo and release a vid on $3 automatic load shedding soon (eg. using microwave briefly turns off electric HW without overloading 30A).

Jim
28 days ago

Hi Mike. We have an EMS installed in our trailer. It came with a readout showing current volts, amperes, and frequency. We monitor this readout regularly, especially in hot weather when the AC is running. By doing this over time we know the load each power hungry device adds. We may need to do manual power management to keep our usage under the 30a available. Over time this becomes a fairly automatic activity. We also understand the base load items such as the refrigerator and converter regularly consume.
Thanks for your informative sessions at the FROG rally. Hope to see you next year.

Sokol Mike
26 days ago
Reply to  Jim

I had a great time at FROG, and I’m already invited back for next year. Glad you liked my RVe seminars.

chris
28 days ago

What you can actually run is based largely on how hot your shore plug gets when you’re trying to run things. At each new campsite I always run the air and maybe some other appliance for a few minutes, then go out and feel the plug to see if it’s heating up. 30a is a suggested maximum, more like 26 is safe.

Last edited 28 days ago by chris
Mike Sokol
26 days ago
Reply to  chris

According to NEMA, the TT-30 connector design has been tested at 125% of rated load (37.5 amps) without overheating. So there’s something unexplained going on if they overheat with a 30-amp load. Now I know that melted 30-amp plugs happen all the time, but I can’t explain just why it occurs. More to study…

Thomas D
28 days ago

You never mention the 80% rule where you calculate the max current that the circuit can carry in what? A half hour? A30 amp circuit breaker should be able to maintain 24 amps steady. And dont forget the breakers degrade with overloads. Plus the switching on and off wears out the mechanism so i see a lot of false tripping. Years ago, Kenmore dryers burnt up more outlets and cords. Like 6000 wattsheater plus on one leg a motor of say 6 amps. Ran right around the 30 amp full load. Kept me busy fixing dryers

Thom R
28 days ago

Mike! You are the man. Your articles are great, I always read to educate myself.
Maybe you could clarify by showing Ohm’s law? Isn’t it watts divided by volts equals amps? Amps times volts equals watts?
Correct me if I’m wrong.

chris
28 days ago
Reply to  Thom R

you are correct

Admin
RV Staff (@rvstaff)
28 days ago
Reply to  chris

Hi, Chris and Thom. Here’s an article of Mike’s that explains Ohm’s Law: Inverters 101: Understanding amps and volts. Here’s the link: https://www.rvtravel.com/inverters-101-amps-and-volts/ And, yes, Mike’s “The Man”! Take care. 🙂 –Diane

David Freidell;
28 days ago

Mike, you started to say its all about the Watts, yet most all of the figures you cite are all noted in Amp hours. Not good Mike, try again. I can look up the conversion math from Amps to watts, but I shouldn’t have to from a professional like you. I do appreciate your help on this. Thanks

Firefly
28 days ago

Actually, he provides amps, not amp hours. That is quite professional of him since amp hours make no sense in the context of load on a circuit. Also quite helpful to provide amps because non-professional RVer know they have 30 or 50 amp service (because that is how breakers are labeled) and can easily subtract the estimated amp draw of each appliance to understand how close they are to the service limit. Thanks for your help on this Mike!

Mike Sokol
28 days ago

Okay I’ll clarify a little more tonight. Guess I should have said it’s all about the amps…😁

Chic Sanders
28 days ago

love that episode of Green Acres.

Follow us!

31,714FansLike
26,412FollowersFollow
66,000SubscribersSubscribe