Virtually every modern RV made, that hooks up to shore power, has what is known as an automatic transfer switch, or an ATS for short. When you are on the road, or not connected to shore power, your electrical fixtures run on 12 volt DC power, which is the reason for your auxiliary battery, or they run off of a powered generator. When you get to a campsite, and you plug into shore power, the RV transfer switch allows you to bypass the generator, and use shore AC power for all of your electrics.
Nothing is infallible, of course, and there may come a time when you plug into the shore, and you’ll get no AC power in your RV. Obviously, the first thing you may think of is that your ATS has gone bad and that it will have to be replaced.
But that’s not always the case. Here are several different tests you can do to troubleshoot the situation and find out why your RV transfer switch is not working.
Check the Breaker Box
Before you do anything else, check the breaker box at the shore power source, also known as the pedestal. Make sure all the outlets look like they are not burned, and that the breaker is flipped “on” while locking securely into place.
If the pedestal breaker wobbles or doesn’t lock, is cracked or looks burnt, you have a breaker problem. If the pedestal and breakers seem in fine working order, then check the breaker box in the RV.
There are so many times when the main breaker, or an appliance breaker, gets thrown just from going down the road and hitting a bump, a quick turn, driving down a rough road or maybe even checking the box before your journey and accidentally flipping the main breaker.
Yes, it sounds like it could never happen to you, but hundreds of people think the same thing every year, they call in a professional to come and check out their ATS, and are embarrassed that the problem was a thrown breaker. It happens more often than you might think.
The Power Cord
Here is another thing that should be checked if there is no ATS power; the power cord. Power cords, after all, are just wires. However, the cord has to support up to 30 amps of juice running through it. A 100 foot long 16 gauge cord may work, but it is not made for that type of power transfer, and the inner wires may melt if used for long stretches of time.
The actual plug might melt where it goes into the shore, or it attaches to your ATS. If the cord ends are blackened and burned, there is a good chance that your cord is the culprit and not your ATS.
If your cord seems fine, a quick and easy test is to hook up a small 120 volt appliance to the end where it attaches to the automatic transfer switch. You will, most likely, need an adapter for this task. If the appliance works, chances are the cord is good. You can also use a voltmeter and test the end as well. If you get 120 volts from the cord, it’s good.
One other thing here. Most shore power outlets are in the 30 amp range. If you have a flimsy cord, it may have difficulty supplying that type of amperage to the ATS. When you connect up to shore power and then plug it into your transfer switch box, you may hear the ATS clicking repeatedly.
That means the inner transfer switch doesn’t have enough amperage to actually switch over. You’ll need to get rid of the cord you are using, and get a dedicated 10 gauge RV cord rated for 30 amps, unless you know specifically that you’ll be staying at a campsite with 50 amp shore power. A 50 amp cord has 3 live plugs and a ground, whereas a 30 amp plug has 2 lives and a ground.
The Transfer Switch
If the cord and breakers are intact and functioning, the next step is troubleshooting the RV transfer switch itself. Finding where it is may be difficult, but it is generally in the same area behind a panel or box where the shore plug connects to it. That isn’t always the case, but that’s the first place to look. If it isn’t there, you’ll have to trace the wiring from the shore plug connection to where the ATS is located.
Make sure the shore power is disconnected and the breakers in the RV are flipped to the “off” position. Once this is done, you can begin to troubleshoot the switch proper. Check all the connections first, on the offhanded possibility that a wire connection has come loose. If you find one, it may be a simple matter of tightening it down and your problem is solved. If all the connections are tight, go to the next step.
Look for a burned connection point, which will generally be where a wire connects to an electrical post on the switch itself. If a wire connection is burned, or the wire insulation is melted, the chances are that you have a bad transfer switch.
If there are no burned wire connections, you’ll have to get into testing the actual circuitry, and if you are not comfortable doing this, or if you have limited do-it-yourself experience, you may want onto pass this up and call in a professional.
Transfer Switch Continuity
You’ll need a voltmeter for this, or find someone who does. Set the meter to 300 volts if your RV uses 30 amps, which will be 120 volts, or set your meter to read 600 volts if you have a 50 amp set up, which means you are running 240 volts.
Turn the pedestal power on and connect your cord to the ATS. Wait about 60 seconds for the switch to activate, then check the voltage where the power comes into the transfer switch. If the voltage from shore reads around 120 volts or 240 for a 50 amp circuit, the shore power is good.
Now, check the power where it leaves the ATS. If it reads the same voltage where the power is coming in, your switch is working. If there is no reading or a reading that is far less than the voltage coming in, then your switch is faulty.
Once you have determined this, and since it is already exposed, it will be easy enough to replace. Just follow the wiring diagram you get with a new one, and you should be good to go.
You’re Not Done Yet
Just when you think you are done, and you have figured out that the transfer switch is actually working, there is one more thing to test.
Your RV’s breaker box. Even if you have checked all the breakers, and they appear to be in working order, if your transfer switch was functioning properly, but you still weren’t getting any power to the RV electrics, the chances are that somewhere in your breaker box you have a faulty breaker.
If you weren’t getting power from the switch to any electrical appliance, it’s a good bet that the main breaker has a short, the contacts are not seated correctly or are corroded. To check it, turn off the power, pull the breaker out of the box, then test the contacts with your voltmeter.
If you weren’t getting any power with the breaker in place, but there is power showing on your voltmeter, it is likely that the breaker has gone bad and needs to be replaced. If there is power at the main, but no power on some appliances, check those individual breakers in the same way you checked the main breaker and replace them as needed.
Just remember, if you are not comfortable working with electricity, have a qualified professional come in and do it for you. Don’t take chances with high voltage.
From the Easiest to the Hardest
A good rule of thumb for any RV transfer switch troubleshooting, or really any electrical troubleshooting on any project, is to start from the easiest thing that may be a problem, and work your way to the hardest. Start by checking the typical things like the plug, the breakers, the outside wiring insulation. Next, check connections, loose wires, and burn marks on the insulation.
Finally, check the switch itself, from melted contacts to voltage continuity input and output. In most cases, one of these minor things will have been the problem, and you will have saved yourself a lot of time if you had jumped right into the worst-case scenario.
There are many a time when people will assume the worst, get the transfer switch replaced, only to discover the real problem was a broken wire in the cord, or a bad breaker at the pedestal.
Always work your way from the easiest to the hardest, and by doing so you may save yourself a lot of time, effort and money.