RV Electricity – Torque those ATS screws properly

By Mike Sokol

Dear Readers,
In my RVelectricity seminars I’ve been demonstrating how to tighten terminal screws in your generator transfer switch. Why should you be doing this seasonally? Well, if you don’t check transfer switch screws for tightness, the combination of road vibration and temperature swings (not to mention moisture) can allow these screws to loosen up and increase the resistance of the connection. And that high-resistance connection can overheat during heavy current draw. Don’t believe me? Well, a picture is worth a thousand words (at least).

Here’s a picture that a reader posted on my RV Electricity Facebook group this week. I’m also including the original question and response from one of my other readers.

Raymond: I lost my transfer switch 1 leg. Could this have been from low voltage?

Don: Not caused by low voltage, more likely to be from loose (road vibrations) and corroded connections. The other terminals show extensive rust and corrosion which leads me to believe that a significant amount of moisture was present in that enclosure. Additionally, it appears that the wires landed to the terminals that have burned may be a smaller gauge? Hard to tell from the photo but they look smaller.

Me: I think that Don is spot on. This was not likely caused by low voltage since low voltage doesn’t increase overall amperage draw, contrary to popular folklore. However, there does appear to be a lot of corrosion on the screws and bus bar, which suggests moisture inside of the ATS (automatic transfer switch).

So what can we all do about it? Well, I believe that all terminating screws in an RV electrical system should be visually inspected and checked for tightness every year or two. But don’t just go wrenching down on every screw in your circuit breaker box or transfer switch. If you do that you’ll likely strip out the screw or break the terminal out of the relay/contactor in the transfer switch.

What you really need is something I’ve written about before, an in/lb torque limiting screwdriver. Note that I said inch/pound, and definitely NOT foot/pound, since these terminating screws need a surprisingly low amount of torque to make a proper connection.

Here’s an inexpensive torque screwdriver I’ve posted about before in my of my Quick Tips. Less than $50 on Amazon, it includes a carrying case and enough bits to tighten most any terminals in your RV’s electrical system. You can buy it HERE on Amazon if you like.

But before you begin, first look on the inside panel of your ATS, where you should find a chart showing just how much torque is required for proper wire termination, usually 35 to 45 in/lbs or so. Here’s a picture of that chart from one of my Southwire demo units.

Now, confirm that ALL electrical power to your RV is off. Remember you’ll be poking a metal screwdriver into a bunch of wiring that could be electrified. So disconnect your RV from shore power, turn off the generator, and make sure your inverter is off. I also disconnect the house battery to be extra safe.

Next, you’ll need to set your torque screwdriver to the correct in/lb value. Don’t be tempted to go with more torque than the chart shows. The designers know exactly how much torque these screws require.

Be aware that you don’t want to just twist each screw clockwise to see if it moves since it could be rusted in place. You’ll want to back each screw out a bit to make sure any corrosion is broken loose. Then simply retighten the screw clockwise until the torque driver clicks. Rinse and repeat with each screw in your ATS and main circuit panel.

Of course, you should also visually inspect all the connections for signs of corrosion, overheating, or damage to the insulation. If you find anything suspicious then it’s time to dig deeper and correct the problem before it gets even worse.

Don’t feel comfortable doing this yourself? Well, I’ll begin teaching this procedure at a number of RV technician classes this fall, and hopefully at some larger RV dealerships. This should take less than an hour of shop time to check wiring if an RV technician is already performing other maintenance on your RV.

And yes, I’ll be demonstrating how to do this in my upcoming RV Electricity Master Class at the RVillage rally. And due to popular demand, I’ll also make a short video on how to properly retighten your electrical connections. See you then.

Hope you had a safe and fun camping season so far this year. Let’s all remember to play safe out there….

Mike Sokol is an electrical and professional sound expert with 40+ 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.

##RVT915