I recently purchased a travel trailer and need to reweld the bumper support to the frame. Besides unhooking the battery, what other precautions must I take to protect the electrical system on my RV? The welder I’m using is a standard 120-volt unit. Thanks for your help. —Tim Kurta
That’s a great question. And I’m guessing that you’re concerned about passing arc welding currents through any of your RV’s electrical system.
First of all you need to observe the obvious safety factors of eye protection, proper clothing, welding gloves, and avoiding flammable material anywhere near or in your RV. I’m only stating the obvious so that none of my readers runs out to Harbor Freight and buys an arc welder to fix something on their RV.
Arc welding is both an art and a science, and you just don’t do it casually since there’s high temperatures and high currents involved. If you’re not an experienced welder, find someone who is. While I’m not a certified welder myself, I’ve worked as a design engineer in a fabrication shop that did a lot of welding, so I was responsible for not damaging anything. And the welders themselves were always asking me the same question you just did for the very same reasons. If any of my readers have additional input on this topic, please write them in the comment section below and I’ll add it to next week’s article.
That being said, let’s see what can go wrong when arc welding on any vehicle. Here’s a diagram of the main components of an arc welder.
As you can see, there’s a ground cable that’s clamped to the work piece, and an electrode holder with a welding rod. The arc welder transformer creates hundreds of amperes of current at a pretty low voltage that pass between whatever is in the middle. That’s what makes the arc itself. Now you may have heard stories about accidentally welding together the wheel bearing on an axle or even the crankshaft bearings inside of an engine in a vehicle, and that’s indeed possible if you don’t do this correctly. And certainly, passing hundreds of amps of current into your RV’s electrical system could be disastrous, so let’s consider those as two different systems.
You are correct that disconnecting your RV’s battery is a good start. But also make sure that your RV is disconnected from any shore power or portable generator. Of course, this is a good precaution when working on any part of your RV’s electrical system in general. Additionally, you don’t want your RV to be secondarily grounded in any other way. So don’t have it hitched to your truck when you’re welding the back bumper on the RV. Keep it electrically isolated from everything else. It’s OK to have it on the jacks as long as those jacks aren’t sitting down on metal plates in a factory floor.
Once that’s done, we now need to consider ground clamp position. I’ve seen lazy welders put the ground clamp on one side of the frame and then weld somewhere else on the vehicle. From the diagram above you can imagine that those hundreds of amps of current will pass through everything else in between. That’s how you accidentally cause arc currents to pass through bearings and damage them. So it’s absolutely critical that you place your ground clamp very close to where you’re going to weld. In your case it should be clamped on the RV frame a few inches away from where your welding joint needs to be. That way the welding currents won’t pass through anything else.
Welding is really interesting and I know a few guys (and gals) who can make it look like a work of art. For instance, TIG (tungsten inert gas) aluminum welding is its own definition of art since the final welding joint should look like a stack of nickles. Here’s a picture of one very pretty aluminum weld. Yes, I may have a strange definition of pretty, but I know a great welding job when I see it.
Let’s play safe out there….
Mike Sokol is an electrical and professional sound expert with 40 years in the industry. Visit NoShockZone.org for more electrical safety tips. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.