🟦 Burned wires in an Automatic Transfer Switch!
Question from a reader about why there's burned wiring in his Automatic Transfer Switch. Time to check the torque...
Hi Mike,
I have a question about my 50 amp class A diesel pusher. We are currently at Bald Eagle State Park in PA, one of my hot lines at the transfer switch seems to be burning up, it smells and is discolored. Is this a transfer switch malfunction, a campground power issue, or could my 50 amp shore power cord be bad? It’s seems to only be happening on the one leg. I need to keep my family and my rig safe, what should I do? Thank you for your time and consideration! - Jeff L
Hey Jeff,
That’s probably due to a loose termination screw in the transfer switch itself. Terminating screws in RV electrical systems lead a sad life. They’re constantly subjected to road vibration and high temperature swings, both of which will loosen the connection. And a loose wiring connection will increase resistance that can cause localized heating under load. Once a connection begins heating up there’s more resistance, which leads to more heating and arcing. And then the wiring insulation begins to break down which creates a fire hazard.
ATS (Automatic Transfer Switches) are especially susceptible to this overheating effect since all power coming into your RV flows though the ATS contacts.
Here’s the fix:
Disconnect all power from the RV (including turning off the inverter)
Loosen the terminating screw on the burnt wire
Strip the insulation back a bit to get to clean copper
Reinstall the wire and tighten the terminating screw to the correct torque
Check and retorque all other terminating screws on the terminal block
More details
I’ve already posted a lot of articles and videos on how to do this. Read my 101 article on how to troubleshoot and retorque terminating screws in your RV electrical system HERE.
Let’s play safe out there… Mike
I'd be replacing that contactor. Might replace both if marginal rating with higher rated ones. I hope there is extra wire to pull in once the bad ends are cut back. Manufacturers are known to be stingy with such things!
I would add...
2A. Remove the terminating screw and use a wire brush to remove any debris or corrosion on the contact end of the screw.
2B. Pull the wires out of the terminal block and cut the wire back to clean copper and undamaged insulation.
3A. Lubricate the screws with dielectric grease. After overheating the screws and the terminal block will be a tight fit.
4A. Overheated terminal blocks (and dielectric grease) will alter the torque needed to achieve the proper tension. This gets a bit tricky as there is no way to determine how much torque will be needed just to run the screws through the terminal, even without the wire being in place. You can use your torque wrench to measure the resistance, then add that to the recommended torque, but the manufacturer would tell you that you cannot rely on the recommended numbers if the terminal is damaged.
Note 1: Once you remove the set screw(s), you may discover that the terminals have a mounting screw in the bottom of the hole. Sometimes, the terminals are replaceable.
Note 2: The termination at the upper end of the contactor are harder to see but look like they also need some attention.
Note 3: See that over-sized neutral wire on the other contactor? That's likely because all the loads are 120vac. Your input cable may be undersized. Also, curious why the input white wire is re-coded black.