By Mike Sokol
Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) noshockzone.org with the subject line – JAM.
Back from our last trip and found charred and semi-melted prong on 30-amp power connection. Never had this happen before. While camping a circuit breaker did pop in my 5er. I reset and looked at CKT/BKR on pedestal. Everything looked good and NO bad electrical smells. Checked all fuses and CBs once home (good). I would have thought the circuit breaker and/or fuse would blow before plug gets this hot. Am I missing anything? Also 30-amp fuse in battery box semi-melted (not blown) – replaced anyway. —Andy Simmons
There were a lot of interesting answers to your question on my Facebook RV Electricity Group. Here are a few good ones:
From Chris Lawrence:
This is sometimes caused by a loose connection at the pedestal.
From Steve Higgs:
Very common for 30-amp connections. They are used and abused more often. Plug and unplug without turning off the power causing poor connection which results in heat.
From Tim Bard:
Poor connection causes arcing.
Arcing causes overheating.
Overheating melts components and can even start fires.
From James Hubbard:
Loose connection or dirty connection gets hot under loads
From Bob Coakley:
Dielectric grease on plug prongs reduces resistance, which may prevent this. Also use it on your trailer-to-truck connection.
From Mike Sokol:
This is generally caused by a high-resistance connection from loose contacts in the pedestal outlet, or corrosion on the plug contact from lack of maintenance. And yes, a lot of continuous high-current draw increases the overheating and meltdown problem.
However, if your connection is loose or corroded you don’t need to draw anywhere near the current that would trip a 30-amp circuit breaker. Even 20 amps or so will overheat a corroded contact. I just covered how to clean and maintain your shore power cords using advanced contact cleaners such as DeoxIT in my RVelectricity Newsletter #24 that published Sunday, and which you can join HERE if you’re not already subscribed.
OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.
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.
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Mike, I noticed that Andy mentioned that his 30 Amp fuse in his battery box had semi melted, but not blown! I was wondering how this would be related to the shore power plug?
Not directly related since the shore power plug is on the 120-volt AC side, and the fuse in the battery box is on the 12-volt DC side. But it does show there’s a lot of continuous current draw, and possibly oxidation on the connections.
A few months ago I went to plug in my surge protector and it looked like that! I clean my contacts, including surge protector, every few locations but not if parked for a long time in one place. Without that buffer would/could it have damaged the RV?
My research says that dialectic grease does not conduct electricity so it should not be applied to conductors as some people profess. Be careful of “experts” with keyboards!
Steven, that’s not correct. While dielectric grease is an insulator, it’s displaced by contact pressure which allows the contacts to conduct electricity. The dielectric grease on the exposed contact areas are what keeps those surfaces from oxidizing. I have white papers on this written by EE’s going back decades, and I’ve done this myself for 50 years. What research leads you to believe that dielectric grease won’t work for this application?
I use the Grease myself to protect the Electrical Connections.