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.
Dear Mike,
Can someone give me a place to purchase a test plug with 50 amp to a Y with 15-amp outlets on each side? I want to test that L1 goes to one side of the Y and L2 goes to the other side. The one I purchased on Amazon sends L1 to both sides. I questioned them about it and they said that is the way they wire it up, which means to test for 110/120 at the end of each side is not possible. I think you mentioned where to get one in a blog post but I can’t find it anywhere. Thanks in advance. —Joe Testa
Hey Joe,
This one did take me a while to find, so I’m not surprised you’re having difficulty finding one with the right wiring configuration. I’ve just called their tech support desk and they confirm that each of the 20-amp outlets is wired to different hot legs on the male 14-50 plug, so this one should do the trick. You can get it from Amazon HERE.
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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Hi Mike, thank you for a most informative service. I have a question that I’ve never seen addressed. The standard dog bone adapter takes the 30 amp circuit and couples it to the 20 amp circuit in a pedestal offering 50 amps, except I’ve never found one that works due to it causing a back feed causing the GFI circuit breakers to trip.
What if I remove one of the AC units power supply lines from the coach’s breaker box, run it through an independent circuit breaker box and then have a separate power cord for just that AC unit and plug it into the 20 amp outlet on the pedestal? The pedestal’s 30 amp circuit would power everything else and I wouldn’t have to resort to paying for 2 $300 electronic power modulation devices. And if my idea is feasible then why doesn’t the RV industry offer this option as standard equipment?
Thanks for your input Mike
The problem is that once you connect the neutral lines together from the two circuits, the neutral currents are intermingled which unbalances the hot/neutral currents on the GFCI causing it to trip. So unless you keep the neutrals of the 20- and 30-amp outlets separate, it will always trip the 20-amp GFCI. There’s just no easy way to do this without transformers to keep the neutral/hot currents balanced. Possible, but expensive.
Am I missing something here.
Couldn’t he just check his voltages at the 50 amp outlet and save $60.00?
I personally don’t know that I would want to plug anything into the 110 volt pigtails of this adapter as it’s going through a 50 amp breaker.
Not much protection if there’s an electrical problem with what I’ve plugged in and using.
I am the original asking party. The idea here was to cater to those who are not comfortable sticking probes into outlets. Not everyone is as savvy with electricity and since it is something that for all intents and purposes is invisible to most people, it is just there until you do something wrong and then you potentially learn the hard way.
What I am doing is producing a series of videos to show people how to take what would be a normal 50 amp plug and with the two 20 amp ends to check for correct voltage and possibly mis-wired outlets using a tool instead of voltmeter probes.
It is NOT to be used for anything other than that, testing the 50 amp outlet.
Feel free to reach out if you’d like to see the video series once it is completed.
Mike thanks for the link, I ended up building what I needed yesterday.
Joe
Joe, that’s a great idea. I’ve also built this sort of splitter for advanced 50-amp outlet testing with a Ground Loop Impedance Tester (GLIT), which is used to evaluate voltage drops, EGC ground impedance, and lots of other things way beyond the scope of this course. However, you are correct that by plugging in a basic outlet tester like this one, you could do a pretty comprehensive 50-amp podestal test without using an actual meter or meter probes. https://www.amazon.com/Prime-Products-12-4058-Power-Monitor/dp/B000BRFTH6/ref=sr_1_1?keywords=Prime+Products+Outlet+Tester&qid=1572871985&s=automotive&sr=1-1
When you get your videos done send me a link for evaluation. If I like them I’ll post a link here. How does that sound?
Mike sounds good, I got it built, just need to go out and test and video it, but it is cold here in Ohio 🙂 Soon as I got it done, I’ll gladly send it to you.
Karl, this isn’t about saving a few dollars. What he wants to show is a simple way for RVers to test the 50-amp outlet on a pedestal without having to use a digital meter and probes. I know a lot of end users who would rather just plug some kind of tester into the pedestal outlet and see the readings. But nobody currently makes a 50-amp outlet tester that simply plugs in. So this is the next best thing. And no, you don’t want to use this sort of splitter to provide power for anything since it’s way too easy to melt down even a 12-gauge extension cord with a 50-amp power source that doesn’t have a 20-amp circuit breaker in the path.