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Thursday, December 13, 2007

Use Your Multi-Meter to Check that RV 50 Amp Receptacle

Not all RV hook-ups are created equal. Make it a habit to check your electric connections BEFORE you plug in your RV power cord. You will save yourself a pile of money and you will be confident your RV site is providing you good electric current. I’ve actually found faulty 50 amp receptacles. The problem could be corrosion, a loose wire or faulty installation. This guy drove off with his power cord still connected to the pedestal and damaged the the receptacle. So, you never know what you’re going to find even at the finest RV parks. In the video at the end of this article I demonstrate how to use your multi-meter to check a typical 50 amp service. Multi-meters are inexpensive and should be in every RVer's toolbox. This is what the inside of a 50 amp receptacle looks like. The “train tunnel” shaped hole is the ground wire (if the cover were on it would be located at the bottom of pattern - it’s the bare copper wire). The white wire is the “common” and feeds under the plastic to the top blade holder in this picture. The black wire on the right and the red wire on the left both carry 120 volts. When you push your 50 amp plug into the receptacle the left blade (red wire) gets 120 volts and the other blade (black wire) also gets 120 volts for a total of 240 volts. To thoroughly check your 50 amp service do the following. 1. Set up your multi-meter (black wire in the “COM” hole on the multi-meter and the red wire in the “AC/DC” hole). Place the wafer switch to 200 on the AC side. 2. Place the pointy end of the red multi-meter cable into the “train tunnel” shaped hole and the pointy end of the black multi-meter cable into the opposite hole. You should read zero which means your ground and common are working properly. 2. Leave the black wire where it is at and move the red wire to one of the side blade holes. The meter should read 120. Move the red wire to the opposite side and the meter should read 120. 3. Leave the red wire where it is and move the black wire to the “train tunnel” shaped hole and read 120. Next move the red wire back to the opposite side and read 120. 4. Leave the red wire where it is and move the wafer switch on the multi-meter to AC 600 and move the black lead to the opposite side from the red wire and read 240. You may get slightly different readings but as long as they are within three or four points from the 120 and 240 readings it shouldn't be a problem. If your readings are weak on one or both sides, your electric system will not appreciate it. You should bring it to the attention of management and move to a different space. However, I would check the alternate space before I moved my RV because it could be a park-wide problem. Caution, electric shock hazards may be present so be very careful when working with electric test equipment. Read and follow the directions and precautions of the multi-meter manual. Keeping you plugged into the grid - Jim Twamley, Professor of RVing

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13 Comments:

  • How about an article on checking
    30A?

    By Blogger Syd, at December 13, 2007 7:51:00 AM PST  

  • I need to also know how to check 30 amp. PLEASE!!

    By Anonymous Windermere, at December 13, 2007 4:27:00 PM PST  

  • So you want to know how to use a multimeter with a 30 amp receptacle - OK, next time I'm at a regular campground with 30 amp service I'll do a video. Right now I'm staying at a relatives' house and building a desk out of walnut for the motorhome. So I probably won't get to it until after Christmas. Thanks for your readership. Jim Twamley

    By Blogger Jim Twamley, at December 14, 2007 10:29:00 PM PST  

  • great information but a small typo. "When you push your 50 amp plug into the receptacle the left blade (red wire) gets 120 amps and the other blade (black wire) also gets 120 amps for a total of 240 amps."
    Might want to edit that to volts instead of amps. Thanks again for the information. And feel free to delete this once corrected.

    Thanks,
    CQ

    By Anonymous Anonymous, at December 15, 2007 3:26:00 AM PST  

  • Isn't it 120 volts, not "amps", on each leg and 240 volts across each hot lead? What is the available amps of rach hot lead?

    Thanks, Fred

    By Anonymous Anonymous, at December 15, 2007 4:54:00 AM PST  

  • Major typo here; otherwise a good article.

    Just under the 3rd picture it states ...(red wire) gets 120 amps and the other blade (black wire) also gets 120 amps for a total of 240 amps... THAT SHOULD READS volts; NOT amps.

    By Blogger Al, at December 15, 2007 5:34:00 AM PST  

  • 240 amps from a 50 amp line? :)

    By Anonymous Anonymous, at December 15, 2007 5:49:00 AM PST  

  • I am curious about your statement, "as long as they are within three or four points from the 120 and 240 readings it shouldn't be a problem. If your readings are weak on one or both sides, your electric system will not appreciate it."
    All the information I find in electrical manuals, and from a conversation with two electrical engineers, indicate voltage ranges from 125 to 100 are well within safety ranges for proper operation of electrical equipment. Occasional 130v spikes for which my surge protector does its job to 95v typically from brown outs most common in CA and eastern US, as long as they are short term, will also cause no problems. Voltage in the 90-95 range lasting longer than 15=20 minutes could harm airconditioners.
    Also, parks get blamed for voltage variations that origionate with the power company. I once watched a camper and a park owner nearly come to fisticuffs over this issue.

    By Anonymous RRR, at December 15, 2007 6:15:00 AM PST  

  • When you push your 50 amp plug into the receptacle the left blade (red wire) gets 120 amps and the other blade (black wire) also gets 120 amps for a total of 240 amps.

    Don't you mean 120 volts??

    By Anonymous Bob, at December 15, 2007 6:44:00 AM PST  

  • Good article--very useful. What about reversed polarity. On occasion my polarity meter has indicated that condition exists and each campground owner/manager scoffs at the notion as "RVers having too many guages, etc.",or "many others have used that site without complaint..." etc, etc. In sum, is reversed polarity a problem when it truly exists, what are the problems that could result and how to believe it and/or combat the polarity problem?
    I look forward to your article on 30-amp also.

    By Anonymous Anonymous, at December 15, 2007 7:01:00 AM PST  

  • Yes, yes, yes. Thanks to all of you for pointing out my mistake, it should be "volts" not "amps" and I have fixed the error. I don't know what my fingers were thinking. Sometimes they just do whatever they want when my eyes aren't looking and my brain isn't engages. Thanks for your comments and your readership. Jim Twamley

    By Blogger Jim Twamley, at December 15, 2007 8:32:00 PM PST  

  • This is Great info. Everywhere I read to "check with a multimeter"; is there a good web site that can give one the Basics of how & when to use this tool? I want to learn! Thank you.
    Rose

    By Anonymous Roseport2000, at January 13, 2008 11:00:00 AM PST  

  • Mullti Meter to check that ups are ceated equal .

    By Anonymous Martina, at August 5, 2008 12:03:00 AM PDT  

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