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block heater trips house GFI

Discussion in 'Gen II Prius Care, Maintenance and Troubleshooting' started by briantompo, Dec 21, 2011.

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  1. briantompo

    briantompo New Member

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    Hello,
    My Toyota engine block heater just started tripping the garage GFI outlet where it worked previously. I've tried different outlets on different circuits as well as different extension cords...all with the same result. The block heater has been flawless in the Prius for about 5 years, and tests OK as far as I can tell. Resistance at 70F is 35 Ohms, open between both prongs and ground, and the ground prong has zero resistance to the chassis. Plug is still like new and nothing changes if I move the plug around or bend the cord. I can't find a short anywhere and the prongs are clean and free of corrosion. A 500W halogen lamp and a circular saw both work in the same outlets, same extension cords without tripping the GFI.

    Can anyone offer any additional troubleshooting suggestions or similar experience with their block heater? I'm out of ideas.

    Thank you, Brian
  2. bisco

    bisco cookie crumbler

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    try a hairdryer? maybe there is some moisture somewhere.
  3. Dark_matter_doesn't

    Dark_matter_doesn't Prius Tinkerer

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    Does the GFI pop immediately or after the heater gets hot?
  4. frodoz737

    frodoz737 The Mechanic

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    Your heater element or cord is shorting or burned out. Check the plug, cord and terminals first for wear, security and corrosion. Contact cleaner is your friend. Removing the element/cord assy will make inspection easier if no obvious damage is found. Wiring can be repaired. Ring the wiring and element seperatly. If all looks good, go to dealer parts counter and ask to ring out a new one off the shelf to verify. If they do not have one, ask someone in service if they will print out the resistance checks for you off the manual. Please and thank you sometimes still works. If not, someone here might give you their resistance readings for a comparison.
  5. briantompo

    briantompo New Member

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    Thanks, so far for the suggestions. D Matter- the GFI pops right away.
    Would someone with a Toyota block heater measure the resistance across theirs and report back? I measured 35 Ohms on mine. The math seems correct for 400ish Watts.
    Thanks, Brian
  6. Chuck41

    Chuck41 New Member

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    Hi
    I measured the resistance of my EBH and it was ~ 35 ohms.
  7. frodoz737

    frodoz737 The Mechanic

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    "I've tried different outlets on different circuits as well as different extension cords...all with the same result."



    Your drawing more amps than your GFI limits while plugged in. My recommendations stand. It is a dedicated system. Worst case it's only $59 and a little time to fix. Best wishes.
  8. jpadc

    jpadc Type before I think too often

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    Brian:

    While you had the ohm meter out did you check the resistance in the cord? Likely you will find that it is bad / shorted. A few of us have found the problem at the 3 prong end due to wear of plugging and unplugging it in an extension cord. With that, of course, you can just cut plug off and replace it. For most of us, unfortunately, the problem is at the connector to the heating element and for that, you just have to replace the entire thing.

    Bob
  9. efusco

    efusco Troll Slayer Staff Member

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    I third the suggestion that it's the cord...they're known to wear out, usually just back of the reinforced area behind the plug. You can cut that off and splice on a new plug or replace the whole EBH and cord set (you can't just replace the cord, usually, b/c getting it off of the EBH is impossible as the whole thing just crumbles.

    I've done both, the spliced fix worked fine if you do a good job. I would, however, suggest you use a small extension on the end of whatever cord you decide to go with. they make some that are about 8" long--let that take the wear/use and wear out, then all you ahve to do is replace the 8" extension instead of fiddling with the main cord.
  10. ursle

    ursle Gas miser

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    I'd pull the heater out of the car and check the chord, if it isn't the three prong plug shorting it could be that the wire was rubbing somewhere and shorted, lots of motion where electricity is concerned, lots of motion where cars are concerned.
  11. kornkob

    kornkob New Member

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    It is my understanding that GFIs can get more touchy as they age and as they see more use. You might consider changing the GFI itself.
  12. briantompo

    briantompo New Member

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    Thanks, everyone for the suggestions. I'll update when I find the problem and repair or replace. I was hoping to avoid removing the heater to troubleshoot but I've exhausted the easy approach. I'm confident the fault is in the heater and NOT the house and unfortunately, it's not the plug or strain relief. Thanks again, Brian
  13. Mendel Leisk

    Mendel Leisk Senior Member

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    If resistance across block heater prongs is (normal) 35 ohms: maybe a problem with your extension cord.
  14. bisco

    bisco cookie crumbler

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    i have replaced a few for this reason.
  15. ngc4565

    ngc4565 Member

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    In that case you have a short between the neutral and ground wires. The purpose of a GFI is to detect this very situation. Try replacing the plug first.
  16. fuzzy1

    fuzzy1 Senior Member

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    No, he has an open between neutral (i.e. one of the prongs) and ground.

    I do hope he used a digital meter, or adjusted the range of his analog meter, to verify that 'open' exceeded something like 100kohms. On an analog meter without a range change, leakage strong enough to trip the GFCI could still register as 'open'.
  17. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Since the OP tested the GFI and extension cord with other devices that require substantial power, my guess is that the power cord to the block heater has an intermittent problem which did not manifest itself during the ohmmeter testing.
  18. ngc4565

    ngc4565 Member

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    No, I beg to differ. The neutral and safety ground should be isolated (i.e. open) at the load. The entire purpose of a GFI is to detect an imbalance of current between the hot and neutral wires. The fact that he sees the same resistance between the hot terminal and the neutral and ground proves that there is a short.
  19. fuzzy1

    fuzzy1 Senior Member

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    Are we reading the same OP?

    I read it as:
    35 ohms hot to neutral (prongs);
    Open hot (prong) to ground;
    Open neutral (other prong) to ground;
    Short ground to chassis.
  20. ngc4565

    ngc4565 Member

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    My apologies - I clearly misread the original post.

    Peace on Earth and happy holidays.
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