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Thread: DC Current Safety Threshold

  1. #1
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    DC Current Safety Threshold

    I just recently experienced an issue where a researcher used electrical test leads to a DC power supply, and then to two separate electrical probes. The DC power supply was rated at 10 VDC with an amperage up to 40A. The test leads were normal leads used for a multimeter, so when the researcher increased the amperage the test leads begin smoking and were damaged. From my experience test leads used for multimeters are designed for 10A not 40A, so to me this is a expected condition. My question since I am not very familiar with DC voltages, would 10 VDC with a 40A load pose a safety risk to an individual if they connected any exposed terminal.

  2. #2
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    10 volts is very, very, very unlikely to pose any risk of electrocution, regardless of whether it's AC or DC. A device that dissipates 400 watts and connections that carry 40 amps are likely to cause a thermal burn, again regardless of whether it's AC or DC.

  3. #3
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    Quote Originally Posted by Nardie View Post
    I just recently experienced an issue where a researcher used electrical test leads to a DC power supply, and then to two separate electrical probes. The DC power supply was rated at 10 VDC with an amperage up to 40A. The test leads were normal leads used for a multimeter, so when the researcher increased the amperage the test leads begin smoking and were damaged. From my experience test leads used for multimeters are designed for 10A not 40A, so to me this is a expected condition. My question since I am not very familiar with DC voltages, would 10 VDC with a 40A load pose a safety risk to an individual if they connected any exposed terminal.
    Test leads are very small gauge wire, maybe 20 AWG or smaller - they will not carry 40A for any amount of time before the insulation melts. The voltage isnt the issue, the amperage is - anyone holding onto that wire would most likely get burned.

    It's kinda like dropping a Crescent wrench across an automotive battery - you wont get electrocuted, or even shocked - it's still just 12V, but the amperage could be 800 amps or more - exploding battery or molten/hot metal could cause substantial injury.

    otoh, you could run a 40A load, AC or DC, across #6 wire indefinitely without problem, provided high ambient temperature and derating for CCC dont come into play.
    Electricians do it until it Hertz!

  4. #4
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    As stated...it's all about current through the body. Higher the voltage, higher the current if you make yourself a circuit. It takes about 0.1 amps to kill, so do the math. But, can you get electrocuted grabbing onto a 12V car battery? YUP! If your hands are sweaty, have acid on 'em and you have a large enough surface area due to the tool you're holding onto. DC is supposedly more dangerous because it is better at sending the heart into fibrillation. All of this is based on our regular safety meetings, though. I'm no Dr. Frankenstein.

  5. #5
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    Quote Originally Posted by meternerd View Post
    DC is more dangerous
    At higher voltage than AC, of course.

  6. #6
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    Quote Originally Posted by drcampbell View Post
    10 volts is very, very, very unlikely to pose any risk of electrocution, regardless of whether it's AC or DC. A device that dissipates 400 watts and connections that carry 40 amps are likely to cause a thermal burn, again regardless of whether it's AC or DC.

    40amps is 40amps voltage doesnt come into it. the leads to test in line amps on a 40amp circuit would have to be #8awg. Which is why rms amp probes are so popular.

  7. #7
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    Quote Originally Posted by Sahib View Post
    At higher voltage than AC, of course.
    Actually, it's the opposite. DC through the heart is more dangerous than AC.
    Cheers and Stay Safe,

    Marky the Sparky

  8. #8
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    Quote Originally Posted by meternerd View Post
    As stated...it's all about current through the body. Higher the voltage, higher the current if you make yourself a circuit. It takes about 0.1 amps to kill, so do the math. But, can you get electrocuted grabbing onto a 12V car battery? YUP! If your hands are sweaty, have acid on 'em and you have a large enough surface area due to the tool you're holding onto. DC is supposedly more dangerous because it is better at sending the heart into fibrillation. All of this is based on our regular safety meetings, though. I'm no Dr. Frankenstein.
    Can you show me a single incident where a person was electrocuted by a 12 volt car battery?
    Cheers and Stay Safe,

    Marky the Sparky

  9. #9
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    Quote Originally Posted by K8MHZ View Post
    DC through the heart is more dangerous than AC.
    A defibrillator sends DC through heart to revive cardiac arrest patients.

  10. #10
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    Quote Originally Posted by Sahib View Post
    A defibrillator sends DC through heart to revive cardiac arrest patients.
    Those patients have afib and the DC is in measured pulses of around 5ms. That is totally different from the effects of steady current DC on a healthy person.
    Cheers and Stay Safe,

    Marky the Sparky

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