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I would assume the currents and voltages produced by a consumer grade multimeter (testing electrical resistance) would not be large enough to produce any danger of natural gas combustion. But I was curious if CSST piping in my home was electrically bonded across its fittings to the manifold (and from the manifold to the black iron gas pipes). As there is conflicting information on the internet about where it is necessary to bond yellow CSST piping (one clamp on the manifold vs one clamp on the fitting for each run of CSST piping).

However, I could not find information online about the safety of using a multimeter in this way, and as I don't fully understand the exact mechanics of how a multimeter measures electrical resistance, I figured I shouldn't just try it, even though I'd assume it's likely fine, and that things are in the millivolt and milliamp range. I've also seen situations where multimeters behaved in unexpected ways and arc flashed, but I think that mostly involves cheap meters and mains voltages.

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  • From the 2021 Oregon specialty plumbing code: "The bonding jumper shall connect to a metallic pipe, pipe fitting, or CSST fitting. [NFPA 54:7.12.2.1]"
    – Armand
    Sep 15, 2022 at 6:49
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    A relevant previous question on the site: diy.stackexchange.com/questions/221839/…
    – Armand
    Sep 15, 2022 at 6:52
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    The incidents you saw likely involved setting the multimeter to current mode and then connecting it to mains voltage. Sep 15, 2022 at 18:56

3 Answers 3

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you can't set the gas inside the pipes on fire, and unless there's a leak there shouldn't be any gas outside the pipes.

The test is safe, most multimetes test resistance at very low power. but a multimeter resistance test is probably not sufficient to be sure that the ground bonding is good, but it will in many instances detect deficient ground bonding.

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  • Understandable! Could you expound on what additional tests would be sufficient to confirm proper bonding?
    – brubsby
    Sep 15, 2022 at 16:45
  • you use a ground bonding tester, a device costing several thousand dollars.
    – Jasen
    Sep 15, 2022 at 20:00
  • Just splitting hairs for fun (I do not wish to buy or rent a ground bonding tester). But a ground bonding tester in this situation would probably be unsafe to use, at the very least until the gas lines were evacuated, as its improved stringency comes from (and I may be wrong) the larger amount of current that would likely melt and possibly arc across points of weak continuity? In addition, the stringency also comes from testing the capacitance and induction of the system?
    – brubsby
    Sep 16, 2022 at 15:30
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Yes, this is safe. A multimeter on resistance mode doesn't put out enough voltage to cause a spark even under the most extreme circumstances.

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As @percynthion wrote, doing a resistance check cannot put out enough voltage to cause a spark.

However, first check for AC voltage. If you have a bad ground and no bond, there could already be AC voltage there. Such voltage could damage your multimeter when checking resistance.

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  • Having 120 Volt on the gas line would be EOL
    – Traveler
    Sep 15, 2022 at 6:16
  • @Ruskes Not necessary full 120 volts. A poor ground giving 20 volts AC would be plenty to fry a multimeter set to measure resistance.
    – DoxyLover
    Sep 15, 2022 at 7:06
  • Only if gas lines are used as grounding rod
    – Traveler
    Sep 15, 2022 at 8:05
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    @doxylover, only cheap brands. quality brands can withstand hundreds of unexpected volts during a resistance test.
    – Jasen
    Sep 15, 2022 at 12:20
  • i 2nd jasen on that, i've accidently measured the resistance of live mains, which for the curious read "OL"...
    – dandavis
    Sep 16, 2022 at 20:53

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