High Impedance Protected Test Points for 115 VAC

[JuliaTruchsess]

FWIW, EN61010 requires "touch current" be limited to 500uArms, and EN62368 to 250uArms. Whatever standard applies to your equipment should specify it as well. A resistor is sufficient (but needs to be rated for the voltage involved, of course).

 

[petersonra]

To expand on your reply, we CAN just make these things ourselves because we are the OEM of the equipment. We get paid to design, build, test, and service our equipment. Rest assured, we will research and test this setup extensively and I'm sure we will eventually get into what the UL requires even though our customer does not require UL testing. This thread was just asking if anyone else has already done this research in an effort to save me a lot of time which saves the US citizens tax dollars.

If an end user in the USA wants to use them they have to be made to the appropriate UL standard and listed by UL. Maybe on a ship designing to a recognized standard does not matter but it does on shore here.

 

[4x4dually]

If an end user in the USA wants to use them they have to be made to the appropriate UL standard and listed by UL. Maybe on a ship designing to a recognized standard does not matter but it does on shore here.

Ships involved have "U.S.S" in front of their name. This is not consumer stuff.

FWIW, EN61010 requires "touch current" be limited to 500uArms, and EN62368 to 250uArms. Whatever standard applies to your equipment should specify it as well. A resistor is sufficient (but needs to be rated for the voltage involved, of course).

Thank you for that information. EN and UL specs are something we do not deal with on a regular basis.

 

[petersonra]

Ships involved have "U.S.S" in front of their name. This is not consumer stuff.

End user does not only mean consumer. OSHA rules generally require listing and apply to most employers.

US flagged vessels are probably subject to some kind of safety rules. I suspect that there is a similar requirement as far as listing or at least complying with a recognized standard goes for ship board use as OSHA requires for employers.

 

[winnie]

That's basically what it is. A voltage divider of the limiting resistor and the impedance of the meter. Did a little benchtop test on my desk the other day and 60K on each leg seems to give great results as calculated. They limit current to right at 1mA when dead shorted and to around .001mA when read with a meter.

I think that what @Open Neutral was suggesting is to incorporate both resistors into the testpoint, with the 'shunt' resistor having a low value so that it acts as a voltage divider.

The system that you've described has 2 resistors; the current limiting resistor and the extremely high (but often only approximately known) input impedance of the meter. This, of course, forms a voltage divider where the value 'seen' by the meter is perhaps 99% of the actual value.

@Open Neutral is saying intentionally create a voltage divider where you have a shunt resistor to ground of perhaps 600 ohms, forming a 101:1 voltage divider. This has the downside that the current limiting resistor is essentially _always_ shorted to ground. But it has the benefits of limiting the voltage on the probe point to a couple of volts, and reducing the 'burden' created by the meter; the meter is now forming a voltage divider with the 600 ohm shunt impedance, not the 60000 ohm current limiting impedance.

-Jonathan