On Tue, Dec 24, 2024 at 02:40 PM, Jim Shorney wrote:
<It shouldn't unless your Fluke has a metal case. There is no return path with a non-metallic enclosure so both you and the meter should be OK. What could cause damage would be the cold end resistor opening up. I've <had one of these probes for years. They used to be standard equipment in TV repair shops. Even given what I wrote above the only thing I touch when doing a measurement is the probe handle and I do not use a mains <powered meter.
<On Tue, 24 Dec 2024 04:52:04 -0800
<"Jim VE7RF via groups.io" <jim.thom@...> wrote:
<IF that return test lead ( that goes to the B- of the supply)? ever opened up / fell off....... the full B+ will then appear on the fluke 87 DVM.? This freaks me out.
--
<73
<-Jim
<NU0C
##? The HV probe just arrived yesterday.? ?They stipulate? that if the return lead goes open, yes, you will end up with full B+ on the return test lead.? ?You will also end up with full? B+ on both? the red / black test leads that plug into the fluke 87.? ?And if the cold end, (smaller 1.1 meg resistor) opens up, you will have full B+ on the red lead...that goes to the fluke 87 DVM.? They tell you to connect the grnd return lead 1st, then the dvm red / black leads, then turn on B+ supply, then attach the probe...last.?
Drawn out on paper, it's just a 1000 megohm resistor in series with a 1.1 megohm resistor...then the grnd return.? The V drop across the smaller resistor is applied to the DVM.? ? I measured? the resistance of the bigger resistor (Between tip of probe + RED test lead).? ?Then measured the smaller value resistor? ( between the red / black test leads).? ? Then the total resistance ( between probe tip and grnd return).?
Point is, you could have any of this stuff go open....... and think there is zero HV...... when actually there is HV present.? ? Mine came with 3 x different types of tips.? Tapered pointed type.? 2nd one is a looped hook.? ?3rd one is a angled flat metal piece, with an arc cut out.... made to engage the threads of machine screws.? ?The 2nd and 3rd types will never slip, or slide off, like the? 1st type.?
Using the power on, extra digit option on the fluke 87 DVM,? it will read down to 1 volt increments, like 2650, 2650 vdc etc.? ? Without the power on option, it reads in 10 V increments.?
It works good, but I would caution folks using them, to be very careful.??
Jim? ?VE7RF
