Fluke 289 v 87V

[jhsellers]

I bought 4 of those Harbor Freight meters for my inverter training classes. The sole intent was for using the diode scale to test Diodes, SCRs and IGBTs in the class room. I told people I didn't trust the meters for high voltage. One person took one out to the lab and put it on a 480v bus. When he changed the range switch from 200 to 700 VAC it exploded. No one got hurt. I threw them in the trash after I mangled them so no one else would try to use them.

Arc flash - the meter range switch was not rated to interrupt the available fault duty on that 480VAC circuit. More electrical accidents are now attributed to arc flash (burn hazard) than they are to shock hazard.

This was my career - analyzing distribution systems for available fault duty, and evaluating equipment to verify it was rated for both withstand and interrupting capacity to break said fault current, should a mishap occur. Both the fault magnitude and clearing time can be used to estimate the expected incident energy (heat) that would be imposed on a worker (at nominal 18-inch working distance) should a fault be initiated. This incident heat energy can cause a serious burn, not to mention the blast that is created. Ongoing testing is still happening (ref. IEEE) to further quantify both the incident heat energy and the blast pressure. (The blast pressure energy occurs because vaporizing copper (solid-to-gas) will expand to roughly 67,000 times normal volume when heated by the fault current.... we're still not able to estimate blast pressure; too many variables.)

Just a bit of trivia,
John

 

[laatsch55]

Cool stuff John...thanks..

 

[Travis Henley]

Arc flash - the meter range switch was not rated to interrupt the available fault duty on that 480VAC circuit. More electrical accidents are now attributed to arc flash (burn hazard) than they are to shock hazard.

This was my career - analyzing distribution systems for available fault duty, and evaluating equipment to verify it was rated for both withstand and interrupting capacity to break said fault current, should a mishap occur. Both the fault magnitude and clearing time can be used to estimate the expected incident energy (heat) that would be imposed on a worker (at nominal 18-inch working distance) should a fault be initiated. This incident heat energy can cause a serious burn, not to mention the blast that is created. Ongoing testing is still happening (ref. IEEE) to further quantify both the incident heat energy and the blast pressure. (The blast pressure energy occurs because vaporizing copper (solid-to-gas) will expand to roughly 67,000 times normal volume when heated by the fault current.... we're still not able to estimate blast pressure; too many variables.)

Just a bit of trivia,
John

Cool John....So were you in Safety and Health or Protection and Control? I was the dude that would receive the exploded meter and analyze exactly what happened to cause the event and develop a procedure and equipment recommendation to insure that it never happened again. I was the Lab Tech nerd.

 

[laatsch55]

I work with hi amperage 480 in the oilfield everyday....and I have had a few "arc flash" events...

 

[Travis Henley]

I work with hi amperage 480 in the oilfield everyday....and I have had a few "arc flash" events...

Serious business.....ive seen coworker leave this planet from a flash.....burnt bad....i mean bad. I worked for the utility company. Y'all stay safe.

 

[laatsch55]

I've seen a guys arm blown off with 4160 and watched him bleed out....not a good thing. I don't mess with anything over 480, except on some hi horsepower electrical submersible pumps that run between 2500-3200 volts, and then I just set transformer taps..

 

[jhsellers]

Cool John....So were you in Safety and Health or Protection and Control? I was the dude that would receive the exploded meter and analyze exactly what happened to cause the event and develop a procedure and equipment recommendation to insure that it never happened again. I was the Lab Tech nerd.

I was in division engineering - building products manufacturing (lumber, plywood, OSB, gypsum); we did everything from power distribution down to plant control. Most of my colleagues were SMEs for process control (programmable logic controllers, distributed control systems), but my focus was plant distribution. Most of our plants have electrical service at the 15kV level; a few took drops from transmission lines at 125kV. We would have one main plant transformer, a medium voltage (MV) switchgear lineup, and one (or a few) feeder circuits to a dozen or so distribution transformers - sized from 1MVA up to 2.5MVA; secondaries at 480V, with low voltage switchgear (LV) to MCC lineups. Our sister division (pulp and paper) used MV motors (2.4kV, or 5kV) where synchronous speeds were required - refiners, vacuum pumps, ball mills, etc. - but building products doesn't use many large motors (>200HP), and most of those are on VFDs, so we rarely use MV transformers for motor control. (predominantly, VFDs are built for LV use - up to 1000HP or so) I spent most of my time on distribution analysis or motor control design.

Thanks for the interest,
And, BTW, I use one of the cheaper Flukes - a 117, I think. (got tired of the really cheap ones going tits up....)
John

 

[Travis Henley]

I was in division engineering - building products manufacturing (lumber, plywood, OSB, gypsum); we did everything from power distribution down to plant control. Most of my colleagues were SMEs for process control (programmable logic controllers, distributed control systems), but my focus was plant distribution. Most of our plants have electrical service at the 15kV level; a few took drops from transmission lines at 125kV. We would have one main plant transformer, a medium voltage (MV) switchgear lineup, and one (or a few) feeder circuits to a dozen or so distribution transformers - sized from 1MVA up to 2.5MVA; secondaries at 480V, with low voltage switchgear (LV) to MCC lineups. Our sister division (pulp and paper) used MV motors (2.4kV, or 5kV) where synchronous speeds were required - refiners, vacuum pumps, ball mills, etc. - but building products doesn't use many large motors (>200HP), and most of those are on VFDs, so we rarely use MV transformers for motor control. (predominantly, VFDs are built for LV use - up to 1000HP or so) I spent most of my time on distribution analysis or motor control design.

Thanks for the interest,
And, BTW, I use one of the cheaper Flukes - a 117, I think. (got tired of the really cheap ones going tits up....)
John

That sounds like enough of a job for 5 or 6 people...at least. Thanks for elaborating.

 

[J!m]

If I had known that, I’d use one to test the ignition spark module I just repaired on Monday.

I would have filmed it too! I estimate the output voltage is over 5000 volts AC to jump the gap in the plasma gun to start the arc. But that is based on spark gap in air, not argon. It’s probably lower in the noble gas but it will ignite on nitrogen too.