Author Topic: DMM Lead Arc getting voltage from power strip  (Read 6185 times)

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Offline DW1961Topic starter

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DMM Lead Arc getting voltage from power strip
« on: July 25, 2020, 08:10:23 pm »


I was checking voltage at a power strip and had an arc that partially melted the tip of my lead (It put a little melt point on it). I may have inadvertently had it on DC voltage. Would that cause an arc, or just an out of range signal on the LED? It's a good way to ruin leads, so I don't want to repeat that if possible.
 

Online Gyro

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Re: DMM Lead Arc getting voltage from power strip
« Reply #1 on: July 25, 2020, 08:25:13 pm »
It seems more likely that you had the meter on a (possibly mA) current range and the brief arc occurred before the meter fuse blew. What meter is it? Does it have separate terminals for the current ranges, or are the mA ranges shared with the voltage ranges (i.e. does it have 3 input jacks or 4)?

It sounds as if you were lucky!
Best Regards, Chris
 

Offline paul8f

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Re: DMM Lead Arc getting voltage from power strip
« Reply #2 on: July 25, 2020, 08:25:37 pm »
Did you have the red banana plug connected to the A or 10A terminal of the DMM by mistake?

If you did, the internal fuse will have done its job, and will be blown. On most DMMs, this will happen regardless of what function you had the dial set to.
 

Offline DW1961Topic starter

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Re: DMM Lead Arc getting voltage from power strip
« Reply #3 on: July 25, 2020, 09:31:15 pm »
It seems more likely that you had the meter on a (possibly mA) current range and the brief arc occurred before the meter fuse blew. What meter is it? Does it have separate terminals for the current ranges, or are the mA ranges shared with the voltage ranges (i.e. does it have 3 input jacks or 4)?

It sounds as if you were lucky!

You just put it on Volts or Amps, and then the SEL button functions as the DC /AC switch. You can also set the decimal readout with RAN button.
The meter still works. It only has two inputs. Here's a picture and link:
https://www.amazon.com/gp/product/B087JMPTRF/ref=ask_ql_qh_dp_hza
« Last Edit: July 25, 2020, 09:33:58 pm by DW1961 »
 

Offline DW1961Topic starter

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Re: DMM Lead Arc getting voltage from power strip
« Reply #4 on: July 25, 2020, 09:35:46 pm »
Did you have the red banana plug connected to the A or 10A terminal of the DMM by mistake?

If you did, the internal fuse will have done its job, and will be blown. On most DMMs, this will happen regardless of what function you had the dial set to.

No Amp plug. I could have had the dial on Amps, which could have created a short, so yeah, maybe. Would having the meter on DC while trying to measure AC do anything except produce an out of range OL reading?
 

Offline DW1961Topic starter

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Re: DMM Lead Arc getting voltage from power strip
« Reply #5 on: July 25, 2020, 09:36:33 pm »
It seems more likely that you had the meter on a (possibly mA) current range . . .

That only produces an OL reading.
 

Online Gyro

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Re: DMM Lead Arc getting voltage from power strip
« Reply #6 on: July 25, 2020, 09:41:04 pm »
Hmmm. From the description it looks as if the current range is only on the clamp jaws (AC only).

It looks as if you might either need to read them manual more carefully in case there are certain button selections that you need to make before measuring voltage, or the design has 'issues'. :-\

There's no way it should arc, even if the Cat II 600V/ Cat III 300V rating is fake!


P.S. Actually, if there is no current range on the jacks and you have to push soft buttons to read voltage, then it has issues anyway!
« Last Edit: July 25, 2020, 09:46:14 pm by Gyro »
Best Regards, Chris
 

Offline DW1961Topic starter

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Re: DMM Lead Arc getting voltage from power strip
« Reply #7 on: July 25, 2020, 09:50:52 pm »
Hmmm. From the description it looks as if the current range is only on the clamp jaws (AC only).

It looks as if you might either need to read them manual more carefully in case there are certain button selections that you need to make before measuring voltage, or the design has 'issues'. :-\

There's no way it should arc, even if the Cat II 600V/ Cat III 300V rating is fake!


P.S. If there is no current range on the jacks and you have to push soft buttons to read voltage, then it has issues anyway!


That's correct. The main function is of an AC current tool.  It's the type you don't need to change Amp plugs. All the buttons do is change between DC and AC, just like a dial indicator would do.

Set it to Current, and it measure AC current ONLY down to 1mA. I tested that last night using separate zip cord plugged into a lamp pulling 9 watts from the LED bulb. It did it!

The RAN function just changed the decimals.

SEL button changes  between DC and AC voltage.

SEL button changes between diode and continuity.

That's it. very simple.
« Last Edit: July 25, 2020, 10:07:01 pm by DW1961 »
 

Offline DW1961Topic starter

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Re: DMM Lead Arc getting voltage from power strip
« Reply #8 on: July 25, 2020, 09:55:55 pm »
Did you have the red banana plug connected to the A or 10A terminal of the DMM by mistake?

If you did, the internal fuse will have done its job, and will be blown. On most DMMs, this will happen regardless of what function you had the dial set to.

The fuse (if it has one) didn't blow. It still measure AC and DC voltage. I just checked the current function and it works too.
« Last Edit: July 25, 2020, 10:06:04 pm by DW1961 »
 

Offline DW1961Topic starter

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Re: DMM Lead Arc getting voltage from power strip
« Reply #9 on: July 25, 2020, 10:03:41 pm »
Since you're all here, a couple of other things I was wondering about:

1. When I use continuity and touch the leads together I still get .2. If I use my other leads, I get 000. Does this mean the leads are introducing resistance?


I wanted to calibrate my soldering station or at least see if the temp is accurate, so I got this meter because it had a temperature and prob function.

However, the prob is just a wire with a little bead on it.

1033010-0


I think it would just melt if I tried to test my iron. So, I'm bummed about that. I should have paid closer attention to the description and pictures.  I still need to review it. I've compared it with my other Amazon multimeter for voltage AC/DC and it's right in line, and the temp was compared to a calibrated food probe. The meter reads about 1.8-2 F higher. I've asked on Amaozn if the unit is fused or not.

Other than that, the outside and function of the unit is solid. The dial is nice and positive, the unit is heavy, the clamp is strong, and the ABS is really thick on it.

Other than the temp probe, I have no use for it really.
« Last Edit: July 28, 2020, 05:13:16 pm by DW1961 »
 

Offline helius

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Re: DMM Lead Arc getting voltage from power strip
« Reply #10 on: July 25, 2020, 10:24:17 pm »
The "wire with a little bead on it" is a K-type thermocouple wire. It is designed for high-temperature use and isn't going to just melt (although the heatshrink could).

Multimeter fuses are for protecting the current shunt, they do not do anything to the volt measurements and those still work after the fuse blows.
If your meter only reads AC amps using the clamp, it is unlikely to have any fuse.
 

Offline DW1961Topic starter

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Re: DMM Lead Arc getting voltage from power strip
« Reply #11 on: July 26, 2020, 12:21:06 am »
The "wire with a little bead on it" is a K-type thermocouple wire. It is designed for high-temperature use and isn't going to just melt (although the heatshrink could).

Multimeter fuses are for protecting the current shunt, they do not do anything to the volt measurements and those still work after the fuse blows.
If your meter only reads AC amps using the clamp, it is unlikely to have any fuse.

Great information. I appreciate you taking the time to share that information. It's very interesting to me.  I see because the Clamp Meter is not a part of the circuit, so there is no danger of shorting it. Again, thanks a lot for that information. Read up a little on the K Thermo material, etc. Much thanks again.


Is there anyway I can modify it to work as a temp probe for my soldering iron?
« Last Edit: July 26, 2020, 04:49:13 am by DW1961 »
 

Offline TheMG

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Re: DMM Lead Arc getting voltage from power strip
« Reply #12 on: July 26, 2020, 01:07:41 am »
I was checking voltage at a power strip and had an arc that partially melted the tip of my lead (It put a little melt point on it). I may have inadvertently had it on DC voltage. Would that cause an arc, or just an out of range signal on the LED? It's a good way to ruin leads, so I don't want to repeat that if possible.

That multimeter does not have any current measuring function on the banana jacks. Thus, you should NEVER under any circumstance get any kind of arc from the leads, no matter which function you have selected! Any half decent DMM should be able to handle its full voltage rating on any voltage range, AC or DC, ohms, continuity, diode check, and any other mode it has, without any damage to the DMM itself or the leads.

Basically this means your DMM is a piece of junk. It's either defective or poorly designed. You get what you pay for.
 

Offline DW1961Topic starter

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Re: DMM Lead Arc getting voltage from power strip
« Reply #13 on: July 26, 2020, 02:08:00 am »
I was checking voltage at a power strip and had an arc that partially melted the tip of my lead (It put a little melt point on it). I may have inadvertently had it on DC voltage. Would that cause an arc, or just an out of range signal on the LED? It's a good way to ruin leads, so I don't want to repeat that if possible.

That multimeter does not have any current measuring function on the banana jacks. Thus, you should NEVER under any circumstance get any kind of arc from the leads, no matter which function you have selected! Any half decent DMM should be able to handle its full voltage rating on any voltage range, AC or DC, ohms, continuity, diode check, and any other mode it has, without any damage to the DMM itself or the leads.

Basically this means your DMM is a piece of junk. It's either defective or poorly designed. You get what you pay for.

I didn't pay for it. It was free. The product description says it will measure down to 1mA AC current. I put a 12W bulb in a fixture and used the clamp. My volts are right at 120V. It did it.

It measured exactly .101 amp.



« Last Edit: July 26, 2020, 04:48:06 am by DW1961 »
 

Offline DW1961Topic starter

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Re: DMM Lead Arc getting voltage from power strip
« Reply #14 on: July 26, 2020, 04:52:09 am »
The "wire with a little bead on it" is a K-type thermocouple wire. It is designed for high-temperature use and isn't going to just melt (although the heatshrink could).

If your meter only reads AC amps using the clamp, it is unlikely to have any fuse.

Just got this back from teh Amazon merchant:

"I received this replay back fro the seller on Amazon, for what it's worth. He is saying it has both current and voltage fuses in it:

"Our products are equipped with professional voltage and current fuses. In case of misoperation and exceeding the maximum voltage/current range, the fuse will be blown first, and then the circuit board will be destroyed."

F-it! I can tear it apart and see if it really does?! It might be interesting. If it has fuses, I'm assuming it has a way to change them. I'll ask the merchant.
 

Offline bdunham7

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Re: DMM Lead Arc getting voltage from power strip
« Reply #15 on: July 26, 2020, 05:07:37 am »

"Our products are equipped with professional voltage and current fuses. In case of misoperation and exceeding the maximum voltage/current range, the fuse will be blown first, and then the circuit board will be destroyed."


Oh dear.  A teardown should be interesting.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 
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Online coppercone2

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Re: DMM Lead Arc getting voltage from power strip
« Reply #16 on: July 26, 2020, 07:35:36 am »
I have seen non obviously destructive sparks (high end meter must have had the protection circuit work) when contact was made with probes on the probe/board junction when using a DMM on voltages higher then its rating on the correct mode (i.e. 2kv). I think maybe it made LESSER sparks near the upper limit of its range.

obviously a mistake (similar equipment but they raised the voltage level between models that had near identical circuit topology/components)
« Last Edit: July 26, 2020, 07:41:23 am by coppercone2 »
 
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Online Gyro

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Re: DMM Lead Arc getting voltage from power strip
« Reply #17 on: July 26, 2020, 11:48:16 am »
The "wire with a little bead on it" is a K-type thermocouple wire. It is designed for high-temperature use and isn't going to just melt (although the heatshrink could).

If your meter only reads AC amps using the clamp, it is unlikely to have any fuse.

Just got this back from teh Amazon merchant:

"I received this replay back fro the seller on Amazon, for what it's worth. He is saying it has both current and voltage fuses in it:

"Our products are equipped with professional voltage and current fuses. In case of misoperation and exceeding the maximum voltage/current range, the fuse will be blown first, and then the circuit board will be destroyed."

F-it! I can tear it apart and see if it really does?! It might be interesting. If it has fuses, I'm assuming it has a way to change them. I'll ask the merchant.

Yep, they're talking complete bollocks.  ::)

DMMs use VDRs and PTC thermistors for voltage ranges, and those only come into play when it is subjected to gross overload.

It will be using a current transformer for the current jaws (hence AC only), but it's easy to clamp the high impedance current output - actually a fuse opening on the output [Ed: of the] transformer would turn it into a very high internal voltage source!

I'd return it as defective - only do a teardown if you don't have to break any seals and hide the serial number. Try to find one that isn't manufactured by "RockSeed"  ;)


P.S. A reputable supplier would apologise for melting the end of your probe, scaring the life out of you, and ask you to return it for urgent investigation - not burble on about its mythical fuses.
« Last Edit: July 26, 2020, 12:30:20 pm by Gyro »
Best Regards, Chris
 

Offline tooki

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Re: DMM Lead Arc getting voltage from power strip
« Reply #18 on: July 26, 2020, 12:37:08 pm »


I was checking voltage at a power strip and had an arc that partially melted the tip of my lead (It put a little melt point on it). I may have inadvertently had it on DC voltage. Would that cause an arc, or just an out of range signal on the LED? It's a good way to ruin leads, so I don't want to repeat that if possible.
Given that the jacks don’t do current measurement, then the most likely explanation is that you inadvertently shorted the probe tips. Either to each other, or across line and ground (since the neutral and ground are connected back at the panel).
 
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Offline helius

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Re: DMM Lead Arc getting voltage from power strip
« Reply #19 on: July 26, 2020, 01:03:28 pm »
Given that the jacks don’t do current measurement, then the most likely explanation is that you inadvertently shorted the probe tips. Either to each other, or across line and ground (since the neutral and ground are connected back at the panel).
This is the most likely answer  :-+
I've had this happen when probing the starter socket of a fluorescent desk lamp. Any time you measure terminals that are close together (and the wires in a power strip can be much closer than is evident from the outside) this can happen. It's good to learn how to use the probe tip insulators if you measure such things.  :-BROKE
« Last Edit: July 26, 2020, 01:05:15 pm by helius »
 
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Offline TheMG

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Re: DMM Lead Arc getting voltage from power strip
« Reply #20 on: July 26, 2020, 04:53:43 pm »
Given that the jacks don’t do current measurement, then the most likely explanation is that you inadvertently shorted the probe tips. Either to each other, or across line and ground (since the neutral and ground are connected back at the panel).

That would be pretty difficult to do on a north american receptacle. The slots for live and neutral are very narrow, in fact the probes on most DMMs insert very snug into them, which doesn't allow for any side-to-side movement of the probes so there's no way you'd be able to short the probes to each other, at least not without bending them.

It is possible however on poorly made power strips if the probes are relatively long for the probe to poke past the back of the receptacle and through the insulation of a wire, or a grounded chassis, but this would be rather unusual as most DMM probes are not much longer than a standard plug end.
 
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Offline DW1961Topic starter

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Re: DMM Lead Arc getting voltage from power strip
« Reply #21 on: July 26, 2020, 07:08:53 pm »


I was checking voltage at a power strip and had an arc that partially melted the tip of my lead (It put a little melt point on it). I may have inadvertently had it on DC voltage. Would that cause an arc, or just an out of range signal on the LED? It's a good way to ruin leads, so I don't want to repeat that if possible.
Given that the jacks don’t do current measurement, then the most likely explanation is that you inadvertently shorted the probe tips. Either to each other, or across line and ground (since the neutral and ground are connected back at the panel).

You mean by pushing the leads into the power strip receptacle and shorting it on the ground in the receptacle?
 

Offline DW1961Topic starter

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Re: DMM Lead Arc getting voltage from power strip
« Reply #22 on: July 26, 2020, 07:15:09 pm »
Given that the jacks don’t do current measurement, then the most likely explanation is that you inadvertently shorted the probe tips. Either to each other, or across line and ground (since the neutral and ground are connected back at the panel).

That would be pretty difficult to do on a north american receptacle. The slots for live and neutral are very narrow, in fact the probes on most DMMs insert very snug into them, which doesn't allow for any side-to-side movement of the probes so there's no way you'd be able to short the probes to each other, at least not without bending them.

It is possible however on poorly made power strips if the probes are relatively long for the probe to poke past the back of the receptacle and through the insulation of a wire, or a grounded chassis, but this would be rather unusual as most DMM probes are not much longer than a standard plug end.

The lead tip is about 3/16th longer than the plug spade. I was having a hard time getting a reading in the power strip. I do remember that and it was not like doing it in a wall receptacle, so maybe I did ground it out. It's a very good explanation.
 

Offline DW1961Topic starter

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Re: DMM Lead Arc getting voltage from power strip
« Reply #23 on: July 26, 2020, 07:18:22 pm »
The "wire with a little bead on it" is a K-type thermocouple wire. It is designed for high-temperature use and isn't going to just melt (although the heatshrink could).

If your meter only reads AC amps using the clamp, it is unlikely to have any fuse.

Just got this back from the Amazon merchant:

"I received this replay back fro the seller on Amazon, for what it's worth. He is saying it has both current and voltage fuses in it:

"Our products are equipped with professional voltage and current fuses. In case of misoperation and exceeding the maximum voltage/current range, the fuse will be blown first, and then the circuit board will be destroyed."

F-it! I can tear it apart and see if it really does?! It might be interesting. If it has fuses, I'm assuming it has a way to change them. I'll ask the merchant.

Yep, they're talking complete bollocks.  ::)

DMMs use VDRs and PTC thermistors for voltage ranges, and those only come into play when it is subjected to gross overload.

It will be using a current transformer for the current jaws (hence AC only), but it's easy to clamp the high impedance current output - actually a fuse opening on the output [Ed: of the] transformer would turn it into a very high internal voltage source!

I'd return it as defective - only do a teardown if you don't have to break any seals and hide the serial number. Try to find one that isn't manufactured by "RockSeed"  ;)


P.S. A reputable supplier would apologise for melting the end of your probe, scaring the life out of you, and ask you to return it for urgent investigation - not burble on about its mythical fuses.

It was free.

What do you think? Tear down? IF it doesn't have any fuses, then they need to be called on that.
« Last Edit: July 28, 2020, 05:13:49 pm by DW1961 »
 

Offline joeqsmith

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Re: DMM Lead Arc getting voltage from power strip
« Reply #24 on: July 26, 2020, 07:59:54 pm »
My guess is you had it in the ohms function.  This will engage the PTC and low voltage clamp and I wouldn't be at all surprised if it caused a small spark.   You would be looking at somewhere around a 3Kohm load across the line until the PTC heats up.   The low voltage clamp is typically less than 20V and won't make much of a difference.  It shouldn't damage the meter but I don't recommend playing with the line. 

In the voltage mode, I wouldn't expect the meter to start to have any effect until you reach what ever the MOVs start to conduct (assuming the meter even has them).   


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