DMM test probes!

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lanchile

lanchile

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Joined 2008
yes, safety is the most important thing ;) it is very important to use the right equipments too. I have seen cheap meters exploding on people faces:eek:
You should always use a RELIABLE meter. one example that happen to my friend a couple weeks ago:
He had a radio shack multimeter and when I saw it, I told him to be careful because I noticed that the meter was acting weird. Well time passed and one day He called me and said, Wooow! I just got shocked with 220 volts:eek: He literately flew across the room! What happen was, He was checking a water heater with his meter and meter showed that was "0" volts in the line....But the line was hot with 220v:eek::eek::eek:...the first thing He did was putting meter in the garbage where it belongs. Now He has a Fluke 177 multimeter;)
Safety first!!!! Make sure before you use your multimeter, check a "KNOWN" working outlet to make sure meter is working. High voltages (220v) can kill you easily:eek:
 
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dmills

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Joined 2008
There have been a few lethal arc flash incidents down to people using inappropriate test equipment or inappropriate probes (The good ones are fused with high breaking current fuses in the probes, most of the cheap ones are not).

Class III is probably ok for most domestic things, with the class IV stuff being better if you are dealing with really stiff supplies (Panel boards and the like).

Amongst industrial electricians there is a saying "In Fluke we trust", it is slightly unfair on the other test gear makers, but holds a grain of truth.

Regards, Dan.
 
lanchile

lanchile

Member
Joined 2008
dmills said:
There have been a few lethal arc flash incidents down to people using inappropriate test equipment or inappropriate probes (The good ones are fused with high breaking current fuses in the probes, most of the cheap ones are not).

Class III is probably ok for most domestic things, with the class IV stuff being better if you are dealing with really stiff supplies (Panel boards and the like).

Amongst industrial electricians there is a saying "In Fluke we trust", it is slightly unfair on the other test gear makers, but holds a grain of truth.

Regards, Dan.
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I would not recommend to use FUSED test leads!!! WHY? Well for safety reason of course! if you blow fuse in the test leads and you do not know:eek:..you can get a big surprise. I would NEVER use or recommend to use a fused test leads;)
 
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dmills

Member
Joined 2008
lanchile said:
if you blow fuse in the test leads and you do not know:eek:..you can get a big surprise. I would NEVER use or recommend to use a fused test leads;)
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That is why you have a 'proving unit' that you use before and after taking a high voltage measurement in order to ensure the meter and probes are functional.

Not fusing appropriately means that a fault in the meter (Say measuring that 400V three phase line on an ohms range and having a transent occur at just the wrong time) can result in the meters circuitry flashing over and huge currents flowing causing arc flash, shrapnel all that stuff (people have been killed).

Now granted these are concerns more when working with multi hundred KVA supplies rather then audio kit or domestic mains.

Regards, Dan.
 
lanchile

lanchile

Member
Joined 2008
dmills said:
That is why you have a 'proving unit' that you use before and after taking a high voltage measurement in order to ensure the meter and probes are functional.

Not fusing appropriately means that a fault in the meter (Say measuring that 400V three phase line on an ohms range and having a transent occur at just the wrong time) can result in the meters circuitry flashing over and huge currents flowing causing arc flash, shrapnel all that stuff (people have been killed).

Now granted these are concerns more when working with multi hundred KVA supplies rather then audio kit or domestic mains.

Regards, Dan.
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I have tested a Fluke 87v and 27FM with 480vac line in all ranges! You can not kill a Fluke multimeter like that:p Again, if you have a good multimeter (FLUKE) you will NEVER need a fused test lead;)
It is safer to use a good,safe, reliable meter without fused test leads than use a bad meter with fused test leads. if you apply big voltage to an unsafe, unreliable meter and switch to other ranges like ohms, continuity etc you will fry that meter with or without fused test leads. So the point here is as long as you have a good ,reliable, safe multimeter(Fluke) You will never need a fused test lead! if you see my other posts, you will see in the Fluke 27FM post a link for the input protection these meters have. Here is the link:http://www.youtube.com/watch?v=zUhnGp5vh60
 
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dmills

Member
Joined 2008
Personally I like a fused Cat III test lead set AND a Fluke (Fluke probes, type FTP1, which will all the instrument to indicate voltage even if the fuse blows)!

On the bench I go for agilent kit often as not, but for the toolbox where it might be subject to abuse and may end up being used on dagerous stuff, Flike every time.

In the UK the HSE Guidance GS-38 requires fused probes for current or voltage measuring instruments used by electricians.

Regards, Dan.
 
sofaspud

sofaspud

Member
Joined 2005
This thread is starting to sound like a commercial.


BTW...
Your friend's main problem wasn't his iffy meter, it was his disregard for safety precautions. Power should have been disconnected at the source before he went to sticking body parts where 220VAC was possible.
 
lanchile

lanchile

Member
Joined 2008
sofaspud said:
This thread is starting to sound like a commercial.


BTW...
Your friend's main problem wasn't his iffy meter, it was his disregard for safety precautions. Power should have been disconnected at the source before he went to sticking body parts where 220VAC was possible.
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it is not a commercial!:p it is to show and let those people know that are looking for a good multimeter and nice test leads that is NOT necessary to brake their bank to get the best they can get for their money....most the time people call it a "review";)

PS: Many times YOU HAVE to work with live voltages to troubleshoot...and if you have a crapy, unreliable multimeter and test leads, you can get a big surprise:eek:
 
lanchile

lanchile

Member
Joined 2008
AuroraB

AuroraB

Member
Joined 2001
Brian... banana plugs is still for sale... :)

Otherwise, there's something strange in these arguments. I've been in the ELN business for close to 40 years, and I've yet to see a fused standard multimeter probe. Specialty probes- yes, but standard-no. I even have a Fluke 20kV ( or is it 30kV) probe that is unfused. Basically all voltage measurements are made with resistive dividers in the meter.
I don't think I've seen a meter without an internal fuse, though - just can't remember ;-)

The main user error with multimeters, is measuring voltage with probes set for current input. Current is usually measured as the voltage drop over a small value resistor, which may do funny things when exposed to higher voltage. An independant test lab did a test with this situation, and all of the medium and higher quality meters survived withiut hickups - except for the internal fuse. One of the really cheap ones caught fire. This was at least 20 years ago.....
Basic user tip: make sure you DO KNOW WHAT YOU*RE DOING !!!
 
PedroDaGr8

PedroDaGr8

Member
Joined 2009
AuroraB said:
Brian... banana plugs is still for sale... :)

Otherwise, there's something strange in these arguments. I've been in the ELN business for close to 40 years, and I've yet to see a fused standard multimeter probe. Specialty probes- yes, but standard-no. I even have a Fluke 20kV ( or is it 30kV) probe that is unfused. Basically all voltage measurements are made with resistive dividers in the meter.
I don't think I've seen a meter without an internal fuse, though - just can't remember ;-)

The main user error with multimeters, is measuring voltage with probes set for current input. Current is usually measured as the voltage drop over a small value resistor, which may do funny things when exposed to higher voltage. An independant test lab did a test with this situation, and all of the medium and higher quality meters survived withiut hickups - except for the internal fuse. One of the really cheap ones caught fire. This was at least 20 years ago.....
Basic user tip: make sure you DO KNOW WHAT YOU*RE DOING !!!
Click to expand...

This is very true. The fuse is pretty much NEVER in the test leads and the meter should almost always have a fuse. There are specialty cases where this isn't true but those are very seldom. For example, a few electricians meters which have a limited current range lack a fuse because the internal resistance is high enough they don't need one. That takes me to my next point, the fuse is ALWAYS on the current ranges while the voltage range will be unfused. The reason for this is that in most quality meters the voltage range has an input impedence on the order of 10MOhms or higher (my desktop meter lists the inpedence to be >10Gohms). While the 10A range on a meter maybe 10milliohms or less. Clearly, with this low of an impedence VERY significant currents can be generated if a user isn't careful (1V = 100A).

Next, about the fuses used. Glass fuses are NOT APPROPRIATE for use in a multimeter. The proper fuse is a high rupture capacity ceramic fuse. Glass fuses often can break currents up to around 100A (though when you exceed their rated voltage this number plummets down to 25A or less), whereas an HRC fuse is typically measured in kA or 10's of kA. Once this limit is breached, the fuse arcs over and its protection is functionally bypassed. Eventually (if not almost immediately) the fuse will explode which can damage the meter if not the user of the meter. Inductive loads and spike surges can easily surpass the capabilities of the cheap glass fuses.

The fuse is often one of a couple different features meant to protect the meter. Things like TVS diodes, PTCs, spark-gaps, etc. A properly deisgned meter will have a combination of these to properly protect the end user. If designed properly, the meter should withstand an multi-kV pulse and not allow any additional pulses. The exact value depends on the CAT rating of the meter.

EEVblog #84 - High Energy Multimeter Destruction - YouTube
 
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