The PTC will do its job of clamping the voltage above that when required.
The MOV is not a requirement, but an additional protection, to back up the PTC.
Actually this is no quite right.
There is no scenario where you will get high voltage transients on the current ranges.
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If you measure current in series within a mains circuit, with high voltage transients present, the voltage will be low across the meter and the fuse will rupture if the current goes high for long enough (doubtful with short transients).
But after the fuse ruptures, whether because of a transient spike in current or an ordinary continuous non-transient overcurrent situation, or some combination, won't the entire voltage of any subsequent transient be present across the fuse? If not, where is the transient voltage going?
I'm certainly not an expert on CAT ratings or testing, but I wonder, if you expect 8000V transients to be present on your mains, how can you be sure they won't ever be imposed across a meter measuring current through those mains?
Well in a case of a transient while measuring the transient also will be present across the fuse .
The 8000 V is the pretended voltage of the IEC 61010 that a multimeter has to withstand without danger the operator of the multimeter in CAT IV 600 V . Well that is not far-fetched , it is a summary of experiences from experts . Here is an example : Some electricians from a overhauling company for subways measured the voltage on the bar where the railcars of the subways are getting the feeding for control reasons . After some time one and another multimeter suddenly died . They are really wondering about that because there is roundabout 800 v dc on the rail and that should not be the problem . But the problem are the transients , they reached 9000 V and they killed the multimeters after a short time
The PTC will do its job of clamping the voltage above that when required.
The MOV is not a requirement, but an additional protection, to back up the PTC.
Actually this is no quite right.If I remember correctly, the MOV is acting faster than the PTC, relieving some of the high voltage, while the PTC is busy heating up to eventually clamp the current flowing into the meter. That's what I meant as back up.
One thing that sticks out to me is that if you really want to be sure, as sure as you can be, that the manufacturer is building meters to the right standards, then you have to check a few things.
#1. Do they have a valid and current ISO900X approval and no violations? This is to ensure that they actually make things the same way every time and don't change their methods without a notification and paper trail.
#2. Do they have a proper third party certification, like UL, to show that their designs and construction methods actually meet the ratings they assert? Do they have a clause in the procedures, as listed with their ISO certification, that demand a new third party testing anytime a new part or change in design is implemented anytime it is different from the originally tested configuration?
#3. Can you find and read a record of their ISO certification and current status?
#4. Can you find a record of their third party testing/certification for compliance to the standard they mark on their meter?
#5. Is the third party certifying lab also ISO certified and can you find their records?
As you can see, the average consumer does not have the resources nor time, and probably not the education, to know what to look for or even where to look. This is assuming an educated consumer. What about all the "noobs" and people who assume too many things? This is where Dave's review and the rantings and opinions of others can help. We try to educate. It is up to the individual to assume their own risk. It is not up to the company selling them something to assume that the buyer knows the risk and understands that the product they have purchased is labelled with lies that could kill them.
In the ideal world, everyone would treat everyone with respect and help ensure each others safety.
In the real world, companies take your money and hope you don't complain or find out they have taken you money based on lies. When some companies in China started putting melamine in baby food to artificially boost the protein content test results, it didn't seem to matter to them that they will literally killing babies to make a bigger profit. The occasional injury or death from wrongly marked multimeters in a few million users world wide probably means nothing in the big scheme of their profits. Most people probably get these injuries or problems and don't know what happened, or have no recourse.
The PTC will do its job of clamping the voltage above that when required.
The MOV is not a requirement, but an additional protection, to back up the PTC.
Actually this is no quite right.If I remember correctly, the MOV is acting faster than the PTC, relieving some of the high voltage, while the PTC is busy heating up to eventually clamp the current flowing into the meter. That's what I meant as back up.
PTCs do not clamp voltage, period. That is the problem with your statement. PTCs limit current.
The PTC will do its job of clamping the voltage above that when required.
The MOV is not a requirement, but an additional protection, to back up the PTC.
Actually this is no quite right.If I remember correctly, the MOV is acting faster than the PTC, relieving some of the high voltage, while the PTC is busy heating up to eventually clamp the current flowing into the meter. That's what I meant as back up.
PTCs do not clamp voltage, period. That is the problem with your statement. PTCs limit current.As the 1KOhm PTC resistance increases as it heats up, the voltage drop across it increases too, so it does clamp the voltage seen by the circuit in the DMM.
Hmmm, I don't remember for all of them. I will have to repeat my tests on video!
Actually I don't think I will. I don't want to potentially destroy all those meters on a test they aren't rated to survive.
You obviously missed the story earlier in the thread of the electrician and some people standing close who died because of a falsely rated meter. Or the story of the electrical workers who had meters dying on them mysteriously because they hadn't received proper training.Not all countries have rules about house owners not touching their electrical distribution boxes.
Never underestimate stupid, or at least ignorance. wavy lines wavy lines
wavy lines wavy linesAnother story of the same house, after removing a breaker with a visible trace of a cable to it, I was ready to cut the cable. A surprise "hit" me as the cable was still hot. I followed the cable branches back still further, and found that it was fed by another breaker on the same phase, in the ON position. A loop circuit. Needless to say I check & double check never trusting what should or shouldn't be, as it CAN be.
So, never say never, sometimes ignorance or sheer stupidity can be laughable or deadly.
You obviously missed the story earlier in the thread of the electrician and some people standing close who died because of a falsely rated meter...