Big Clive's "Trashy" meter, unboxed ( Duratool D03047 multimeter )

[switchabl]

Cat. I 300V is a 1,500V impulse, Cat. I 600V 2,500V and there is no "500V" mains category.

That would be "overvoltage category I", not "measurement category I" which used to be defined in IEC 61010-1. The latter just means that the measured circuit is "not directly connected to mains". The necessary overvoltages ratings are supposed to be application-dependent and are supposed to be documented by the manufacturer.

EDIT: "There are no standard transient levels defined for these circuits. An analysis of the WORKING VOLTAGES, loop impedances, TEMPORARY OVERVOLTAGES, and TRANSIENT OVERVOLTAGES in these circuits is necessary to determine the insulation requirements and short-circuit current requirements."

[floobydust]

Duratool D03047 multimeter, suitable for mains measurements or not? 

[switchabl]

Well, assuming the CAT I label is not fake, so long as your mains is "not directly connected to mains", you should be fine. 

[Someone]

My home has a tiny little service coming into with a small distribution transformer.  Nothing like the feeds for the buildings where I worked.    Outlets at my house are several feet from the main feed and are behind small CBs which is behind another small one.  Worse thing that will happen if I pull and outlet and short the wires, I blow a breaker.  Hardly CAT III or risk of an arc flash.

So what's the supply impedance at those socket outlets?

I'll try and make a few measurements today with my tiny home wires.  I assume you will do the same so we have something to compare.  If not, I can measure some larger circuits.
...
I assume because we are talking commercial vs industrial, you want to keep this below 250V? Are you wanting any other metrics or just the impedance for the three legs?

I'm out of that work these days so don't have the instrumentation to hand. It would be very interesting to see just how high impedance can get on your "wimpy" installation. (over here the target end to end is less than 5% droop so there is an upper ceiling).

But as this keeps coming back to the same point, it will be possible to find all sorts of installations that will have prospective fault currents and robust voltage filtering/complex impedances that they could well be safely measured with a lower category meter. That is entirely expected since the standards have to cover worst case installations.

The "argument" is back to front, if people want to claim the category ratings are excessively strict then it is on them to show every installation meets their new criteria, on the other side I only need to show/find a single example at the limits to demonstrate they are sensible (quickly shown by the current capacity of residential feeds and GPO circuits with their associated maximum droop).

[Someone]

Duratool D03047 multimeter, suitable for mains measurements or not?

If you plugged that into mains power in Australia and something went wrong, it would be on you since the meter is not rated for that. That's going to be the same in most "developed" countries.

[David Aurora]

I turn the switch off before changing them, because I'm not a fucking idiot. To each their own though I guess 

What if it's a two (or three) way switch and you don't know if it's on or off? Do you rewire your house first?

If it was really a safety concern (which it's not, but I'll play along and pretend we're talking about a broken bulb where you need to grab the base or something) I'd flip the breaker or grab a chicken stick. I'm guessing this is the bit where you remind us you're a hero and you'd do it with your teeth because you're super tough and cool and physics don't apply to you?

Just to recap- THIS is the argument for why that meter is suitable for high voltage work? Because people change light bulbs? Cooooool.

[joeqsmith]

My home has a tiny little service coming into with a small distribution transformer.  Nothing like the feeds for the buildings where I worked.    Outlets at my house are several feet from the main feed and are behind small CBs which is behind another small one.  Worse thing that will happen if I pull and outlet and short the wires, I blow a breaker.  Hardly CAT III or risk of an arc flash.

So what's the supply impedance at those socket outlets?

I'll try and make a few measurements today with my tiny home wires.  I assume you will do the same so we have something to compare.  If not, I can measure some larger circuits.
...
I assume because we are talking commercial vs industrial, you want to keep this below 250V? Are you wanting any other metrics or just the impedance for the three legs?

I'm out of that work these days so don't have the instrumentation to hand. It would be very interesting to see just how high impedance can get on your "wimpy" installation. (over here the target end to end is less than 5% droop so there is an upper ceiling).

But as this keeps coming back to the same point, it will be possible to find all sorts of installations that will have prospective fault currents and robust voltage filtering/complex impedances that they could well be safely measured with a lower category meter. That is entirely expected since the standards have to cover worst case installations.

The "argument" is back to front, if people want to claim the category ratings are excessively strict then it is on them to show every installation meets their new criteria, on the other side I only need to show/find a single example at the limits to demonstrate they are sensible (quickly shown by the current capacity of residential feeds and GPO circuits with their associated maximum droop).

Home lab is two floors away and diagonally opposite of the feed.   Testing my distribution block at 20A, the drop is about 11.2%.  ASCC is about 0.25kA line to neutral.  As I said wimpy and hardly anything that concerns me.   

***
If I skip the AC strip I normally use and go directly to one of the outlets  I measure a voltage drop of 6.3% at 12A.   Hot is 0.38 ohms, neutral 0.20 ohms and ground is 0.04 ohms.    ASCC is 0.26kA.    Scary stuff. 

***
I have an outlet I use for my small MIG welder that on the same floor and much closer to the feed point.   4.5% drop at 12A.  7.3% at 20A.    Hot is 0.31 ohms, neutral is 0.1 ohms and ground is 0.04 ohms.   ASCC for this outlet measures 0.39kA.   

The house has mostly tiny little 14AWG wire.  With all the concern I am guessing Australia uses 0000 AWG to wire their homes. 

***
Tried an outlet at work for the fun of it  ASCC was 1.96kA.  A little better but still hardly a concern.  We don't have arc flash signs on every outlet.  Maybe that's code in Australia for all residential outlets. 

I have been at factories that had to plan ahead with the power company before switching loads.  It's a different world than my home.

[joeqsmith]

I turn the switch off before changing them, because I'm not a fucking idiot. To each their own though I guess 

What if it's a two (or three) way switch and you don't know if it's on or off? Do you rewire your house first?

If it was really a safety concern (which it's not, but I'll play along and pretend we're talking about a broken bulb where you need to grab the base or something) I'd flip the breaker or grab a chicken stick. I'm guessing this is the bit where you remind us you're a hero and you'd do it with your teeth because you're super tough and cool and physics don't apply to you?

Just to recap- THIS is the argument for why that meter is suitable for high voltage work? Because people change light bulbs? Cooooool.

I just screw in the new one with it live.  Then again, with these new LEDs,  it's rare.

[David Aurora]

I turn the switch off before changing them, because I'm not a fucking idiot. To each their own though I guess 

What if it's a two (or three) way switch and you don't know if it's on or off? Do you rewire your house first?

If it was really a safety concern (which it's not, but I'll play along and pretend we're talking about a broken bulb where you need to grab the base or something) I'd flip the breaker or grab a chicken stick. I'm guessing this is the bit where you remind us you're a hero and you'd do it with your teeth because you're super tough and cool and physics don't apply to you?

Just to recap- THIS is the argument for why that meter is suitable for high voltage work? Because people change light bulbs? Cooooool.

I just screw in the new one with it live.  Then again, with these new LEDs,  it's rare.

Yeah, anyone with half a brain can replace a bulb without killing themselves, I was just indulging their point by trying to find a situation where it might actually be a problem 

[Someone]

If I skip the AC strip I normally use and go directly to one of the outlets  I measure a voltage drop of 6.3% at 12A.   Hot is 0.38 ohms, neutral 0.20 ohms and ground is 0.04 ohms.    ASCC is 0.26kA.    Scary stuff. 
***
Tried an outlet at work for the fun of it  ASCC was 1.96kA.  A little better but still hardly a concern.  We don't have arc flash signs on every outlet.  Maybe that's code in Australia for all residential outlets.

>1kA is fairly common here on residential GPOs but it's kept simple so there are no special warnings or differentiation, people treat all outlets as equivalently dangerous (just like 61010). Would I measure any of those examples with a meter containing unbranded/unknown 20x5mm fuses? nope.

[joeqsmith]

I have no reason to measure my line voltage.  I can just look at the lights and see if they are dim.  If I want to look at some sort of device hanging on the line, I tossed together a simple box with a transformer and current sense so the equipment is isolated. 

I use these cheap meters on the bench and while I may frequently run experiments in excess of a kV,  it's hardly a concern.  When I benchmark the meters, while the generator's outputs are not directly connected to the mains (for safety), the small one is still 20J.  Not the most safe thing to play with but I have a fair bit of safety designed into the system.  The scary one in the half cycle simulator as we are now around 600J.  Photonic Induction would call me a chicken but I use a chicken stick any time I use that thing and keep the outputs shorted when not in use.    I consider it CAT1 but by no means that that suggest it is safe to play with.   

I've shown various loads including meters, fuses and light bulbs attached to that generator.  Hardly any concern about an arc flash at 600J.  It will cause a light bulb to shatter.     

[joeqsmith]

....
Why are there many threads about meters, and no threads about household appliances and electrical devices? There are millions more of the latter, and a proportionately higher hazard, statistically.

I think I mentioned I had to repair our microwave a while back.  Turned out the fuse had popped.   Sent the wife out to pick up a new one and when I get home, I get the story of how the parts store wouldn't sell the fuse to her.  The told her they wouldn't sell any parts for the microwave because of the hazards.   People die playing service man with them.   

Wife begins to tell them that she had watched me pull trip the CB before opening it.  Then how I showed her all the bits and how I made a few comments about the design and why things were laid out the way they were for safety.  Then she tells them about this long stick I had used to touch some things inside before I did anything inside.   They said your good, and sold her the fuse.        I can't blame them.   

[rsjsouza]

I love this story, Joe. My wife would probably be able to tell the same details, although the trick is in the convincing and assuring tone... 

[joeqsmith]

My home has a tiny little service coming into from a small distribution transformer.  Nothing like what feeds for the buildings where I worked.    Outlets at my house are several feet from the main feed and are behind small CBs which are behind another small one.  Worse thing that will happen if I pull an outlet and short the wires, I blow a CB.  Hardly CAT III or risk of an arc flash. 

Same here. That's why I wasn't worried about measuring the mains with my Big Clive special.

Knowledge is power.

Ignorance is bliss. Like a chinese fortune cookie, "May your multimeter's spacings be auspicious".

I think so far it's magical opinion and unicorns telling us the DT830 is OK at x volts. Or we can argue it's the requirements at fault - the IEC overvoltage categories are wrong. Not that the product has ever been tested or evaluated to meet its fake claims.
Strange for EE's to discard science for a cheap "trashy" cause.

"Hardly CAT III" you'd need to run a Dranetz to convert speculation and gut feel to fact. I've used loggers in facilities to see if power is a problem with equipment failures. Like making a measurement with some test equipment 

It's not something I would normally care about but with member Someone asking,  I provided ASCC measurements for my home at a few locations which included my office.    Sadly, Someone did not have the basic tools to make the measurements they were asking about.  I thought it was odd that anyone with keen interest in mains safety wouldn't have some basic tools available at least to measure in CAT II.     Maybe you do and can make a few measurements in your own home that we can use as a comparison.     

I want to be clear that those measurements have nothing to do with the high voltage experiment I ran with the two DT830s.  Those power supplies will have far less energy available than my small transient generator.  And as I said, the DT830 presented enough of a load on the one that the current folded back and we could only reach 1.1kV.  So that's 1.1kV/1Meg or 1.1mA.  Is that's scary stuff for a meter?  Depends on the energy available.   Basically, I am referring to the output filter on these supplies.  If I placed some large, low ESR capacitors directly across the supplies output and let them charge up before attaching the meter.  As soon as I connect the meter, the current is no longer limited to 1.1mA.   The energy is 1/2 CV^2.   So a 33uF cap would provide around 20 Joules.  I posted a link the the DOE safety guidelines and I'm sure all the safety minded folks like yourself understand there  is some risk  working with even 20J.     Will it explode a hand held meter, hardly.   Could it kill you, sure.  Does what I show have anything to do with AC mains measurements or safety standards, not at all.

Let's see your data.

[joeqsmith]

I love this story, Joe. My wife would probably be able to tell the same details, although the trick is in the convincing and assuring tone... 

  I'm sure if you put your wife and mine in a room, they would have similar stories to swap. 

[IanB]

It's not something I would normally care about but with member Someone asking,  I provided ASCC measurements for my home at a few locations which included my office.    Sadly, Someone did not have the basic tools to make the measurements they were asking about.  I thought it was odd that anyone with keen interest in mains safety wouldn't have some basic tools available at least to measure in CAT II.     Maybe you do and can make a few measurements in your own home that we can use as a comparison.

To clarify, did you make these measurements by putting a load on the circuit and measuring the drop in voltage?

I think there would be an interesting difference here between countries. In the USA I commonly observe a voltage drop when loads are applied, for example the lights dim when a clothes iron or laser printer cycles on and off, or even when a neighbor's aircon unit starts up. I think everyone is probably familiar with this.

In the UK, I have observed no such effects. The electrical supply is often very stiff, such that the the first time I was in the USA and observed lights dimming I was quite surprised. Some reasons for this might include that in Britain the distribution transformer is commonly a large pad mounted unit that supplies a whole block of houses, therefore it will have a consequently low output impedance. Secondly, the distribution cabling under the street is correspondingly large, since it has to carry enough current for all the houses connected to it. Thirdly, in most houses the power circuits are rated to carry 32 A, even though individual outlets are limited to 13 A. Any UK electricians here can probably give an estimate of the typical short circuit current available in such an installation.

[Fungus]

In the UK, I have observed no such effects.

In the UK they use a ring main system so there's probably less impedance to the sockets than your average USA installation.

https://en.wikipedia.org/wiki/Ring_circuit

[joeqsmith]

It's not something I would normally care about but with member Someone asking,  I provided ASCC measurements for my home at a few locations which included my office.    Sadly, Someone did not have the basic tools to make the measurements they were asking about.  I thought it was odd that anyone with keen interest in mains safety wouldn't have some basic tools available at least to measure in CAT II.     Maybe you do and can make a few measurements in your own home that we can use as a comparison.

To clarify, did you make these measurements by putting a load on the circuit and measuring the drop in voltage?

Yes.  I'm not sure how else these instruments would work.  With mine, I can program the load.  I provided that detail in the post.   

I think there would be an interesting difference here between countries. In the USA I commonly observe a voltage drop when loads are applied, for example the lights dim when a clothes iron or laser printer cycles on and off, or even when a neighbor's aircon unit starts up. I think everyone is probably familiar with this.

I am not sure how many homes are fed from a transformer here.   It's not the entire block.   Maybe five homes.  Mains are underground and transformers are on slabs.   
Transformers are tiny as you would expect.   There is a main feed line for these transformers.  I believe then each home is fed as a star. 

I have not seen (light bulbs do provide a simple, sensitive detector) any transients from the neighbors.  In the house, the  A/C, sump,  clothes drier, oven and stove would be the largest loads but I don't see any effects from them.  Even back when we were using incandescents.    The problem here is that the grid is not stable. 

In the UK, I have observed no such effects. The electrical supply is often very stiff, such that the the first time I was in the USA and observed lights dimming I was quite surprised. Some reasons for this might include that in Britain the distribution transformer is commonly a large pad mounted unit that supplies a whole block of houses, therefore it will have a consequently low output impedance. Secondly, the distribution cabling under the street is correspondingly large, since it has to carry enough current for all the houses connected to it. Thirdly, in most houses the power circuits are rated to carry 32 A, even though individual outlets are limited to 13 A. Any UK electricians here can probably give an estimate of the typical short circuit current available in such an installation.

I assume its all considered magical opinion and unicorns unless measured.     While nothing to do with my kV DT830 demonstration,  I wouldn't mine seeing what the people who are concerned, measure themselves, in their own homes.   

[AVGresponding]

In the UK, I have observed no such effects.

In the UK they use a ring main system so there's probably less impedance to the sockets than your average USA installation.

https://en.wikipedia.org/wiki/Ring_circuit

It's becoming increasingly common to use radials instead of rings. It's annoying for me because it's a lot harder to get two 4mm² T+E into a back-box than two 2.5mm², especially given the ever decreasing space available as they shrink containment down to save money   

Even worse when you have to pull it into conduit!   

[IanB]

I assume its all considered magical opinion and unicorns unless measured.     While nothing to do with my kV DT830 demonstration,  I wouldn't mine seeing what the people who are concerned, measure themselves, in their own homes.   

Fair enough. Which is why I would curious if any UK based electricians here could indicate what kind of prospective fault current would be measured at a typical UK 13 A wall socket? (It would be a range, obviously, but typical/min/max would be interesting.)

[Fungus]

Fair enough. Which is why I would curious if any UK based electricians here could indicate what kind of prospective fault current would be measured at a typical UK 13 A wall socket? (It would be a range, obviously, but typical/min/max would be interesting.)

Wikipedia says typical UK ring circuits have 30A fuses and 2.5mm² cable.

[joeqsmith]

Seems like it would be fairly common information and easy to find but my search was a bust.   I did come across this site for the electrical workers.  Mostly seems related to industrial environment. 

https://forums.mikeholt.com/threads/available-fault-current-approximation.2568479/
https://forums.mikeholt.com/threads/ascc.60843/
https://forums.mikeholt.com/threads/voltage-drop.25793/
https://forums.mikeholt.com/threads/nec-240-86-series-ratings.15668/

***
Article on testers
 
https://www.workingre.com/electrical-receptacle-testers-demystified/

Audio buffs are concerned with it..  The sound of a top of the line audio system would certainly be degraded if plugged into my lab's outlets.   

[Fungus]

All UK mains plugs are required to have BS1362 fuses in them, and the biggest fuse is 13A.

[Someone]

Sadly, Someone did not have the basic tools to make the measurements they were asking about.  I thought it was odd that anyone with keen interest in mains safety wouldn't have some basic tools available at least to measure in CAT II.

Really? Plenty of CAT III meters here, but I dont not have either:
mains impedance measuring tool (as to measure the earth and lines individually)
or
some significant and benign load (such as a resistive heater or load bank) to do a simpler line-neutral measurement

Sure that second item might be somewhat common, but the first is specialist, and I wouldn't call either route "basic". We know the ceiling to impedances here because Australian installations are required to maintain a maximum droop under their full load.

[joeqsmith]

Really.