Error of % + digits?

He is just an arc flash away from making an ash of himself.

Reply to
Michael Terrell
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Yes.

I've seen what happens when you connect two phases to one phase equipment, it's quite amusing.

And I don't respect things that will probably never happen.

Reply to
Commander Kinsey

I've done that actually, just scorched my hand for a couple of weeks.

Reply to
Commander Kinsey

Ah, I didn't know that existed. I thought you only got 120 when you centre tapped a single 240. If you're gonna use three phase, wouldn't you want more voltage?

Reply to
Commander Kinsey

Isn't that really hard to work out? We use cross sectional area in mm. Which is really easy to imagine. With the added bonus that a higher number is thicker. It's also pretty handy as a rough guide that 1 square mm carries 10 amps.

Seriously? Wow. Why would you nbot measure a thickness in a unit of distance?

We use microns.

Depends if something else is in the way. I'd always try to use round numbers.

Reply to
Commander Kinsey

If you had respected things that probably would never hapen, you would not have scorched your hand.

Reply to
Ralph Mowery

sheet metal in mm (1.6mm, 0.65mm etc...) plastic sheet in microns 40um etc. electric wire in square mm. fencing wire in mm diameter.

Yes, if that is the right size. buildings are usually specified in multiples of 100mm. often multiples of 300mm or 1000mm furniture usually in multiples of 25mm

Factory door sizes are 620mm + multiples of 50mm, but not all openings are the right size for the factory door.

Timber sizes for dressed finger-jointed framing timber are accurate to withion 0.5mm are are certain preferred multiples of 5mm eg: 70x35 used mainly for non-structual walls. 90x45 used mainly for structural walls.

The stud spacing and top-plate height will typically be some multiple of 50mm So a lot of the cutting for studs, and blocking is at multiples of 5mm. that's if you're not using pre-fabricated framing.

Carpenters use millimeteres. they say centimeters are for tailors, and inches are for cobblers.

--
  Jasen.
Reply to
Jasen Betts

The separate amps jacks exist for at least two reasons:

1) If the range switch also switched in/out the current shunt, then the user could accidentally create a short circult across the probe tips simply by turning the range switch to or across the amps measurement ranges. Even if they were quickly turning /across/ the amps settings ranges, a brief short circuit would be created, which would cause damage to the meter as well as the device under test depending upon what was connected at the time. 2) By having the amps jacks separate, the range switch itself does not have to have contacts beefy enough to carry the current for the amps settings. Remember, when measuring amps, the current being measured flows *through* the meter itself. This would require very different (and likely much more expensive) range switch contacts.

Some meters do have sensors for the amps jacks that sound an alarm if the probes are inserted in the amps jacks but the range switch is on a different setting than amperes.

Reply to
Rich

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Then you put the amps ranges on one end of the dial. You would never go= through them. And what idiot turns the dial while it's connected?!

Or a relay.

Reply to
Commander Kinsey

Some meters have range switches that rotate through a full 360 degrees with no stops - there would be no "end of the dial" in those instances.

And even with an 'end of the dial' there is still the possibility of landing 'off by one' while turning the dial.

The same idiot who'd leave the leads plugged into the amps jacks and then attempt to measure the voltage of a car battery (or some other low impedance high current voltage source).

I suspect you would find changing the range switch while connected is much more common than your response implies. Esp. for switching up/down a range for meters that are not auto-ranging.

Which also equates directly to added expense vs. having the user themselves be that "relay". And for battery powered meters, shorter battery life (due to the current consumed by the relay coil).

It is also possible (this is a guess in my part) that the CAT ratings specify separate amps jacks for an added safety factor of "user must deliberately move lead to obtain short circuit through meter".

As well, the user who'd leave the leads plugged into amps, and then try to measure voltage on car battery or other high current source is also just as likely to leave the range switch in the amps setting (after having measured current somewhere) and subsequently try to measure voltage. It is not possible to fully protect users who don't pay attention from doing stupid things. Either they forget to unplug from the amps jack, or they forget to switch away from the amps range, either way they get a local fireworks display of their own doing.

Reply to
Rich

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Then don't make them like that.

Then have a gap which is connected to nothing.

Wrong. You adjust the dial to what you want to do, not remembering what= you were measuring yesterday. Having only one thing to change makes it= way easier to get it right.

It only has to get over 20 amps to f*ck the meter.

Meters should always auto range. Mine all do, and I've never even consi= dered adjusting the dial while it's connected. I'm not going to change = between resistance, current, and volts and want to leave it connected to= the same thing.

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No, because you save on an extra socket.

Latching relays use very little indeed, like the one in my room thermost= at. 2 AA batteries last years.

Then they're fools, because now "user can obtain short circuit by forget= ting he was measuring current yesterday, or because a colleague was with= out him knowing". If it was selected on the dial, there is no possibili= ty to make a mistake. You select what you want and that's what you get.= It's illogical to have one thing pointing at volts while another thing= is expecting current!

Anyway, a simple fuse would solve all this. All you lose if you make a = mistake is a fuse, not the internal workings of the meter, the test lead= s, the thing you're testing, and possibly your face.

y

Nope. I pick up a multimeter and set it to what I'm about to measure. = Same way as I don't drive into my house because I left my car in forward= gear yesterday.

People make mistakes. The best equipment prevents this. My VW Golf for= example would not allow me to select 1st gear when going 100mph. It wa= s quite clever in fact. I could do that on purpose and it would drop on= e gear at a time to slow the car as quickly as possible to assist the br= akes in an emergency. And yes I did try it a few times, one time I scar= ed the shit out of the passenger (who had never seen an automatic gearbo= x before).

Reply to
Commander Kinsey

I often leave the leads connected to a Simpson 260 and change voltage ranges. Where I worked there were so many wires in a conduit carrring

120 VAC control voltage it was difficult to tell if the voltage was 'real' or induced by the coupling. I found out that if I started on the 500 volt range and then switched to the 250 volt range if the meter pointer stayed in the same relative position I could then switch to the 50 volt range and the meter pointer would still be near the same relative position if the voltage was induced. If the pointer changed positions to follow the 120 VAC when going to the 250 volt scale the voltage was real.

I doubt that the CAT rating requies seperate Amps positions for the leads. Fluke uses special fuses in their meters to get the CAT ratings. They do not have a seperate jack for the ohms settings either which is more likely where the meter would be set. Most of the time the circuit would have to be broken and the meter inserted to measuer amps.

As you say it is impossiable to fully protect everyone from doing somethen forgetful or stupid, but having a $ 300 meter instead of a $ 5 dollar one goes a long ways.

I do have a Fluke test meter that is purty much fool proof up to 600 volts and rated CAT 4. A T1000. It only measuers AC amps by passing a wire through the prongs. It does have a switch for voltage and ohms. I have on purpose set it to ohms and put it across a fuse in a 480 volt AC circuit to see if the fuse is good or bad. No problem to do this.

Reply to
Ralph Mowery

Better to use something that draws bit of current, like one of those screwdrivers that lights a neon through your capacitance.

With a bad fuse it doesn't blow up?

Reply to
Commander Kinsey

Interesting....

Yet you said this yesterday:

From: "Commander Kinsey" Date: Thu, 16 Jul 2020 20:09:20 +0100 Message-ID:

...

I find it crazy that you can select volts and have the wires in the amps holes. ... I've broken a meter doing that, just measuring the

...

One aspect of "set it to what I'm about to measure" should normally include: "are the leads in the correct jacks".

Reply to
Rich

No it does not . It is designed to protect its self from voltage on the ohms scale. They are only about $ 130

Even better is a quick tester by Fluke. it has 2 leads and about 8 or so leds on it. Both it and the T1000 look similar to bannanas, even yellow in color. The 2nd tester is fully automatic. Connect the two leads to anything under 600 or so volts. If voltage, the leds light up , the more for more voltage. Anoter is for AC or DC. If there is less than about 200 ohms and no voltage, there is a led and buzzer for that.

About as fool proof as they make it for quick tests.

Reply to
Ralph Mowery

:

No, because it's illogical to change two things to set one thing.

Reply to
Commander Kinsey

Howe does it measure ohms and distinguish its own current from the current from the circuit? That's if you're testing a DC circuit.

Does it check for current if there's no voltage?

Reply to
Commander Kinsey

No, it is designed to protect its self.

Reply to
Ralph Mowery

Just how can there be curent if there is no voltage ?

There is no current by the leads, but works like a clamp on meter to check for AC Current. Does not do DC current.

There can be voltage but no current.

Reply to
Ralph Mowery

No such thing as a troll, just someone you disagree with.

Reply to
Commander Kinsey

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