Products > Test Equipment
Big Clive's "Trashy" meter, unboxed ( Duratool D03047 multimeter )
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IanB:

--- Quote from: wasedadoc on April 27, 2023, 04:51:05 pm ---The neon screwdriver would come out of that drawer in the kitchen that has the non-cooking items such as string, Stanley knife, spare keys, candles, fuse wire, tap washers etc.

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You forgot the rubber bands and batteries  ;D
Fungus:

--- Quote from: wasedadoc on April 27, 2023, 04:51:05 pm ---The neon screwdriver would come out of that drawer in the kitchen

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Make sure it's a certified CAT III screwdriver, not a fake Chinese one


Gyro:

--- Quote from: IanB on April 27, 2023, 03:13:24 pm ---Some meters have a multi-gigaohm input impedance, and while I don't know how this is implemented, I would guess the input more or less is going directly to the gate of an FET? If that is the case, is there any way these can have robust input protection?

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In the case of the Datrons that I'm familiar with, there's a 100k 10W resistor chain before the bootstrapped protection diode (well, JFETS and Zeners) network on the Hi-Z input ranges. I'm not as familiar with other brands.
switchabl:

--- Quote from: IanB on April 27, 2023, 02:34:25 am ---I have a small question for everyone in this thread: do your lightbulbs have a CAT rating on them? When you twist a bulb into its socket, do you ever worry about it exploding in your hand? Do you wear safety glasses and rubber shoes when you change a lightbulb?

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I realize that this is a rhetorical question but the thread seems to have gone sideways anyway. So, here is a fun fact: a lightbulb ("self-ballasted LED lamp for general lighting services by voltage above 50 V") has to be tested to a withstand voltage of 4 * nominal line voltage + 2000 Vrms between the contacts and any accessible parts for 1 minute in an environment with >91% humidty. Around here that works out to roughly 4kV peak.
AVGresponding:

--- Quote from: Gyro on April 27, 2023, 09:23:41 am ---Using DMMs on the mains is somewhat overrated (no pun intended). In a lot of cases it rather akin to beginners getting their first fancy scope, having nothing to look at other than the cal output, and being hypnotically drawn to the nearest mains outlet.

Most use cases are establishing whether mains is present or not, rather than measuring its voltage to within a few volts. Electricians use proper 2-pole testers for such purposes, together with a simple proving unit. These are inevitably at least 600V Cat III. The cheaper professional ones have a basic LED bargraph voltage display, the slightly more expensive ones, an LCD voltage readout too. They normally have a basic continuity and phase rotation tests too, with the same Cat rating. No finger-trouble  controls, captive probe lead, and they still give a live voltage indication even if the batteries are flat or missing.

Decent qualtity second hand 2-pole testers can be picked up quite cheaply on ebay (Don't go to Ali!). When you get one, you should carry out the inspections detailed in the manual - check for cracks, lead damage, tug test etc. And verify that they indicate correctly. Proper safe isolation procedure requires indication verification before and after checking the circuit of interest. That's where the battery powered proving unit comes in. You can get those on ebay too, but it's easy enough to make your own with a simple self oscillating inverter - this is pefectly safe to do, if you don't get a reading on the proving unit then any test on the mains circuit is automatically invalid.

Most measurement tests involve a safely isolated, dead circuit. Once the circuit is proven dead and preferably locked off with a clip on the breaker, you can perform resistance measurements etc. Proper second hand insulation and continuity testers (again with the comfort of Cat rating), are again easily available on ebay. They will probably be past their calibration date, but are very easy to verify with a bunch of low and high value resistors and a Cat 1 1kV DMM.

The only other live tests are beyond the capabilities of a DMM anyway. Ze / PSC (prospective fault current) tests require a dedicated tester as does RCD trip current / trip time. RCD testers are also pretty cheaply available too (again they may be past cal, but if an RCD trips at 1 x In and holds at 0.5 x In then it is good enough. RCDs have test buttons anyway.

In summary, there is very little reason to be using a DMM on a live mains circuit.

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Ah, the good old days... sadly, my Fluke T5-1000 uses 2x AA (rechargeables work fine, which I prefer even though I can get free industrial Duracells at work), as do many two-probe testers these days.

In point of fact, a DMM does have a place in the electrician's toolbag. The continuity test that a pair of Steinels or an installation tester can do has a maximum of a few hundred ohms, the insulation tester function can only measure by using 250V or more, at 1mA, which is death for many things you might find connected to your fixed wiring.
A real case scenario for this happened a few weeks back, when we were trying to track down an earth fault on a fire alarm. The insulation tester I had brought had a maximum resistance reading of 200kΩ, before the insulation test ranges. The installation tester had continuity only. The earth fault, as it turns out, (I took my F87V in the next day...) was around 360kΩ, so we couldn't see it with any of the testers (it wasn't possible to remove all the fire alarm devices on a section, and naturally enough, that was the offending section) at the first attempt. Still, we got a full weekend of overtime out of it, so no complaints...

Also, though I don't get to play with UPS's at work these days, you definitely need a DMM for that, also if you're playing with VFD's, and almost all PLC /automated machinery.


One of the electricians that joined us recently has a bloody neon screwdriver; I keep threatening to throw it in a skip if he leaves it unattended. If he wields it anywhere near a DB or panel board, I will rugby tackle him to the floor and smash that piece of shit with a club hammer.
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