Please halp me understand my Fluke 116

[HVAC Guy]

I am new so bear with me. I have been using a Fluke 116 HVAC DMM for a while. Purchased based on company reputation for 150 US dollars. Replaced a Entech cheapy (at least I thought). While I was watching one of Daves videos (great job by the way, funny as hell most of the time) I decided to peek inside my 116. What!!! there are no fuses! I can't beleive it. I have been sticking my probes into electricty and there are no fuses to protect me from being electricuted? You have to be kidding me. My cheap 40 dollar Entech that I replaced has fuses. So I went to the Fluke website to see what is protecting me and my DMM. It says: Surge protection   6 kV peak per IEC 61010-1 600 V CAT III, Pollution Degree 2. What does that mean? I can't beleive that Fluke sells a DMM that has no fuses, what is up with that. Can anyone tell me how this unit is protected? Will that surge protection protect my 116 without having to replace it should I stick my probes where they don't belong?
 

[T4P]

There isn't a high current range so honestly, fuses aren't necessary since their purpose is only to protect the DMM in current range

[Excavatoree]

That's correct.  No fuse can protect you from being electrocuted; only YOU can do that.

The fuse protects the meter, and is only necessary in current mode because the meter's impedance is low - the current could be high enough to damage the meter if there were no fuse.

If there is no current mode, or in voltage mode of a meter with a current mode, the impedance is high - the meter circuit protects itself. 

Now, there are protection devices to protect the meter from over-voltage, but these aren't fuses. 

You are protected by the features Dave mentions - the blast protection provided by the case seal, etc.

[HVAC Guy]

Okay, I understand that I think. I guess I thought that the 600v needed a fuse. Should the protection that you mention on the current side blow will the unit be dead?

[saturation]

Most DMMs use some combination of PTC, MOV or gas discharge tube to protect you against high voltage, if they blow the unit will die.  If microamps is all you need in your work, you can never make the mistake of attaching the amps range while measuring volts, and blow a fuse; that's the only reason fuses are there.  The PCB is also designed to prevent high voltage arcs internally and shunt that to the protective devices. All DMMs will die if they are subject to very high voltage, that's how they'll protect users, fuses are there only because of user error.

CAT III means the meter is rated to work from a junction box and forward to branch circuits, i.e., mains receptacles within a room and devices connected to these receptacles.  Pollution Degree 2 refers to typical conditions of humidity or condensation found in an office type room that could could form unintended conductive paths within a DMM that is being used to measure live circuits.  This conductive path could cause a user harm, so a DMM designed for Pollution Degree 2 uses circuit designs to defeat those conductive paths.


http://www.es.lancs.ac.uk/electron/htmdocs/polldeg.htm

[HVAC Guy]

Thanks you for all your answers. I am not sure I understand everything you guys said but I can at least now research your answers to better understand. Thanks again for your help.

[TriodeTiger]

I am unsure of the other answers too - You can still put uA in to 120/240VAC, right?

A novel measurement. I took out my ExTech 210 and measured the resistance across uA mode, however that only appeared to give ~100 ohms. I had to while it was on or it was open loop, so I'll scratch that for now.

I then thought of shunt resistors in general, would they be the same values for each range? I'd say generally you'd want them to be low for high current (fuses are a must... 120VAC/0.1 ohms =...1.2kA!), however in mA and uA mode...You may approach the kilo and megohm ranges...

Dave's uCurrent adapter seems to not (10 ohms for uA?), but his goal was to lower burden voltage. A few kohms may keep things safe though in yours.

Heh, free bit of learning either way for me.

Alexander.

[saturation]

You could see it this way. From Fluke's site, the maximum input voltage is 600V and the maximum input current is 600uA then the maximum power dissipated inside the meter by sense resistor/s are: V x I =  0.36W.  A small 1W resistor can dissipate this much heat ~ indefinitely.

To limit current to 600uA for 600V, the sense resistor would be ~1 Mohm range.

[alm]

They don't state the burden voltage, but I highly doubt that it's 600 V, so the sense resistor will probably be much lower. But even in loZ mode the input impedance is only 3 kohm, which will also safely handle 600 V continuous. Not sure how they handle the dissipation, limited duty cycle?

[saturation]

You're right alm.

Whatever the actual resistance is, its far far higher than what we expect in an ammeter.  I think the 'ammeter' mode is another voltmeter range calibrated in uA.  Its designed for a specific application, for measuring current in flame rectification.  Conduction through a flame has very high output resistance, so adding series x,x00 ohm resistance to measure its voltage drop and converting it to current can do the job.