Bench multimeter calls for ground (which I do not have) - Page 1
Forum section: electronics / beginners

author: xlzslayer
author_rank: Contributor
timestamp: March 28, 2025, 03:48:43 am
content: I recently treated myself to a Fluke 8808A, I wasn't going to, I was going to get a cheaper handheld meter, but I couldn't resist the deal I found right before I was going to purchase the handheld meter.The meter isn't here yet, I actually purchased it from abroad (USA) and have a family member that will be bringing it with them soon. As the responsible person I am, I checked the manual, figured out I'll need to change the line fuse since we use 220v here, but was also met with a big warning in bold text:QuoteI live in Lebanon, we only really have 2 prong outlets in apartments and houses, I believe the grounding is done externally. How big of an issue will it be to plug the meter straight into a 2 prong outlet? If it is an issue, can I do something about it?

author: bdunham7
author_rank: Super Contributor
timestamp: March 28, 2025, 04:20:17 am
content: You'll need to pop the fuse holder out and then the voltage selector block and flip that around to the 240 setting, but if you don't have the MDL 1/16 fuse by then you can run it for a while with the MDL 1/8 as that will blow and prevent any fires. The ground issue can be handled with a separate ground wire from a grounding rod or plumbing to the small ground screw on the back of the unit. The center pin of the input plug is connected directly to the chassis, so I wouldn't ignore the grounding issue. If you have only two-prong plugs on your cord but IEC C13 plugs on the other end, what do those look like? Power cords like that here exist, but they don't have any hole in the center so you cannot plug them into 3-pin equipment sockets.Edit: If you are going to have trouble getting the exact MDL 1/16 fuse and if there is still sometime, you might want to order some now and have them brought with the meter. They're 3AG-sized (6 x 32mm) and you shouldn't substitute anything else for MDL.

author: xlzslayer
author_rank: Contributor
timestamp: March 28, 2025, 12:55:25 pm
content: I'll be trying to get the exact fuse replacement required, but it'll be quite a bit later (a month or so). I didn't realize that fluke listed the exact part number for the fuse until recently, and said family member will be coming today-tomorrow for a few days and will be leaving again for a month or so. I can run the meter on a 120v transformer in the meantime, will that suffice temporarily?We use an EU variant of the C13 that allows you to connect 3-pin equipment sockets into 2-prong outlets (check attached image). The grounding issue will be a bit difficult to fix, I live in an apartment and we use PVC pipes (or some other kind of plastic) for our water supply. I don't really have access to a grounding rod, nor do I have a place to plant one in the ground. Not having a dedicated ground hasn't been much of an issue for other appliances, just little zaps here and there, but the meter is a different type of instrument so it got me a bit worried after seeing that warning.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: March 28, 2025, 01:14:50 pm
content: Open your service panel and look for a ground.Also, and I'm no expert, but GFCI could be useful here. My old house had no ground wires (except bathroom) but had a GFCI panel. It passed inspection.The bathroom had to have a ground and it's own local GFCi for code. I had that rewired.Notre the service panel was grounded although most of the house wasn't......Also, are the receptacles in the bathroom grounded?

author: Doctorandus_P
author_rank: Super Contributor
timestamp: March 28, 2025, 02:37:40 pm
content: The most important thing will be the voltage selection. In the US a lot of 120V stuff is used, so verify and fix that voltage setting when you get your DMM.As for the protective earth. It's sort of important, and a bit more so when working with electronics. It's also important for PC's.Here in the EU, mains voltage sockets both with and without protective earth are used. In my living room where I wanted to use my PC and my electronics workbench, there was no PE, so I pulled the GND and phase wires out of the tubing, added an earth wire, and then put them all 3 back in the pipe, and I changed the wall sockets. In the metering cabinet there is usually a connection for PE.If you don't have PE on a regular PC, then you may feel a tingling feeling when you touch it. This is because there are filter capacitors connected between PE and both live wires (or Live and GND). As a result, PE (and the whole outer case of the PC) has half of the mains voltage when the PE wire is not connected externally.I'm not familiar with electrical installations in Lebanon, but I guess it's not the most developed country. If you don't have a PE connection in your house at all, you can make your own. You can make it from a copper water pipe of a few meters long, and then drive it vertically into the GND (of course depending on local GND conditions).There are different ways of getting such a pipe in the ground, one way is to connect it to a pump, and then force a lot of water throught the pipe. The water will wash away the soil at the end of the pipe, so you can sink it slowly into the ground. Another way is to make (buy?) an adapter for a hammer drill, and then use the hammer drill to push the pipe into the ground. First dig a shallow pit, so you can connect the PE wire to the pipe under the ground, and you can cover it up without anything visible above ground. You can search youtube for video's about the details.In the old days PE was sometimes connected to the water distribution network, but as plastic water pipes have become more common over the last 50 years, this is now deprecated where I live.

author: ejeffrey
author_rank: Super Contributor
timestamp: March 28, 2025, 02:54:20 pm
content: Quote from: JustMeHere on March 28, 2025, 01:14:50 pmThat's not super useful if the OP lives in an apartment and the service panel is not near where they will use the meter.QuoteGFCI alone isn't really ideal for test equipment like this. GFCI will shut off the power to the instrument if the instrument itself develops a ground fault. However with test equipment the concern is that you might connect energized equipment to the meter. GFCI on the meter circuit can't protect against that. So it's definitely better if you can find an actual ground somewhere.

author: bdunham7
author_rank: Super Contributor
timestamp: March 28, 2025, 02:55:08 pm
content: Quote from: xlzslayer on March 28, 2025, 12:55:25 pmYou don't need to get a Fluke-specific fuse (p/n 163030), but you do want the MDL 1/16. These are commonly available here and the eBay ones typically aren't fake. Sure, a transformer will work, if it is an isolating transformer that's even better.QuoteThe meter is no more or less hazardous than other appliances and instruments that should be grounded. The front panel inputs are all guarded (isolated) from ground or power and the only way the chassis would be energized is if there were a failure of the internal primary wiring (power switch and inlet) or transformer. Without a ground the chassis could float up to some voltage or could have AC leakage current energize it to some potential but without much current. This might cause increased residual counts in the AC ranges or give you a slight buzz if you handle the meter.

author: pqass
author_rank: Super Contributor
timestamp: March 28, 2025, 04:01:50 pm
content: Giventhese pictures of the insides, I don't think there is much shock risk with an unconnected ground because:a. the front panel is all plastic with rubber buttonsb. the input jacks are floating (all meters in this class have floating inputs)c. use of a quality, galvanically isolated transformer power supplyThe notice is CYA (cover yer ass).The only remote danger I see is that the transformer primary windings shorting to the core; energizing the case.If you're concerned,a. don't touch the painted metal case while plugged-inb. use an insulated pad under your feetc. use on a non-metallic bench.d. wrap metal case with insulated sheet (allowing for air exchange)Disclaimer: use at own risk.Haters: you may now begin to tell me I'm very wrong.

author: TimFox
author_rank: Super Contributor
timestamp: March 28, 2025, 04:17:52 pm
content: Assuming the power entry connection employs a standard three-terminal line filter:Whatever the case of the filter (connected to the third prong that is not connected with a two-prong outlet) is connected to will see an AC voltage equal to half your single-phase voltage (120 V for your 240 V feed) in series with a medium capacitance from the filter. With some equipment, that might be metal that you can touch. If the Fluke carefully insulates everything you can touch from that connection (e.g. BNC shells), then you are safe, unless that insulation should fail. The design of these filters limits the capacitance to ground to keep the current to a non-lethal value, but it can be a noticeable jolt. At work, we named that jolt the “Dan effect”, as in “It’s hard to shock Dan, but…” after he encountered an ungrounded Diesel generator at a foreign construction site connected to a grounded system.

author: bdunham7
author_rank: Super Contributor
timestamp: March 28, 2025, 04:57:09 pm
content: Quote from: TimFox on March 28, 2025, 04:17:52 pmThis meter actually doesn't, AFAIK (unless it is well hidden) and it just has a inlet/switch/fuse/voltage selector block all combined in one unit. No need for filters as it as a plain EI transformer on the input and the transformer primary is the only load. Also, the meter is a CAT I/1000V rated DMM and the front panel is nonconductive. I measured the chassis leakage current on my example at less than 10µA. At 220V I expect it will be a bit higher. The real hazard would be that the OPs unit is damaged or has some malfunction, as the primary power input is present on bare metal parts inside the bare metal chassis with only some space and air between them. If nothing goes wrong there's no real shock hazard but physical damage, moisture or a stray spider might change that.

author: TimFox
author_rank: Super Contributor
timestamp: March 28, 2025, 07:08:38 pm
content: Quote from: bdunham7 on March 28, 2025, 04:57:09 pmThat makes sense. I can't find the manual for this unit online: since all the possible power cords available for the unit are standard 3-prong plugs (for various jurisdictions), what does the "third prong" actually connect to inside the Fluke unit?

author: bdunham7
author_rank: Super Contributor
timestamp: March 28, 2025, 07:46:54 pm
content: Quote from: TimFox on March 28, 2025, 07:08:38 pmIt is connected directly to the chassis via a short wire.

author: TimFox
author_rank: Super Contributor
timestamp: March 28, 2025, 08:00:59 pm
content: Quote from: bdunham7 on March 28, 2025, 07:46:54 pmWith no capacitors between either line and that internal connection?

author: TimFox
author_rank: Super Contributor
timestamp: March 28, 2025, 08:13:32 pm
content: What is the unit at the left of the photo, marked "KG"?

author: bdunham7
author_rank: Super Contributor
timestamp: March 28, 2025, 08:24:16 pm
content: That's the part that holds the fuse and voltage selector block. With those pulled out, you can see the unit is otherwise empty. The only way I see to get any non-trivial leakage to the chassis would be via the transformer, which as you can see has a ground shield. The entire board and front panel are isolated and floating with the exception of a small section where the serial port is connected and that is separated with optos and large gaps.I found a link to the Schurter KG series IEC inlets:https://www.schurter.com/en/datasheet/KGThe CG version with line filter is available as well:https://www.schurter.com/en/datasheet/CG

author: TimFox
author_rank: Super Contributor
timestamp: March 28, 2025, 08:53:43 pm
content: Thank you

author: xlzslayer
author_rank: Contributor
timestamp: March 28, 2025, 09:32:44 pm
content: Quote from: bdunham7 on March 28, 2025, 02:55:08 pmI see. Is an MDL fuse just a slow blow glass fuse of a certain size?Quote from: bdunham7 on March 28, 2025, 02:55:08 pmOh okay, glad to know that the front panel inputs are isolated, was a bit worried about that. Yeh small zaps from the enclosure won't be an issue, you kinda get used to it here since you grow up with some other appliances behaving like that, you start learning to put on some footwear or to not touch the wall etc. to avoid making a path to ground. A drift in AC measurements kinda sucks if true, but I care less about AC accuracy. Perhaps I can test how much it drifts by temporarily acting as a path to ground myselfThank you for the help, I really appreciate it! Do you think I should bother with adding any type of protections? As scary as it looks, I don't think the primary power input will end up causing issues, but that's just my unprofessional opinion. i could probably coat the bare metal or put an insulative sleeve around them?

author: bdunham7
author_rank: Super Contributor
timestamp: March 28, 2025, 10:19:42 pm
content: Quote from: xlzslayer on March 28, 2025, 09:32:44 pmIt is a specific type of slow blow fuse that works well with small power supply transformers. It is 3AG sized, so the old-school glass fuse dimenstions. The MDL 1/16 or MDL 1/16R has a high enough resistance that it will limit fault current to <5A @ 220V even with a direct short and under those circumstances will clear the fault (blow) in less than 10ms or half a cycle. Great protection against accidents but very rarely blow in normal operation. Any 1/16A (62.5mA) slow-blow fuse would be OK, but I'm not sure what else there is.QuoteAs I said, the overall design is no more or less hazardous than everything else around your house that was intended to be used with a ground. It is pretty high quality with low leakage, so I'd say if there's no physical damage and you keep it dry, you probably won't have a problem. I'd still rather see you get a ground setup, but a GFI/RCD might be an acceptable substitute from a safety standpoint.

author: golden_labels
author_rank: Super Contributor
timestamp: March 29, 2025, 07:57:29 am
content: I don’t know, what system Lebanon uses, but in many countries old unearthed 2-wire systems were updated, so the neutral wire became neutral + earth. This is being done without touching apartment’s installation. So in most cases people never realized that: while they themselves were in work, electricians came and attached a few wires in the switchboard. If that’s the case, you only need to replace the outlets.An electrician will be able to confirm, what kind of an installation you have. They’ll also mount new outlets for you.A PEN wire is inferior, compared to separate N and PE. It also brings its own unique risk. But it’s still much better than no earth.

author: tatel
author_rank: Frequent Contributor
timestamp: March 29, 2025, 09:53:31 am
content: Quote from: xlzslayer on March 28, 2025, 12:55:25 pmI'm probably missing something? That IEC you show has earth connection. Two prongs and that metallic strip. The jack should have two holes and a couple of metalic contacts. This is where earth connection is made. Of course, it could be that the electrical installation in your building is defective or anything.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 29, 2025, 10:08:42 am
content: Quote from: golden_labels on March 29, 2025, 07:57:29 amWhen GFIs are used it very much depends and it could be preferable to not have PE connected.

author: tooki
author_rank: Super Contributor
timestamp: March 29, 2025, 10:43:58 am
content: Quote from: xlzslayer on March 28, 2025, 12:55:25 pmThe image attached to that reply shows a standard grounded European (combined Schuko and French) plug.

author: bdunham7
author_rank: Super Contributor
timestamp: March 29, 2025, 02:38:12 pm
content: Quote from: golden_labels on March 29, 2025, 07:57:29 amIDK if that's really an improvement here. If the PEN system is all the way to the sockets, then any failure along the way results in floating up to mains voltage. I think the meter is much less likely to fail internally than the electrical installation.

author: Terry Bites
author_rank: Super Contributor
timestamp: March 29, 2025, 03:05:37 pm
content: Local ground is usually created by bonding to incomming neutral and internal metal pipework. Its not a wire from the electricity supplier. You can optionally bond it to ground stake outside.If you have an identifiable neutral then thats the way to go.

author: xlzslayer
author_rank: Contributor
timestamp: March 29, 2025, 03:42:40 pm
content: Quote from: tatel on March 29, 2025, 09:53:31 amYes, the plug is meant to be used on grounded outlets, we don't use them on grounded outlets. They fit, so it's what people use, that's really all there is to it, that's the standard here, pretty advanced right?What I said above still applies as the standard in the country, but looking back at it, my home setup is quite a bit unique. It's been rigged where some outlets of a different color can be supported by a main UPS during power outages (The UPS is not currently present/in use), It's been rigged to support a generator powering everything in the apartment, and it's been rigged to support a first party and a third party power provider for when one goes out. The first party power provider is the government, which has been very inconsistent in the last few years. You also made me look again at my outlets since they're not the standard here, my father did the electrical installation around 10 years ago. The outlets do indeed have ground metal contacts, European style, but I always thought they were just dummies, not actually grounded.I took some measurements. I do want to note that I'm currently on third party power. Live and Neautral measured ~231VAC, Live and Ground anywhere between ~75-85VAC measured at a few minutes apart, Neutral and Ground ~55VAC. So the ground is connected to something, but it's not earthed properly?

author: bdunham7
author_rank: Super Contributor
timestamp: March 29, 2025, 04:06:41 pm
content: Quote from: xlzslayer on March 29, 2025, 03:42:40 pmYou'll get odd results using a handheld DMM with 10M input impedance because you're measuring small amounts of leakage current. This is why the LowZ function was introduced. If you don't have LowZ on your meter, then try putting a 100K 1W resistor in parallel with the meter (very carefully, make something safe to connect all that) and see what your voltage looks like then. Your measured voltages are entirely consistent with the possibility that the grounds are not connected to anything. OTOH, it is also possilble that your third party power supply is not ground referenced.

author: Xena E
author_rank: Frequent Contributor
timestamp: March 29, 2025, 04:26:48 pm
content: Be very carefulxlz slayer.I have experienced domestic instalations where outlets have had ground connections that were connected together but not to ground!What you may be measuring is some artifact caused by something plugged into another outlet.X

author: xlzslayer
author_rank: Contributor
timestamp: March 29, 2025, 08:05:04 pm
content: Quote from: bdunham7 on March 29, 2025, 04:06:41 pmOh I see, yeah my handheld meters don't have that feature, however I just received the Fluke meter! I assume it should show better results since it has lower input impedance:Live and Neutral measured 226VAC, Live and Ground 22VAC, Neutral and Ground 8VACSince the values are lower, I assume they're closer to the reality that the ground isn't connected to anything?

author: bdunham7
author_rank: Super Contributor
timestamp: March 29, 2025, 10:48:39 pm
content: Quote from: xlzslayer on March 29, 2025, 08:05:04 pmYes, that does seem to indicate that your "ground" is floating free, perhaps along with some leakage from other things around the house asXena Esuggested.

author: tatel
author_rank: Frequent Contributor
timestamp: March 30, 2025, 02:42:00 am
content: Quote from: xlzslayer on March 29, 2025, 03:42:40 pmWell to have these ground contacts connected all you need is to make another wire to pass trough the plastic tubes of the electrical installation. That way hopefully you can get to street level where a copper rod 20 mm diameter 2 meter long could be nailed into earth. Probably after drilling trough concrete. That's easily seen here on old buildings.However we have here about 2000 mm rainfall/year so there is quite a bit of moisture in the soil. On a dry climate that earth connection could have too much resistance. Perhaps, if the building has the structure made of concrete, could you make the earth connection to the rebar inside the concrete?AFAIK, to use a water pipe for earth connection is forbiden here.I think any local electrician will know about the climate and all those exotic power sources you are compelled to use, therefore could give you the best advice abouth this matter.

author: themadhippy
author_rank: Super Contributor
timestamp: March 30, 2025, 03:01:59 am
content: Quotewhich will do nothing if the electrical network isn't connected to mother earth,even an rcd/gfi is about as much use as a chocolate fireguard in such cases

author: bdunham7
author_rank: Super Contributor
timestamp: March 30, 2025, 03:16:34 am
content: Quote from: themadhippy on March 30, 2025, 03:01:59 amIf the line and neutral are actually completely isolated then there's no (single touch) shock hazard in any case. In reality, there will always be leakage from various devices. A real ground will prevent the things attached to it from floating up from ground, the remaining hazard is if your location (where your feet, etc are) are not at the same ground potential.

author: Xena E
author_rank: Frequent Contributor
timestamp: March 30, 2025, 05:52:12 am
content: *Beyond the issue of the multimeter*Without a designated neutral tied to ground from whatever source of power that is being used, (inexpertly installed emergency generation is notorious for this), then installing an unconnected random earth could just be making the situation more dangerous.It's sketchy.If you have no control over it, be very wary.X