Is this household voltage safe?

user11

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I'm in Australia and our nominal voltage is supposed to be 220-240AC, I stuck my admittedly cheap multimeter into a power outlet and it is reading 265V, it reads a fully charged AGM new battery at 13V DC and it gives the same reading for charged NiMH batteries as my Powerex battery charger, so it does seem to be functioning correctly at least at low voltages.

265V though does seem high, it's more than 10% over the nominal voltage. Is this likely to be the multimeter or is it possible that the house really could be putting out 265V or even 270 at the power outlet?
 

TinderBox (UK)

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265v is a bit high, Is your DMM a true RMS version, A lot of cheap meters are not, and give a wrong voltage, or it could just be out of calibration, It`s best to have 2 meters of different brands so you can check them against each other and see when one is out, simply vibration in the back of a car or dropping can affect the calibration.

https://www.youtube.com/watch?v=XUdRW0XgYQs

John.
 
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user11

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OK thanks that was a most enlightening video. I've just got a cheapie multimeter, I wouldn't use it a lot but I am needing to track down some possible stator problems and wiring problems on my bike so I'll be wanting to get something more reliable but I don't want to spend professional money. The local electrical shop has this one available at the moment, it's a decent price, do you think that I could expect it to be a decent quality? By that I mean accurate.

https://www.jaycar.com.au/economy-true-rms-autorange-multimeter/p/QM1321


EDIT: thanks terjee, I did come across that earlier today! I'm in QLD, so looks like we're still 240, testing again, it's bouncing between 265 and 270! on my cheap meter.
 
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terjee

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As to the question of it being safe if it really is outside spec, it really depends on what you mean by safe. No mains voltage is safe to touch, so I'm assuming you're thinking of damage to equipment, fires etc.

It's too complicated to give a single simple answer, but you could rate it as some increased reason for concern at least.

Tempting to suggest you look at the empirical evidence you already have. If it's never been a problem, that's pretty significant. If your feel like all your electronics is dying prematurely, that's a different issue.

Mains power is horribly messy business, and quality manufactures design for that. Even though nominal rating is often 230V, they're usually designed to handle voltages a good bit above it.

If you've verified that you do have a TrueRMS meter, I'd still fire off an email to you local power company though.

No reason to start pulling all your circuit breakers, but doesn't hurt to be mindful of excessive heating or any other similar issues.
 

NoNotAgain

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Located in the US, but I've had voltages as high as 155 volts verses the 120v standard.
My batter UPS system flagged the voltage, checked the second UPS and also had high voltage light displayed.
Fluke 85V which is true RMS verified 155v.
Local power company came out to find transformer had gone bad.
 

hazard2036

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Some one asked this question on Ozbargain i think they where WA unless it was you?

I still think its okay even if its on the high side. But you really need a true RMS meter get a proper reading?

What model meter do you have?

Also the Jaycar meter is fairly basic you can get a better meters for around the same price. I use a Uni-T UT139C it is a good meter its actually re-branded and sold at Supercheap auto for like $90 dollars if you buy the Uni-t meter you can get it around $50
 

user11

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@hazard, not that was not me. I only really ended up here because I was wondering about the accuracy of my cheap meter, I am not really interested in measuring household AC voltage, it's really the electrics on my bike that I'm most concerned about. Specifically I am suspicious that my stator is not running correctly. At 2500 RPM it's putting out 14.5V at the battery terminal which is good, (recently installed new AGM Battery) however when revving to 5000rmp the voltage drops down to 13V. There are 3 wires coming out of the stator, and when I check the resistance on pairs of these wires (3 different pair) I am getting a resistance of 2.5 Ohms and I'm told that indicates that the stator is not working properly.

However and this is the point of this thread really, I'm wondering if I can trust this reading. Tomorrow I'm going to check the AC Voltage coming off the stator and hopefully it will be 75V.

What I'd like to know is, if this is what I'm testing, resistance and perhaps AC voltage off the stator, do I require an RMS meter for this, because I have just come across this ... https://electronics.stackexchange.c...e-rms-applicable-only-to-measuring-ac-voltage which seems to indicate that under particular circumstances that an RMS meter would not be ideal.

So finally the basic fluke 101 is not an RMS meter and it's a known quality and only $63 so for the purposes of my auto needs will this meter be suitable? Maybe the cheap meter I already have is giving accurate reading but as someone said earlier, it's good to have two to compare.
 

BB

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Years ago (decades) I defined our power supplies (computer) as 190 to 265 vac. 265 vac was for our Australian customers.

Have you asked the utility what their take on the line voltage was?

-Bill
 
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user11

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OK I think an update is necessary here. I'm not really fussed about the AC readings although it was a bit alarming, I was more wondering if I could trust my cheapo DMM. Turns out I can't. Ended up purchasing the Fluke 101 which solved my problems of the weird continuity readings on my stator. Basically my Voltages from the RR was dropping from 14.4 to 13V from 2500 to 5000rpm. Turned out some contact cleaner fixed that!

So yes, I have learned that cheap multimeters are just not worth the anxiety. I really thought they'd be fine for simple low voltage work, but apparently not. Also Fluke 101 tested the AC house Voltage at 246 which is within tolerance.
 
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louie

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A couple of thoughts here.

OP's basic problem is a cheap, inaccurate meter, not really whether its true RMS or not, although true RMS would more likely show up on a decent meter.

Decent meters without true RMS are usually made to show the RMS value of a sine wave at mains frequency (50-60Hz), and should say so. Mains voltage is really close to a sine wave. Today it is cheap to produce a digital meter with pretty accurate DC and true RMS AC, but only up to typically 400Hz. It costs real money to get really good DC and AC accuracy (say, less than 1%) and good frequency response for AC measurements. Some people will look at a meter's specs and see that it measures frequency to maybe 1MHz, but this always refers to the frequency COUNTING function, not the AC measurement range.

Cheap meters can sometimes be OK for low voltage DC and ohms tests, but their typical failing is safety. There is a lot of energy available when testing mains (in any country). All it takes is a mistouched probe, mistakenly setting the meter to ohms, or a meter with a design inadequate for mains voltages and you could have a meter literally explode in a ball of flame in your hand. A good meter is designed to minimize the danger, but apparently some vendors choose to be dishonest in marking their safety ratings. That said, I did try a free Harbor Freight DMM in my mains (carefully) and found the reading wildly off compared to my Fluke, Brymen and even a Kill-A-Watt.

There's lots of interesting chat on meters in the nice Aussie EEVBlog site:
http://www.eevblog.com/forum/testgear/

Fluke makes great kit, but they do have products that may not be appropriate for your use. Only their most expensive handheld meters have AC response up to 100kHz, so anything else may not work well if you need to measure AC and harmonics like that. But I think every Fluke should measure mains voltage accurately.

The link about true RMS not being good only shows the difficulty of calculating accurate AC measurements - it's much harder than DC. And users don't usually have options to turn true RMS off. As always, the user should know what they are doing and the limitations of their equipment. DMM specs are trickier than most would believe, especially regarding AC.

I'm not sure about measurements of your stator generator. It may be DC, but pulsed according to RPM and really AC+DC unless filtered and smoothed. That's another measurement problem.
 
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