Estimating KWh electicity billing using clamp-on amp meter

[dpb]

On 5/30/2011 8:57 AM, Home Guy wrote: ...

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Maybe he's mixing readings between meters... :)

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[dpb]

On 5/30/2011 9:03 AM, Home Guy wrote: ...

Basically, yes. In theory it could be like three single-phase meters each connected across a phase and neutral. But, it ain't quite so easy as generally there isn't access to the N and it turns out one can show that the equivalent of connecting three to a common point ends up that one of the three can be eliminated leaving that one only needs two even for unbalanced loads.

I have vague recollections of this in power circuits 101, but that's been nearly 50 years now... :)

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[krw]

It's gotta be that way, or power (energy) out power (energy) in. The universe gets pissed-off when that happens.

[dpb]

On 5/30/2011 8:12 PM, [e-mail] wrote: ...

Well, yes, that's what it is that allows as how it can be shown that only the two are needed...I was trying to smoosh over the details here on purpose of trying to not write a theme but at least brush by the route... :)

[bud--]

Peak and off-peak isn't all that easy with the old meters, but I thought that was one of the capabilities of the new "smart" meters. Also 'talking' to the occupant.

Demand is a common method for utilities to level the peaks for reasons that have been well covered. Around here the demand shows up as a penalty charge, not a kWh rate multiplier. For industrial metering "reactive power" (kVARh) metering is also pretty common - again a penalty charge. The penalties are high enough to provide a real incentive. Some installations with backup power run the backup to shave peaks.

If I had the questions Home Guy did I would talk to the utility. Leave the door unlocked? Why repeated numbers? Why wide variation? Estimates?

With a 400A service the current metering will use current transformers. There is likely a CT cabinet with a utility seal. Unless the disconnect is ahead of the CT cabinet I don't see a reason why the door can't be left unlocked. I don't see why it can't be unlocked anyway - the occupant has to have access to the disconnect.

[bud--]

As a ghost of 101 - I think you want Blondel's theorem. Probably the only time it will appear in this newsgroup.

[krw]

Demand metering requires a demand meter, too. Peak/off-peak metering has been done for decades without "smart meters", though usually with two meters. FWIG, almost all old-style mechanical meters will be gone in a short time.

That doesn't make any sense.

That makes even less sense.

Are you mixing VARS and demand?

He says no, but...

[Home Guy]

Obviously you didn't.

^^^^^^^^^^^^^^^^^^^^^

Yes, I have the time to entertain tangents to the thread I started, which includes showing what a moron you are when you don't read what others have posted.

Why do you refuse to admit you were wrong? Diversion isin't an answer.

[Home Guy]

I'm in Ontario, Canada.

[Home Guy]

The city where I live owns and operates the electicity distribution utility and the water supply.

Which is going to make it tricky for the water department because most homes have been retrofitted with time-of-use electronic electricity meters which have some sort of RF wireless communications link which is supposed to act like some sort of long daisy-chain communications channel and pass all their readings through each other to collection points or nodes. Which means that the water department is going to have to hire their own meter readers when the electronic power meter network becomes operational.

I think they'll partner with the natural gas people, since they still also have to have a person come by and read the gas meters.

[Twayne]

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Your quote is not a cut/paste of the actual words, which is too bad; looks like you paraphrased it to suit yourself or t was somehow not the rght one as it doesn't mention residential/company connections and several other things. That one very gross spelling error hurts you too; it stands out like a sore thumb.

[krw]

Why don't they just piggyback the water meters on top of the power meters? There are no meter readers here. It's all "smart grid".

[krw]

But no time to research your own damned problem.

Of course you're too stupid to figure out that I have read the whole silly thread. You really are an ass.

I said you fond ONE counterexample, dummy. Why do you snip context? The fact is that you aren't looking for an answer, troll.

[krw]

Sure you can. I do it all the time. Some can't be edited (depending on how it was created) or cut but just because it's a PDF doesn't mean you can't cut-n-paste from it. You can highlight, underscore, add notes, and do a *lot* of things to a PDF.

[Robert Green]

I'd be reluctant to say that. Once a thread gets to a certain level of "tension" it becomes more a question of ¿Quien es mas Macho?

Checking what I have for the beginning of the thread (and my newserver gets swamped when those Teranewsians' server fails ) he started, at least, asking three specific questions:

1) when coming up with a total current measurement, do I include the current flowing on the neutral line? 2) He was looking how to calculate the "worst case" (all loads operating simultaneously I assume) 3) He wanted to know if there was an error in how he intended to calculate a maximum load.

That's at least why I recommended the Kil-O-Watt. He described a large number of easily tested, non-hardwired loads on his premises.

I do see in reviewing the thread from top down that his 1st line reply to RBM was:

"RBM used improper usenet message composition style by full-quoting:"

Maybe that's his newsreader automatically set to net-nanny "FULL ON" (-: So maybe you're right, the OP has a bit to learn about not biting the hand that's feeding him and was contributory in this interesting thread turning slightly sour. My mistake.

Because I've had my own tangles with bad meters and something the phone company called a "left on" connection (that actually turned into a national security matter), I pay attention to news reports of billing errors. This could just as easily be a screw-up with his electric company's billing systems. They are forever futzing with their programs to account for new "revenue streams" and fees and could have made any number of mistakes. Based on the level of errors I've seen reported in DoD studies, shift happens. A decimal point here and there, the wrong variable name, etc.

While you may be perfectly correct in why the readings show the way they do, there are a lot of other explanations. But it terms of learning, I think we (and perhaps he) have learned some critical things. You can't meter the neutral of a three-phase feeder and expect to get information about total usage, only the level of imbalance of the downstream circuits. We've learned that it's unusual not to be able to see your meter whenever you choose to, but apparently not universal. That's something for the OP to work out between himself, the power company and his landlord. As nearly everyone has said, to solve the puzzle more information is needed.

But I don't think it could ever hurt him to spend $25 on a Kil-O-Watt meter. He indicated from the start he wanted to measure total wattage, and the KOW will do that far better for the gear he has than any tong meter I know of. It calculates true wattage and can measure average usage over long periods of time. Going to the power company to investigate further knowing *exactly* what he's got in his office will let them know that he's done his homework, at least. That's important in dealing with them.

-- Bobby G.

"When the universe comes to destroy man, man will still be nobler than that which tries to destroy him, because in his death man knows he is dying and of its victory, the universe knows absolutely nothing." - Pascal

[dpb]

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Indeed it could...

I never said (and hopefully didn't imply by poor wording) my idea was the only possible explanation; simply a theory (apparently refuted, eventually).

OP is the (new, but not terribly so iirc 6yr) owner of the building so I'd presume he has some pull w/ the landlord... :) It would seem anything about the lock on the cabinet/meter that he would be allowed to do by whatever limitations placed by the utility/city could have been resolved in that time. If the limitation is only inertia on his part, that's another kettle...there's insufficient information to know _why_ it is currently as it is.

It's a commercial building w/ 3-phase service and the loads he mentioned were a few computers, basically. The Kil-O-Watt meter can monitor them but it'll do nothing for what is most likely by far the majority of the load which will be the 3-phase lighting, possibly water heater and other service loads. It'll be measuring the noise around the edges.

The characteristics of the peculiarities aren't likely to be explained by a loading issue anyway imo. The doubling of the readings in months that are roughly a year apart is just not credible as an ordinary event of somebody left the lights on over a weekend. It's either an accounting issue, an error in the reading or the like that is artificially being induced somewhat like your above suggestion (or mine of a different yet similar mechanism) or there's a _major_ intermittent load or fault somewhere on the system.

Either of those isn't going to be found by a minimal one-time guesstimate of the maximum possible monthly usage even if he measures an instantaneous 3-phase usage correctly and it certainly won't be found by poking around on one computer supply at a time.

$0.02, imo, ymmv, etc., etc., etc., ...

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[bud--]

I maybe should have said more.

A demand meter will show a "demand", which is kWh over a short time period, maybe 15 minutes. The maximum demand for the billing period is indicated and read, and the demand register is reset. I haven't looked at a utility rate structure, but basically the kWh demand is multiplied by a $number to give a penalty which is added to the bill. The higher the kWh demand the higher the penalty.

The penalty can be quite high and provides an incentive for the customer to use one of many "peak shaving" techniques.

Similarly the VAR meter (which for mechanical meters is a second meter) registers the reactive power 'used'. (This flows from the utility and back to the utility and is not actually used.) The kVARh in the billing period is multiplied by a $number to give a VAR penalty which is also added to the bill.

This penalty is high enough to promote using power factor correction caps, or other techniques, to improve the power factor.

The utility can, and does, correct the power factor. They can also improve the power factor caused by harmonics (I don't know if utilities do). They can't fix high demand.

[dpb]

On 6/1/2011 5:47 AM, Robert Green wrote: ...

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I did intend to indicate and give credit that he did recognize he needed the full 3-phase usage only that it seemed as though had hard time coping with what he proposed is too rudimentary to help much (or at all) in resolving his problem...in that even if he knew the answer he proposed it doesn't get anywhere at the root cause of the symptom.

[Robert Green]

Agreed. He's gonna have to call the power company, like it or not. At this point he at least needs their interpretation of the bill. Then he can either accept it or refute their explanation but at least he would have a better understanding of what's (allegedly) going on.

-- Bobby G.

[krw]

I understand all that, however...

...a fixed penalty vs. a rate penalty doesn't make sense, is what I meant.

Rolling blackouts. ;-)