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3 Phase Demand Charges?

Machinery_E

Titanium
Joined
Aug 19, 2004
Location
Ohio, USA
The former owners of my building were using quite a bit of power, the electric bill was running about $500-800 a month, putting it in the "medium service" category. I called the power company up and I asked them if they could change things so it would be cheaper since I'm not using nearly that much electricity...they put it in the "small general service category" and its okay there as long as I don't go over 10KW...

Now whats the 10KW, is that the max amount of power the meter detects going into the building? (Ie. 10,000 watts all at once?)

On the bill under usage it has-

Meter reading

0 KWH
1.760 KW

So that kind of concerns me, I really haven't used any kind of power, but the meter is reading almost 2 kw already...FWIW the meter is a digital one...

Thanks!
Eric
 
I would expect the KW value is the peak demand, averaged over some very short time interval, which was measured during the month.

Electric companies tend to set a rate per kilowatt hour based on peak demand. The total bill equals that value times the KWH used.

- Leigh
 
Larger services are billed using two values. The total usage in kilo-watt hours and the demand charge. If you require electricity to start and run a 500hp. motor on occasion, the utility has to be able to meet that "demand" on the grid and charges accordingly.Double check with your utility, however your 10 kilo-watt ceiling is demand based, not cumulative.
 
That's GOT to be 10 kilowatthours.

You'd be limited to 43 amps TOTAL for your building if that were a peak demand figure. What they probably mean is the average kilowatthours (KWH) for the month. If you exceed an AVERAGE of 10 kilowatthours in the month, they'll put you back up into the medium category. I think the 1.76 is probably the current "instant" average. Kinda like the cars that have the instant gas mileage figure on the dash. I think you're probably a LONG way off from your 10 KWH limit. :cheers:
 
1.760 kW is an instantaneous reading, probably the demand its recorded in testing, etc. You buy power by the kilowatt-hour (KWH) and since you've used no power and the reading is 0 KWH, the meter and the usage agree.

What they're saying is that as long as your demand stays under 10kW you won't have a demand charge. If the demand exceeds 10kW then you'll have a demand charge that'll typically recur every month for a year. If your demand during the month when you first exceeded 10kW was 15kw, and 3 months later you have an 18kW demand, then the demand charge will increase and will be based on the 18kW demand, and will be on the bill every month for a year from the date when the 18kW demand occurred.

You'd have to check with your own power company to find out the exact terms of their demand charges, such as how long the charge stays on the bill and the time required at a given demand before it resets the demand portion of the meter.

Progress Energy is a little kinder to us than your utility. We've got a small commercial service category and as long as we don't exceed 35kW twice, or 50kW once, during the year, we don't have a demand charge. Our meter will record any demand that endures for 15 continuous minutes.

I'd say it'll be near impossible to keep the demand under 10kW unless you're working by yourself and only using home shop size machines. Demand charges can be a major part of a commercial electric bill so you want to do whatever you can to stay away from them. A typical hot water heater will have a pair of 4500W heating elements in it. They're not typically wired where both can be energized at the same time, but even one of them will pull 4.5kW. If you've got one and its typically only used for hand washing, I'd put a timer on it so it only runs during hours when the shop is shut down. It'll maintain the temp fine thru the day due to the insulation in the jacket.

What you have to keep in mind is that, once you exceed the max demand, you pay the charge per kW from zero, and not from whatever amount you exceeded the 10kW. Say the demand charge is $6/kW and your demand exclusive of a HW heater was 9kW. If that heater happens to come on during a period when the 9kW demand is already occurring, your demand goes to something around 12kW assuming the heater is single phase. Because that heater came on for 20 minutes during that time, you'll pay a demand charge of $72/mo for the next 12 months. It can add up real fast.
 
This is one reason that one does not see a lot of
utility-supplied three phase power in home shops. The
demand charge issue.

I've only ever seen one shop, with three phase power, and
no demand meter. And that meter went back I think into
the early 20s. I told the guy buying the building, "never
let them in to change that meter...."

Jim
 
I agree 10kw probably won't be enough to keep you from paying demand charges. You may want to talk to the power company, to see if there is other levels of service available, and if so, at what pricing.

They may have set you up with the 10kw service, knowing good and well you will exceed it...
 
Thanks for the input guys! Excellent info!

I've only ever seen one shop, with three phase power, and
no demand meter. And that meter went back I think into
the early 20s. I told the guy buying the building, "never
let them in to change that meter...."

I think there used to be a non-demand meter like that where I'm at now...power company came in around 2000 or so and changed it over to a digital one (ie. demand meter)...unfortunately, I'm afriad if they decide they want to change the meter there's not much choice in the matter... :(

Won't the power company tell you what the charges are?

I'm kind of scared to call them up and ask them...:D One inquiring about such things might invite some unwanted attention...but I did find this online-

Energy supplied hereunder will be delivered through not more than 1 single-phase or 1 polyphase
meter. Billing demand in KW shall be taken each month as the single highest 30-minute integrated peak in KW as registered during the month by a 30-minute integrating demand meter or indicator, or at the Company's option, as the highest registration of a thermal-type demand meter. For accounts over 100 KW, monthly billing demand established hereunder shall not be less than 60% of the greater of (a) the customer's contract capacity in excess of 100 KW, or (b) the customer's highest previously established monthly billing demand during the past 11 months in excess of 100 KW. In no event shall the monthly billing demand be less than 5 KW for any account.

I'd say it'll be near impossible to keep the demand under 10kW unless you're working by yourself and only using home shop size machines.

Very true, so far I have been able to stay under 10KW here...just trying to make plans for the future in getting stuff installed at the new location...like I just got a CNC lathe that has a 15 HP main drive motor on it (runs pretty much everything on it, so its about running all the time the lathe is on) So it would be a good deal just to run the lathe alone if need be to avoid the demand charge...

FWIW They roughly charge 13.80 a month plus 5.33 cents a KWH for the small general service (under 10KW) The next larger service is 24.00 a month, plus additional costs for transmissin, distribution (even if you don't use any electricity) (must be the demand charge) The electricity is a little cheaper at 4.77 cents a KWH, however it can be much more expensive with the demand charges, up to a max of 14.35 cents per KWH!


So I guess the question that remains is what does KW stand for? By what I found with what the power company said in their online document, it isn't an average use of KWH like JunkyardJ said...:(

Eric
 
10KW is not a whole lot of power, only about 14 or so horsepower total. Between a 5hp compressor, office AC, lights and a couple of computers you have just about hit that number and you haven't even turned on a machine yet. I know my AC unit has got to be about 4KW at least, then there is the electric hot water heater, and two PC's with 450 watt power supplies, three big monitors, a bench full of electrical test stuff, phones, fridge/freezer, dehumidifier. Like I said, 10KW is not a whole lot of power.
 
Here goes, if your total average (integrated) demand over any 30 minute period exceeds 10kw they will stick you with a demand charge which will remain for the next year. If you shop employs more than 1 person or you can run 2 automatic machines at once then it will be difficult to avoid that charge. The trick with demand charges is to keep a steady work load, if you can keep 2 automatic machines going at once then do not let any demand charges stop you, product out the door pays the bills. What you do not want is to run high demand machines occasionally.

Air conditioning and water heating will need to be managed that sort of load is great for incurring demand charges. Things like compressors are less of a problem due to their low average power for general shop use. Sandblasting is another matter but fortunately it is usually only for a short duration.

FWIW 5.33c kwh is cheap power I am paying around US 13c /kwh with no demand charges (my power company doesn't charge for demand or power factor) and US$9 per month base charge.

Demand is measured in kw power usage is measured in kwh
 
Your 15HP machine will pull 14 KW or more, depending on efficiency, at full power.

The good thing is that you have a 30 minute integration time.

That means you must AVERAGE over 10 KW for that time to incur the charge. it is NOT a matter of peaks.

You could conceivably pull 29 KW for 10 minutes, and nothing for the next 20 min, and have no demand charge.

And, a 15 HP machine won't pull 15 HP unless loaded down to full power. So if the machine is loafing as it cranks out small parts, you are fine. Only if you ask it to do some serious hogging out will you get up towards the 15 HP (plus losses0.

Then also, there is part change time, tool change time, and all the various small times that the cutter is not actually cutting. Those add up, and will reduce the net integrated power.

But get a gas water heater! Why waste that much power on a support function?
 
Machinery E, why don't you call or go to the power company and ask them what the term means? I think they could tell you exactly what they are reffering to.
 
Go back and read the exact wording, JST. The 30 minute integration time is
at the discretion of the utility company. They reserve the right to use PEAK
values for determining the demand charges.

Folks the trouble here is clear. The utility *will* tell the customer what the
charges are. Once the bill is sent!!

Basically their approach is, "this is a big mystery and we can charge whatever
we want. If the algorithm used to compute the bill results in a low number that
displeases us, we reserve the right to generate a new algorithm that gives us
what we want."

One reason that converters are so popular I guess.

Jim
 
Even the thermal demand meter has an integration time. Likely to be much shorter though, I agree.
 
Folks the trouble here is clear. The utility *will* tell the customer what the
charges are. Once the bill is sent!!

Basically their approach is, "this is a big mystery and we can charge whatever
we want. If the algorithm used to compute the bill results in a low number that
displeases us, we reserve the right to generate a new algorithm that gives us
what we want."

Jim

That’s not entirely true. Power companies (and co-ops) are regulated utilities here (Illinois) and I believe it is the same in all fifty states. What this means is the rates they charge are set with government approval, and must be applied equally to all customers. Where they play games is in how they classify the customers. Likewise, the charges for service connections, line extensions, etc. are fixed, but often times just what work is required is open to interpretation, and that’s where the extra charges start to build.

One strategy I’ve found useful when I have a problem understanding what they intend to charge me is to call the state agency that regulates the utility, in my case the Illinois Commerce Commission. In other states it may be called the Public Utilities Commission. Google for a web site for your state’s agency. They should have a complaint number.

In Illinois one can call for a clarification without filing a formal complaint. The Commerce Commission won’t give the answer; they call the utility and ORDER them to explain the charges. I’ve done this twice over the years, and each time it has resulted in the phone ringing off my desk that afternoon as the utility wanted to find out what the problem was. NO ONE at the utility wants to be the guy that brought down the regulatory scrutiny on his department.

Typically, they won’t admit they are wrong, but by the same token, they really want the issue to go away, and so will work to resolve the issue so that it does not fester into a formal complaint. The two times I’ve done it, I wasn’t completely satified, but the outcome sure felt better than their initial no-compromise demand.

[FONT=&quot]Dennis[/FONT]
 
What you do not want is to run high demand machines occasionally.

Exactally! Since I don't have anything too big going on at the moment, I want to try to keep costs down as much as possible...going over one month and getting nailed for a year with higher charges isn't too good...like running the 15 HP motor in 28 min. "spurts" would be a good deal to save on the demand charges...of course if the meter is setup that way...I guess the way to do it is to get the ammeter and check what stuff is pulling and see what the meter registers...

BTW, I don't plan on running the hot water heaters or AC, the main thing is to provide for the machine's needs, not mine...:D

Machinery E, why don't you call or go to the power company and ask them what the term means? I think they could tell you exactly what they are reffering to.

Yes, but what that causes them to change the demand metering from 30 min to instant/peak...or something worse? :eek:

Eric
 
When I was building my shop at my home I asked the lineman about 3ph and he said they could probably do it even though it's a subdivision because it's ag2 zoned. He said I would not like the cost of the power and after he explained some of the way they charge for 3ph I agreed and am using a phase convertor now as I had been all along.

Eric, I am sure the changes they quote are using their fudge factors. They will make sure you pay dearly for 3ph and if you are not using enough they will some how raise the price with a fudge factor.
 








 
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