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Splitpair
Premium
join:2000-07-29
Cow Towne
kudos:3

1 edit

2 recommendations

Electrician's Math and Basic Electrical Formulas Free PDF

From the Mike Holt web site. Electrician’s Math and Basic Electrical Formulas Free PDF Download!

»www.mikeholt.com/download.php?fi···Math.pdf

Wayne
--
If you cannot fix it with a buttset and some beanies you ain't a technician.



whizkid3
Premium,MVM
join:2002-02-21
Queens, NY
kudos:9

Great find, Splitpair.

Although there are no illustrations, problems, tutorials and it may not be for beginners; since Splitpair has put us in the spirit of giving, the following is handy sheet of formulas from Kerite that I use all of the time:

Useful electrical formulas

The only one I feel is missing from this list is as follows:

kW (kiloWatts) = kVA (kiloVoltAmps) x p.f. (power factor)

They have quite a few other gems (See the bottom two sections on the page):

Kerite



61999674
Gotta Do What Ya Gotta Do
Premium
join:2000-09-02
Here
kudos:1

Yeah the wonderful Power Factor multiplier.
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whizkid3
Premium,MVM
join:2002-02-21
Queens, NY
kudos:9

Power factor is nothing more than the percentage of how much power is used out of the total power that must be supplied. The 'other power' - not used ' is stored in magnetic and electric fields, and is returned to the system each cycle. It is not lost power, nor can the utility charge you for this power (primarily because it is not read by a Watt-meter). Unfortunately, it can only be calculated if you know the reactance and resistance of the system (and then with difficult math to some). It can be measured.

The reason it is important, is that the electrical system must be sized to handle the total power supplied, which is more than the load requires (except for purely resistive loads). It becomes very important when designing for transformers and motors, for example.


contsole
Premium
join:2003-12-30
Wethersfield, CT

said by whizkid3:

... nor can the utility charge you for this power (primarily because it is not read by a Watt-meter ....
I realize this is Home Repair and not Industrial, but I saw a bunch of 3 phase stuff listed so ...

In a commercial or industrial setting the utility DOES in fact charge for the "lost power." They can use a peak and hold PF meter (not common) or a 15 minute averaging PF meter (common) or install a Volt-Amp-Reactive-Hour ("lost power") meter next to the Watt-Hour (regular) meter. When your have both meters you can calculate the month-averaged PF.

Since the utility has to generate, transport and deliver this power they are entitled to charge for it. For residences, it's simply already built in to the rates.

LeeWL

join:2002-11-10
Morrisville, NC
reply to Splitpair

Nice info in these posts. I keep menaing to put something similar together to point to as reference with tenants when they start asking whay they can't use the full 20 amps on their circuit and we are "making" them put in more than they think they need or when they come in with wildly wrong calculations and try to argue with me.



psafux
Premium,VIP
join:2005-11-10
kudos:2
reply to Splitpair

Thanks Splitpair and whizkid3. im looking at becoming an electrician, very good reading!
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61999674
Gotta Do What Ya Gotta Do
Premium
join:2000-09-02
Here
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reply to whizkid3

Yeah I know that



whizkid3
Premium,MVM
join:2002-02-21
Queens, NY
kudos:9
reply to contsole

said by contsole:

In a commercial or industrial setting the utility DOES in fact charge for the "lost power." They can use a peak and hold PF meter (not common) or a 15 minute averaging PF meter (common) or install a Volt-Amp-Reactive-Hour ("lost power") meter next to the Watt-Hour (regular) meter. When your have both meters you can calculate the month-averaged PF.

Since the utility has to generate, transport and deliver this power they are entitled to charge for it. For residences, it's simply already built in to the rates.
True, they have to generate, transport and deliver the power. I have never seen a tarriff schedule from any utility for commercial or industrial, that has rates charging anyone for reactive power; other than having a threshold that must be met. Nor have I seen the utilities installing reactive power meters. Of course, that doesn't mean it isn't done; just that I haven't seen it. The utilities will, however, specify the minimum power factor that your facility must meet; otherwise your rates will go up. At that point, it becomes less expensive to use power factor correction (usually capacitor banks), then to pay the utility.

I had a client recently, that has about 12MVA of UPS power. All of the UPSs were running between 30 to 40% loaded, creating a serious leading power factor at their utility supply (about 68% p.f.). The utility increased their rates by about 30%. (We are talking millions of dollars per year.) They must have been monitoring their reactive power use; or they checked it after seeing a serious total reactive power use on those feeders, of which 50% to 80% of the power supplied on these feeders was being supplied to this one customer.

On the other hand - you're right - the utilities aren't doing anything for free. The extra capacity of generation, transmission, etc.; required to supply reactive power, are being paid for by their consumers; but not on an individual basis, unless of course you exceed their threshold. We all know there is no such thing as a free lunch.


jrs8084
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join:2002-03-02
Statesville, NC
kudos:1
Reviews:
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Some very helpful and patient people took a lot of time to explain to this neophyte what pf is, and why it is important. It didn't make sense until I started looking at graphs at what was happening each cycle.

For a few years, I had heard my company was getting fined for our power usage, and they were demanding we install a capacitor bank to correct it. Now, I know it was a low pf.

The company kept paying the fine, rather than installing their requested equipment. I guess the power company got fed up, and now has a meter that measures supplied power. It shows a pf of .79 (and I hear that is the monthly average). If we are using 20% more power than what we were paying for (before), I could see why they were mad.
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