Why isn't 3 phase available for homes???
- Thread starter Kyle_in_Tex
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texbaylea
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We had 3 phase at our home in Dickinson. The house was very near a school so it was available at the pole, just had to add a second transformer. The only 3 phase equipment was the A/C units, Lennox, by the way. This was the early 70s and the price delta was only about 12% as I remember. Those units ran for more than 25 years. They were due for replacement at the time we sold primarily because of corrosion, mainly on the coils. They had been submerged in the flood of "79 but I washed them out and flooded them with WD-40 to dry them out and they went to working again. Did have to replace the contactors within a few months. I did the same with all the major appliances and they continued to work for several years.
Vernon
Vernon
dubba
Gold Member
In my area most of the savings from using 3 phase on larger motors is because of the way the electric company bills business accounts.
We pay for usage & peak demand. By using 3 phase equipment the usage stays approx the same but the demand per input is lower. The current combined demand charge in my area is $6.88 per highest average KW demand.
So from tommu56's example on a motor run for 1 hour continuously-
one horse motor 120v 16.amps = $13.21 demand charge
same on 3 phase 7.2 amps = $5.94
We pay for usage & peak demand. By using 3 phase equipment the usage stays approx the same but the demand per input is lower. The current combined demand charge in my area is $6.88 per highest average KW demand.
So from tommu56's example on a motor run for 1 hour continuously-
one horse motor 120v 16.amps = $13.21 demand charge
same on 3 phase 7.2 amps = $5.94
BillyP
Veteran Member
dubba said:
I don't know a thing about 3 phase so excuse my ignorance.
But this one horse motor that's pulling 16 amps would be pulling 16 amps if it were wired for 240.
How could a 3 phase one horse motor only pull 7.2 amps?
tallyho8
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BillyP said:
If a 110v motor pulls 16 amps then that same hp motor running on 220v would pull 8 amps. They would both use the same number of watts.
The difference is that a 110v line has one 110v line and a neutral and pulls 16 amps on that one line.
The 220v line is actually two 110 volt lines in different phases and the motor pulls 8 amps on each line.
The 3 phase uses 3 lines in different phases. Now, someone explain the way to figure the amps on 3 phase to us.
BillyP
Veteran Member
tallyho8 said:The difference is that a 110v line has one 110v line and a neutral and pulls 16 amps on that one line.
The 220v line is actually two 110 volt lines in different phases and the motor pulls 8 amps on each line.
The 3 phase uses 3 lines in different phases. Now, someone explain the way to figure the amps on 3 phase to us.
Yes I understand the amp draw...
120 volt motor = 16 amps on line 1
240 volt motor = 8 amps on both line 1 and 2 which = 16 amps.
What I don't get is how a 3 phase motor can pull less amps through the meter.
Is it as simple as wire size and voltage drop?
caver
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Three phase
A = Kva x 1000
1.73 X E
A = Kva x 1000
1.73 X E
tallyho8
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BillyP said:
I don't believe that 3 phase pulls less amps through the meter, just less amps on each line. But your electric meter measures the electricity you use in watts, not in amps. Since your watts are the same, your electric bill would be the same for residential use.
For business usemost utility companies charge by demand also. Your demand charge is figured by the highest amount of killowatts or amps, depending on your utility company, that you use in a certain period of time. If you have a high demand for only one minute, the utility company can put a surcharge on your bill for demand for many months.
As an example of their demand charges, I owned an air conditioning company that I closed every winter for 3 months and only used a night light and a burglar alarm. My bill was usually only $25 a month minumum during those 3 months. One 4th of July we had a shindig and had 4 people come in campers and used my electricity for their air conditioners in addition to the amount I was regularly using. Though my bill was only about $15 more that month than usual for the campers, it raised my demand and surcharge so that during the winter months when I was closed my minumum bill went up to $50 per month. So those campers who only used $15 in electricity raised my bill over $90 that year.
And, no, I have not figured out how 3 phase would reduce a residential electric bill and am waiting to see if anyone can explain it in a way simple enough for me to understand it.
BobRip
Elite Member
BillyP said:
There is current flowing through 3 wires instead of just 2. So for the same power and same voltage the current is less. The current in each leg is 120 degrees out of phase with the other two wires. I suggest you do a search on 3 phase power and read up. It's not real complex, but it's been 30 years since I studied it.
The life of the three phase motors is longer mostly because there are no starting capacitors or relays. These tend to fail. Parts that are not in a product cannot fail and cause problems.
SpringHollow
Elite Member
In this area, the meters used to just measure the amount of amps being pulled through the leg with the most amps. So if you had only an air conditioner running, the same cooling capacity would cost you half as much to run on a 220V unit versus a 110 V unit. In reality, many things are on at once so that the difference between the two legs usually is not real large unless someone put all of the high demand items on one leg. A good electrician would try to balance the load between the legs by moving circuits. This was done to even out the demand on the bus of the panel and to save on electrical costs.
I do not know if the newer meters work the same way now or not.
Ken
I do not know if the newer meters work the same way now or not.
Ken
