3 phase electric Question

disneyjoe7

If a house has a 3 phase input then I think it's 120vac on each leg to neutral, but isn't that 208vac for any 2 leg electric appliance? Like the Dryer, Whole AC, or the Hot water tank? I seen that today, but I didn't have a meter with me.

obieone

Unless you live in a SPECIAL house, you don't have 3 ph. You have 2 hots and a neutral(ground).L1, L2, N. And yes they're 2x120vac.

disneyjoe7

Well it's a SPECIAL house, Not my house but my sister in law house and yes it's 3 phase. A electric person how fixed something for her before seem to think it was business before, but this is a residence home area.

I-SIG

Yeah, most houses have 1-phase, 120/240V AC power. Either hot leg should be 120V. Together you should have your 240V.

It could be possible that you are fed from a 3-phase, delta-connected transformer bank, however you still receive the same voltage unless some idiot ran the "wild" leg to your house, in which case you would have 1-120V leg and 1-208V leg. Phase-to-phase they would still be 240V.

The other possibility is that you live in a condo or an apartment and the entire unit is fed by a 3-phase Wye-connected transformer. Here, you should have 120V on any one leg, and 208V phase-to-phase.

At your meter base, you should be +/- 5%. Most appliances these days are usually safe to be on either 208V or 240V, but check with the manufacturer to be safe.

SKsolutions

obieone wrote: »

Unless you live in a SPECIAL house, you don't have 3 ph. You have 2 hots and a neutral(ground).L1, L2, N. And yes they're 2x120vac.

The extra one is R, for reverse

obieone

Sorry, my mistake. O.K. your s.i.l. has 3 ph. What's your concern?

disneyjoe7

Well I have to break out a meter to see the voltage in this house, but most 240vac would be ok with 208vac that's cool.

obieone

I've got 250 vac across L1 &L2:eek: Nothing has blown up yet.:rolleyes:

ben62670

208 is like 120(not interchangable). Read from hot of each leg coming in to the ground. If it is truly 3 phase you could have 3 120's, 2 120's, and a 208, or 2 120's, and a 240. They call the 208's, or 240's the high leg. You can not use either with anything in your house. These are reserved for industrial type of equiptment. You can take the reading from the main breaker too.
Ben

disneyjoe7

The power is feed from above drop, the house in question is 3 wire and has a large commercial electric meter, the house next door has 2 wires and a normal looking meter. The whole thing started when I decided to check and find what was needed to fix up my sister in laws house. The hot water tank needs to be replaced, then I was told it has tripped the breaker twice. I asked which one she didn't know, where I thought maybe a bad breaker. I opened box and found that the hot water was to a 20 amp breaker, which I believe should have been a 30 amp with a 4500w upper and lower heater. Then I seen the 3 wires feeding main breaker, then everything else. An electrician who fixed something said it most of been a repair garage / business once with that power. Who stated have the electric company rewire house for normal 2 wire but all is the same as I seen.

BTW 3 phase I thought was only 208vac or 480vac, I assumed this had to be 208vac if 120vac was a voltage leg for lights / tv's and what not. But I never heard of 120vac 3 phase, so I need to break out meter and maybe take some pictures. Next weekend.

Really odd I know.

ben62670

From my limited experience with 3 phase I have only seen the three type I have mentioned. Get busy with that mm, and let us know:)
Ben

obieone

disneyjoe7 wrote: »

BTW 3 phase I thought was only 208vac or 480vac,

This is correct. There is no 3 ph. 120(at least I've never seen any)
If it's tripping the breaker at 208, that makes sense, but 240 should squeak by.
My recommendation, hire an electrician/ hvac co. to diagnose the situation and repair it, for insurance purposes

ben62670

obieone wrote: »

This is correct. There is no 3 ph. 120(at least I've never seen any)
If it's tripping the breaker at 208, that makes sense, but 240 should squeak by.
My recommendation, hire an electrician/ hvac co. to diagnose the situation and repair it, for insurance purposes

And fire prevention.

BTW my friend sparky got hit with 480. It wasn't pretty. Big flame ball, the floor was wet, I was 17, and freaked out:eek:!!!

disneyjoe7

obieone wrote: »

This is correct. There is no 3 ph. 120(at least I've never seen any)
If it's tripping the breaker at 208, that makes sense, but 240 should squeak by.
My recommendation, hire an electrician/ hvac co. to diagnose the situation and repair it, for insurance purposes

I question the whole house, but understand it's been like that since she bought it 6 years ago. The electric hot water tank is tripping breaker which is a pure resistance load. I would understand better if the AC was doing it, but the WH? Then the trouble is what I work 4pm -12am where she like 8am - 5pm job, so it's pretty much a "Weekend Warrior" thing.

I-SIG

2 of the 4 most common 3-phase voltages in North America involve 120V.

In a Delta-connected transformer, you have 2 legs, phase-to-neutral, that should be 120V. On the 3rd "wild" leg, you should have 208V, phase-to-neutral. If you put any combination of 2 out of 3 of these together, you should have 240V phase-to-phase.

In a Wye-connected transformer, all 3 legs, phase-to-neutral, should read 120V. Connect any 2 of 3 and you should have 208V phase-to-phase.

The Delta connection was popular for farm and other rural applications. You had your 120/240V connection to feed the farm house, but you also had 3-phase available for wells, grain elevators, or whatever other equipment was needed. It is also good for homeowners with small shops as well. One downside to Delta-connected loads is that it is harder to balance the connected load. One advantage to the Delta connection is that if you just want to run a motor, you can have a 3-wire service (no neutral) and save a little money.

The Wye connection has become the most common 3-phase connection. Most strip malls and other commercial developments run 120/208Y. As I stated, most home appliances can be run at 208V, but check with the manufacturer to be sure. Most fast food places and the such will also be 120/208Y.

The other most common 3-phase voltages are the Delta-connected 240/480V, mainly used in farms and very old industrial applications and 277480V Wye-connected. Most grocery stores and big box stores operate at 277/480Y as well as larger industrial applications and large wells and booster stations.

Some huge industrial facilities may operate at 600V connections, but those are rare, custom instances. Large, single-customer complexes may be primary-metered. In other words, they are metered at the same voltage that the power company runs on the power poles. Most common is 7200/12470Y although many utilities (like my employer) operate distribution voltages as high as 14400/24900Y or even 34500Y.

Wes

disneyjoe7

Wes,

Thanks for the great info. From what you stated I assume a delta wired house. The house was built around 1965 in Kissimee Florida pre Disney days, so I could say yes rural at the time.


My concern or question is what I understand or lost on. In a normal house the 240 isn't really 2 phase correct? So how does 3 phase work a non phase appliance motor? Working around 3 phase before I know a motor is pissed off (starting to smoke and or glow) really fast if a phase was lost.

So I guest my question is if the AC can work ok with 2 wire of 3 phase system, is it as efficient working that way?

I-SIG

Yes, in a normal house, the 1-phase transformer provides 2-120V legs. The secondary winding is split in 2 by the ground connection, thus giving you 240V when the 2 legs are put together.

Unless the A/C in questions is some large (over 5 ton) package unit, then it doesn't matter whether it is 1-phase 240V or multi-phase 240V. The unit would be designed to only accept 2 "hot" legs. In other words, you only need 3 wires: (2) hot and the neutral.

As for efficiency, the higher the voltage, the higher efficiency, so 240V (1-phase or 3-phase Delta) would be preferred over 208V. The lower voltage makes the unit draw more amps because the output of the compressor is fixed, regardless of voltage.

Efficiency is why transmission lines are run at crazy high voltages, up to 765,000V. No different for your A/C.

Wes

disneyjoe7

Interesting that you stated 5 ton, as many homes in Florida have this size. But she ok as its only a 2.5 ton unit.

disneyjoe7

So what I googled Phase A & C are 240vac where Phase B is for 3 phase motor only.
Where A & C are 120vac to neutral where the B phase is or should be 208vac to neutral, if I understood that right. I don't believe I will ever see a house like this again in my life time, unless I buy a barn / farm. Looking at main breaker they are feed top to bottom can I assume starting at top A B C?

nadams

How many amps is the main breaker in the panel?

Also, you can get 3 phase to a residential building, if you go through the proper hoops saying you need it. I see some guys over on www.garagejournal.com that are running 3ph, so they can run industrial motors that they get from auctions and the like.

Myself, I'd just be happy if I had 200 amp service to the house... I'm still running an old 100 amp service from the 60's when the breaker panel was first put in.

disneyjoe7

nadams wrote: »

How many amps is the main breaker in the panel?

Not sure, I didn't even know at first it was the "Main Breaker" as I thought it was a 240vac breaker at first. So when I question what breaker was Hot Water tank I tripped that one and the room lights went off, which I stated well that's F*&K'd up :eek: :rolleyes:

I-SIG

disneyjoe7 wrote: »

So what I googled Phase A & C are 240vac where Phase B is for 3 phase motor only.
Where A & C are 120vac to neutral where the B phase is or should be 208vac to neutral, if I understood that right. I don't believe I will ever see a house like this again in my life time, unless I buy a barn / farm. Looking at main breaker they are feed top to bottom can I assume starting at top A B C?

Never assume the phasing!!!!! Check it with a meter!!!!

A lot of utilities will run B-phase in the center, but my cooperative runs A-phase in the center. The IOU I worked for during college had A, B, & C-phases in the center depending on which small town and which substation you happened to be fed from.

Wes

disneyjoe7

I-SIG wrote: »

Never assume the phasing!!!!! Check it with a meter!!!!

A lot of utilities will run B-phase in the center, but my cooperative runs A-phase in the center. The IOU I worked for during college had A, B, & C-phases in the center depending on which small town and which substation you happened to be fed from.

Wes

Isn't this dependent on the electric panel?

But I was going to check wires to main break finding what was what, then looking for voltage between feed wiring to circuit breakers out to determine how this panel is wired internally.

petrym

You guys are melting my brain. As a crew chief on AF jets I used 120V 400Hz 3-phase power from the -60 units. That's all I knew about it!

ben62670

Steve what is your goal here? If I was you I would just stick with the normal 120v, and 240v, and leave the high leg alone. When are you going back?
Ben

disneyjoe7

Ben,

Just trying to do some repairs in the house for her. I came across the electric panel due to the hot water tank leaking and in need of replacement. I question the following, her electric bill for AC cooling, the hot water tank tripping breaker, the electric cover missing screws and loose. Then didn't state this but putting the cover back on the lights go out.... Nice. Removed cover and found main breaker was arcing a little due to bad or loose connection where it plugs into the metal leg / tabs. Turn it off then removed breaker to sit back down to clean up connections and then I said it should be replaced also. When I was told yes that was stated before, so just looking for info and what her options are at this point vs. her money she can put into house.

She if needed can get someone to due the electric box change out, but I wonder if her electric co., would redo feed to house for $0 or what so she knew. Or even if that necessary as that seems ok, but need to verify everything so she not tripping breakers.
The main box seems original to house which is 40+ years old. Of course the 3 phase panel and breaker them self can't be cheap as it’s not common. Looking to get back to her this Sunday maybe.

nadams

Check with a local supply house about the breakers. For my old 1960's panel, the breakers that are in it are no longer made. However, there's a newer model of breaker that fits, even though its not cross-referenced anywhere. the guys there just looked at the breaker I brought in and said, "yeah, I think we've got something here that would work"

disneyjoe7

Well at least I believe this panel was made by Square D at least that is what I seen on a breaker sitting around so parts shouldn't be too bad.

ben62670

I'd change out the panel to a standard one, and drop the high leg. You can get a panel real cheap at HD or Lowe's with a decent assortment of breakers.

disneyjoe7

Ben, not comfortable with a complete change out as the feed to house would need to be dropped or taped off. Something which is out of my area of work. She works for a company which has many contractors which would be happy to help her out if needed. But think your idea of dropping the high leg and wiring it as standard is best.

ben62670

You don't have to drop the lines. You can just omit the high leg at the meter can. I did this at the warehouses I lived at in FLA quit a bit. Too many people where playing in the panels trying to add circuits not knowing that one of the lines was 208. You could tell when they did this. The smell of ballasts burning was not too uncommon. The best way to tackle this is have the electrician pull the meter out, and run new wire to the panel. If I were closer I would do this for you. It is not a real hard job. The hardest part is putting all the household circuits in the new panel, and make sure you have a clod water pipe ground, and good earth ground. Where is this? Is the panel buried in the wall?
Ben