208V 3phase service

I don't see why it would not work you would be 12 volts low if need be you could use a 12 volt boost transformer perry

Thanks Perry.

The issue is not the ability to make it work, but the fact that the equipment, which is a gas fired heater is rated for 220/240 and there is only 208V available on site.

208V will cause equipment failure over a short period of time as it is outside the +/- 10% rule.

So you have an electric fan and an ignition circuit! The fan will run a bit slower and the spark will not be so intense! I can't see much of a problem with that! But, I may be wrong! The 10% rule? Do you mean the 4% V.D rule? That is for the cable that supplies the power, not the equipment! If the voltage drops more than 4% than the cable supplying the juice is too small and needs to be upgraded or even the main line is too small and needs to be upgraded! I would ring the manufacturer of the heater and ask for their advice! There maybe something inside that we don't know about!

Depends on the equipment! Two legs of a 3phase supply at 208v maybe adaquate for the equipment! All depends on what equipment you are refering to!

The equipment is a gas fired pool heater. The internal circuitry is engineered for 220/240VAC. The manufacturer is stating that using 2 of the 3 legs will create 220V.

I am saying he is wrong because it is not possible with a total available voltage of 208V.

I'm not sure if we have a Y-Delta or not. But even so, I am saying that no matter how you add up the legs on a 208V service we will not achieve 220/240.

Tell me if I'm wrong!

Your are correct, we can not achieve 220VAC from 208 VAC service, except adding one transformer with 208VAC pri. and 220/240 VAC sec.

Your equipment will be operated well in 208 VAC but the blower motor will be hotter than in 220VAC. Don't worry about it.

For example, now I am using a single phase motor: Alcatel with 230 VAC and It being operated well in 210 VAC for 3 years.

you lied, it is not 230VAC. I think it is 220VAC

In power distribution 208v 3 phase Y connected power is considered nominal 220v. They use 208v because of the square root of three (1.73..) relationship to get 120v for your standard household current (i.e. 208v / root 3 = 120v). What I'm trying to say is this: If you have a three phase circuit it's bad practice to connect a single phase load without balancing all three legs or current flows in the neutral from the transformer (required in any circuit), this in turn causes a voltage drop (in the neutral) which will lower your 120v capacity (if you have any 120v loads connected). Control circuits typically use 120/220 single phase power to control three phase loads (motors, heaters, etc.) so you can see the results of this folly. Tell your contractor to check the NEC for residential installation requirements for multiphase power.

Seems everybody agrees you're going to get 208 V. Now the question is will your equipment work at 208 V.
If the only motor in your pool heater is a induced flu motor (fan motor) you probably would not have a problem, at least with the motor itself. Starting torque is not a problem with motors used in this application,however A borderline low-voltage situation will result in increased slippage (lower rpm).

If the induced flu motor does not rotate fast enough you could end up with insufficient airflow to authorize the main burner.

Pumps are completely different. Starting torque could be a problem, but probably wouldn't be, however you could easily end up pulling excessive amperage, and a motor that is overheating.

As far as your control voltage. Multiple tap Transformers are readily available. I.e. 120 V or 208 V, 240 V. Many times equipment is supply with this type of transformer, this allows adjustment of the primary voltage to match the supplied voltage.

The question that remains, is there a good reason to use this piece of equipment, instead of locating a more suitable piece of equipment.

RIGHT Mr T

Says it all

Maybe the rep is refering to a 480V 3 phase service. That would give you the necessary voltage by tapping off of two legs. Or possibly the 208V is what your lighting is operating at. I'd question the people knowledgable in your service which they are refering to and take it from there.

Good Day Every One!

480v 3 phase is 480v phase to phase or 277v phase to neutral Y with center tap (4 wire system used for lighting ) or delta 3 wire no 277v.

I think the 3 phase 208 will work just fine for a 220v fan motor using 2 phases it's close enought but if your looking for 240v you could add a buck-boost to get you closer. You must have a Y 208 3 phase 4 wire system I'm thinking the igniter and controls are 120v (or maybe T-Stat is 24v with a transformer internal in the unit.)

A set of buck-boost transformers is a cheep fix assuming your load is low and just a fan should be.

your answer is smack on. the maker is trying to do a c.m.a move/

The electrical service in a residence in the US consists of two of three phases generated by the power company. Each phase is a sinusoidal waveform with an RMS voltage of 120V nominal when referenced to the neutral. The phases are 120 degrees out of phase with each other (the peaks and valleys don't line up). A device that is rated for 240V uses both 120V phases separately from each other (usually required for an electric motor). There will be two "hot" wires (usually red and black wires) and one neutral wire (white).

If the voltage is measured between the two "hot" phases" the RMS voltage will be 208V and will appear to a load connected to them to be a single sinusoidal waveform (usually used for a resistive heating element). A device rated for 208V uses both "hot" legs and NO neutral wire.

I agree.

I think he has a 1 phase 220v motor not 208 3 phase with a supply of 208v 3 phase Y. It's been my experance that a 220v load 1 phase (induction motor) will run just fine on 208 1 phase. I have seen aplications were they require 220v to operate if so a buck-boost is cheep and quick. In most cases nippled right of the panel feeding the equmient.

As far as you house stove, the heating unit isn't fussy if your a little low on the v's it just won't get as hot.

"I would not hook up 220V single phase motor to a three phase curcuit. You will be missing 60 degrees of emf per revolution."

120/208 V is RMS values, so the phase shift between phases is taken into account when the 208 value is calculated. The difference between 208 and 220 is less than an acceptable 10%.

I have run motors rated for 220 1 ph on two legs of 120/208 3 ph many, many times without any problems. Check out NEMA.

Section 9.9.1 of "Information Guide for General Purpose Industrial AC Small and Medium Squirrel Cage Induction Motor Standards states that "Alternating current motors shall operate successfully under running conditions with rated load with a variation in the voltage or the frequency up to the following: a) Plus or minus 10 percent of rated voltage, with rated frequency for induction motors."

US residential services are NOT 2 of the 3 phases. The typical residence is supplied by a SINGLE PHASE transformer with a center tap on the low voltage winding. The primary of the transformer is connected between one distribution phase and the grounded distribution neutral. The secondary of the transformer provides 240V full-winding (end to end), and 120V half-winding (end to center-tap). The center tap is the neutral point of the single phase system, and is bonded to ground at both the transformer and the service equipment.

The phase angle between the 240V wires is ZERO, not 120°, because THEY ARE THE SAME PHASE. The phase angle between the two half-windings is also zero if polarity is preserved. If the polarity is reversed (keeping the same test lead on the neutral wire and moving the second test lead from one hot wire to the other), the waveform will appear 180° out of phase with the other half-winding.

Both 240V single-phase and 208 3-phase equipment may or may not require a neutral, depending on the equipment itself. Most controls use 120V, so a neutral would be necessary in both cases. Power equipment (motors, heating elements, etc.) with no internal controls usually do not require a neutral connection.

Bad information is worse than no information.

Some US residential services DO USE 2 of the 3 phases of a wye low voltage distribution system, wherein the voltages are: line to neutral is 120 VAC, and line to line is 120√3 = 208 VAC, single phase. The two 120 volt legs are 120 degrees out of phase, which is why 120 + 120 = 208.

I have worked on such systems in New York City for Consolidated Edison. In NYC, it is not uncommon to see some Air Conditioners, motors, and compressors rated for 208/220 VAC, or 208/230 VAC single phase.

It is also common to see Autotransformers applied to step up 208 VAC to 220 or 230 or 240 VAC. (I had to use three such Autotransformers to properly supply the 3 phase input to a 12,000 volt 90,000 watt Czochralski furnace for growing laser crystals. An autotransformer is an electrical transformer with only one winding. The winding has at least three electrical connection points called taps, one at each end, and one somewhere in between. See any elementary transformer text.) Another problem I have encountered pertained to welding transformers, where for example, a 220 volt 60 amp input single phase unit develops arc initiating problems when supplied by 208 VAC. Welders usually need every last volt at arc start.

In such cases, you special order a 208 VAC unit, or you step up the 208 VAC supply to 220 VAC with an autotransformer.

Or, if you are adventurous and experienced and very competent and very well equipped, you open the welder's case, void the warrantee, and add a properly located 208 volt tap to the 220 volt primary winding.

I agree that some high-density urban areas use 208 3phase, especially if they are supplied by network service (NYC in particular has rules against overhead utilities in the urban core). However, that's a very small portion of the residential market in the US. Outside of the central areas of NY, Chicago, and a few other large metros, it's just not economical to run 3-phase when there's only 20-30 single-family customers per city block, non of whom have any need for a 3-phase service.

Most of Queens, the rest of LI, and all of the suburban areas run single phase laterals anywhere beyond the main pole line of the distribution feeder, just like the rest of the country.

The guy is right, you can use 2 legs of a 3 phase 208 vac circuit to operate a single phase 220 volt piece of equipment. However, if you use a 3 phase circuit supply, you will unbalance the circuit and current will flow in the neutral to balance it. This is not good, especially if you are using 120 vac supplies with the neutral (i.e. phase to neutral). So to sum up, in an emergency I would use that setup, but NEVER in lieu of a normal 220 single phase supply. BTW (by the way), 208 volts is considered to be 220 volts (Y connected source), and 240 usually comes from a delta connected transformer supply.

Old ways die hard in the electrical field (no pun). The old Voltage was 110/220, then it was 115/230, then it was 120/240. Now its 125/250 nominal. The increase is due to the average current used in the household has increased. If you increase the Voltage you can deliver more power for the same size wire. It works like this P=E X I.

Power available= E (voltage) X I (current). The insulation value of household wire is 300V.

It was found that as you used more power the Voltage would decrease because of internal resistance of the tranformer. All values are rms.

Any time you add a transformer to attain the correct voltage, there is a trade off in "power in vs. power out". The loss will increase increase the cost of operating the equiment. It isn't too much, but in this time of rising costs, any savings (or avoidance of increased cost) should be factored in your decision.

"pwr2the people" is spot on with his reply.

One thing to be kept in mind is that the original poster was provided new equipment from the manufacturer. While there are many ways we could make this thing work, it's unreasonable to expect the purchaser bear the risk of equipment failure because the vendor didn't do his job. 208 is a standard service voltage; if the equipment will accept that voltage without voiding the warranty, it should be listed on the nameplate.

I'll take a lot more risks with my own equipment (e.g., helping my daughter turn a vacuum cleaner motor into a hydro generator for science fair) than I will with a client's. The customer deserves my best effort.

Just quit your bitching and hook up the darn motor, it will either work or it won't...