120/208V or 277/480V.... huh?

Tony... when connected to the 208V supply, line-currents Ia, Ib, and Ic will be 62A, 47A, and 62A, respectively.

The values obtained are based on the following:

o The resultant load is an Unbalanced-Delta.

o At 208V, the 7.5kW heating-elements (call R1, R2, R3) will each require 6.5kW.

o At 208V, the 4.5kW heating-element (Call R4) will require 3.9kW.

o Load distribution is: R1 (6.5kW) between Line A and Line B; R2 (6.5kW) between Line B and Line C; and R3 & R4, in parallel (10.kW), between Line C and Line A.

Anyone, except PTM's, may contact me off-forum if detail is needed!

Regards, Phil Corso (cepsicon[at]AOL[dot]com)
 
S
Phil,

I don't think your kw derating by voltage is correct. The voltage and current are both reduced by 13.3%, giving an overall power decrease of 25%.

He didn't say his heaters were single phase, and immersion heaters in this range are commonly available in three phase. When I select them, the threshold is either 3kw or 4kw, can't remember which, and in a case like this, where only one heater would have ended up selected as single phase, I would have put that one on 3-phase as well to maintain a balanced delta.

So I'm going to say his total HEATER load, presuming 3-phase heaters, is (3 x 7.5 + 4.5) * 0.75 / 208 / sqrt(3) = 56.2 FLA. He still has to add in the motors, and one other wild card is that heaters of this type vary significantly in actual kw. The mfgr might build two nominal 7.5kw units and one might come out at 7.0 and the next at 8.2 or something.
 
W

I think that it should be noted that with a 208 VAC supply, your heaters will supply roughly 13% lower heat capacity for your process which may be create operational problems. This may be fixed using buck-boost transformers or a different distribution transformer ( e.g. 480/240VAC).

I have not used the below company but they have an explanation of buck-boost transformers which are commonly used to boost voltage from 208 to 230 VAC.

http://www.acmepowerdist.com/pdf/Page_104-109.pdf

William (Bill) L. Mostia, Jr. PE
Sr. Consultant
SIS-TECH Solutions, LP

Any information is provided on Caveat Emptor basis.
 
Steve, my calculation of power at 208V is incorrect. It is 75% of their 240V rating. But the calculations for amperes are not based on power. Instead, I used phase voltage, 208V, and element resistance. I believe you must agree that at rated design voltage of 240V, the resistance for a 7.5kW element is (I apologize to the PTMs for using formulas) Vab^2/Pab, or 7.68 Ohms. The corresponding resistance for the 4.5kW element is 12.8 Ohms.

Regarding your interpretation of configuration, i.e., multiple-elements per phase, vs my using one-element per phase (except for the 4.5kW unit) can only be settled by Tony! He did say 3-7.5kW elements. Also, I did not interpret Tony’s post to include motors.

Regards, Phil
 
S
<i>Steve, my calculation of power at 208V is incorrect. It is 75% of their 240V rating. But the calculations for amperes are not based on power. Instead, I used phase voltage, 208V, and element resistance. I believe you must agree that at rated design voltage of 240V, the resistance for a 7.5kW element is (I apologize to the PTMs for using formulas) Vab^2/Pab, or 7.68 Ohms. The corresponding resistance for the 4.5kW element is 12.8 Ohms.</i>

But for a resistive load that's the same thing (assuming we neglect the change in resistance due to running at lower watt density -- most materials change in bulk conductivity with temperature). Whether we note that the voltage across the load and the current through it have both decreased 13%, giving a total power decrease of 25%, or whether we pretend to ignore current and go with P=E^2/R (which amounts to the same thing), we end up at the same place.

<i>Regarding your interpretation of configuration, i.e., multiple-elements per phase, vs my using one-element per phase (except for the 4.5kW unit) can only be settled by Tony!</i>

True enough.

<i>Also, I did not interpret Tony's post to include motors.</i>

He said "My electrician also stated that the motors will run hot at higher current if rated for 240 volts and run on 208 volts. Is he correct?"

Regards, Steve
 
Steve, I apologize for not being clearer with my calc comment.

I meant that I didn't use "Power" in the Unbalance-Delta equations to determine phase-currents and line-currents. Thus, the values I originally presented are still valid for the Calculation-Basis shown!

An aside: the corresponding currents for the original design basis (240V), i.e., Ia, Ib, and Ic, are 71A, 54A, and 71A, respectively. Phase-sequence used is A-B-C

Regards, Phil
 
> Can you get 208v to supply something (as per the nameplate requirement)from a
> 240/120 household system?

I am also looking this answer but did not get it yet
 
C
Yes, with a transformer. You need a center tapped secondary to give 120/240 single phase with neutral.

The primary connects to any two 3 phase wires. That's why machine tools
for world wide use are so full of transformers.

Regards
cww
 
D
Ken Ken, You say that you "can't spel" as if that doesn't matter. I am not very good at spelling either, so I use a dictionary as needed. Since you didn't bother to use a dictionary as you wrote your post, I can't help but wonder if you might not be a bit slow to look up details in the NEC as appropriate. The original poster may not have as much experience as you do in wiring, but he is at least trying to look up the information that he lacks. Who would you rather trust, the guy who thinks he knows it all and won't look it up, or the guy who knows he doesn't know and double checks?
 
B
> Ken Ken, You say that you "can't spel" as if that doesn't matter. I am not
> very good at spelling either, so I use a dictionary as needed. Since you
> didn't bother to use a dictionary as you wrote your post, I can't help but
> wonder if you might not be a bit slow to look up details in the NEC as
> appropriate. The original poster may not have as much experience as you do
> in wiring, but he is at least trying to look up the information that he
> lacks. Who would you rather trust, the guy who thinks he knows it all and
> won't look it up, or the guy who knows he doesn't know and double checks?

Unfortunately, many chunks of the NEC are not for amateurs. Looking it up does not mean a guy who does not know any better will get clued in correctly. The guy who does not know and looks it up may end up thinking he knows, but still not know.

Let me ask what should be a simple question.

What color should the grounding electrode color be?

Hint - the grounding electrode conductor is the conductor that connects the grounded conductor (often the neutral - but not always) to whatever grounding electrodes(s)such as ground rods you may have.
 
E

edwin Valerio

Only have 125 coming from one wire in electrical panel. Other wire is dead. Tried to check if there was a fuse box or something and did not find any.

What to do?
 
Jim says,
Simply put, you will need an additional transformer designed to operate on your shop's primary high voltage to run 240vac equipment.

You cannot run 240 equipment on 208.

Your electrician has understated the consequences and in fact, any attempt to operate 240vac (2 or 3 wire config) will likely burn your new equipment up.

Remember that the operating voltage and amp draw is not the only consideration-the inrush current on start up of motors will exceed the amp rating of the start and run capacitors for motors because of the lower voltage, and if equipment is loaded down by the work it does, it will likely get "hot enough to fry chicken" and then just quit. And any warranty will be voided by operating the equipment on the incorrect voltage.

I've installed additional transformers for a dedicated machine or application. (they're usually small enough to hoist up in the air and mount on building steel with unistrut if floor space is at a premium) This is usually in older shops that were wired for 220/440 with a high leg (3 phases-2 phases are 110vac and one "high leg" is between 190vac and 210vac-wiring receptacles to high legs in panels usually results in burned equipment-if you see a pattern of two single pole breakers and an empty space repeated in the panel that tells you that it's an old, 220 high leg transformer-however, you can use the high leg with a 120 v phase for a two or three wire breaker and it will work).

Most new factories and shops are equipped with 277/460 transformers for the fluorescent lighting, sighting lighting (luminaires) and heavy shop equipment, and additional transformers 120/240 for receptacles, copiers, water heaters, fire alarm, security and additional control transformers low voltage apps such as a doorbell or other equipment that offers 120/240 wiring options. (Sight lighting ballasts for instance offer multi voltage wiring options and the higher the operating voltage the more economical it is to run) All of the step down and isolation transformers work with the same primary high voltage, which in my US STATE OF DELAWARE starts at 12,700 VAC 3Ø and may be as high as 22,000 VAC 3Ø primary voltage.

So, a small, dedicated transformer that steps down your shop's primary supply voltage to 240/480 3Ø with a minimum 100 amp secondary rating (allowing 20% headroom over the new equipment's, rating) should be on your "things to buy" for Christmas list.
 
> a house you can run 12/2 to a 240 and your computer will use less amps and that means less your electric bill will be. I have wired buildings that have had over 25 panels in them. Guys in this they are no romex here you make your own circuits and you have to know what you are doing. When you see something that like 120/208 or 277/480 this means something a lot of motors have taps to <

I would like to see your calculation for power consumption if you believe 240V is cheaper than 120V to the same load. Power (watts) is P=IE (current times voltage). If you draw 10 amps at 120V, you will draw 5 amps at 240V so...

P=10x120V = 1200 watts
P=5x240V = 1200 watts
 
Tim... you probably have done some investigation of branch-circuit losses. Some advocate the use of Power Factor Correction (PFC) devices, for energy-use reduction.

My study, to the Florida EPA, showed that increasing branch-circuit wiring for major appliances, by one-size, will achieve the same savings at a fraction of the cost!

I am talking of new house wiring, of course!

Regards, Phil Corso
 
J

Jim Eylander, Jr.

120/208 power is derived with a "Y"-connected transformer, whereby the Neutral (which is then bonded to Ground) is common-tapped to the center of all three phases at 120-degrees of phase shift. 208-volt power only grants 75% of 240-Volt power, so motors will definitely run hotter on 208 than 240 if they are not specifically wound for 208, but most of them, particularly small or fractional horsepower motors that are multi-voltage rated, are able to handle the additional heat. The 120-Volt designation is for what each leg of the 3-phase power's potential is to Ground, or Neutral Center-tap. The 208-Volt designation is the potential between any two legs of power. Typical household current is 120-240 VAC Single-Phase, which is derived from a single transformer at 180-degrees of phase angle, the two poles of the power being center-tapped and bonded to Ground for the 120-Volt designation, 240-Volts between the output legs (Secondary winding of the Transformer.) 120-240 VAC 3-Phase is derived from a "Delta"-connected Secondary winding, whereby the Neutral only comes halfway between two of the windings, the third being "wild," which will have a fluctuating voltage to ground between around 140 to 208 Volts, hence the term "Wild Leg," designated by orange or red tape on the conductor. Any device or appliance requiring 120-volts will burn out if connected to the wild leg, so since most office buildings and non-industrial commercial buildings utilize a lot of 120-volt circuits, it's much more practical to serve 120-208 VAC to the structure, since the motors for HVAC systems usually are 208-240 VAC rated. I've been a Journeyman for nearly 40 years, and to my dismay the majority of Electricians, even in the Union, are just "installers," pipe-benders and wire-pullers, not being diligent enough to truly learn the basis of their trade. Consequently, far too much "knowledge" that is divulged by them is little more than "urban legends," and not based on truth. BTW, 120-VAC household current will KILL you just as fast as the industrial 277-480-VAC will if you are caught in the circuit's path across your heart. The 60-Hertz power will fibrillate your heart to nearly explode... "Don't try this at home" is a GOOD rule for those without proper training and supervision!!!
 
>Thanks Jim Eylander, Jr.,
>
>Finally, a good, clear explanation.

Hello friends, this is Agate, I am electrician in profession. I would like to say that plenty of great advice is available here actually.
 
A brief history: When Thomas Edison built the Pearl Street Station in New York City, electricity became a hot item - every city wanted some! It was wonderful to have electric street lights, and businesses started installing lights AND motors. It was all DC (Direct Current) - Edison was firmly against AC all his life. The severe drawback to DC was that after a few miles of wire, the lights wouldn’t light any more - too much energy was lost in the power lines.

The city of Buffalo wanted to get electrical power out of Niagara Falls, which was about 20 miles away, but DC power could only go 3 to 5 miles at low voltages. George Westinghouse got the contract, and hired Nicola Tesla to make it work. They knew they had to use AC, because with AC you could transmit power at high voltage to reduce the line losses, and then use step-down transformers at the other end to get safer, user friendly voltages.

The severe drawback was this: the lights would light but the motors wouldn’t run. Since the AC goes positive then negative, the motors would just vibrate in place.

Tesla figured out how to send five parallel power lines out from the generator at Niagara Falls, each line connected at even spaces around the generator. As the rotor was turned by the waterfalls, it passed all five power pickup points during each rotation, one after another.

The voltage in each line looks like each of the others - a sine wave of voltage going on continuously, but each one is phase shifted from each of the others. At the user end, they could make the motors turn by applying the five phases to a motor, hence creating a rotating magnetic field to pull the rotor around. This solved the whole problem - high voltage AC for long distance transmission and multiple phases to make the new AC motors turn.

Present Day Power: Now we use three phases instead of five. If you look at all three simultaneously, it looks like this:

Almost all high power electrical transmission is done using this kind of three phase power - three separate power lines, each identical to the others in voltage, but the sine wave is phase shifted from one to the other by exactly 120º, or 1/3 of a cycle. Almost all businesses receive power from the utility company as three phase power.

The final voltage step-down transformer at any business might be inside or outside of the building, and it’s almost always a three phase Delta-Wye transformer. It produces three legs of 120 V. electricity, phase shifted from each other as shown above. When you measure the voltage between any two of the phases, it’s 208 Volts AC. So you can get any of the following combinations out of any ordinary three phase circuit breaker panel anywhere in the country:

120 Volts single phase - use any one of the three available legs.
208 Volts single phase - use a two pole breaker, and any two of the three legs.
208 Volts three phase - use a three pole breaker, and all three legs.

Since the watts needed by the load is derived from Volts x Amps, some servers now use 208 Volts single phase instead of 120 Volts. You can get more watts at the higher voltage, without increasing the wire size for higher amps.

UPS’s up to 3000 VA are nearly all 120 V. single phase units. 120 Volts goes in and 120 Volts comes out. External Bypass is easy, because the input voltage matches the output voltage.

Single Phase UPS’s from 4 kVA to 25 kVA almost always take 208 Volts input, but the output might be any of the following: (Caution! This can be very confusing.)

a). 208 Volts single phase (no neutral wire, and no 120 V. output).

b). 120/240 Volts split phase, which is two legs of 120 volts, one going positive exactly when the other goes negative - a phase shift of 180º.

c). One leg of 120 V. and a second leg of 88 V., at 180º phase shift. This provides some 120 V. output and some 208 V. output: 88 + 120 = 208.

d). Two legs of 120 V. with a 120º phase shift, same as the input. This version is more recent. It requires two separate inverters in the UPS, but it’s the easiest style to bypass externally because the input and the output match.

With single phase UPS, it’s important to understand exactly how your UPS works and what additional transformers you need to supply the voltage you want, for output power or for the ability to install an external bypass switch.

Three phase UPS’s start at about 10 kVA, and go as large as 1000 kVA. Most models below 75 kVA are 208 Volt input and output, while most larger models are 480 V. input and output. You can buy models with 480 V. input and 208 V. output, but we strongly recommend matching input and output voltages to allow for installation of an external maintenance bypass switch.

In the range of 10 kVA to 25 kVA, you can purchase either a single phase or a three phase UPS. The single phase units are typically less expensive than three phase (less electronics inside), but many facility managers don’t like to put so much single phase load on their system - it’s harder to keep the three phases balanced.
 
> Can you get 208v to supply something (as per the nameplate requirement) from a 240/120 household system?

if the load is resistive it is possible
 
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