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Bin510 (Industrial) (OP)
10 Jan 05 12:25
As a european supplier we are confused with the various terms and numbers used for power supply specs in north america. Terms like nominal system voltage, nominal utilization voltage, service voltage and service&utilization voltage in relation with 460 or 480VAC, resp. 575 or 600VAC do not mean a lot to me.
What i need to know is what i get if i would measure it out of the transformer stepping the voltage down from medium voltage to low voltage. Is it 460 or 480V resp. 575 or 600V?
Which of the two values need to be used for calculations, eg. for a transformer stepping down the voltage from 480/460 to 400VAC (europeean system voltage)? The 20V difference can make a difference there!

Thanks for your help in order to lift the fog i am sitting in!
Helpful Member!  dpc (Electrical)
10 Jan 05 12:30
If you measured at the transformer, you would generally have something close to 480V and 600V.  That is the nominal voltage.  Transformers are typical rated for 480V and 600V.  

Motor are rated for 460V and 575V to allow for the inevitable voltage drop between source and load.  

You should really obtain a copy of ANSI Standard C84.1 which explains all this in detail if you are thinking about providing equipment for the North American market.  

alehman (Electrical)
10 Jan 05 21:35
Normally step-down transformer secondaries are rated at the higher voltage, e.g. 208V, 480V or 600V (600V is rare).

Don't European systems work the same way, e.g. 400/380V?
Helpful Member!  busbar (Electrical)
10 Jan 05 22:09
 
C84.1 terms 480 and 600V as nonimal system voltages and 460 and 575V as nominal utilization voltages.  System voltages are associated with electrical-distribution equipment, and utilization voltages are typically on labels of ‘end use’ equipment, like motors.

An good overview on 60Hz voltage selection is chapter 3 of IEEE Std 141-1993 {Red Book.}

600v is more prevalent above the 49th parallel—Canada.  480V is more prevalent below the 49th parallel—US.
  
Helpful Member!  jraef (Electrical)
11 Jan 05 3:35
"600v is more prevalent above the 49th parallel—Canada.  480V is more prevalent below the 49th parallel—US."

Except when it's not!
As a gross generalization, much of the equipment in industrial applications in Canada is 460V, probably because that way companies that do business on both sides of the border can move equipment back and forth. It is mainly commercial ad institutional equipment that is run at 575V, i.e. commercial building HVAC systems, government facilities such as schools and hospitals, water / wastewater treament equipment etc. Lumber, Mining and Oil, the 3 biggest industries in Canada, are almost all 460V, so if your product is going into one of those, I would check before assuming they want 600V.

And conversely, if your product happens to be for the US textile industry (whats left of it), centered chiefly in the Southeast, then be forewarned that 600V is common for them! I have no idea why though, unless maybe they bought the machinery from Canadians!

"Venditori de oleum-vipera non vigere excordis populi"


jraef (Electrical)
11 Jan 05 3:39
And please excuse my prodigious use of commas in the above post!  

"Venditori de oleum-vipera non vigere excordis populi"


Bin510 (Industrial) (OP)
11 Jan 05 8:56
Thanks for your help.

I have now the ANSI C84.1-1995 standard.
If i have understood that right it would mean the following:
-System voltage is the voltage a power system is designed for (usually 480 or 600VAC)
-Service voltage is the voltage i should be able to measure after transformation from medium to low voltage at the point where it connects to eg. a factory (between 456 and 504 or 570 and 630VAC)
-Utilization voltage is the voltage i should be able to measure ate the point where my equipment is powered from (circuit breaker cabinet) (normally 460 or 575VAC respectively in the range of 440 and 504VAC or 550VAC and 630VAC)
Conclusion: my equipment needs to be designed for beeing powered with 460 or 575VAC.

I understood that the whole terminology ahs to do with historical differences in earlier power systems but the difference from 480 to 460 (600 to 575) have also to do with the assumption of power loss between the point of connection to a power system and the utilization equipment.

Did i get that right?

alehman: to answer your question i can say, that europe has harmonized its power systems. The harmonized system voltages are 400VAC (former 380VAC) for 3 phase systems and 230VAC (former 220VAC) for single phase systems. Most of the europeean countries have changed already to the new voltages, some are still on their way (eg. England, Ireland, ...)
tinfoil (Electrical)
11 Jan 05 9:47
jreaf: I cannot speak about western Canada, but the vast majority of commercial and indistrial customers in Ontario, Quebec, and Atlantic Canada use 600V as their nominal main supply voltage.

Notable exceptions are the auto makers, where the 'big 3' standardized their equipment to be 480V for internal standardization reasons.

I must disagree with one of your statements - Lumber/Paper is mostly 600V.

I cannot comment on Oil.

There are a few other 480V services, generally Cdn subsidieries of american companies.

I would endorse your general comment to always check with the customer for the specifications for equipment.


Bin510: Most supplying utilities will usually try to maintain a 'tighter' voltage range. For example, the utility where I am uses a range from 580V to 625V AT THE SUPPLY POINT, which is usually the secondary terminals of the distribution transformer.
dpc (Electrical)
11 Jan 05 11:55
Bin510

I think you've got it - except for:

"-Utilization voltage is the voltage i should be able to measure ate the point where my equipment is powered from (circuit breaker cabinet) (normally 460 or 575VAC respectively in the range of 440 and 504VAC or 550VAC and 630VAC)"

On a nominal 480V system, the voltage measured at the panelboard will normally be much closer to 480V than to 460V.

The utilization voltage refers to the voltage at the equipment itself, allowing for the additional voltage drop from the distribution panel to the end-use load.  

But the ANSI standard gives the range your equipment should be able to deal with.  
alehman (Electrical)
11 Jan 05 22:37
dpc makes a good point. System voltage drop is usually not as much as the standard allows for, particularly on 480V and 600V systems. It is common to see close 480V or sometimes higher at utilization equipment.

Also, the U.S. NEC recommends a maximum of 5% total voltage drop between service and utilization, which would be 456V for a 480V service.

bin510: A point of interest, I recently completed a project in Brazil which required 380/220 and 220/127 systems. The change to 400 had not occurred there, although there are many standards throughout Brazil.
busbar (Electrical)
12 Jan 05 23:15
 
Recurring use of terms system and utilization {voltage} in C84.1-1995 bears review in understanding terminology used to differentiate 480-600V and 460-575V.   

FWIW, there is also CSA Std CAN3-C235 1983 (R2000) Preferred Voltage Levels for AC Systems 0 to 50,000V
   
ters (Electrical)
13 Jan 05 14:58
The low voltage distribution in North  America will never be standardized as it is the case in Europe.  While the Europe seems to have only one low voltage distribution level for just about anything, including industry, commercial sector and households, which is  400/230 V (or around that number, 380/220, 415/240) whereas, in a WYE  connection 230 V is phase to neutral voltage,  North America seems to have at least 4 different systems:

600 V (sometimes called 575 V), used mostly in Canada and for industry only, sometimes the secondary winding  is in WYE offering so  phase to ground voltage of 350 V (rarely used, sometimes for street lights)  while sometimes secondary windings are in DELTA and used only as a three phase motor supply or similar.

480 V (sometimes called 460 V)  mostly used in industry in USA,  but many times in Canada  too, sometimes offering also  WYE connection  creating  phase to neutral voltage 277 V  that may be rarely used  for something.

To add a bit to confusion, not only  that voltages are not standardized, but not even frequency. A few  600 V industrial systems in Canada are still running on 25 Hz and some isolated generation islands are still producing 25 Hz or old 25 Hz generators are being replaced by 60/25 Hz static converters...      

208/120 V. This is a three phase WYE system mostly used for commercial   facilities such as stores,  office buildings, etc.  Three phase (208 V) is used for more demanding equipment such as  air-conditions, while phase to neutral 120 V feeds   lights, receptacles, etc.

2 x 120 = 240 V. This is a single phase distribution commonly used in households.  The secondary winding  has 240 V from end to end and 120 V from each end to the middle tap which is grounded. Some people like to call this “two phase system”  which isn’t quite the case.  Households have a choice of using 120 V (for most equipment) or 240 V for more demanding ones (such as ovens).
jraef (Electrical)
13 Jan 05 16:30
"I understood that the whole terminology ahs to do with historical differences in earlier power systems but the difference from 480 to 460 (600 to 575) have also to do with the assumption of power loss between the point of connection to a power system and the utilization equipment."

Actually, you are sort of off on a tangent here. In no cases should a system voltage be referred to as anything but what the utility says it is. When the term "utilization voltage" is used, it is referring to the nominal voltage RATING of the piece of equipment, not anything measured at the equipment. Do you see the subtle difference there?

The MOTOR is rated for 460V operation, because it can tolerate + or - 10% of THAT rating, i.e. 414 - 506V. That is where the issue of voltage drop is accommodated.

If the motor were rated for 480V it could only tolerate a low voltage of 432V. But if the utility already drops to 432V (still being within their stated limits), AND you have enough distance to drop another 2%, your motor is only getting 423V and is overheating at an exponential rate.

By designing the motor for a slightly lower utilization voltage, both the acceptable tolerance of the utility AND a small amount of drop over distance is accommodated.

Bottom line, don't get hung up on these semantic differences. Everyone is talking the same language, just from different points of view!

"Venditori de oleum-vipera non vigere excordis populi"


alehman (Electrical)
13 Jan 05 22:24
One point of clarification on ters's comment - 480/277 volt system is becomming the norm for moderate to large commercial facilities (office buildings, etc). The neutral is usually solidly grounded and lighting is connected phase to ground for 277 volts (all numbers being system voltage). Small transformers located around the building step down to 208/120 for receptacles, etc. This arrangement is more or less standard in much of the U.S. for larger new buildings.
skiier (Electrical)
13 Jan 05 22:41
Been an Electrician in Ontario for 18yrs. 600/347 is THE standard in Canada. Most car plants I have been in use 600V and step down 480v for American equpiment. Yes that's right a step down T/F. I have never seen a 480v "BUS" in any car plant in Canada. I may be wrong on this point but I do not ever remember seeing a 480V bus anywhere accept in the States.
347V is commonly used for lighting ccts in most industrial applications. Smaller wire for the same load saves on installation and maintenance costs. This is common practise here.
mc5w (Electrical)
14 Jan 05 4:32
For that matter Acme has a wye-wye autotransformer that economically steps down from 347Y600 to 277Y480. U.S. regulations require that the primary circuit MUST have a neutral wire connected to the transformer neutral.

You also need to allow for voltage swells. On some 480 volt systems the voltage can rise to 500 or even 525 volts during light load. Quite a few plants have manually controlled power factor correction capacitors and if accidentally left on over the weekend will cause a voltage rise that can toast solid state equipment. Same problem can also occur if machines are shut off during lunch and the electrical utility's capacitors are on a simple timer that does not shut itnoff during lunch.

If you engineer your equipment to withstand a voltage swell to 500 volts against 480 volts indefinitely and for a few minutes at 550 volts, that will give enough time for an overvoltage relay to shut off the power if your application is very sensitive to overvoltage.

In the case of rectifiers, the power supply capacitors need to be rated for a D.C. bus voltage that is twice the A.C. phase to phase voltage. If there is power regeneration you need a voltage differnece as to when a braking resistor cuts in and so forth. The diodes need to be rated for at least 4 times phase to phase voltage but in no case less than maximum D.C. bus voltage plus the clamp voltage of A.C. side surge suppressors.

Rectifiers tend to convert any kind of voltage spike to useful D.C. current. If there is no bleeder resistor or braking resistor your power supply will blow up when there is no load on it. The reason why some electronic ballasts burn out when the lamps do is that there is no bleeder resistor and/or switched clamping resistor.
Modula2 (Electrical)
14 Jan 05 8:45
Bin510, my understanding of European terminology is, for example, with a transformer open circuit voltage of 400 V, motors rated at 380 V, then the system would be called a 380 V system. In North America, we would call that a 400 V system. So, we have a 480 V transformer open circuit voltage, with utilization equipment, such as motors, rated at 460 V, and the system is called a 480 V system. Distribution equipment, MCC's, panels, etc., are rated at 480 V. The utilization equipment rating of 460 V recognizes the obvious voltage drop that exists in distribution. System voltage, whether 600, 480, etc. are a multiple of 120 V or 120 x 1.73. Utilization voltage (575, 460, etc.), a multiple of 115 V or 115 x 1.73.

In the 1960's it was changed from the old 115 system multiple and 110 utilization multiple. Prior to that it was 460V system and 440 V utilization.

Any comments?
dcriner (Electrical)
14 Jan 05 22:00
You are a European manufacturer hoping to penetrate the U.S. market. Based on the basic questions you are asking on this forum, I strongly suggest you employ engineers experienced in U.S. codes and practices. I fear that you are destined for frustration.
busbar (Electrical)
15 Jan 05 14:15
 
dcriner has a good point.  Many national consensus standards are written in a necessarily terse manner, so that unless one has experience in how the standard is applied, reading it a dozen or 100 times doesn’t give it any more meaning.

From C84: “Voltage ratings and other characteristics of the various classes of 60-hertz electric equipment are established in other standards.”  That does not mean, “You are reading the wrong document.”  It means, “This may not be the only place you find 60Hz-voltage ratings.”  Elsewhere, there is the famous disclaimer: “Not intended as a design specification nor an instruction manual for untrained persons.”
  

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