Three phase voltage level in US. 4

[Audun]

What is the "normal" three phase voltage in the US ?
440V, 460V or 480V ?? Offshore is normally 440V but motors made in US are 460V and someone claims 480V. Do you use 460V motors as a standard?
Since I'm in Europe I have no clue, but need the info....

Audun

 

[Kiribanda]

Hi Audan,

Please refer ANSI C84.1-Electric Power Systems & Equipment Voltage Ratings (60 Hz) for nominal voltages based on ANSI/ IEEE which are widely used in NA.

Kiribanda

 

[jghrist]

The standard motor voltage is 460V, but the nominal service voltage is 480V. This provides for voltage drop in the premises wiring.

 

[busbar]

 
Different categories are centered around terms—Equipment Nameplate Voltage Rating and Nominal System Voltage.

A terse abridgement of C84.1-1995 is ARI Std 110-2002 for systems 600V and under.

http://www.ari.org/std/forms/110.html

is free to "qualified" recipients... (Form to complete)

[C84.1-1995 is a for-fee publication by the National Electrical Manufacturers Association, described at nema.org]

 

[jraef]

Part of the reason for confusion is that when the US was electrified in the early decades of the last century, many utilities were not only short sighted, but a little greedy. They sometimes purposely distributed different voltage levels so that users in overlapping areas could not easilly switch suppliers without undergoing capital expenses. That was fixed with regulation later, but the legacy lives on. For instance some older distribution systems are still 440V delta, some 460V delta, some 480/240V "Red Leg" delta and most newer systems are 480/277Y. That is why 460V was adopted as a standard equipment voltage since it still falls within an acceptable range for all of those supplies. For the most part though, consider the standard distribution level (above 240V) to now be 480V and the motor utilization voltage as 460V as described by everyone else above.

"Venditori de oleum-vipera non vigere excordis populi"

 

[mc5w]

Orignally, house current in the US was 100/200 volts and then Thomas Edison bumped up the voltage to 110/220 so that the customers at the far end of the system would get 100 volts instead of 90 volts. The customers at the far end then demanded 110 volts so he bumped up the generators to 120/240 volts. He then told the far away customers the 110/220 was good enough. This is partly how Japanese house current is 100 volts.

The American National Standards Institue Class A limit is 110 to 120 volts against a 120 volts base. Multiply for other other voltages. The class B limit for short term abnormal conditions is 105 to 125 volts.

The voltage goal is 120 volts at the secondary terminals of the distribution transformer. After allowing for voltage drop the motor needs to be able to operate at 440 to 480 volts under normal conditions and 420 to 500 volts abnormal.

Most of out 230/460 volt dual voltage motors are now designed able to tolerate operation off of a 120Y208 volt commercial power system using only 1 connection for both 120Y208 volts and 240 volts. Thanks to advances in insulation and magnetic materials the only 200 volt motors still being made are specialized motors such as submersible well pump motors. I have also seen motors built to run on 50 Hertz 220Y380 volts (Britsh) 500 volts (German) and 60 Hertz 416 volts (Australian and Paraguayan) and 480 volts (US) without changing any taps - the machine has dual diameter belt sheaves for dual frequency operation.

How we have 120/240 volts 4-wire delta 3-phase a.k.a. red leg delta a.k.a. rural delta was to have a cheap way to supply farms and residential air conditioning with cheap 3 phase power. Two transformer in the open delta configuration would be used to supply small amounts of 3 phase and in the case of load growth we would upgrade to 3 transformers using a 3-wire wye primary. The National Electrical Code official color for the high leg is orange but that conflicts with the 277Y480 volt colors - I would use orange with red stripes as a compromise.

Back in the mid 1960s central air conditioners had to be 3 phase because single phase motor technology was not good. Even though todays single phase air conditioners are better some utilities have gone back to requiring residential ari conditioners and heat pumps that are over 36,000 BTU per hour to be 3 phase. This is because a 3 ton heat pump has a 4.5 horsepower freezer compressor in it anything over that size needs to be 3 phase.

Mike Cole, mc5w@earthlink.net