Loads for 3-phase 120/240V electrical service

[katwalatapan]

Hello,

The electrical mains at one of the facility that I'm looking at is rated at 225A, 3-phase, 120/240V. I couldn't find the plans for it, so I'm assuming it to be delta configuration, which then essentially allows 1-phase(neutral) 120V, 2-phase 240V, 1-phase(high leg-neutral) 280V, and 3-phase 240V.

I wanted to inquire if a load rated at 3-phase 208V could be served using the available 3-phase 240V? I understand if the service is 3-phase 208V and if the load is 3-phase 240V, it would cause overheating of the equipment, so would it be true the other way round?

Thank you.

 

[Desrod2]

Depending on where you are, operating voltage could reach up to 252 V (5% over voltage) or 264 v (10% over voltage). This means that you will be operating your equipment at 127% of the nominal voltage. In the past, I have seen motor rated for either 3 phase 550V or 575V (US std) used in Canada where the std 3 phase voltage is 600 V. Worked well for a while when they were located at the end of feeders. Burned within months after we constructed a new substation and they end up connected at the beginning of the feeder where the service voltage was in the upper 600V band (up to 660V). Be careful! Check with the equipment manufacturer.
Desrod

 

[jghrist]

Does the 3Ø 208 V load require a neutral?

 

[crshears]

"...1-phase(high leg-neutral) 280V..."

Um, shouldn't that be 208V single-phase? I checked a related post, and it looks like that's what waross said...

CR

 

[waross]

Four wire delta is rated at 120:240V single phase and 240V three phase.
Look at the transformer bank.
120:208V Wye.- One hot leg from each transformer, the second line bushings on each transformer are connected together and the neutral conductor is connected here. The connections are changed internally so that the transformer puts out only 120 Volts. Only two of the three secondary bushings are used. The third secondary bushing is not connected internally.
120:240V Four wire delta.- The transformers are connected in delta. The left bushing of each transformer is connected to the right bushing on the next transformer to form a ring or delta. One hot leg from each jumper.
One transformer has the neutral connected to the center tap bushing.
The wild leg is 208 Volts to neutral but it is not common practice to connect loads from the "208V "wild leg" to the neutral.
You need to check your connections or your voltages before we waste any more time on this.
As for supply voltages and overheating, it depends on the load. Some loads overheat on over voltage, some loads overheat on under voltage and some will do both.
Re: 575 Volt motors. The standard motor voltages in both the US and Canada are multiples of 115 Volts. The standard supply voltages in both the US and Canada are multiples of 120 volts.
115V motors are used on 120 Volt systems.
230V motors are used on 240 Volt systems.
460V motors are used on 480 Volt systems.
And in Canada,
575V motors are used on 600 Volt systems.
550 Volt rated motors would be about 50 years old and were used on 550 Volt supplies. Both ratings have been obsolete for many years.
The wild leg is 208 Volts single phase, but the OP wants to connect a 208 Volt 3 phase load to the 240 Volt panel.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[katwalatapan]

Thank you for the responses and additional insight.

The clarification that I'm seeking for is in practice are equipment rated at 208V, 3-phase fed by 240V, 3-phase supply?

 

[tesladog58]

Ok, guys, are dealing with 2 different service types, 120/208V 4w WYE connection, and 120/240V 4w DELTA. A 120/208 service the voltages are 120 degrees for the phase angle on each phase (example of phase angles A-120 phase, B-204 phase, and C-360 phase). in a 120/240 delta the single phase load is 180 degrees per leg, but it is 120 degrees per leg on the phase.

Just saying this why you find Skilled Trades people not very happy with the choices that are made by ENG. group. Just saying you need to NOT mix voltage and service type up, if you do not understand the difference between a WYE and DELTA connections for voltage and service types, look it up in the books

you can do all the math you want it's still not the some.
Just an Power Lineman's thoughts on this

 

[dpc]

in practice are equipment rated at 208V, 3-phase fed by 240V, 3-phase supply?

Not in general. These are two different service voltages. Depending on the type of load, it may work OK or it may not work. In the US, 240 V three-phase is becoming fairly uncommon. The 'wild leg' creates a lot of problems and it is best avoided. If you need three-phase power, go with 208/120 V, or 480 V.

 

[SteveWag]

To the OP: What is the load: motor, motors, heat device, lighting device, bench grinder, CNC machine? Answering this would allow a more direct answer to your question.
Steve

 

[RivetheadAZ]

You can use buck-boost transformers to provide the necessary voltage from 240/3 to 208/3. Although as some have pointed out the wiring depends on requirement of the load. We have used buck-boost in many configurations including providing 240V/3 phase from 208V/3 phase wye systems up to 800A. But you have to be aware of the neutral connections. Sola hevi-duty makes buck-boost transformers and has a number of wiring diagrams on their website for many different configurations.

Operating loads significantly above their rated voltage is not a good idea. Like Desrod says, check with the manufacturer.

 

[JohnMcNutt]

In practice, 208v motors get run off 240v frequently and it usually works fine.

However, if I am being paid by somebody to make recommendations as to the type of system, there is no way I would recommend running any 208v machine off 240v directly. If it smokes, they are going hire somebody else to figure out why and when they see the mis-matched name plate, they are going to point the finger at whoever said it was OK, even if it is not the cause of the problem (which would be hard to figure out either way).

If the owner suggests that we do it direct, that is a different story. You have to take into consideration the value of the machine/motor, and the likelihood they will blame you anyway. Consider the risks and benefits.

There may also be the possibility of reconnecting motors for the different voltage.

 

[katwalatapan]

Thank you very much for all the responses. It does provide a more clearer understanding of the issue.