Power Problem

Indeed. The OP would do well to have a local qualified Electrician review the proposed installation and properly assess the cabling and overload protection. In the UK, such individuals would be following the provisions of BS7671, which gives full protocols for a safe and correctly-documented installation that would satisfy the end-user's fire indemnity insurance provider.

The principle involves putting an unbalanced load onto the supply. All single phase connections present imbalance and the trick is to spread them around the phases so as to minimise the neutral current. So the proposed installation should not be viewed in isolation.

The detailed design of the arrangements lies squarely in the domain of the Electrical Engineer. If the requisite skills are not to hand, then for safety's sake the deployment of someone who does has them would be highly recommended as a minimum, and mandatory in some jurisdictions.

And <...480/277 3P...> is not <...high voltage...> as the boundary between "low voltage" and "medium voltage" is generally taken as 1000V; from the information presented the proposed installation lies entirely in the "low voltage" domain.

480V L-L it is then. Thanks for the advice.

FYI:

Please note,there is a big difference between an equipment bonding conductor,and a Grounded conductor.The terms lead to much confusion even among experienced electricians.GROUNDING conductor is the equipment grounding conductor.It is connected to a separate bus bar terminal in the panel,not to the neutral bus bar terminals.The GROUNDED conductor is connected to the ground rod.The Grounded and Grounding conductor are bonded together in the main panel only,but in sub fed panels,they must not be bonded together.In single phase systems,the Grounded conductor is used as the neutral,and carries the unbalanced load,but the Grounding conductor is to prevent shock hazards from the equipment and carries no current except in a fault condition.

The first question is how large is the 1P compressor motor? That will determine the size of the transformer. The second item is a 277V to 230V transformer exists somewhere, but it will be expensive. It would be a better choice to get a standard 480V to 230V single phase step down transformer and just wire it between any two of the three legs of your 480V source. Please note that a neutral is NOT the same as a ground.

Hi Rick,

Usually 3 HP but some manufacturers do a 4 HP.

It is illegal for anyone to perform electrical installation or repair unless properly licensed in the state of Florida, or one of the reciprocal states. Do you know the difference between Grounded, and Grounding conductor? If you are licensed, consult your local inspector, or AHJ. They will be glad to advise you. If you are not licensed, you are subjecting yourself to potential liability if something goes wrong.

We work worldwide. This site is not in Florida.

We are not installing the transformer, just providing it.

The compressor is for a bulk CO2 storage vessel, it is 1 HP.

Are you able to say which country or even continent, this thing is to be installed in?

It will be here in the US.

You still need to have the customer tell you if phase to neutral or phase to phase is required or if it does not matter. -- JHF

Probably from a cost point of view why not just replace the single phase motor with a 480V 3P motor and Appropriate 3 P pressure switch. Here 3P motors are as cheap as chips much cheaper than either 1 P motors or transformers and the transformer needs adequate fuse/ CB protection all adding to the cost.

3P motor removes the imbalance problems.

Stef. Good idea!

Although from my experience of compressors, the OP needs to be aware that the motor could be a 'special' with a mounting frame to give correct alignment and fit of drive shaft couplings. ...something the manufacturer might supply - but at a price.

Still, a good idea.....an option I would explore first.

I'm told that there are no daft questions but this might come close: what is the supply frequency on the rating plate of the compressor and of your 480V supply?

I only ask because 230V 50Hz is the normal single phase supply in Europe and 480V 60Hz is, I think, the normal 3ph supply in North America.

See #20⇑.

In my opinion you have a network of 400 V and 50 Hz [U.K.] and a motor of 480 V and 60 Hz. That means, since 400/50=480/60 the motor has to work well.

The 230V/ 50Hz is a red herring as we know now that the plant is in the US. A single phase supply from 480V/ 60Hz supply would be 276V/ 60Hz. The options are then:

1. replace the motor with a 1ph 276V 60Hz m/c or
2. use a 3ph 480V 60Hz m/c.

The load is only 1hp so the higher efficiency of a 3ph m/c bill be outweighed by the additional cost of control gear, A 2.7A out of balance load should be tolerated in a well designed industrial distribution system so the single phase motor is probably the one to go for.

That only leaves the mystery of the 230v 60Hz motor. That would need a transformer as the fluxing level would be different. Protection of the system with regard to neutral points and earthing has taxed better minds than mine in this thread so that is clearly also a concern. You are right, a 400v 5Hz motor would be happy on a 480v 60Hz supply, electrically at least; whether the compressor would be happy with the over (or under) speed is a different matter. When I lived in Japan in the 1990s many of my American friends bought Japanese domestic market white goods that ran on 100V/ 50Hz, took them home on repatriation and ran them on 110V/ 60Hz perfectly happily. Unless there is a power network in North America that uses 400/230V 60Hz for low voltage distribution, I am struggling to understand how or why one would use such a machine. I look forward to being educated!

Here is a group who would know better than many of us engineers. They are a mixture of licensed Electricians as well as electrical inspectors (ie AHJs). Their job is to be safe and legal.

https://www.electrical-contractor.net/forums/ubbthreads.php

This is a question for the customers chief engineer or head of facility maintenance. In the absence of either it will depend on the phase balance of the customers' electric system. If that is unknown, it must be measured before an answer can be given. There can be either a situation where you MUST use one phase to neutral and others where you MUST use line to line (phase to phase). You cannot use a general rule to make this determination. As others have mentioned, be sure you have a good understanding of the difference between the neutral and ground, the proper way to ground a separately derived system, and the required disconnecting means both upstream and downstream of the new transformer. Pretty simple stuff for most electricians. - JHF

I used a motor-generator set when we built systems for foreign countries and had to test them here. As I recall, they are cheap and reliable, and completely isolate the load from whatever power you have: M-G set

Here's a list of folks who make them: M-G makers