UK Large single phase motors in the UK

[SquarePeg]

Why is it that I could easily find a 10HP 220V single-phase motor for sale in the USA but in the UK I nobody has anything larger than 5HP?

 

[pc1966]

The simple DOL start-up current for a 5HP motor is quite a lot for a domestic single phase supply that might have a 60A-100A fuse at the cutout, so my guess is anything over that would need a 3-phase supply anyway and then it is just better for the motor design to be 3-phase when possible.

I am sure there are others on this forum who know a lot more than I do though!
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What is it for?

If you really need to run a 10HP motor from a UK single phase supply you might be able to get a soft-start drive that takes a single phase 230V feed and drives a 3-phase motor, but I doubt it will be cheap!
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OK, quick search finds this:

Static Converter High Power 7.5kW

www.hucol.co.uk

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You would be best to contact the supplier to discuss what you are trying to do, as I see the spec there has a single-motor limit of 5.5kW presumably relating to start-up surges, etc.

 

[Lucien Nunes]

It's an interesting question. It's likely that a prominent manufacturer such as General Electric decided to offer them in their catalogue, and all their competitors followed, and they sold enough to be worth keeping on with that product line. Motors are heavy and historically were made to meet local standards, so they were not often shipped internationally. The larger market in the US would have better supported a niche line, and 10hp single-phase is rather niche because as PC1966 says, at that size a 3-phase motor is definitely a better motor if you have 3-phase available and many users of heavy plant would have.

Which brings us to the next point - population density and agriculture. Where population is sparse, electricity distribution is expensive. Line plant dominates the cost and any way to save money on that such as single-phase transmission is important. But agriculture often benefits from mechanisation and sometimes requires large motors, so I am guessing there has historically been a greater installed base of large motors on the end of very long transmission circuits to rural areas, per capita in the US compared to the UK, hence a greater market for 10hp single-phase types.

 

[snowhead]

What is the motor going to be fitted on and where, Domestic or Commercial / Industrial?

As above, there's no chance of it running on a Domestic single phase supply.

In the USA domestic properties typically have a 200amp supply.
100a is the max you'd normally find in a U.K domestic property.

 

[westward10]

It is probably down to practicality, a 10hp single phase 230v motor is going to run at approx 40-45A you then have to take into consideration starting it where a dol method would be in excess of 120A. Compare this to three phase and those currents would be less than half of a single phase motor. You would also have to consider the type of motor because if it not permanent split it will incorporate centrifugal switching which may well be prone to failure due to currents involved.

 

[Lucien Nunes]

All true enough, but notwithstanding snowhead's point that US PoCos will often provide 200A 120-0-120 split phase in preference to 100A 3-phase, these arguments are more pros and cons of large single-phase motors in general, whereas the original question is why there is a difference between the two countries.

Re. starting, they would often use a series-parallel starter so not necessarily quite as dramatic a starting current as DOL. Another territorial factor that relates to starting current was the prevalence of single-phase repulsion-start induction-run motors in the USA, which may have arisen from the wider early adoption of mechanised refrigeration with non-hermetic compressors, for which RSIRs are well suited. RSIRs are amazing if you are not used to them, they will start on a whiff of current with impressive torque.

 

[SquarePeg]

What is the motor going to be fitted on and where, Domestic or Commercial / Industrial?

As above, there's no chance of it running on a Domestic single phase supply.

In the USA domestic properties typically have a 200amp supply.
100a is the max you'd normally find in a U.K domestic property.

It's on a rural (ex farmhouse) property fed with overhead lines (100A main fuse). I was hoping to find a 7.5HP motor but I guess i'll have to make do with 5. It's to power a hydraulic press...

 

[Lucien Nunes]

Hydraulic pump duty is great for motors with limited starting current availability. They generally start unloaded with little inertia, so can be started very softly. A 1-3 phase inverter and 3-phase 230V motor might be your solution if the cost is bearable.