How powerful are phase converters?

An issue with phase converters is their power rating. Up until a few years ago manufacturers used to place a fairly arbitrary label on their converters in horsepower and then advise clients to buy a converter "two to three times the size of the largest motor or larger". Well such a vague piece of advice is not a great deal of use, and even though some ambiguity will always arise from the necessary translation of a client's mechanical need into a manufacturer's electrical rating, most (not all) phase converter manufacturers have now moved to a system where they label their converters clearly as to maximum and minimum useful power ratings (in both horsepower and kilowatts, and taking into account internal parasitic power losses) for typical single motor and multi-motor cyclical duty. Provided this has been done correctly by the manufacturer there is generally not much point in buying a much larger phase converter than they advise, unless you are considering purchasing larger machine tools in the future. Equally it is unwise to buy a smaller converter on the basis that you are just a 'hobby' user as the phase converter is typically most stressed at start-up, which is an unavoidable element of the duty cycle and because an overstressed phase converter will in turn stress your machinery and can cause its motor(s) to burn out.