Here's a run-down of the factors to be considered by those needing to power electrical equipment.

There are benefits to using equipment powered by electric motors. Not only is the weight of such products significantly lower than their petrol-powered equivalents but, generally, operators are also exposed to less vibration, noise and emissions. The downside is the requirement for an appropriate power source.
Generators can be used to power a range of items — from lighting equipment for outdoor events to running lightweight hedgetrimmers or chainsaws. However, with numerous models and options available, choosing a generator can be a daunting task and would-be purchasers are plagued by “analysis paralysis”. Yes, we are talking watts, volts and amps — but it need not be difficult if you grasp the basics of how electricity is measured and then remember a few simple rules.
The most important piece of information you need to know is how much electrical power is required. You won’t want to lose the convenience of a compact generator or waste money by selecting one that is too big for your needs. On the other hand it is pointless buying a generator that does not produce sufficient power. So how much is enough?
Generators produce AC voltage. It’s like the power supplied to your home by an electric company, but whereas that power is sufficient to power all the devices required, a portable generator is limited.  The power output of a generator is directly related to the engine horsepower of that generator.
The amount of power a generator can produce is rated in watts and is called the “rated power”. This is the power a generator can produce for long periods of time and is usually around 90 per cent of “maximum power”. Consider this when calculating the highest power application you are likely to need on site.  Wattage requirements will vary from brand to brand and from model to model so it is wise to check the actual requirement stated on the label or in the manual (see calculation tips). It is important to be accurate because generators must never be operated at their maximum output for more than 30 minutes.
It is also essential to understand the type of load the equipment places on the generator. Lighting, for example, is a resistive type of load — it is constant. A generator’s rated power will be sufficient to power resistive loads of that amount so, for instance, a generator with a rated wattage of 2,300W could power 23 100W bulbs. However, equipment that has an electric motor is a reactive load and requires a “starting wattage” that is larger — as much as up to three times larger — than the “running wattage” requirement. As a rule of thumb, taking the running wattage and multiplying by three will determine power requirement, unless the appliance is under constant load, eg lighting.
Add the wattage requirements for all the electrical tools and equipment that you might want to run or start at the same time. This will be the minimum wattage needed from the generator —though it is better to have more than you think you need. Now divide the total watts needed by 746 to give the approximate horsepower of the generator.
Generators comprise engine, alternator, electrical outlets, circuit breakers, controls, metal frame and (most likely) a fuel tank. Obviously you need to consider the type of fuel — petrol, diesel or liquefied propane gas (LPG) — and size of the tank, but you should also pay attention to engine details. Choose an engine brand that you know and trust, and for which servicing, repairs and spare parts are readily available. Check whether the engine is an overhead valve (OHV) — these tend to be easier to start, are quieter when they are running and produce lower emissions. Most OHV engines have a cast-iron sleeve liner in the cylinder to reduce wear.
The alternator is also a major component. It produces the electricity so it should be robust. Consider the electrical outlets on the generator and check they match the tools you want to power.
Features will vary depending on brand and model. Your work and the location will help you decide which are necessary. Consider electric start for easy firing, low oil shutdown in case operators forget to check levels and idle control so the engine can throttle down when no power is drawn from the alternator. And think about how the generator is to be handled, moved and stored. Some are offered with wheels and lifting hooks.
As with all horticultural kit, construction must match the expected use in tough, outdoor conditions. Warranty conditions should be studied carefully and back-up services investigated.

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