DG Maximum Output Power

One does not generally calculate this; instead, one looks it up on the DG nameplate, or on its data sheet. In many if not most cases, kva and kw are both given. Often kw = 0.80 x kva. If the engine rating is in hp, kw = 0.746 x hp (minus some small drive losses).

I believe the British Standard allows 110% of the continuous rating for 1 hour in each 12 running hours. Note this is for a new engine - also the overload will increase wear at more than 110% - worse on engine already working hard (turbocharged). Also you have to deduct the generator losses from the engine shaft power to get output kW - generator efficiency varies about 70 to 95% from, say, 2 kVA to 500 kVA.

Please explain. If 110% is the new 100% then 100% is still the maximum output.

_{"Confused" of Dodman's lane.}

Dear PWS,

The question wrote "maximum" and "safe" not "continuous" (or efficient or economic).

The British Standard can happily allow 10% overload for 1 hour because on a diesel rating it just uses up life (compare the power of a 2 litre petrol car engine with a diesel of 2 litres - same poppet valves etc but much higher exhaust temperature with petrol). N.B. a [direct injection] diesel only typically burns 70% of the oxygen it sucks in - the limitation is incomplete combustion and exhaust smoke - but it is easy to increase the fuel! The AC generator cannot be overloaded much because the engine limits at 110% - in any case they are usually made to class B temperature rise (120 'C max) but have class F insulation (140 'C max). As for BS7671, it is mostly about cables - fuses/CBs have about +/- 10% tolerance on the fusing current for a given time - and the famous BS1363 plug with earth pin, fuse and shutters uses a BS1362 fuse specified to blow in not more than 1 hour at 160% rated continuous current.

Regards,

67model.

Which standard, please?

Ancient history BS 649, as far as I remember. Replaced by BS ISO 8528 no doubt!

Shouldn't the circuit protective device(s) operate in the event of an overload, so as to protect both the unit and its internal/external wiring [British Standard 7671]?

Or are these "frigged out" with jumper wires and matchsticks?

Just go by the manufactures data, that way you won't invalidate any guarantee. To deliberately over load a machine is shear folly!