Reply to post: Re: Do you recall the smell of burning UPSes in the morning?

Re: Do you recall the smell of burning UPSes in the morning?

Circuit breakers and fuses do not usually provide protection against a small but persistant overload. They must be rated to allow for brief overload situations (e.g. at startup). But if the overload lasts for a long enough time, components can get hotter and hotter until they burst into flames or create a fault (e.g. go high resistance) which results in a sudden massive power overload in the component without any current increase. You can provide thermal protection and/or slow-blow breakers or fuses, but there will usually be a particular overload level that will fail to trip such protection while creating a hazardous situation over time.