Circuit protection (was: RE: Latest addition : PDP 11/70)

Tony Duell wrote: [snip] Certainly in the US. Typical branch circuits are 15 or 20A at a nominal 115V (although voltages between 110 and 130 are common, largely as a function of how the single phase was derived). The NEC doesn't consider the fact that a given appliance that's plugged into such a branch circuit may have an attached cord that is rated at less that the rating of the branch to be an issue; it simply requires that in the absence of a overcurrent that the rating of the cord match be appropriate for the current draw of the appliance. The rational is that since the NEC also requires fast-acting circuit protection devices with the ability to interrupt at least 10,000A that a catastrophic failure won't have time to cause significant heating in the cord. Of course this doesn't address the issue of devices which may fail at a current draw that is substantially above the devices nominal draw but less than the rating of the branch -- but then neither do individually fused outlets unless you are careful to change the fuse each time you connect a device -- which I've certainly never observed happening in my visits to the UK. Instead almost all appliances and devices are required to have some level of internal protection -- be it fused, breakered or thermal -- before they can earn a safety rating (in the US we're typically talking about UL) -- without which it's very difficult to actually _sell_ something. -- Chris Kennedy chris(a)mainecoon.com http://www.mainecoon.com PGP fingerprint: 4E99 10B6 7253 B048 6685 6CBC 55E1 20A3 108D AB97