How long does it take a solar EMP to reach earth?

Answer 1

Until the men from the power company come to fix it, usually.

An EMP is quite like a lightning strike in its effect. Anything semiconductor based can probably be popped straight in the bin; semiconductors are fragile to EMP and any large voltage spikes on the earth plane. Switchgear, Transformers and cabling are more physically robust and they may survive but transformers and switchgear may trip, which in turn may or may not require some intervention from the power company. Cables and transformer windings may burn out, in which case the power may be off for quite some time. It all depends on the size of the pulse and the proximity of sensitive equipment.

You haven't been watching Ocean's Eleven, have you....? No, I haven't been (I only know what I can find out by reading the polls on People's Choice Awards), I was just wondering how long you'd have to wait before it would be safe to turn on the car (which was not running at the time the EMP came) without it getting fried (if possible after this EMP). The bad news is that modern cars make extensive use of semiconductor technology in their engine management systems, so after an EMP your car may well not start, whether or not it was running at the time. That goes for all semiconductor based devices. With silicon-based technology, any sizeable EMP, for instance from a nuclear airburst, means Back To The Stone Age.

Answer 2

It depends on the velocity of the coronal mass ejection; we've had flare gas reach the Earth in as little as about 18 hours, but normally it is 2-3 days.