Hi. Can you help with my idea. Recently I managed to blow one of my usb ports when I accidentally caused a dead short circuit whilst using my Arduino.. That was not the end of the world because i was using an old desktop machine. Unfortunately I have a disability which now means I can no longer sit at my desk. I am forced to use my laptop and do not want to damage it in any way.
My Idea is to use a resetable fuse in a tiny project box so that if anything goes wrong the fuse will trip saving my usb controller. I can sort that part out fine. I thought about using a solid state relay in conjunction with the fuse and have a little button to reingage the relay after a trip out or when I plug in my usb lead. I have no idea about solid state relays and what type of circuit I need to use. Will I nead a single or double pole. Is it even feasable.
Thank you
thought about using a solid state relay
Yes, you could use a Solid State Relay.
An SSR is not much different than a standard relay
A Standard Relay has a Coil Input, while an SSR has an Opto-Isolator Input
A Standard Relay has NC / NO contacts, while an SSR has a semiconductor switch.
Will I need a single or double pole.
Single pole.
and have a little button to reingage the relay after a trip out
Maybe, the N.O. Pushbutton could energize an SCR
The SCR latches ON and energizes the SSR opto-isolator input
When power is lost from either ...
a) "blown" Resetable Fuse or
b) Power Down
then the SCR de-energizes and the SCR turns off.
Must press the N.O Pushbutton to Turn ON, again.
Alternatively you could simply use a mains powered USB expander hub. This will provide isolation from your PC
There is some confusion here. You cannot use a SSR to control the 5 V in your USB line. They are designed to switch mains, or at least substantial voltages and currents and generally, AC, not DC thought there are special designs for DC but again, mains voltages. They lose a volt or two in the process.
jackrae:
Alternatively you could simply use a mains powered USB expander hub. This will provide isolation from your PC
Whoah! You sure got that wrong! 
(I thought about that possibility when I first saw this query. 
)
Most "powered" USB hubs have all +5 V output lines connected directly to the input line and the input from the 5 V adapter. This is actually not at all surprising, as otherwise they would have to use high quality logic-level FETs to switch the alternate power sources and - they just are not that sophisticated at all. So that gets you nowhere.
That said, you could use such a high quality logic-level FETs to provide such safety switching - effectively making a sort of specialised SSR (but not with opto-isolation 
) of your own.
What you really want (though USB ports are supposed to be immune to short-circuiting as part of the specification) is a Polyswitch as is used on the Arduino UNO and similar.
With a resettable fuse, I don't see why you'd need a relay.
(I was thinking about a powered USB hub too... I didn't realize the computer's USB power was connected.)
You could build your own power-isolated USB adapter. That is, a little box with USB in and USB out with the data lines and ground simply passing-through, but with nothing connected to the 5V on the PC side and a separate 5V supply for the device-side. That wouldn't protect the data lines from screw-ups, but it would protect the computer's USB power.
Or if you are not using USB power, you can simply cut the 5V wire. You could do that by simply cutting-open a USB cable and wrapping it with electrical tape after cutting the power wire, but it would look ugly.