Like in the movies, is there really one wire to cut that will disable the bomb, and one (or many wires) to cut that would cause the bomb to detonate?
Only if you have a bomb made for the movies! You are not likely to have the expertise to disable a REAL BOMB so leave the wire cutters in your tool box, put on your tin helmet and dive for cover.
Might have some luck cutting the wire to the detonator. But I’m not an explosives expert, so don’t try this at home.
Use your water cannon to seperate the detonater from the detonatee.
You could build a bomb that behaved like a movie bomb, if you wanted. But you almost certainly wouldn’t, in real life.
The simplest bomb is an explosive fitted with an electric detonator. The detonator has two “leg wires” sticking out of it. The bomb should have a battery with a timer attached that will connect the battery to the leg wires. This causes a bridge wire, like a bulb filament, to get hot inside the detonator and the thing is triggered.
Such a simple bomb would be very easy to disarm. Cut either of the legwires, stop the timer before it reaches zero, pull the cap out of the explosive, or remove the battery, and the bomb is disarmed.
If you want to make a bomb that’s hard to disarm, put the thing inside a locked box. Fit it with burglar-alarm type sensors - tilt switches, trembler switches, a light sensor so it has to be disarmed in the dark, and already you have a device that’s much too dangerous to deal with in the classic “movie” way. That’s why bomb squads use remote-control robots if possible.
The classic “movie” bomb is always open - there’s never any difficulty in getting access to the rat’s nest of wires inside. That’s a peculiar feature for a start. It’s major anti-tampering feature appears to be a number of dummy wires which trigger the bomb if cut. That’s not too difficult to arrange, but it’s an odd way to go about things.
This is going to primarily depend on whether the person who built the bomb is expecting anyone to find it and try defuse it.
There may be a small subset of would be terrorists who have watched too many James Bond films, booby-trapped it anyway, but still managed to avoid the bomb blowing up whilst still on their work bench :rolleyes:, but in general if the bomb isn’t expected to be found then it should be pretty easy to defuse by cutting the circuit to, or physically removing, the detonator.
I’d imagine that this is especially going to be the case for most military munitions (or bombs hastily jury rigged out of such), they will be designed to blow up under a very rigid set of circumstances and it will be intended that it should be as easy as possible to stop this occurring at any other time.
Paging Tripler.
Grab the cat!
Does anyone remember Special Bulletin, and the nature of the anti-tamper devices in the bomb?
Here’s the real life version of the fancy locked-box bombs described by matt and used in Special Bulletin, mentioned by Johnny L.A.:
Scroll down a little to check out the actual bomb, covered with toggle switches and filled with 1000 lbs of explosives.
As it turned out, the bomb squad couldn’t defuse it and it ended up destroying much of the hotel, but nobody was hurt.
James May did a special recently where he showed the method to disarm unexploded Nazi bombs. It involved drilling a tiny hole into the fuse mechanism and pouring in a heavy salt solution to bind the gears of the clockwork timer mechanism. No wires to cut at all.
Most bomb-disposal prefer to simply clear the area and then blow the damn thing up. No point in risking lives - including the lives of the bomb-disposal guys - just to prevent some property damage.
Need answer fast?
Your question assumes that bombs are made to some standard. They are not. You could easily design a bomb to function in a number of ways. Cutting q wire could be good or bad. Removing a battery or timer connection would generally be helpful, but not necessarily.
This is why bomb experts try to analyze the remains of a bomb or a failed one. The same people tend to do things the same way because it helps protect them. Therefore, if you know your enemy, their standard weapon may be disarmed with knowledge. When the police run across the occasional bomb, they usually try to place it in a safe container and take it somewhere to detonate it and then examine it because the lone “nut” may do something unusual.
Yep, that’s the TV/movie standard, though. Typically someone finds the bomb (probably with a timer that makes a “ticking” sound, or in the more modern productions has a helpful digital display) and even some faraway expert they reach on the phone (or perhaps walkie-talkie) can tell them that a particular wire has to be cut. Without even having seen the device.
Some tricky bombmaker should try using a red wire where the white wire is called for in the standard bomb plans, and vice-versa. That’d teach those meddling kids!
Most yes, but there were ones that they didnt want captured or moved.
Otara
That’s an interesting extortion note. I wonder if anyone has ever succeeded in getting paid such a big ransom and getting away with it.
It would depend. Did the bomber follow the uniform bomb build code or not. If they did then you know that you could cut the red wire but not the blue wire.
And have the bomb go off when then timer hits 00042 rather than 00000. 
Most bombs set in the U.S. are extremely unsophisticated. Pipe bombs being among the most common.
The most complex that I ever dealt with involved a 55 gallon drum filled half way with gasoline with cannon fuse stuffed down into the top bung hole of the lid. 25 yards away the cannon fuse was stuffed up into a large hollowed out table candle. The perp lit the candle wick and walked. The “bomb” should have gone off about 2 hours later, when the candle wick burned down enough to hit the cannon fuse which would have burned down to the drum and ignited the fumes hovering inside the half filled metal barrel.
Cannon fuses are thick, and insulated. The candle flame wasn’t hot enough to burn through the coated insulation and it snuffed itself out when it got deep into the wax to the point of the fuse.
This was 20+ years ago and had this bomb succeeded I’d have a cite for you.