ELI5: does cutting the wrong wire to a bomb really sets cause an explosion like in movies? With the circuit cut, how is the bomb activating?
ELI5: does cutting the wrong wire to a bomb really sets cause an explosion like in movies? With the circuit cut, how is the bomb activating?
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In electronics wires are usually used to send signals or commands like “please explode now” sent from the controller to the bomb.
BUT sometimes those commands are like “don’t explode yet, don’t explode yet, don’t explode yet” and when you interrupt the wire.. it explodes.
To be more clear: there’s 2 circuits. The inhibitor/temporizator – and the one that actually does the job (unless told also) – and the second one is obviously hidden in the core of the bomb.
Imagine the pin of the grenade: if you remove it, it will explode.
No general way of telling that. It all depends on the specific circuit, so the whole idea of cutting the right or wrong wire is absurd.
One could design a circuit where there’s a bunch of »sense« wires. You could send a current through these and if any of them is cut, activate the explosive.
Circuits are not like »if one wire is gone, the whole thing is done for«. Each component and section can have different tasks depending on their design and what they’re supposed to do. By combining different blocks, they can work together and fulfil a larger operation than each subcomponent could on their own. Taking one subsection out could lead to others triggering other behaviour.
IF the bomb is made to do a check that it can get a response or not from a chip on the other end of a wire and it doesn’t it can go off. So it really depends on if the bomb maker put in that fail safe
Bombs are going to generally be pretty diverse in their triggering mechanisms, but one thing that is pretty common in a terrorism-type of situation is a sort of dead man’s switch. Basically the triggering mechanism is powered separately and set to “go”, but the triggering mechanism is inhibiting it actively until the trigger is set off (ie the timer or whatnot). So if the circuit from the trigger is interrupted, it is no longer inhibiting the detonator, and it goes off.
So yeah, wrong wire can definitely set a bomb off. But there’s no standard “bomb”, as most of these things are homemade by mentally ill people.
No. That’s not how bombs work. That’s a trope from TV and movies for drama and tension. There are possible configurations where a bomb could be designed to detonate if tampered with (for example, cutting a wire might trigger a backup circuit), but bomb techs don’t disarm bombs by guessing which wires to cut, and there’s no “red wire vs green wire” dramatic moment. That’s simply not how bomb disposal works.
For 99% of bombs there’s one wire leading into the bomb, and cutting it will stop the bomb from going off.
But.. the 1% are tamper resistant or trapped, and might have a secondary detonator inside the bomb set to detonate it immediately if a circuit is broken. Figuring out how a trapped bomb is set up and disarming it safely can be very hard.
That would depend on how it’s wired, but some bombs would be wired with what they call a “dead man’s switch” – which the easiest I can explain it would be, imagine you were holding down a brake lever on your bike… holding that lever down means you’re safely stopped, not going to roll down any hill…
Now someone comes along and cuts the cable of that brake lever, brake is no longer engaged, you roll down the hill and into traffic!
So, back to the bomb, that “dead man’s switch” is keeping the bomb disabled and over-riding the regular detonation method, it’s been wired that way as an anti-tamper measure.
Cut that wire and the “brake” is no longer engaged and the bomb detonates instantly.
Movie bombs are plot devices. Cutting the wire is just a stock scene that creates suspense. Asking about their logic here is kinda moot.
Real explosives are built depending on their purpose. You don’t really need to worry about people cutting wires when your bomb is a missile or an undersea mine.
As for improvised explosives, it depends on the creator. There’s nothing stopping someone from adding decoy wires that detonate the bomb when cut, if they really want to get in touch with their inner supervillain. With electronics, you can detect a wire being cut. The question is, who would go through that trouble?
It really depends how the bomb’s detonating system is built. You have two main ways to get that behaivour :
* add bullshit wires who’s only function is to detect when they’re cut (meaning someone’s trying to defuse your bomb) and use that information to command hte explosion
* have a currnet running in the wires that keeps the bomb from exploding. Cut the wire, no more current, boom. That could be done with an electromagnet that keeps a spring compressed – cut the wire, no more current, the electromagnet cease function, the spring springs and commands the detonation.
That’s why most bomb disposal is done using things like a high-pressure water jet, shotgun blast or the like to try to demolish the system so fast it doesn’t get the chance to command the explosion.
Bombs can function in many different ways, so this is an extremely broad response that will, upon closer investigation, have holes for the sake of brevity and simplicity.
The explosive itself will have to be detonated in a specific way (detonation cord, shock tube, other methods). This step can be triggered by any number of standard or creative ways, but we will skip over this.
The core of your question is “how does cutting a specific wire either cause or prevent detonation?” The answer depends on how the detonation process is designed to happen. There are almost an unlimited number of ways that a person could configure these things.
Here is an example:
Method 1: Red wire runs from a microcontroller to the detonation circuit. When red wire is energized, detonation circuit is complete, and device activates.
Method 2: Blue wire runs from a microcontroller to the detonation circuit. IF blue wire EVER becomes de-energized, THEN energize the red wire (start Method 1).
See how these things can be used together? It’s up to the designer to make these choices. It is up to the defuser to understand the designer and correctly un-do their choices.
Edit: typos.
It depends entirely on how a given bomb is wired. A bomb could be set up to explode if a given wire was cut… but typically such things are reserved for fiction to add drama. Also explosive devices that are custom made by lone criminals aren’t going to have an instruction manual for someone back at headquarters to read out over a radio.
The premise of “cutting the wrong wire” is presumably that the circuit that would detonate the bomb is still intact, so that would be why the bomb could explode. A circuit intended to prevent tampering might depend on a constant signal that cutting a wire could disrupt, triggering the bomb. But bespoke bombs aren’t usually designed for a dramatic scene of a technician with wire snips sweating over multiple wires. If anything they tend to use the same color of wire for everything.
While there are examples of custom devices built with intricate mechanisms and traps, most often bombs will be made from mass produced explosive devices such as artillery shells simply wired to a cell phone or remote trigger. There is no “wrong wire” to set it off.
According to Wikipedia, the Germans in both World Wars saw the fear generated by delayed-action bombs and actively researched detonators that would activate while the bomb disposal team was trying to defuse it. So it is a plausible storyline for a bomb to be over-engineered in that way.
I’ve seen a bomb disposal expert claim it wouldn’t be too difficult to design a bomb that cannot be disarmed once armed, so take that as you will.
Plot device, nothing more.
It really comes down to who made the bomb and how.
My bombs, for example, don’t have any wires or electronics. Just some a rat trap, a nail, and a shotgun shell or a bunch of silver fulminate or tannerite.
For legal reasons, I have to tell you that it’s fun to set these off in the woods by throwing rocks at them.
No, most of the time, just pull the detonator / blasting cap out of the “C4” and you’re 95% there. If it’s a single detonator, just cut one of the wires.
I always assumed it was basically a trope …. Interesting
The booby trap bombs are Hollywood staples for schlocky action nail biters. The point of a bomb is to explode. Building complex booby trapped timers and wiring systems is counter productive as they introduce excess failure points. Most bombs have remote triggers, not timers and definitely not booby trapped timers.
For one, never assume wire color matters. The red wire can be anything or a dud.
Tamper resistance through something like an AND logic gate. Bomb doesn’t go off as long as it’s getting two inputs from both detonators. One the manual arming device, the other the remote detonator receiver. If it loses one signal, boom.