solid detonator leg wires? solid circuit wires? why?

Does anyone know why commercial detonators have small gage solid conductor leg wires? And why only solid conductor wire is recommended in a blast circuit?

I have an idea, but I cannot be sure. I have some electrical/physics knowledge, and I understand that both solid wire and stranded wire have advantages, but I do not understand the details as to the why solid wires are chosen in commercial caps. There is so much unreliable info on the web about comparisons between solid and stranded wire - especially as it pertains to the home audio and data communication industries. Some of the info is contradictory. It is hard to sift through it all.

Here is what I know on the subject: The DC current carrying capacity between solid and stranded wire is negligible in most cases.

I understand that skin effect allows higher frequency AC to travel easier through stranded wire than it does through solid wire because of the increased surface area due to multiple strands. Although, at least a high frequencies, I believe that the benefit gained from skin effect is in turn lessened by the slight inductances that can set up between individual strands. Then there is the matter of corrosion throughout a stranded wire on the surface the strands or between strands that grows with time. No doubt these inductances etc. degrade signals - I am assuming that that is the main reason that CAT5/6 is solid conductor. It seems that stranded wire is only advised for CAT 5/6 when patching and where physical stress is expected on the wire.

I am aware that DC voltage is used to fire a detonator. However, at least in case of an EBW, foil, etc., the current pulse rise times are so fast that, the waveform appears as critical as the current and voltage delivered. High frequency? at least for one pulse?

Then there is the notion of physical durability of wire. In cases of physical usage, stranded wire outperforms solid sire due to its flexibility. However a detonator is not a repeated use item.

I am sure that stranded wire will work in a blast circuit in the real world. There are plenty of sites for homebrew detonators that instruct the maker to use stranded wire. But, I am specifically speaking of the sole use solid wire in commercial caps. I have read that article about the failure of the IED that Ted K made and tried to use. Apparently an EOD investigator concluded that had he used solid wire the IED would have detonated. So, solid wire appears critical doesn't it.

Theories -

Stranded wire - reasons to use:

  1. flexibility?
  2. skin effect allows for faster rise time in detonation pulse?

Solid conductor wire - reasons to use

  1. inflexible, possibly wires assist in physically holding the detonator in place?
  2. inflexible, leg wires are not expected to be bent many times
  3. lack of skin effect not benefit not a problem - likely true with slower caps
  4. lack of skin effect not benefit not a problem - waveform not critical affected for EBW etc..
  5. broken wire can be discovered easier than with stranded before use
  6. less possibility of corrosion buildup as between strands in stranded wire
  7. less possibility of inducing current into stranded wire broken strands from ext RF source
  8. more reliable connection when wires are twisted?

I hope I am not to far off in my theories. Please feel free to comment on my theories and to any specific relevance to an explanation as to why solid wire is chosen in commercial detonators. Any other info is appreciated.


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I am guessing 4 and 5, but on McGuiver, #1 (for solid) always helps with the C4.

Whenever I watch a crime show where they are disarming a bomb, I wonder two things:

1) Why isn't there a standardized color code convention, the bomb squad is left there to guess red or blue, very inefficient. 2) Why not just nip the wire right at the detonator and be done for the day?

Does anybody remember the extorti>Does anyone know why commercial detonators have small gage solid

Reply to

I guess the terrorists would have to agree on whether to follow the ANSI or IEC color codes. I suppose they could check with the AHJ for the appropriate codes. But then you know how lax those inspectors are getting lately.


Reply to
Paul Hovnanian P.E.

Well, thanks for the ideas everyone, I am sure everyone can see that there are different ideas out there - I posted this question with a couple of other engineering/physics groups - same result.

I am thinking that the idea of the lack of integrity/reliability of the individual strands in stranded wire, which could result in insufficient current carrying ability and might not allow detonators to function properly, seems like a good answer as far as the functioning of the wires. I also see the logic in the other ideas about ease of handling.

However, as you can read on the web, various states i.e. PA, NJ etc. not only require by law that detonators have solid leg wires - but that all wiring in the blast circuit be solid conductor also.

This leads me to again see the logic of the idea the physical integrity of the wiring - which in turn relates to the integrity current capacity - is seen as critical enough to induce both, the manufacturers to assemble detonators with solid wires, and individual states to pass laws requiring that solid wiring be used for detonators and detonator circuits.

PS I am glad for the replies and that a couple of people actually found the question intriguing, I at first thought that no-one would reply.


Reply to

I imagine a sophisticated device will have multiple detonators, with a small current running through each, and a current sensor.

Current in any detonator drops, *boom*


Reply to

In short - not insufficient carrying capacity - rather, 1 stray wire from a stranded wire connection, either intact or broken off and laying across a gap, either as a conductor or arc source, make things go boom when they are not supposed to.


Reply to

Skin affect in stranded wires is the same as solid ones *unless* the individual strands are insulated from each other. That is not common in most stranded wire (although you can purchase specially made wire that does have individual strands insulated).

As far as on the detonator itself, I am not sure. But the few times I've seen such things wired up on documentary shows (never trust Hollywood), the connections are made by hand twisting the wires together (or they use non-electric prima-cord). Ever try twisting stranded wire to solid? Usually the solid wire doesn't bend at all and you end up with the stranded wire just wrapped around the solid one. Not a very good connection mechancially speaking, jiggle it a bit and the stranded wire slips right off the solid one.

Now imagine you've set this all up and the charge doesn't blow when you try and fire it. Somewhere, you suspect, a twisted connection has come apart. Do you want to wiggle all the connections to try and find the one that's bad???? "Hey guys, I think it's this....BOOOM"

Simple, reliable connections is always a plus.


Reply to

On 17 May 2006 18:22:54 -0700, "chemstu" Gave us:

Not true. Unless they are individually insulated from each other along their length, they become integrated together, and skin effect is nullified as the wire is seen as one larger conductor from a field propagation POV.

IF they were individually insulated from each other along their length, you would have the beginnings of a Litz Wire configuration, or at least would be able to see some of the effects you refer to and that true Litz Wires sport.

Reply to
Roy L. Fuchs

On 17 May 2006 18:22:54 -0700, "chemstu" Gave us:

You should go back and study your electronics.

Reply to
Roy L. Fuchs

On 17 May 2006 18:22:54 -0700, "chemstu" Gave us:

Nope. Also, insulated conductors do not corrode (at least not the way you make it sound). That is the whole point of the insulations aside from keeping them from touching each other making undesired conduction paths.

Reply to
Roy L. Fuchs

On 17 May 2006 18:22:54 -0700, "chemstu" Gave us:

Now you are starting to get yourself a clue.

Stranded wires can flex hundreds of times with no damage to the conductors.

Solid wire can only be flexed a couple of times before wire damage begins.

The reason is that copper "work hardens". That means when you take a solid wire (or bar) of copper, and bend it, the micro-crystalline structure of the media in the region in and around the bend "work hardens". Then, when you bend it back, you create small tears in that micro-crystalline structure and the process of wire breakage begins.

This occurs when the bends are sharp, and fast and forced on the copper. In a stranded wire setting, the bend is managed better and has a much reduced net damage on the wire as a whole as well as less on any individual strand in the bundle.

Reply to
Roy L. Fuchs

On Thu, 18 May 2006 22:19:28 -0700, "Paul Hovnanian P.E." Gave us:

Shove it in... shove it in... --TV commercial

Reply to
Roy L. Fuchs

On 19 May 2006 09:49:57 -0700, Gave us:

Yes. There is never full knowledge as to whether there is a redundant or not either. If there is one sitting out, exposed, it could even be a dummy (likely too).

WITH a current sense on it... again... BOOM!

Bada Big Boom!

Reply to
Roy L. Fuchs

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