Broken spokes mystery?

I have build last March a wheel with Formula hubs CXP22 rims and ACI black double butted spokes. Over the last 4 weeks I had 3 broken spokes. All spokes brake just after the nipples.
Any idea what’s wrong??

Not sure about the black ACI spokes, but the silver double butted ones on my self-build wheel have served me well (2500+ miles) on my 32 hole CXP22 rims with on-one hub.

Found the following extract at :http://www.myra-simon.com/bike/wheels.html
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And yes, spokes do break, but it's not usually as the result of an impact, typically they just break as you're rolling along. Spokes break as a result of fatigue. If your wheel is loose, then every time the wheel goes around, it flexes a tiny bit, and eventually it breaks. In fact spoke breakages are the most telling sign of wheels that don't have high enough tension. If your spokes are tight, the spoke doesn't move as the wheel turns, so they can last much longer. Thus a high-tension wheel is one that will last a long time with few spoke breakages.

Usually they break if the spoke tension is uneven around the wheel.
Could be that those spokes are made of cheese (breaking usually happens at the 'shoulder' not near the nipple) but typically it's wheel builder error.

Spokes tend to break in series - once one has gone, the rest are more likely to - the change in tension can exacerbate the beginnings of stress fractures and the like.

Thanks to all of you…I will try to (re)tension a bit more the spokes.
Also, from what I remember I put oil between the nipples and the rim but did not oil the thread of the spokes in the nipples, could this be another reason?

PS: I forgot to mention that are all in the rear wheel.

Are you lacing 3x or radial or what? Front or rear wheel? You shouldn't need to oil the nipple. I think some people use thread locker stuff but only on radial lacing patterns as it's hard to stop the spokes twisting during building.

I am lacing 3x...rear wheel...

Thanks to all of you for your comments

I decided to leave the bike in my LBS to replace the last broken spoke and have the opinion of the mechanic for my build. He said that I did a good job building the wheel and he could not see any good reason for the spokes barking.
I think that the ACI spokes are of just basic quality and with combination with the weight (myself 85k + rucksack 5-10k + the lock 2k = around 95 kilos) and the bad London roads they brake.

Still, I will spend some time this weekend to check the tension of each spoke and to tighten them a bit more…lets see?????

Any tips on how to check all spokes are evenly tensioned???

http://www.sheldonbrown.com/wheelbuild.html

because your wheel shows signs of under tensioned spokes, if you tension the others now, it might not be a good idea cos the remaining spokes are also fatigued from the flexing, making them weaker.

It's a huge pain, but if it were me i'd buy a new set of spokes and rebuild the wheel.

p.s there are spoke tension gauges out there, but you can usually feel the tension in the spokes by hand and guesstimate it.

If you wanna be truly exact buy a spoke tensioner or just feel the tension and guesstimate it to a close, all round even tension.

The nice part of the story is that I ride a 150 kilometres Audax this Sunday!!!!…I will get a dozen of spokes with me to be on the safe side!!!!!!!

This will sound silly but you can easily check spoke tensions by plucking them like a harp - it will not tell you the right tension, but an unevenly tensioned wheel will have very differently sounding spokes, and it may then give you some ideas where to begin retensioning. If it is beyond anything minor and unless you know what you are doing, and have a jig, I would suggest taking it to a builder to retension

Let’s see I’ll give it another try this weekend with retensioning…anyway, every problem for good…next time I will have more experience with wheel building ;-))))))))

ACI DB are fine!