The 3500kg in NCC advice sheets refers to the suitability of the designated breakaway cables for use on braked towed vehicles up to 3500kg GVW.
In the Alko.com shop they show the two types of cable. The older style with the spring clip is stated as for looped operation. But the Alko website refers (via link) the reader to documents issued by the NCC. Here the assembly is dealt with in two sections. One where there is a designated attachment point and the other where there is no designated attachment point. With a designated attachment point the old style Alko cable should still be looped. Where there is risk of confusion is that the NCC document also states that the cable can be clipped directly, but with the proviso that the clip must be strong enough and have the makers approval to do so. For the old style breakaway clip Alko clearly state on their website that its for looped usage, and should not be directly clipped.
Where the towbar has no designated attachment point the NCC documents referenced by Alko advise looping the cable (either type of cable) around fixed towball. But for a detachable towball the guidance of the manufacturer or supplier must be sought.
My detachable Witter has two relatively small holes in its fixed section. Neither are large enough to loop my breakaway cable. The towbar handbook doesn't support looping the cable around the lowball, and neither would I. So my options were to either buy another breakaway cable, with the new Caribiner clip (assuming it would fit the holes) or provide a suitable attachment point for which I use high strength carabiner mounted is such a way that any pull on the breakaway cable is along the longitudinal axis of the carabiner. I could not loop the breakaway cable around the towbar as its too far back under the car and the cable would be too tight and not have a good alignment.
In answer to Prof Johns comment it could be either. If an older style cable is looped around a designated attachment point or fixed lowball, then I would expect either the cable to brake, or something at the caravan end to break. Preferably the latter. For the new Caribena clip which is designed to clip onto designated attachment points or be looped around a fixed towball there could be three points where it may fail after doing its job. But again the best designed failure point would seem to be at the caravan brake attachment. There are also the breakaway cables which have a Key Ring type of appearance which fits at the brake end. Think Alko used to call them "burst rings" so perhaps that's where the designed failure point is.
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