T-leads are of course insulated but unshielded. We often have 6 in a terminal box (3 phase leads and three nuetral). Sometimes the routing gets tricky and it's difficult to separate the conductors to prevent them from coming too close along their length (I'm not talking abou the terminations). I usually tell our guys to get as much spacing as reasonably achievable and a half inch if possible, but when it gets tight, I get asked what is the real minimum that we could live with if we had to (because correcting it can involve a whole lot of work).

To my thinking, it's the same as minimum clearances we expect to see phase-to-phase in endwinding crossover region. Arguably it should be a bit higher in the T-leads because they are more susceptible to movement over time, but the endwindings are still my benchmark because there are similar insulation dielectric constants and in both cases we expect to see most of the voltage to appear across the air gap distance between the external surfaces of the insulation.

Of course if you place the T-leads too close, that's not an immediate failure, just a location for partial discharge to start working.

So my thought is around 0.25" minimum spacing phase to phase. Maybe a bit lower phase to neutral. And if the situation demanded (because the work involved in creating more space was prohibitive) I might even go lower. We do inspect the motors terminal boxes every 12-18 months. I've seen a lot of small spacing and direct contact (with resulting range of small gap distances adjacent to the contact on the round profile) and I've seen resulting white powder on surfaces but never any failures from that (maybe just lucky?).

What's your thoughts? Do you have any references?

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(2B)+(2B)' ?