George,

you want help for a very very special case: Road bus powered by high voltage. Isn't it so hard to believe, that grounding rules are different to normal cases? Normally, bus does not get it's power by high voltage. Then, chassis is connected to ground terminal of battery, in the very most cases. All recommendations connecting the shield to bus chassis or ground of battery are valid for this normal situation. And if you are NOT giving this important detail, that your bus is high voltage powered, at the beginning, you get all this valuable information relating to normal bus situation. Is this so hard to understand?

You have a completely wrong idea of what 'shunting' means. It's not to shunt EMI to a certain place, but to shunt it away from sensible parts of electronics. And this is done by surrounding whole application by a Faraday cage and having it connected for EMI and ESD events to signal ground. If you use mains transformer powered nodes, the introduce of PE is essential. Either because safety rules force it, but also, because mains voltage is referenced to PE anyway. To shunt EMI and ESD events to PE makes only sense, if somewhere in your application signal ground sees a low ohmic connection for EMI and ESD events to PE. This IS the case with proper designed applications. And so, Erik is fully right, when he told you, that cable shield should be connected to PE, where possible.

If you don't have mains voltage, and you don't have any referenecing to PE, then of course it makes no sense to connect shield to PE, because it doesn't exist, like in a bus or aeroplane. But your postings were so vague, that it was not clear that PE does not exist. You sounded only, that you don't want to connect it to PE. But if you are in an industrial environment like factory, you have to make such a comnnection, if you want or not. Think about safety rules, which force this. And so, it's absolutely correct, when Erik insisted in connecting shield to PE.

So, when you don't have bus chassis or battery connected low ohmicly for EMI and ESD events to signal ground, because with your high voltage bus road application this is strictly forbidden, then of course it makes no sense to connect shield to battery or bus chassis. Then you must connect shield to signal ground of your application. If now EMI or ESD event is hitting your shield, interference is shunted from electronincs away, to signal ground.
You told you worry about, whether this would cause shifting of signal ground. And as I already told you, this shifting of signal ground would also result, when having no shield at all!! Because if EMI and ESD event is present and hit your application your signal ground will shift in any case. But with one remarkable difference: Without shield EMI and ESD event will be shunted to signal ground THROUGH sensible parts of your circuit. But WITH shield same interference will be shunted directly to signal ground, WITHOUT flowing THROUGH circuit and possibly damaging it.

You worry about shield potential, when driving up a hill. But why don't you worry about leakgae currents coming from high voltage section??? If you have something 'really' floating and high voltage is connected to it, this is a very dangerous combination. So, there must be either double isolation or some shunt for electrostatical charge. But how to manage this can only tell you APPROVED SAFETY ENGINEER!!! Did you already contact him?

Man, you are playing with your life. Are you sure you know, what you are doing??

Kai