AFAIK, much stricter standards apply to electrical work and equipment over 50 volts, might not apply to an owner driver working on their own vehicle, but would apply to employees in vehicle repair or maintenance facilities, and probably also to employees carrying out basic checks on a company vehicle.
The proposed new vehicle electrical voltage is a 36 volt nominal battery, with 42 volts nominal on float charge with the engine running.
It was proposed to make 24 volts/28 volts the new standard for cars, but a cynic like me suggests that this was rejected because 24/28 volt equipment is already a low priced commodity in widespread use for trucks and buses, no profit there. Something new, different and expensive is needed.
It has been rumoured that the 36 volt nominal battery is to consist of two batteries in series each of 18 volts nominal. 18 volt batteries are not used or useful for anything else so will no doubt be hugely expensive. 3 batteries each of 12 volts generates no "continueing revenue stream" for the vehicle builder.
Rules in other countries differ in detail, especially as regards the cut off voltage, but are similar in principle.
AFAIK the limit in some countries is 42 volts (old lamp catalogs list 42 volt lamps for safety inspection lamps) I once found a German machine for the wet diamond cutting and polishing of concrete floors , this used a 3 wire, 3 phase supply of 42 volts between phases.
