I can't speak for him but my opinion (especially if you have a smaller neutral then grounded conductor where permitted) that if you can't tell what is hot and what is not maybe you better call someone that knows what they are doing. I have run into hundreds of improperly identified grounded conductors over the years yet was able to look at how it was connected and say to myself that better be a grounded conductor or we have a problem, or something along that kind of story line.
For those that open a panelboard and see all black incoming supply conductors and are lost because they have absolutely no idea what voltage to expect on what conductors need to take a good hard look at if they are cut out for this career - JMO. Seems obvious to me the one landing on the neutral bus is very likely going to be the neutral, if it is a 250 volt max design panelboard, it is probably 120/240 or 208/120. If it is 277/480 design panelboard it is likely 277/480 but could be lower voltage (but very rarely is). If there are still questions get your meter out and do a little more investigating, it isn't that hard if you have any interest at all in this trade.
:thumbsup: