Hot tub wiring

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How can I identify the neutral coming out of a whip that is connected to my hot tub without tearing the panels off the hot tub. There’s 3 black wires and one ground so one of the black wires are the neutral how can I identify the neutral 

 

[Murdoch]

Mate -- recommend you get your user name changed pronto before you get spam filling up your inbox.

 

[Sharpend]

Are the individual cores numbered or marked in any way? 

And ill second the change of name. 

@Doc Hudson