tonearm cable, do you need one?

Zu Audio Phono cables with ground wire are excellent!
You need shielded phono cable.
Read more here.

And on ebay you can find their auctions for Mission Phono RCA cables with starting price at $1, normally goes for $80-100 on those auctions. They are great for the money! 

If your phono cable does not have this third ground wire then you can still try it, and if you hear some hum then you can’t use it without separate ground wire, just try it.

@petg60 he’s asking about RCA to RCA type, his TT has RCA output with ground pin.

The difference between phono cable and interconnect cable is SHIELD , not a ground wire. Do you understand why 99% phono cables are shielded? The signal from phono cartridge (especially MC) is much lower than line level signal from any other component. Without shielded cable you can hear a radio signal in your speakers or noise and hum when you connect it to your tonearm/turntable with MC cart.
Some interconnects are shielded, but most if them are not shielded and using them instead of phono cable is bad idea.

As for the ground wire you can use any thin wire (it will not affect sound quality) between turntable ground terminal and phonostage ground terminal if needed.