Disclaimer: I'm no electrician, and I'm no Arduino expert. That said, my system's Arduino is directly connected to the SSRs, and it seems to be working fine. The control voltage of my SSRs (cheap Ebay ones that get shipped to you directly from Asia) is 3-32VDC, and the Arduino pins output at 5VDC.
Edit: and yes, like DeNomad said, 40 mA. Like I said, I'm not an expert...