Mastech HY-3005D-3 Earthing and common ground issue

[Jwillis]

I have a problem that I didn't have before. The Positive and Negative(common ground) should float independently from Earth ground, correct?
I was trying to work on a op amp powered with a dual rail supply from HY-3005D (in series mode to give me +15v 0v -15v) . Signal from AWG and oscilloscope to monitor the output with my oscilloscope. I hadn't even connected the the circuit yet but was creating a common ground with Hy3005D power supply, Oscilloscope and AWG. Oscilloscope and AWG work fine until I connect the 0v centre tap of supply and the slave side shorts out.
I done this configuration without any issue before. Power outputs of power supply should be independent from earth ground.