I am repairing a SMPS and as i stated want to connect my scope to the primary side to check a PWM chip. so the primary is a hot ground and the oscilloscope is at earth ground like the secondary side of the SMPS. Kind of concerned that i am going to burn out my scope. I have an isolation transformer i use also a load light. I usually plug the SMPS into the isolation transformer. the isolation transformer has pass through grounding, which i can disconnect the ground, it's a Hammond transformer in a metal box i made. in general is pass through grounding a good idea for isolation transformers since the ground goes back to the circuit breaker box and is connected to the neutral?

 

I don't see the need to cut ground. You need to isolate Line and Neutral.