Question regarding 3rd wire grounding and safety

Bitrex · 12th February 2009, 04:37 PM

I'm wondering, when one connects the 3rd wire ground to the chassis of an amplifier to prevent the chassis going hot in case of a fault, doesn't this negate the safety benefit of floating the secondary of the primary transformer from the line side? Since the chassis is grounded at the IEC connector on the primary side, and probably through the input/output jacks on the secondary side, I would assume that it is now possible to be shocked just by touching the amplifier B+ or B- supplies and some grounded object, instead of having to touch both sides of the secondary transformer that's completely floating. Is this correct?

jjman · 12th February 2009, 05:36 PM

If I understand the question, yes. Although the HV secondary in the power transformer is center tapped or bridged from ground anyway. So the safety ground is not needed to get shocked while touching the B+ and the chassis.

12th February 2009, 04:37 PM	#1
Bitrex diyAudio Member Join Date: Jan 2009	Question regarding 3rd wire grounding and safety I'm wondering, when one connects the 3rd wire ground to the chassis of an amplifier to prevent the chassis going hot in case of a fault, doesn't this negate the safety benefit of floating the secondary of the primary transformer from the line side? Since the chassis is grounded at the IEC connector on the primary side, and probably through the input/output jacks on the secondary side, I would assume that it is now possible to be shocked just by touching the amplifier B+ or B- supplies and some grounded object, instead of having to touch both sides of the secondary transformer that's completely floating. Is this correct?

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12th February 2009, 05:36 PM	#2
jjman diyAudio Member Join Date: Jan 2009	If I understand the question, yes. Although the HV secondary in the power transformer is center tapped or bridged from ground anyway. So the safety ground is not needed to get shocked while touching the B+ and the chassis.

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