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Class II with Chassis earth bond?

Former Community Member
Former Community Member
The floating output of a Class II product, if measured to Earth may present a voltage of 80-100V AC, The reason is that there is a small capacitance connected between the output side (low voltage output) and the input side (mains) of a switch mode power supply from the safety approved Y-capacitors.

The limits for this leakage current is internationally set to safe values for humans (<250uA). The Voltage is therefore regarded safe to use, and expected.


My preference in such situations therefore to isolate the electrical parts from any user accessible metal parts, to prevent  users noticing a tingle when touching them.


My questions relates to using a bond from the accessible metal parts to a safety earth instead.


1) The earth is not required for safety, only comfort but could it affect leakage current?


2) The application is a pre-existing installation, an LED strip powered from a class 2 supply with the led tape mounted to a metal extrusion which itself is mounted to a metal container. If the extrusion were to be earthed to the metal enclosure, would the assembly then be treated as class I or remain class II ? 


3) Which standard(s) should I be referring to find these answers.



Parents
  • I have this every day. I have a class 2 TV, as most are. I have a class 1 Audio system which I sometimes use for the TV sound (much better frequency response and quality). I plug the Hi fi into the headphone jack, which is connected to the isolated voltage of the "chassis" as we used to call it. So I have a class 2 equipment with an earth connection. The only problem is during plug in I have to remember not to have the amplifier turned on as the floating AC voltage makes it output a very loud hum, probably driven by several volts AC at least (the hi fi is quite powerful at least 120 dB SPL). This is not particularly dangerous electrically but does assalt the ears and partner! A solid Earth to the TV would be a good idea. The TV would still be class 2 isolated but the PSU output would be Earthed. No problem, mains isolation is better than required and the appliance still meets class 2 requirements but has a 3 core mains cable, the mains voltage is still isolated by double or reinforced insulation.
Reply
  • I have this every day. I have a class 2 TV, as most are. I have a class 1 Audio system which I sometimes use for the TV sound (much better frequency response and quality). I plug the Hi fi into the headphone jack, which is connected to the isolated voltage of the "chassis" as we used to call it. So I have a class 2 equipment with an earth connection. The only problem is during plug in I have to remember not to have the amplifier turned on as the floating AC voltage makes it output a very loud hum, probably driven by several volts AC at least (the hi fi is quite powerful at least 120 dB SPL). This is not particularly dangerous electrically but does assalt the ears and partner! A solid Earth to the TV would be a good idea. The TV would still be class 2 isolated but the PSU output would be Earthed. No problem, mains isolation is better than required and the appliance still meets class 2 requirements but has a 3 core mains cable, the mains voltage is still isolated by double or reinforced insulation.
Children
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