I'm been tasked to fit a power entry system and filtering to a faraday cage to near TEMPEST specifications. The cage/shielded enclosure is to contain two desktop PCs. The specifications are stringent, if not paranoid, but I can't help but thinking they are much more approachable than imagined. The paramount objective is to completely eliminate all noise and interference entering the enclosure, including any routes on the power and earth lines.
One such configuration, which may seem controversial is this:
AC outlet -> UPS
UPS -> Toroidal isolation transformer
Toroidal -> Filters
The AC is a normal domestic outlet.
The Toroidal isolation transformer creates a floating supply and eliminates the need for an earth, and thus common mode noise/interference (not having an earth would save cost on the filters too).
The filters are capacitor feedthrough type to eliminate normal mode noise and high frequency intererence between the power lines.
Live is fed through the capacitor, whilst the casing of the filter has to be conductively connected 360* to the shield to prevent RF radiation entering the enclosure. Neutral, being the return current for the noise would actually be connected to the casing of the filter, and thus the shield.
I understand that in normal applications, neutral would never be 'case ground' for appliances, although historically it has been. Protective measures on the power lines could ensure that insulation faults were detected and power removed immediately. Given that on a normal AC outlet neutral and earth are connected at the nearest service entry anyway I was thinking this would be acceptable.
Are there any overriding considerations that would would deem this not acceptable?
Standards regarding separately derived systems, isolation transformers, floating supplies, etc... seem to be contradictory sometimes.
Any help would be much appreciated.
One such configuration, which may seem controversial is this:
AC outlet -> UPS
UPS -> Toroidal isolation transformer
Toroidal -> Filters
The AC is a normal domestic outlet.
The Toroidal isolation transformer creates a floating supply and eliminates the need for an earth, and thus common mode noise/interference (not having an earth would save cost on the filters too).
The filters are capacitor feedthrough type to eliminate normal mode noise and high frequency intererence between the power lines.
Live is fed through the capacitor, whilst the casing of the filter has to be conductively connected 360* to the shield to prevent RF radiation entering the enclosure. Neutral, being the return current for the noise would actually be connected to the casing of the filter, and thus the shield.
I understand that in normal applications, neutral would never be 'case ground' for appliances, although historically it has been. Protective measures on the power lines could ensure that insulation faults were detected and power removed immediately. Given that on a normal AC outlet neutral and earth are connected at the nearest service entry anyway I was thinking this would be acceptable.
Are there any overriding considerations that would would deem this not acceptable?
Standards regarding separately derived systems, isolation transformers, floating supplies, etc... seem to be contradictory sometimes.
Any help would be much appreciated.