On 3/5/13 7:08 AM, Jim Lux wrote:
On 3/5/13 5:42 AM, jhowson4@xxxxxxxxxxx wrote:alright so apparently i missed something all these years. I thought you wanted to separate the two grounds and because the HV was grounded you should only use the RF ground in that system, but apparently not, you use both. You want to connect the ground on your transformer to the house ground, make your circuit like you have shone, and connect the bottom/inner turn of your primary to the base of your secondary.No.. there is no good reason to connect primary to secondary. Some people do it for historical reasons, but for the vast majority of cases this isn't a good idea. If you are using a Neon Sign transformer, or anything with a grounded centertap, connecting primary and secondary as you describe is DANGEROUS. On a typical NST driven primary, both ends of the primary are "hot" relative to ground.
I missed the reference to the single ended NST with one end grounded. In that case, the danger is not as high.
However, you generally do not want the primary connected directly to the secondary in any case: the spark from the secondary is a nice low impedance, and you don't want to make it easier to have someone/something hit by a spark connected to a HV source with more current.
In typical cases, of course, the substantial impedance of the secondary winding would be in series as well, but there are cases of injury (and death?) when a connection was made between the primary winding and a person via a streamer. So that pushes for making the primary winding generally "isolated" from ground, so that if something "grounded" (e.g. a person) happens to touch it, the hazard is less.
OTOH, you want some non-infinite impedance from primary to ground to limit the voltage rise between HV windings in the transformer and the core.
The NST (4kV, 50mA) for my SGTC is a single end type with one of its secondary winding ends attached to the metal casing.
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