Let me be clear, I am not using an extension cord and would certainly not run it behind a wall or in conduit if I did use one. Any electrical work will be done to code by a licensed electrician. I thought I would run it by you guys to have a better understanding so that I can have an intelligent conversation with my electrician.
The reported power consumption of an ST70 is 190W, which is close to 2A. Probably more since its a rectified load so the peak current will be higher. Watch the ammeter. If it goes much above 2A stop. You don't want to damage your isolation transformer. Its fused so make sure its the right fuse.
If an american@115V and 60Hz promotes GFCI I would take it really seriously (@230VAC 50Hz only thing between you and an early grave is lousy ground connection ).
Would never dream on anything else.
Regarding the variac, consider it to be appliance ,ie connect with cord in outlet.
I like to build all of this stuff into a 3U or 4U rackmount enclosure. Isolation transformer, variac, current limiting (more on that in a moment). Put a good EMI filter on it. This serves two purposes - keeps power line interference out of your measurements, and keeps your experiments from affecting other equipment in other parts of your house or building.
This makes it "portable" (even if it's 80 pounds), which can be extremely useful, and makes it easy to repair if you blow it up. I like to add a current transformer with a BNC on the front panel. This combined with an isolated voltage sensor makes looking at power factor a lot easier.
As for current limiting:
I mostly use ferroresonant transformers (CVTs, SOLA transformers, whatever you want to call them) for this. I feel that it works a lot better than a light bulb that inevitably leads to major sag under load, which switching power supplies do not take kindly to.
This makes it "portable" (even if it's 80 pounds), which can be extremely useful, and makes it easy to repair if you blow it up. I like to add a current transformer with a BNC on the front panel. This combined with an isolated voltage sensor makes looking at power factor a lot easier.
As for current limiting:
I mostly use ferroresonant transformers (CVTs, SOLA transformers, whatever you want to call them) for this. I feel that it works a lot better than a light bulb that inevitably leads to major sag under load, which switching power supplies do not take kindly to.
That is doable if you limit transformer size, not only for weight reasons but size. 3 HEU is probably to small to fit all. Especially the front mounted variac. The rest can probably fit well.
Exactly how are you planning to use the CVT? Putting on the outlet of the variac kind of forfeits is function , obviously. But what happens if the load is a variac? The variac would have a more or less constant input voltage.
Arent CVTs insulating BTW? So that removes the need for an insulating transformer.
All electronic appliance must be designed to take a power sag, and if it is current limited the risk of total destruction is reduced. The fuse in the variac is there to protect the variac.
I dont see much added value in a CVT, but a lot of heat loss instead. AFAIK the CVT is a very heav beast with not so great efficency , even at no load ( I had an old Phillips one, 3H (Heavy, Humming, Hot) ...
Exactly how are you planning to use the CVT? Putting on the outlet of the variac kind of forfeits is function , obviously. But what happens if the load is a variac? The variac would have a more or less constant input voltage.
Arent CVTs insulating BTW? So that removes the need for an insulating transformer.
All electronic appliance must be designed to take a power sag, and if it is current limited the risk of total destruction is reduced. The fuse in the variac is there to protect the variac.
I dont see much added value in a CVT, but a lot of heat loss instead. AFAIK the CVT is a very heav beast with not so great efficency , even at no load ( I had an old Phillips one, 3H (Heavy, Humming, Hot) ...
3U is just enough space for a typical 10A variac on the front panel. 4U if you want a bigger variac than that. I squeezed a 2 kVA toroidal isolation transformer in mine with space to spare and it still weighs less than a Crest 8001.
CVTs have one very useful feature - in a significant overcurrent, the iron comes out of saturation, and the output voltage on the tank circuit collapses. Quite a few old-school pulsed power supplies used CVTs to control the charging current to large cap banks, and although not especially efficient (and quite archaic), it actually works quite well and is almost bulletproof.
I usually use the CVT on its own, not with a variac. Yes, they're inefficient (core losses = maximized), but quite useful. With very old equipment it usually doesn't matter (powering a tube amp from an 80V supply probably won't hurt it), but quite a few switching supplies and regulated supplies have UVLO thresholds that roughly 105V input voltages.
CVTs have one very useful feature - in a significant overcurrent, the iron comes out of saturation, and the output voltage on the tank circuit collapses. Quite a few old-school pulsed power supplies used CVTs to control the charging current to large cap banks, and although not especially efficient (and quite archaic), it actually works quite well and is almost bulletproof.
I usually use the CVT on its own, not with a variac. Yes, they're inefficient (core losses = maximized), but quite useful. With very old equipment it usually doesn't matter (powering a tube amp from an 80V supply probably won't hurt it), but quite a few switching supplies and regulated supplies have UVLO thresholds that roughly 105V input voltages.