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Registered Member #1500
Joined: Sat May 24 2008, 04:38PM
Location: Ojai, Ca.
Posts: 44
I recently finished my 14400v 5KVA PT cabinet - nice epoxy transformer! I have decided to ground H2 to RF ground and the cabinet . This implies the inner turn of the primary is also robustly grounded to RF ground. This would be a disaster waiting to happen if the RF ground was lost. How much more dangerous or not do you think this setup is? It has the advantage of keeping the lower secondary turns and the inner primary at near the same potential avoiding a flash over in closer wound primaries.
Registered Member #477
Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546
This is a popular configuration. I don't see loss of RF ground as the danger, incidentally. You still have to get yourself across both legs of the HV somehow. With RF ground firmly planted, it's actually *easier* to do that, isn't it? (i.e., touch the non-grounded leg--you're already standing on the other one).
Also, it's probably good to be sure that your transformer is designed to support having one leg of the HV grounded. Not all are. Yours, having a common ratio (and, accordingly, an *uncommon* delta voltage), probably is. Does it have a "Y" or "wye" rating (e.g., 14400 / 24940Y Volts). If so, you should be good. Else, consult the documentation for your transformer. I have several PTs that are meant for delta connections only, and the documentation actually states that you must derate them if you intend to use them single-ended (i.e., you need to reduce the voltage).
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Personally, I'd want the eht inner wire BONDED to utility earth and transformer frame.
You could put a heavy-duty air-core inductor in this line and use a suitable capacitor (and spark gap) to go to RF earth from the winding side of the inductor. I'm not an expert, it's just what I'd do.
i.e. I think there are legal and liability issues ... check your local legal representativve !
Registered Member #477
Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546
Sulaiman wrote ...
Personally, I'd want the eht inner wire BONDED to utility earth and transformer frame.
<snip>
i.e. I think there are legal and liability issues ... check your local legal representativve !
Sulaiman, your response has, I think, more to do with where to put the RF than with mains-frequency safety, yes? The arguments for/against connecting your utility and RF grounds are age-old, with lots of speculation and little actual science, AFAICT. Personally, I wouldn't feel any safer around the HV output of a utility transformer based on what kind of ground I'd connected one end to. In any case, I need to assume that I'm basically standing on a low-impedance path to one end of the transformer's HV output, and therefore that any contact with the other end is lethal, right?
Regarding legal issues: I don't think the electrical code in any U.S. municipality has any provision for running utility transformers inside your house, nor does the FCC provide for any of the radio interference a coil might produce. In other words, I think you're "on your own" already. I'm not sure what specific grounding code violations you'd be setting yourself up for (again, in the U.S.) unless perhaps you re-bonded utility ground and neutral somehow (something that is definitely verboten).
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Single horn verses dual horn HV supply
