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RE: MOTs in series

The practical limit for MOTs in series is four in air and six or eight under oil.  This assumes the center of the string of series connected MOT secondaries is at ground potential.  Not only do you have to worry about the secondary arcing to the core, but also the core arcing to the primary, if the core is at elevated potential.
Yes, you can parallel primaries.  I have 6 MOTs with the secondaries in series, under oil.  The 120 volt primaries are in two banks of three in parallel, each bank going to a different circuit breaker in my house breaker box.  The outlets/breakers don?t have to be in phase, since you can swap the connections on the primary.  Mine are not so as to balance the load across my 240 volt feed.

From: Tesla list [ mailto:tesla@xxxxxxxxxx]
Sent: Tuesday, January 02, 2007 8:26 PM
To: tesla@xxxxxxxxxx
Subject: MOTs in series

This is probably a stupid question, but I was wondering what exactly the problem with having several MOTs in series is.  The web sites that I have found that discuss this topic all say that the problem is that the insulation on the secondary isn't sufficient to prevent arcing to the core, but what if the core is at high voltage as well?  Like, if the secondaries were strung together, with the hv output of one secondary attached to the core of the next MOT?  I think that each MOT would not have a potential difference from the secondary to the core of more than the original rating for a single MOT, and since the primaries are electrically isolated from the high voltage across the secondaries, arcing to them shouldn't be a problem, unless maybe something on the secondary was grounded.  Is this correct?
Also, I was wondering if you could parallel the primaries instead of connecting them in series, so that different MOTs could be connected to different outlets/circuits/breakers (assuming they were all in-phase).

Thanks a lot,

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