Re: [TCML] Centre tapped mot stacks

[Scott Bogard <sdbogard@xxxxxxxxx>]

Hi Greg,
     I see no reason to ground them, in fact I never ground my MOT stacks
anymore, and I've successfully run 3 Stacks as a result.  On the off chance
they are recommending grounding from a safety perspective, my answer to
that is no sane human has any business near a MOT when it is running,
grounded or no, without safety precautions that would make grounding
pointless anyway (chicken stick and high voltage insulated gear.)  But no,
I've never seen a performance benefit, and honestly sometimes MOTs seem to
fail faster when grounded, but that may be in my head.  My advice is let
them float, hopefully others will comment...

Scott D Bogard.


On Tue, Sep 10, 2013 at 10:32 AM, Greg Peters <greg.j.peters@xxxxxxxxx>wrote:

> Hi all,
>
> Excuse my ignorance - I seem to be missing something obvious. I am about
> to try a mot stack for the first time and  confused about something.
>
> Most 4/6 pack mot stacks I have seen have the middle two transformer cores
> grounded and the outer two or three cores floating. I can see that this
> appeals because it effectively halves the voltage swing with respect to
> ground, which on first inspection seems safer.
>
> However, I am wondering if we would be better off running the all cores
> ungrounded, in effect creating one single floating secondary, akin to a
> pole pig or potential transformer, etc? Is it fair to say that running the
> secondary in a centre tap configuration references it to ground and hence
> creates a PD between the secondary and primary windings (which are also
> referenced to ground through the neutral conductor)?
>
> Is it possible that this would encourage arcing from the secondary to the
> primary (probably via the core) on the outer mots?
>
> Would it be better if all cores (and hence  secondary windings) were left
> floating, removing any tendency for arcs between the two?
>
> I know I am missing something but I just can't figure out what it is.
>
> The only thing I can think of is that it increases the voltage stress on
> any given transformer but as far as I can tell each transformer secondary
> sees ~2kv across it whether it is referenced to ground or not?
>
> Someone please tell me what simple law of electronics am missing!
>
> Many thanks,
>
> Greg.
>
>
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