Re: Preventing a REALLY expensive mistake.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Mark Broker by way of Terry Fritz <twftesla-at-uswest-dot-net>" <broker-at-uwplatt.edu>


>
>>
>>
>> 1. The building is fed with 1-P 240VAC, and will be upgraded to 3-P 480VAC
>> (for the elevator of doom), should I keep the 1P service as well? or just
>> have the landlord upgrade from one to the other?
>
> Presumably, when they bring in the 480, they provide local transforming down
> to standard 240/120?  Otherwise you'll have to do it yourself.  If it doesn't
> cost anything, I'd leave the existing service in. 

Typical 200V 3phase service is 208D/120Y, and it's generally not wise to run a
240V nominal load on 208V....   I don't know what the "standard" is for 480V
3ph....


>
>>
>> 2. Will a system of 10 seperate 8-10' ground rods driven vertically around
>> the buildings exterior and all laced together for a massive ground system be
>> an good enough protection for the computers and other electronics? Is there
>> a better way?
>
> Not necessarily... The key is to keep your electronics grounds separate from
> the power grounds (hence the prevalence of those orange Isolated Ground
> receptacles) until you get back to the common panel ground.  If you don't
> make loops, you're less likely to pick up noise.. 

Seperate grounds for the HVL and comp labs.  I'd imagine that the "fuse box"
ground would be sufficient for the comp labs, as long as the ground doesnt' go
through the HVL....  An RF grounding scheme like you mention I think would
suffice for the power levels we'll be running there (unless the room is bigger
than 100'x100'x40'tall, then I would imagine ~50kVA will be the absolute max).



>
> Run the sensitive loads off an isolation transformer.  

Run the HVL off isolation trannies to keep the "bad" stuff off the grid.  Lots
of RFI filters, too.  Enclose the HVL in a faraday cage.  Perhaps metal screen
over chicken wire?  Or conductive paint, as Marc suggests (cool idea, btw).



>
>>
>> 4. I remember reading about garage coilers who have had discharges through
>> the roof, can this happen on a solid concrete structure? (There will be
>> classrooms under the H.V.L.)
>
> Concrete may or may not be a good conductor. 

I've read that it's an "OK" conductor at RF.  Meaning it conducts, but has a
high resistance.  Use a faraday cage on the floor, too.


>
>>
>> 5. I've heard of coils being mounted inverted from the ceiling. How is this
>> done? Why? What are the advantages of this setup? Can it be used to make
>> near vertical discharges to the floor?
>

There are such things as transmission lines.  Run a wire from the topload away
from the coil, and then downward.  Suspend the wire from the ceiling with kite
string.


Mark B