[SEDXC] Traps? > 440 3 phase

[Ed Tanton]

I used to be less than comfortable around anything higher than 120 
VAC 1 phase until I had to wire up a company project using 440 VAC 3 
phase. It was to test the temperature effects on a (nearly) VW-sized 
steel utility cabinet when it had ~ 5000W of strip heaters mounted inside.

I did all the wiring. We put a zillion copper-constantin thermocouple 
junctions around the outside of the cabinet along with some inside. I 
connected all these pairs to a very low contact resistance switched 
analog meter. I also had mirror scale analog voltmeters and ammeters 
measuring each leg.

All this was assembled in an ordinary office room with drapes over 
the glass wall and the A/C sealed off. Once we began testing, 
measurements of the power in each leg (and hence the total power 
input to the strip heaters) and the temperature at each 
copper-constantin thermocouple were taken every 15 minutes. If you 
have ever seen these old-style mirrored-scale meters, recall that 
they have big, shiny, nickel-plated thumb-nut contacts. The meter 
'array' was about a square meter... actually a little longer than 
that in one direction. In order to take all these measurements, I had 
to lean out over the whole thing, leaning on one carefully placed 
arm, and get the exact mirrored reading. It usually took two leans to 
get the ones that far away. It would have made OSHA absolutely hysterical!!!

The bottom line for me was that I still greatly respect 120 VAC, but 
do not consider there to be much difference between 120 & 440. You 
screw up and you're just as dead. The reason for bringing all this up 
is to agree with John that you can pack an awful lot of watts into 
440 VAC three-phase. Anyone running THAT kind of line is SERIOUS. 
Look at the graph illustrating three phase capabilities at 
http://www.3phasepower.org/3phasewiring.htm . You can see that if all 
the power is related to what's inside the sinewaves, adding the 2 
additional phases increases that net, available power while keeping 
the wire sizes the same.

And oh yes... the net answers we obtained regarded the long term 
temperatures you could expect all over such a cabinet when you had 
5000W of continuous power inside. We could then accurately predict 
the cabinet temperatures for various power levels The MOST 
INTERESTING result came when we added a couple of simple 120 cfm 
muffin fans internally-doing nothing more than circulating (NOT 
exhausting) the air inside the cabinet. Once the temperature 
stabilized, and we then turned on the fans, the net temperature 
everywhere was reduced 10 degrees!!!

At 11:55 AM 12/17/2006, John Harden, D.M.D. wrote:
>There have ALWAYS been individuals running that kind of power...... The
>FCC used to go to QTH's and take a field strength reading outside. Then
>they would go in and ask the individual to tune the linear to legal
>power. They had them cold when the new field strength reading was 1/10
>the original reading!!!
>
>There are two dead give-aways....
>
>1) Water cooling systems (pipes running into the shack).
>
>2) 440 Volt, 3 phase power going into the shack
>
>I remember a ham being electrocuted in the 1960's when he touched the
>pole transformer he was using for a plate transformer. Reverse pole
>transformers were common..... Put 230 volts single phase on the
>secondary and get out several thousand on the primary.
>
>73,
>
>John, W4NU

Ed Tanton

website: http://www.n4xy.com

All emails <IN> & <OUT> checked by
Norton AntiVirus with AutoProtect

--------------------------------------------------
"Right is right, even if everyone is
against it; and wrong is wrong, even
if everyone is for it."

William Penn
--------------------------------------------------