A little warning is in place:
When you run 120 volts supplies on outlets on different phases but common
return, be aware that if they are of the "old" type, diodes feeding directly
into capacitors, so called "top-" or "pulse" rectification, due to the
harmonics in the currents through the supplies, the current will add up, not
subtract in the return line. You can end up with 40 amps in the return line
with both lines loaded to 20 amps. I have seen this happened in computer rooms
in schools where they had many computers loading 2x120V outlets. If you use
power supplies with phase factor correction this is not an issue.
73 de,
Hans - N2jfs
-----Original Message-----
From: Jim Thomson <jim.thom@telus.net>
To: towertalk@contesting.com
Sent: Fri, Jul 30, 2010 5:04 am
Subject: [TowerTalk] shack wiring
Date: Thu, 29 Jul 2010 11:09:46 -0700
From: "Jim Brown" <jim@audiosystemsgroup.com>
Subject: Re: [TowerTalk] surge protectors
Another suggestion. run 20A circuits (#12) for anything that may get a lot
of electronic stuff plugged in, with a dedicated neutral for each circuit.
For long runs, pull in #10. If you do the math, you quickly realize that
20A will run a LOT of ham gear, everything but big power amps. That big
13.8V power supply is only dragging about 700W out of the wall to provide
40A continuous DC, enough to have two rigs keydown in RTTY at the same
time. AND you can greatly reduce those peak power requirements by using
smaller power supplies to float deep dischrage batteries.
### If I remember correctly, in our BC electrical code, IF you opt for
a 20A circuit [120 vac] and use 12 ga Cu , and also a single 20A breaker,
the 120 vac outlet must be of the 20A rated variety ! The 20A rated
120 vac outlets don't resemble the normal 15A variety. They use a
weird 20A 120 vac outlet... which requires the mating plug. I think
one blade was straight.. and the 2nd one had a right angle to it, such that
normal appliances,etc, could not be plugged into it. IF a regular 120 vac
outlet is used, and V drop is a concern, sure, you can use 12 ga wire... but
you must use a 15A breaker. 10 ga CU won't fit most 120 vac outlets anyway.
[ they will take 12 ga max]
## IF you want to save on wire, I see no reason why you can't run 240 vac
+ neutral to a duplex 120 outlet... then break the tab off... and then they
share a
common neutral. This is done all the time in kitchens. Then you can suck 15A
per
outlet. The neutral current is the difference between the two loads.
## depending on how far the shack is from the main 200A panel.... I decided in
my
case, to go to plan B... and simply install a 100A sub panel on the other side
of the
shack wall [ unfinished part of the basement, where the 200A main panel is
across the
basement from the 100 A sub panel]. Sub panel was cheap... and is wired back
to main
panel with 3 ga CU. Then it's real short lengths [ like <10'] of 120/240
wiring from
100A sub panel to shack on other side of wall. Then I'm not gobbling up
umpteen
breaker positions in the main 200A panel either.
## each amp gets it own real short dedicated 240 vac circuit [10 ga]. Also
loads of 120 vac
circuits.[12 ga] It's actually an excellent way to go. Instead of really
long multiple runs back to the
200A main panel [ with huge ga wire, so no V drops] , I end up with really
short multiple
runs to sub panel.... and zero V drops. It makes for a cleaner install, and
WAY less clutter/mess.
Dunno what the smallest size sub panel you can get these days. Even a 40-60A
sub panel,
fed with 8-6 ga cu would be a winner... and still provide loads of power. In
the winter time,
after dinner / late at night, I use a 1 kw electric heater in my tiny 8' x 10'
shack. Makes more
economical sense vs running a gas furnace, and heating up the entire 2000 sq
ft house.
During the day time, we will use the gas furnace. At night, we use the gas
fireplace upstairs
in living room... and the 1 kw space heater for my radio room. I have a 5
kw
heater in the
workshop next door, which takes no time at all to bring my real small work shop
up to temp....
I only use the 5 kw heater at night.
## that was another reason to just install one sub panel..and be done with
it.
The 5 kw
heater in the shop next door is 6' away from the sub panel. The 1 kw
heater
in the shack
is 12' away from sub panel. Feeding real short multiple runs through one
wall, is a LOT easier
than drilling out umpteen ceiling joists.
later.... Jim VE7RF
For a serious multi-two setup, I'd do two 20A circuits and two 240V
circuits. One 240V circuit is plenty for SO2R, but you want the second
circuit if two amps will be in TX at the same time. One 120V circuit will
run all the transceivers and support stuff for multi-two -- the second
circuit is a spare, or for non-electronic stuff. Years ago, N6RO was wired
with six 120V circuits and six 240V circuits, and it's plenty for his 5-
transmitter multi-multi setup. His shack is in his barn (attached to the
house), and he installed a local panel in the shack. This makes the wiring
to his outlets much shorter, improving voltage regulation. Naturally, you
also want big feeders to that panel.
73, Jim K9YC
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