[TowerTalk] Fwd: shack wiring

Sun Aug 1 08:43:25 PDT 2010

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 at telus.net>
To: towertalk at 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 at 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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