I have a sub-panel in my greenhouse that is fed by an incoming wire from th
e main house panel. The incoming wire is directly feeding a 30 amp breaker
, therefore I can disconnect the power to the panel by simply tripping the
breaker therein. (Also within the panel are two additional 15 amp breakers
, one for lights and the other for a single outlet.
I've always liked the convenience of the "breaker input" instead of hard wi
ring the input directly to the panel. Does this method meet code? Any haz
ards? Any down-side?
Thanks for all replies.
On Saturday, August 24, 2013 9:47:29 AM UTC-4, Ivan Vegvary wrote:
the main house panel. The incoming wire is directly feeding a 30 amp break
er, therefore I can disconnect the power to the panel by simply tripping th
e breaker therein. (Also within the panel are two additional 15 amp breake
rs, one for lights and the other for a single outlet.
wiring the input directly to the panel. Does this method meet code? Any h
azards? Any down-side?
The code requires that all equipment be installed in accordance with it's l
isting and marking. If you check that equipment in the listings you will f
ind that you are instructed to use a tie down kit when using a plug on brea
ker as a main breaker for the buss that it plugs on to. That is so that th
e breaker can not be readily removed from the buss while it's buss clamps a
re energized. Install the listed tie down kit and you are good to go.
Is the feeder to the greenhouse panel three wire or four?
Is your greenhouse a detached structure in relation to the building in whic
h the Service Equipment that supplies the feeder is located?
If detached when was it built?
Has anybody pointed out that breakers are designed to be ON most of the
time, and once in a while kick OFF? and Switches are designed to be turned
ON or OFF a lot? Simple thought process suggests that abusing a breaker
to use it as a switch is going to have some long term, unexpected
consequence. Like not turn ON when you want, or not kick OFF when you
On 8/24/2013 11:13 AM, firstname.lastname@example.org wrote:
In my former church, the breakers were used to turn on and off the
lights in the church, built in 1984. They were not, iirc, rated for
switching duty. After a few years, many started getting hot to the
touch. They were replaced with SWD. And, in time, they started failing
the same way. There were 13 such switches each controlling 2 light
fixtures. I always wanted to put relays downstream to control the
lights. There were about 3 or 4 different lighting patterns used
depending on the building use, but it wouldn't be difficult to have
groups of relays doing the job. Never did it as I moved. In another
commercial building I specified SWD breakers to control TV studio lights
and the powers to be, put in a breaker box and a separate switch box
because, as they told me, breakers used as switches make for bad
breakers. This was in about 2001.
The breaker panel is/has been the switching panel in the church here
"since forever". It was replaced from the 1920's original in the
early-mid 60s and hasn't yet had a failure since. Some circuits are all
fluorescent, most aren't but nothing bad has happened in 50 yrs or so.
I've never tried to discover what the rating is; I'd suspect there being
some other issue w/ the gear in your aforementioned location.
On 8/24/2013 9:13 AM, email@example.com wrote:
From the UL "White" book:
"Circuit breakers marked 'SWD' and rated 347 V or less are suitable for
switching fluorescent lighting loads on a regular basis at their rated
Circuit breakers marked 'HID' have been investigated for switching
high-intensity discharge lighting loads on a regular basis at their
I don't believe using "SWD" breakers on ordinary loads that are switched
is required, but it is a real good idea, particularly when they are
readily available. The only breaker I looked at recently (SquareD 20A)
was marked both SWD and HID.
SWD and HID ratings are probably for the increased arcing from an
inductive load. It would be interesting if they are tested for more
on-off operations than an 'ordinary' breaker.
You will see lots of things done, but that does not make it correct.
There are some breakers that are also designed to be used as switches an can
be cycled off and on many times with out a problem.
NB that that applies only to fluorescent or high-intensity lighting
circuits. I'd have to look up precisely the Code definition of
"lighting circuit" to have 100% confidence but I'm pretty sure it
doesn't include a general circuit that has one or two fluorescent
fixtures included but is fluorescent-only or almost only load on same.
The "main" he is using is not normally used as a switch but it gives
him the ability to kill the panel if needed. The one breaker he is
using as a light switch should be rated SWD. It is done every day in
thousands of commercial and industrial buildings.
Your simple thought process needs to go a complex step further to
understand this, I guess.
On Saturday, August 24, 2013 3:24:54 PM UTC-4, firstname.lastname@example.org wrote:
the main house panel. The incoming wire is directly feeding a 30 amp brea
ker, therefore I can disconnect the power to the panel by simply tripping t
he breaker therein. (Also within the panel are two additional 15 amp break
ers, one for lights and the other for a single outlet.
wiring the input directly to the panel. Does this method meet code? Any
hazards? Any down-side?
To be completely precise it's not flowing either direction. It's vibrating
back a forth a tiny bit.
If I remember correctly, code "requires" a breaker in the main panel to
feed the sub panel. Your 30 amp breaker protects the wiring that runs
from the main panel out to the sub panel in your green house. If you were
ever to cut the wire with a shovel or something, that breaker is what
would prevent the whole system from shorting out.
The 15 amp breakers in your green house protect the wiring for your
individual light and outlet circuits.
Your configuration is normal, and I have the exact same setup powering a
sub panel in my shed.
However, unlike the main panel, the neutral bus should be isolated from
the ground bus in the sub panel. You should also have an additional
ground rod installed out at the greenhouse to suppliment the ground at
The US power grid uses "alternating current" (AC). The electrons flow
from positive to negative, then reverse to flow backward from negative to
positive (rising and falling in a sine wave). In the US the current
alternates back and forth like this 60 times a second (60 hz). So
technically, the electricity is flowing in both directions.
From a practical standpoint you have a supply (the power grid, generator,
etc.), and a load (lights, heaters, radios, computers, etc.). Without the
load, current isn't flowing either direction. :)
On Fri, 30 Aug 2013 14:48:36 +0000 (UTC), HerHusband
There are exceptions but that's certainly the way I'd do it. The
issue wasn't feeding the sub through a breaker in the main, though.
The issue was feeding the sub *backwards* through a breaker in the sub
(with a breaker also in the main). This normal.
True but irrelevant. There is a "source" and a "sink". The breaker
can't tell the difference, so it doesn't know it's being back-fed
(which is the subject under discussion).
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.