We're getting ready to get ready to install magic smoke-in-a-tube in
the....covered patio... and I've been reading electrical books like I was
drinkin' for my SATS... Still having some hesitation at the number of
circuits, cable routing/layout.... general juju...
We want to install a 100 amp subpanel in the patio, and we have 200 amp
service to the house. We removed electric baseboard heaters a couple of
years ago and they were on 3, 20 amp 220 circuits, so that frees up some
The patio is 24 x 36, and at 3 watts a SF, I've figured that would take
about 30, dual tube 4' florescent lamps, plus detail lighting. This would
work on two 15a circuits, by my numbers, but was hoping for three - two for
the general shop lighting, and another for the studio and finishing room -
roughly 1/3 of the area.
On 220 v, I have the 3hp TS, a 1.5hp jointer, an air compressor and a dust
collector - The work ahead may (I hope) justify a shop - bot, and their
website says that it takes 15a at 230. The heaviest load I would run at the
same time would be the DC and the 'bot... I also have a 220 v wall heater -
so I'm at 2 circuits here, anyway, no?
I was thinking of 3 additional circuits for power - 1 20 and a pair of 15's
(wired for 20), and an isolated 15a electronics circuit, then two additional
15a (wired 20a) circuits - one for power outside the patio, and another for
By my count, here's what I have:
3 15a lights
1 20a power
5 15a misc
2 20a tools/heater
HELP! I'm going circuit crazy! How much power do I need for a 1-2 person
shop? I guess we could look at separate electrical service, but we've done
well with the local building department and don't want to run into a hornets
Talk about overbuilding.....
No real need for 3 circuits here. You'll want to have the overhead lighting
in 'banks' (each with its own switch) anyway, so that you can turn on
'some' of it, without necessarily turning on everything. Split the lighting
in each area, across the two circuits, and you're not 'in the dark' anywhere
with a single circuit failure.
You need 3, probably 4, here. heater needs its own. air comp can/will kick
on at the most inopportune time, depending on size it may call for it's own
circuit. TS and jointer can share a circuit. Shop-bot should be on its own
You _want_ *lots* of circuits.
"service" to the panel does _not_ match the total possible load of all the
circuits. It is less. often *considerably* less.
4 240V 20A circuits
2 120V 15A light circuits
5+ 120V 20A 'utility' circuits.
(minimum 2 for the studio/finishing area,
minimum 3 for the main area)
Next, look at 'worst case' use, what all _might_ be running at once:
circa 25A of 120V lighting. (equiv 12.5A @240)
heater 18A @240 (max allowed on a 20A circuit)
shop bot 15A @240
DC 12A @240 (assumes moderate size)
air comp 12A @240 (assumes moderate size)
misc. 10A @120 (clock, radio, coffee-maker, fans, etc.)
You're looking at about 75A max draw. (85A with 'biggish' DC and air. comp.)
Well _under_ the capacity of a 100A sub-panel/distribution. The fact that
when you 'total' the breakers, it comes up to 145A @ 240 is not important.
Now, if the air comp is something that you power up only when you're using
it. that drops out. if the DC is 'small', and the shop-bot doesn't draw
a full 15A, and you have limited 'misc', you could probably get by with
60a distribution to the sub-panel. But, I wouldn't recommend going that way.
Note: I'd run all the 'utility' circuits as 20A, simply because that means
that you can plug a 'power hog' device into a circuit that has "something
else" already on it. While it's unlikely that you'll have anything with a
tail that needs more than 15A, the ability to use, say, a 9A device on the
same circuit with an 8A one _is_ handy.
Corollary: put in *lots* of outlets. Figure out what you think you might
need, and then "double it". Then interleave the circuits, so that multiple
circuits are 'convenient' to any given location. I tend to favor 'quad'
boxes, with each of the two duplex outlets on a separate circuit.
If you have the ceiling height, consider metal halides. NOT mercury
vapour, halogen or sodium.
In my old shop I converted from 28- 8' tubes to 6- 400watt halides.
There are 75 watt halides which will give you the same light as 4- 8'
tubes. Fluorescents use about 2.5 times more power and the light is much
more balanced to daylight than fluorescent ..(which is why pot-growers
The reflectors come in different patterns, so do a bit of homework.
You'd be amazed at how much better your sanding job suddenly becomes.
The initial outlay is a bit more, but most bulbs last 25,000 hours.
Current flourescent technology is actually more efficient than metal halide,
has a better color rendition index, and distributes the light better.
Compare lumens/watt for metal halide and flourescent. Only the very advanced
ceramic metal halide lamps are close to T5 flourescents. As far as lamp
life, flourescents last longer if you replace the MH before the output and
color goes to hell. Metal Halides use to be the lighting of choice for
gymnasiums, etc., but flourescents are taking over as a more energy
efficient alternative. Only drawback is more lamps to change.
That is really interesting. I must admit, I made those changes
10+ years ago and haven't followed any further developments in
You got me curious now. Special ballasts? Any of them retro-fit?
Retrofits involve the ballast and the sockets, so it's rarely worth it
unless the fixtures are built-in to a special ceiling or hard to replace for
some other reason. T8 is probably the most economical way to go for home
use. Fluorescents have been recommended for ceilings under 15 feet for quite
a while, the only change has been the development of T5 High Output lamps
which have made it possible to put together fixtures that can put out enough
light to compete with metal halide on a practical basis in high ceilings. T8
lamps are available in similar fixtures, it just takes a few more. Check out
the following report, for our purposes compare the lpw (lumens per watt) of
T8 to metal halide.
Also look at the lumen maintenance and CRI. I was a big metal halide
believer until I looked into the new fluorescent fixtures. BTW, for either
lighting system, programmed replacement of all the bulbs/lamps at the same
time will maintain the lighting quality and output. It is more critical with
the metal halide, however.
When I made that conversion to halides, The two things I noticed that my
electric bill went down and I could see more.
The shop had 14' ceilings and 1/2 of 5000 sq ft was properly lit, the
rest being storage.
In winter, I had the overnight temp down to 40 F, turning on the 80,000
BTU natural gas forced-air furnace on in the morning.... the Fluorescent
lights would flicker for the first half hour...the Halides stopped that.
The other justification was that I bought 8 (used 6) halide 400 watt
units for 20 dollars apiece with a box of about a dozen new bulbs thrown
in. The local YMCA had a garage sale. All I had to do was change the
taps so they would run on 220.
Being a point-source, the halides did show sanding marks extremely well,
I know this, because the solid surface section was all fluorescent and
the light was more spread out favouring a bad sanding job.
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