Electrical Wiring Question

Page 1 of 2  
I'm trying to turn my 1-car, 70 year old garage into a workshop. At the moment, it has two 15 amp lines run through 1/2 metal conduit. The wire is 14 ga, and there are two hots, one neutral and a ground. I'd like to increase this a bit. I was thinking of putting in a sub-panel. I'd like to be able to run the new wires in the same conduit, as it's a little too frozen here at the moment for me to dig a new trench. My idea was to replace the 14 ga wires with 10 ga. According to my sources, a 1/2 metal conduit will take 5 - 10 ga wires, and so 4 should be no problem. My understanding was that if the run was under 35 ft, that each of the 10 ga. hot wires would support 30 amps, and hence that I should hook each hot wire to a 30 amp breaker in the main box. The salesman in the Menards electrical section told me that this wasn't right. The four wire system would only support 30 amps. Any comments?
-Peter De Smidt
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Hopefully, these are fed from one duplex circuit breaker. If not, it's a Code violation and a fire hazard.

insulation on the wires, but for the types of wire that you'd buy as single wires (not cables) at Menard's, yes, the Code allows 5 or even 6 #10 wires in a 1/2" conduit.
Please note, however, that there is a *large* difference between the number of wires the Code permits in a conduit, and the number of wires that can be easily pulled through the same conduit. Even though the Code permits five #10 wires in a 1/2" conduit, you will encounter substantial difficulty in trying to pull them through it.
If you succeed in pulling four #10 wires through this conduit, you're still limited to a 30A version of what you have now: two 30A 120V circuits with a shared neutral. What will you do with a 30A 120V circuit? Not too many 120V tools require 30A.
It would help a lot if you provided more information about what your objective is. What tools do you want to run in your garage/shop, and how much current do they require?
-- Doug Miller (alphageek at milmac dot com)
How come we choose from just two people to run for president and 50 for Miss America?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 26 Jan 2004 15:29:58 GMT, snipped-for-privacy@milmac.com (Doug Miller) wrote:

Yes, these are on one duplex circuit breaker.

My plan was to install a subpanel, and then run the necessary 120 and 220 circuits off of this. At the moment, my only big piece of equipment is a 2hp table saw. I'd like to rewire it for 220. At the moment, I'm going to use my shop vac with a HEPA filter for dust control, although down the road I'll probably want a 220 DC system. For lights, I plan on using a 400 watt HMI light, and maybe a few small task lights. Eventually, I hope to add a planer, jointer... but these will only be run one at a time. For heat, I'm hoping to install a used high efficiency furnace, but at the moment all I have is a 1450 watt space heater.
Peter
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
You might need more juice than that. Do this calculation:
Add the most power-hungry stuff you will be using at the same time:
The 2HP Table saw - 220V @ 8-9 Amps (See your motor for this exact amperage)
Dust Collector - 220V @ ??? Amps
Lights - 110V @ 4 Amps + other lights
It seems to me that you will be close to maxed out from the start.
If you are willing to forgo the bigger DC and TS, then you are fine, but it would sure be frustrating to not be able to get a bigger machine because you only have 30A coming into your shop.
--
gabriel

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

and two 20a 120v circuits, but you can't fully utilize the the 240v and 120v at the same time.
You have to figure out exactly what you need, and see if you have enough juice. But, bear in mind that saw and planers only draw their rated current when they are being heavily used; which probably isn't for more than a minute at a time. So, you can fudge a bit, because your 10a wires/breakers will allow 35a for a minute or two.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The circuit ampacity must be based on the heaviest loads that can be placed on it *simultaneously*. In your case, that looks like table saw + dust collector + lights + heater.
A 2hp table saw doesn't draw the full 2hp most of the time. Likely continuous load is in the neighborhood of 6A to 8A at 240V (1440 to 1920VA). A decent 240V dust collector is probably going to draw somewhere around 10A as well (2400VA).
Figure about 2000W total for your heater and lights. (2000VA)
The dust collector, lights, and heater are "continuous loads" as defined in the NEC and the ampacity of the circuit(s) supplying them is required to be derated by 20%. Thus to supply the total of 4400VA for these loads, you need a circuit rated at a minimum of 5500VA. Add 1440 to 1920VA for the table saw, and you're at 6940 to 7420 VA -- which is 29 to 31A at 240V.
So a 30A 240V circuit is _just_barely_ adequate, and leaves you _no_ room at all for adding additional loads.
And that's assuming that you're going to be able to pull three #8 wires through a 1/2" conduit in the first place. :-)
-- Doug Miller (alphageek at milmac dot com)
How come we choose from just two people to run for president and 50 for Miss America?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
One thing he might do to make this easier to pull is to install conduit bodies at both ends of the underground part of the run to get short pull points. If you do run 3 wires you are depending on the conduit as the grounding path or you are setting up a 3 wire feeder and regrounding the neutral in the garage. Both require driving a ground rod at the garage. (actually every scenario of a sub panel does).
See this from the 2002 NEC handbook
http://members.aol.com/gfretwell/subpanel/bdg2subpanel.htm
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

wouldn't be a big hardship to turn it to low (or off) when he needs to use the saw.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
What about hanging a sub/pony panel in your garage and feeding it with 220v and 3/8 in your conduit.
Cheers,
Andy
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I'd like to be able to do that, but according to my Black and Decker _Advanced Home Wiring_ only two 8 ga wires will fit in the conduit. I wish that I could install bigger conduit, but I wouldn't be able to do so until spring. It'd be nice to do a little woodworking now :)
-Peter
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

the insulation is type THHN or THWN. As I noted in another post, however, what the NEC permits in a conduit, and what is physically practical to try to pull through it, are two different things.
-- Doug Miller (alphageek at milmac dot com)
How come we choose from just two people to run for president and 50 for Miss America?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 26 Jan 2004 09:04:52 -0600, Peter De Smidt wrote:

The fact you are posting here would seem to indicate that you are unsure of wiring and buiding codes. Your best and safest bet is to contact your local building or electrical inspector to ask for their recommendations. Other than having to pull a permit, the advice should cost you nothing. In our community, a homeowner can do his/her own wiring as long as it is done up to code.
Another choice is to pay an electrician as a consultant with the understanding you will do the grunt work.
Trusting the advice given in newsgroups is always iffy. There is much good advice here but how do you know which is good and which is not?
Bad wiring can cause fire as well as physical harm. Unless you are absolutely sure and comfortable with wiring and electricity, seek the right advice. 'Tis but a very small price to pay for contentment.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
First of all, be sure the person giving you advice is qualified to do so. You're missing a lot of better input, so I'll give it a shot.
First of all, the NEC (National Electrical Code) specifies that circuit breakers must be sized such that they do not exceed 80% of their trip capacity under normal circumstances. If you are running motors that pull high currents for a short time (saws, planers, jointers come to mind) either at start-up or during operation, you work from maximum normal operating current, not peak-load current. A #10 wire can carry 30 amps. A 30 amp breaker is allowed to carry a steady-state load of 24 amps. Thus you can use a 40-amp breaker on 30-ga. wire for motor loads (actually you can use a 50-amp breaker if you're running an arc welder). Local codes might vary, but I got this from a retired industrial electrician of substantial experience. You have to go to the NEC and look in the area that talks about motor and welding loads.
Since it's cold, I suggest pulling the 14-gauge wire and replacing it with 10-gauge with a 30-amp breaker. Run 4 wires, black, red, white, and green into a subpanel in the garage. Put a 40-amp breaker in the main panel, then connect the white to the neutral bus in the main panel and sub-panel, connect green to the safety ground bus (where all the bare wires are) in the main panel, and to the safety ground bus in the sub-panel. DO NOT INSTALL THE BONDING SCREW IN THE SUB-PANEL! This is necessary in order to keep neutral currents from flowing through the safety-ground wire (required by code).
Connect the red and black wires to the L1 and L1 lugs on the sub-panel and to the 40-amp 2-pole breaker in the main panel. Install a 20-amp 2-pole breaker for your table saw's 240-volt (not 220 -- that's a European voltage) receptacle and wiring, then put in a pair of single-pole breakers for two 120-volt, 20-amp circuits, using the normal wiring methods.
Then, when the frost is gone and spring/summer arrives, put in a bigger conduit (1" would be nice, but it's a 70-year-old garage, so no sense in overdoing things) and run #8 copper with a 50-amp breaker to the same sub-panel. You can then put in a second 240-volt circuit, or just run the TS and DC from a single 30-amp, 240-volt circuit with multiple receptacles like I do in my 26 x 30-foot garage/shop.
I built my own home (7500 square feet plus garage) in the 1970s, and the state electrical inspector took great pains to catch me on a code violation. He came up with nothing. :-) I got my license as a registered professional engineer in 1980, and have been wiring homes from time to time since the 1950s. I also was responsible for specifying wiring and grounding for industrial electricians in a semiconductor manufacturing plant in the 1970s.
You really should get an electrical permit and have the work inspected by local officials to protect yourself anytime you do this kind of work if you are not absolutely dead-certain you know what you are doing. If you don't, get someone who does to help you. Do-it-yourself books might be useful, but they're no substitute for first-hand, first-rate knowledge and experience, and wiring screw-ups can and have killed lots of people.
I saw a situation years ago of a homemaker who could have been killed. She complained of sparks between washer and dryer. If she had touched them both at the same time, she's have possibly been dead. Some idiot "wired" 240V into the trailer for a dryer and got the wires on the wrong terminals in the receptacle so there was 120 volts AC between the dryer cabinet and the washer.
For more about overload protection for electrical motors as well as grounding and other info, see
http://cnets.net/~eclectic/woodworking/Cyclone/ClarkeMotors.htm
Since you are considering dust collection, invest some time getting educated on dust collection at
http://cnets.net/~eclectic/woodworking/Cyclone/index.cfm
and when you're ready for a really exceptional cyclone dust collection system in kit form so you can save some bucks and get the satisfaction of building it yourself while getting first-class results, check out
http://cnets.net/~eclectic/woodworking/Cyclone/ClarkesKits.cfm
Clarke
Peter De Smidt wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

In the rest of your post you preached about following code, but is this not a code violation, at least in many places? I've heard everywhere that a 240V circuit should go to a single device/plug only...
--
gabriel

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It is certainly common enough to have an oven and a cooktop on the same circuit.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Clarke,
I highly doubt that you will find an electrical inspector willing to pass a residential installation that protects a #10 conductor that is protected by either a 40 or 50 A breaker. Even though the current carrying capacity of a #10 THHN is > 40 A, the NEC limits it to 30A. Can you get away with it? Probably. Will meet code and pass an inspection? I sincerely doubt it.
-- Al Reid
"It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." --- Mark Twain

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Clarke Echols wrote:

on it. That exception is meant to allow motors to start without tripping the breaker.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Yes, 10 ga wire is good for 30A.
Depending on the number of bends in the conduit, it may be a difficult 'pull'.
For a sub-panel, you need 240V "to the panel". So, the 4 wires gives you *one* 240V circuit, which will have 2 hot wires, each connected to one pole of a 'double pole' breaker. This will be a 30A 240V breaker.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Fat chance of pulling 5- #10 wires in a 1/2 inch conduit. Ain'T gonna happen. Besides it is against the electrical code.
On Mon, 26 Jan 2004 09:04:52 -0600, Peter De Smidt

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Site Timeline

Related Threads

    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.