I plan to add two 30-amp circuits to my garage. One will be a 120V circuit and the other a 240V circuit. I purchased 100 ft. of 10/3 gauge wire for the 240V circuit. Can I use that for the 120V circuit too and just tie off one of the hot wires on each end or do I need to purchase additional 10/2 gauge wire for the 120V circuit? Also, my local code requires GFCI protection in garages. Is their such thing as a 30-amp GFCI circuit breaker or GFCI receptacles that will accept 240V plugs?
Thanks,
Lyptus
Replies
Sounds like you should think about a little panel. They are not too expensive. You can put a 30 A 240V GFI breaker in the panel.
First, is this a detached garage? If so you are limited to ONE circuit, which can be a feeder to a sub-panel.
But in any case a sub-panel in a garage where you are install mutliple circuits is always a good idea.
Now exactly what is the 30 amp 120 volt circuit for. That is unusal size and I don't know of any equipment that uses it.
The code only requires GFCI protection 120 receptacles (and there is some exceptions to that). So verify exactly what the city requires.
When you look at the catalogs for the breakers you will find that there are all kinds and size beside what is sold at the home horror stores.
You can check on line with the brand and series that you have to see what GFCI breakers that they have.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Hartmann:Aren't you a little worried about a 100 foot run of 10 awg to feed a 30amp circuit?
"Aren't you a little worried about a 100 foot run of 10 awg to feed a 30amp circuit?"A. He never said that he had a 100 ft run.B. I would like to find out more about what he is doing before making such comments.C. 100 ft is about the limit, but need to pull out the calcualtor to verify it..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Well, right -- but he said he bought 100' of 10-3 for the run. As you well know I am mostly ignorant, with the proverbial "little knowledge" that is a dangerous thing, Bill, but IF he really needs 30 amps of power, wouldn't he likely need #6?
Well to be honest I also though that he had a long run, that is why my question about it being detached. But then I realised that he also wanted to use some of it for the 120 run."Bill, but IF he really needs 30 amps of power, wouldn't he likely need #6?"How do you come to that. #10 is rated for 30 amps (even more if was not Romex).Now voltage drop wise he might have to up the wire size for the 120, if it was a 100 ft. But not the 240 circuit.http://www.csgnetwork.com/voltagedropcalc.html.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I'm not arguing, Bill. You have guided me several times. However, I used Mike Holt's wire size calculator set for a 3% drop for 240 at 100 ft. It called for #8. If the circuit was 120, it called for #6.
So, I figured that if he was really going to have 30amp loads, he'd need at least #8 if he ran a 240 circuit to a subpanel and branched the 120. If he ran a 120 circuit, he'd need the bigger wire.
If I am wrong. I'd appreciate knowing why -- not for argument, but really so I'll know. VD worries me. A bad case of VD can really mess things up.
Edited 1/2/2007 11:01 pm ET by Joe Sullivan
Maybe Lyptus bought 100' of cable because that was the smallest precut length of 10-3 at the place he bought it? If his 240 run is <50', he may want to save some bucks by using the remainder to wire his 120 circuit instead of getting a second mortgage to buy more copper.Like Bill Hartmann says, the OP never said he had a 100' run, only that he bought 100' of 10-3.Bill
Thanks for your replies and sorry for not including more detailed information. The service panel for my house is in my attached garage and it has space for additional breakers. I am planning to add a 50' 240V 30-amp circuit to run my new Rikon 18" bandsaw (220V 12amp). I am also planning to add a 120V 30-amp circuit to accomodate my 15-amp tablesaw and 15-amp dust collector on the same circuit. For the bandsaw, I realize that I only need a 240V 20-amp circuit but I'm increasing the amps to 30 in case I decide to upgrade my dust collector to a 2HP 220V model in which case I can put both the bandsaw and the dust collector on the same circuit. I tried to save money by purchasing 100' of 10/3 wire rathter than 50' of 10/2 and 50' of 10/3. This said, I still need to know whether I can use the 10/3 cable on a 120V circuit and just tie off the extra hot line? Also, the type of receptacle that fits my bandsaw plug only has two live connections and a ground. Where should I connect the extra live wire coming from the 10/3 cable? Is it possible some 220V circuits can be run using 10/2 cable? - Lyptus
You have enough questions that I suggest you sit down with a licensed electrician; it will be well worth the price of the service call. Some 220v appliances do not need a neutral. They only need two 'hots' and a ground. I run a neutral anyway, at least as far as the box on the wall; down the road you may get a different appliance that does need a neutral. Second, it is improper to use a larger breaker for a combination of loads. The bandsaw ought to be protected by a breaker no larger than 20 Amp. For all I know, you have a similar situation with your table saw / dust collector arrangement. Your wanting to allow for future growth is a good plan. A better way is to set up a separate panel to serve your shop, and have a separate circuit for each tool. If you want two things to operate together (such as a saw and a dust collector), the way to do that is with a "contactor" and a "control circuit." Again, a journeyman electrician ought to be able to help you with this.
I am also planning to add a 120V 30-amp circuit to accomodate my 15-amp tablesaw and 15-amp dust collector on the same circuit. For the bandsaw, I realize that I only need a 240V 20-amp circuit but I'm increasing the amps to 30 in case I decide to upgrade my dust collector to a 2HP 220V model in which case I can put both the bandsaw and the dust collector on the same circuit. I tried to save money by purchasing 100' of 10/3 wire rathter than 50' of 10/2 and 50' of 10/3.
This said, I still need to know whether I can use the 10/3 cable on a 120V circuit and just tie off the extra hot line?
Also, the type of receptacle that fits my bandsaw plug only has two live connections and a ground. Where should I connect the extra live wire coming from the 10/3 cable? Is it possible some 220V circuits can be run using 10/2 cable?
Keep in mind also that code specifies that wire size be upgraded one size for a motor load. In addition, wiring to code limits will often give you startup problems on woodworking machinery.
At startup, your tools will draw approximately 3x rated current - but you should be fine with a 30A 120V circuit, as long as you don't start more than one tool at a time. However, I would use at least 8 guage wire - you will get drop in 10 guage for that distance, and it will cause slow startup (and thus motor overheating) on your tools. It will likely shorten the motor life.
Yes, you can just cut back or wirenut off the extra wire.
A 220V circuit requires 3 wires total - 2 hots and a ground. Some appliances, like dryers and ranges, are also 120V devices, so they need a neutral as well. I have never seen a woodworking machine that was not straight 220V, no neutral.
To wire your bandsaw, connect the two black wires to the double pole breaker, and the bare wire to the ground. At the bandsaw end, connect the black wires to the blades of the receptacle and the bare wire to the ground pin.
But you would do well to get some local advice from someone who knows what they are doing. 30A@120V is enough power to really hurt you, start fires, and vaporize wire.
"Keep in mind also that code specifies that wire size be upgraded one size for a motor load."What code is that. It certain is not in the NEC..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
You folks have made me think real hard about this task. I contacted my bandsaw manufacturer (12amp 220V) and they said that a 20amp 220V circuit and 10/2 wire should be sufficient and that a 30amp circuit would be less protective of the bandsaw motor than a 20amp circuit. Based on this discussion, it sounds like it would be better to also install two 20amp 120V circuits (vs. one 30amp 120V circuit) to run simultaneous machines like a dust collector and table saw or dust collector and planer (all 15amp 120V machines). For those circuits, I imagine 12/2 wire should be sufficient if I only run one machine per circuit. It sounds like some of you are arguing for using 10/2 wire for a 50' run supporting a 15amp motor. Isn't that overkill? I don't want to risk damaging my motors but I also would much rather use smaller gauge wire if it really won't make a big difference.I plan to install all wiring through exposed metal conduit. - Lyptus
Take a careful look at the instructions on all your machines. A lot of motors can be wired either for 120 Volts, or for 240 at only half the Amps (Volts times Amps stays the same).
Think about future upgrades to the shop, too. Especially that dust collector -- 15A/120V isn't much of a dust collector.
-- J.S.
Sounds like you are on a better path. The manufacture suggests using a 220v 20amp. line so that is what I would use. 12/2 would be fine for under a 50' line. As noted earlier tape the white neutral black and us this and the original black for the hot lines and the ground for ground (if you use conduit. buy a red and black single line for hots and green for the ground) This could also be #12.
Installing two 20 amp. lines for your other tools is a better/safer idea than your first suggestion.
As far as overkill, the 12 amp. pull on the saw X 1.25 is 15 amps. Using #12 is still overkill. I run a 15 amp table saw on a #12 20 amp line. I have no problems. I have never heard of shorting the tool life when running @ 75% the circuit.
Are you planning on returning the #10 wire? It can still be used for all three applications, but is a pain to work with in the boxes.
"Keep in mind also that code specifies that wire size be upgraded one size for a motor load."
What code is that.
It's the NEC - it's in the footnotes.
Here is a reference:
http://ecmweb.com/mag/electric_guidelines_motor_installations/
NEMA standards and Art. 430 of the NEC provide specific electrical and mechanical installation requirements and recommendations covering motors and motor controls.
- - - - - -
SUGGESTED READING
Standards: NEMA MG2, Safety Standards For Construction and Guide Far Selection, Installation, and Use of Electric Motors and Generators. For ordering information, call 1-202-457-8400.
EC&M books: EC&M's Practical Guide to Motors and Motor Controllers; Understanding NE Code Rules on Motors and Motor Controls (2nd Edition). To order call 1-800-543-7771; or fax 1-800-633-6219.
EC&M articles: "Protecting High-Efficiency Motor Circuits," June 1995; "Effectively Applying Premium-Efficiency Motors," March 1995; "Answering Twenty Key Questions About Premium-Efficiency Motors," October 1994; "How Loads Affect the Efficiency of Motors," August 1994; "What Makes a Motor More Efficient?" May 1994. For copies, call 1-913-967-1801.
Edited 1/4/2007 8:43 am ET by woodturner9
First of all the NEC does not have foot notes except for the tables. But it does have fine print notes.I went through all of the FPN in part 430 and did not see it.And I read all of part 430 section II, which is the part on feeders, and did not see any requirement or suuggestion to upsize by one size.There are a number of specific requirements. But that is not one of them..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
First of all the NEC does not have foot notes except for the tables. But it does have fine print notes.
I went through all of the FPN in part 430 and did not see it.
So you didn't read the footnote that says for a motor installation, use 1.25 times the load current for the motor for the wire size tables?
Do the math - it's one wire size. I can't find the online code at the moment, will have to look up the specific footnote where is states one wire size larger when I get back to the office and have the code book in front of me.
wire is upsized by 125% of FLA ....if a single motor will be running continuously !.
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.Wer ist jetzt der Idiot
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"So you didn't read the footnote that says for a motor installation, use 1.25 times the load current for the motor for the wire size tables?Do the math - it's one wire size. I can't find the online code at the moment, will have to look up the specific footnote where is states one wire size larger when I get back to the office and have the code book in front of me."The 1.25 time is not in a foot note. It is right there in the code.But that is not one wire size. You do the calculation and then that determines the wire size.In his one exampe he had a 12 amp motor (using that as HP is not availble) then a #14 wire can supply 12 amp load.Multiple it by 1.25 and you have 15 amps. Can still be served by a #14 circuit..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
So for my 12amp 220V bandsaw I hear a concensus that running 12/2 wire on the 20amp 220V circuit is perfectly adequate. For my other tools, table saw and dust collector, they're rated at 15amp 120V. Multiplying this amperage by 1.25 yields an 18.75amp pull at start up so it sounds like I'll be o.k. with 12/2 wire on the 120V circuits too. So basically, I just need to buy about 100'+ of 12/2 wire. Did I miss something? Lastly, can I run all three wires through the same metal conduit and just branch the conduit and wires into different receptacle boxes where needed? If so, what size conduit would you recommend for running the three 12/2 wires? One inch diameter? What about using PVC conduit for indoor exposed runs?Thanks again,
Lyptus
So for my 12amp 220V bandsaw I hear a concensus that running 12/2 wire on the 20amp 220V circuit is perfectly adequate. For my other tools, table saw and dust collector, they're rated at 15amp 120V. Multiplying this amperage by 1.25 yields an 18.75amp pull at start up so it sounds like I'll be o.k. with 12/2 wire on the 120V circuits too. So basically, I just need to buy about 100'+ of 12/2 wire.
I personally won't use less than 10 guage in a shop. Not a code requirement, but it limits dimming of the lights and heating of the motors on startup.
I gather you aren't running anything over 1 HP? If any of those motors are over 1 HP, either they are lying about the HP rating or current rating (which is far too common, unfortunately).
Keep in mind that wire LENGTH affects required guage as well. Up to 100 feet or so you are usually OK with the base numbers from the table.
One thing I don't understand. Aside from planning for the future, why install a #10 wire on a 20amp circuit. Won't the breaker shut off before the extra capacity in the wire is utilized. The only reason I can see now for using #10 wire is that I might upgrade the breaker in the future to 30amp and run both my bandsaw and a 2 hp dust collector on the 30amp circuit with #10 wire. However, is this a bad plan. Should I use dedicated 20amp circuits for all 2hp machines or can I put both on a 30amp circuit with a #10 wire?- Lyptus
Aside from planning for the future, why install a #10 wire on a 20amp circuit.
Two primary reasons:
1. The run may be too long for a 12 guage wire, so code requires 10 guage
2. The voltage drop in a 10 guage wire is less than in a 12 guage wire, so that for motors and other large startup loads, the 10 guage wire will maintain closer to full voltage, resulting is less heating of the motor, less dimming of lights, etc.
Thank you for your reply. I will be running 12 - 15 amp motors on the 20amp circuits and my longest run is 40-feet. Given this, isn't 12-gauge sufficient or would you still recommend 10-gauge wire.- Lyptus
It would depend on the price of wire and my bank balance. I'd be a little inclined to tip towards #10 for the future.
-- J.S.
For that load and distance #12 is fine.http://www.csgnetwork.com/voltagedropcalc.htmlEven at a full 20 amps at 120 you only have a 2.6% drop.There is nothing in the code that sepecifies the maximum distnace or voltage drop. But there is a FPN that suggest 3% max drop.At 15 amps it is only a 1.9 percent drop.Also note that the desgin standard for motors is not 120 (240), but rather 115 (230)..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I will be running 12 - 15 amp motors on the 20amp circuits and my longest run is 40-feet. Given this, isn't 12-gauge sufficient or would you still recommend 10-gauge wire.
I would still go with 10 guage, based on my engineering experience and woodworking experience. In part, though, it depends on what you are running. For example, a tablesaw starts with a lighter load than a planer, etc.
The problem is that at startup, the draw is approximately 3 times the nameplate rating. Your 15 amp motor will draw something like 45A at startup, briefly. This will cause a voltage drop in the wire, and if the voltage drops enough, the motor startup will be delayed, causing more heating and shortened motor life. 10 guage wire minimizes the drop, relative to 12 guage.
For your 15A motor, code says that the circuit rating needs to be 18.75A, so 12 guage wire and a 20A breaker meet code. For little or no real cost difference, though, I would use 10 guage wire.
Rec.ww published a motor FAQ a few years back that you can probably find on the web and may be of some help as well.
Doesn't the 20% over-current rule only apply if there are more than 1 outlet on the circuit in question?
Doesn't the 20% over-current rule only apply if there are more than 1 outlet on the circuit in question?
There is a 1.25 scaling factor for motor circuits. Whether it is REQUIRED by NEC in this case is open to interpretation, but in my opinion it's a good practice.
It's certainly cheaper than getting a motor repaired, the R/I Unisaw motor I had fixed lately cost me $200. That'll pay for a spool of wire or two.
Bill, I believe he's talking about article 430.22.
430.22 says "for a circuit supplying a single motor used in a continuous duty application" so I'm not sure that applies in this case.Steve.
I went through all of the FPN in part 430 and did not see it.
I'd SWEAR it siad (or used to say) explicity one wire size larger, but I sure can't find it - maybe it was dropped in more recent versions of the code.
In any event, motor conductor sizing is governed by 430.22(A):
"shall have an ampacity of not less than 125 percent of the motor's full-load current rating as determined by 430.6(A)(1).
Guess my memory is not what it used to be :-(
> Yes, you can just cut back or wirenut off the extra wire.
Please wire nut it and coil it neatly in the back of the box. If you cut it short, you might be SOL on putting it to good use in the future.
-- J.S.
Please wire nut it and coil it neatly in the back of the box. If you cut it short, you might be SOL on putting it to good use in the future.
Yes, that is good advice.
"I am also planning to add a 120V 30-amp circuit to accomodate my 15-amp tablesaw and 15-amp dust collector on the same circuit."That is why I asked. I was afraid that you where going try something like that.If you run a 30 amp circuit them you need to install 30 receptacles and change out the plugs on the equpment to 30 amp plugs.NEMA 5-30 for the 120 and 6-30 for the 240.Note, they are not downward compatabile like the using 15 amp plugs in 20 receptacles.In would run two separate 20 amp circuits..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
"Now exactly what is the 30 amp 120 volt circuit for. That is unusal size and I don't know of any equipment that uses it."
One possibility that comes to mind for a 30 amp 120 volt circuit is a travel trailer or RV outlet.
What is the 120v 30 A circuit for?
It could be helpful to you to install a subpanel in you shop area. supply it with a 50amp breaker and feed it with some #6 cables in a conduit. Also see if you ts motor can be rewired for 220.