So here’s what might be a stupid question…..
I’m running a new circuit in my shop for a 220V tool. It’s pre-wired for 220, and the nameplate on the 2HP motor says 15A @ 235 volts, or 30A @ 115 V.
I know from my experience with wiring 110V circuits that 14ga wire is adequate for 15 amps, 12ga for 20 amps, and 10ga for 30 amps.
Since the tool is wired for 220 volts, it will be drawing 15 amps, right? So is 12ga (or even 14ga) wire sufficient? Does each of the two wires carry half the load, or am I looking at this in the entirely wrong way?
Thanks in advance.
Replies
#12 will be fine. Amperage is amperage as far as the conductors go.
The voltage is not an issue until the voltage starts to get near the capacity of the insulation to keep it isolated. House wiring is rated at 600v.
Thanks.
So now I'm wondering why my electric water heater uses 10 gauge wire. It's on a 30-amp breaker. Is the 10ga overkill?
I'm interested in this answer as well. I want to put in a 220v water heater at some point. On a 30 amp breaker. Sure would be nice to not have to pay extra for 10ga romex. I have plenty of 12ga.Kinda hope this gets answered before I go to town in about 10 hours...
The person you offend today, may have been your best friend tomorrow
12 is for 20a max.
You need at least 10 fo a 30 amp load. (if your water heater was 110v it would need a 60a breaker)
12 ga. is rated for 20 amp. 4LORN1 reccomended 12 for the table saw b/c it will pull close to 15 amp under load. To close to the 15 amp max for 14 ga. wire to be comfortable.
A 220v/30 amp water heater needs 10 ga. Same thing as the table saw. With both elements heating, it will pull over 20 amp, so you need to go to the heavier guage.
EOS
Dave
Thank you Martha and Dave both.I guess I'll have to pop for that coil of orange romex...
The person you offend today, may have been your best friend tomorrow
There use to be a mom and pop hardware store around here, that would sell romex, by the foot. Always saved me $$ when buying the heavier guage wires for small jobs.
How much you need?
I may have < 100' laying around, I could send ya.
Dave
I only need like 40 feet or so. Maybe 50.I like the orange stuff because it has 4 wires. I prefer to run that ground wire as well.
The person you offend today, may have been your best friend tomorrow
I have to go to town today anyway.Let me see if I can get it by the foot first.I'll bet I can.
The person you offend today, may have been your best friend tomorrow
Excuse me for mentioning . . . Them. I will whisper. home depot, by the foot. shhhh!
Thanks, I have never tried to buy the smaller ga. wire by the foot there. I have purchased no. 6 and above by the foot, and just assumed the smaller stuff was prepackaged. I noticed they had 50 and 100' packages, but the cost per foot was much higher than a standard 250' roll.
I buy most of my electrical supplies from a supply house less than a block from my day job. I pay a little more for romex sometimes, but I can call in an order and pick it up within and hour or so. No searching long isles for something they don't have, accepting lesser quality material, or getting the "blank look" when I ask a question. No checkout lines either, and they even load it on my truck for me!
Ahhhh, true customer service!
Dave
FWIW - A water heater only uses one element at a time. It's required to use 10 ga wire and a 30A breaker because it is considered a "continuously loaded" appliance and must have a branch circuit rating of 125% of the marked rating. For a 4500W element at 240V that is 18.75A times 125% equals 23.4A, hence the required 10ga/30A circuit.
>>FWIW - A water heater only uses one element at a time.I have seen elec water heater instructions which give various possible combinations, including simultaneous.I don't know how common "simultaneous" operation is; I don't see enough elec water hetare to draw any conclusions, although in my area I've only run across a couple wired to provide for simultaneous operation.I don't know about yours, but my church isn't a hotel for the holy, it's a hospital for sinners
Sojourners: Christians for Justice and Peace
I may be mistaken but it seems like the ones sold as "rapid recovery" could energize both simultaneously.
The subtle parts of the code mentioned before (like rating water heater supply at 125%) are excellent reasons why some of us non-trained folks should be extremely careful when attempting electrical work.
"I like the orange stuff because it has 4 wires. I prefer to run that ground wire as well."
the color coding just indicates gauge (size/diameter of wires)- in this case 10g- not number of conductors. 10/3 will have a black, red, white and a naked ground wire. 10/2 will have a black & white plus ground, but the sheath will/should be orange on both.
m
Makes sense. I'll take your word for it.The only 10ga that I have seen lately has an orange sheath, and 4 wires. :)
The person you offend today, may have been your best friend tomorrow
I have a piece of a coil of 10/2 wg (orange). Black,white and bare ground is all you need for a water heater. Just tape the ends of the white wire with red or black tape to indicate it is also hot.
Send me an e-mail: [email protected] if you don't have any luck at the big box.
I'll fix you up, USP freight. My holiday treat.
Dave
I still didn't get in there today.I hope to make it tomorrow. I'll let you know.
The person you offend today, may have been your best friend tomorrow
Now you got me courious.
My HWH in the shop is electric, and I have yet to turn it on (real men don't need no stinkin hot water--- course I haven't taken a shower out there yet, either <g>).
I think I'll turn it on tommorrow and use a clamp on amp meter to see if only one or both elements get hot.
I'll report back on Friday.
Dave
So we'll make it MOST electric water heaters use one element at a time. The top runs first, putting hot water in the area where it discharges (hence the "rapid recovery" feature). The lower element runs most of the time heating the cold water where it enters and maintaining the temperature. It is usually this lower element that goes bad first.
Yea, I know. I've replaced a ton of bottom elements in residential, apartments, and some commercial. Just never checked to see which one was hot first, second, or simultaneously.
My shop HWH manual did not give the operation sequence, and durring the install I did not look at the wiring schematic. I'll just put the clamp on meter on it later today.
DW is doing the second grade Christmass party at the grandsons school right now. Unfortunately he is home with the stomach flue today. Poor fellow missed the field trip to see The Polar Express, the class party, and may be under the weather for his BD tomorrow.
Water heater can wait untill she is home to look after him, before I satisfy my curriosity.
Dave
I have seen commercial hater heaters rigged to use more than one element at one time. Up to six elements at 480v.I have never seen one designed for residential use use more than one element at one time. Usually the lower element runs until the temp drops too low then the upper one kicks in while the lower goes off. I always thought it was a strange setup.Why the upper element would be better to run, as opposed to just sticking with the lower one, when the unit is almost out of hot water is beyond me. Both elements are the same wattage. Just one a bit higher up on the unit.The thermostat on these units is like a three-way switch. It can only run one element at a time.
Hot water rises. There's maybe 10 gallons above the top element in a typical tank. When the top element is on, only that ten gallons is heated, so it warms up rapidly. When the bottom element is on it heats all the water in the tank, so it takes a lot longer to get hot.
Check your local codes! No I am not a electricn'
Normal situations.
Gauge Amps
14 15
12 20
10 30
8 40
6 65
Go up a size for more than 100 foot runs and when the cable is in conduit or ganged with other wires where they can't dissipate heat easily.
Just a thought.. I used 6 Guage from main panel to my shop panel. Never regretted it. Little extra cost but that was when copper was cheap! Besides you never know if you will need 'just one more outlet'.
Keep in mind that you are dealing with a motor circuit - different rules apply.
It is my understanding that as a general, but only partially accurate rule of thumb, you can "undefuse" motor circuits 1 "step" because most of the current draw is just for a brief period during startup, so there isn't time for heat to build up.
In all cases, however, go with the equipment ratings and requirements and the code requiremnts in your area.
I don't know about yours, but my church isn't a hotel for the holy, it's a hospital for sinners
Sojourners: Christians for Justice and Peace
That would be true for most standard duty motors, where it just starts and runs. This is a tablesaw, and the loads can very greatly, depending on material, blade selection, and sharpness.
Tools of The Trade had a recent article on tool ratings, i.e., horse power, torque, etc. Most manufacturers list horse power by no load speed, and amp ratings at the motor stall draw. Basically, whatever yields the bigger advertising number. There seems to be no industry standard for any tool ratings, so in that light, I would oversize the wiring.
Dave
"Tools of The Trade had a recent article on tool ratings, i.e., horse power, torque, etc. Most manufacturers list horse power by no load speed, and amp ratings at the motor stall draw. Basically, whatever yields the bigger advertising number. There seems to be no industry standard for any tool ratings, so in that light, I would oversize the wiring."That would be for a portable tool with a universal motor.For those with induction motors they are all (except air compressors) use NEMA ratings.With consumer level air compressors the motors are not marked with the horsepower, but will be marked as "spl" (special). The current rating at NEMA specs is listed.The "so called horspore rating" is stuck on the compressor.
There is large section of the code book that deals with motors. But it also includes things like shunt wound DC motors and adjusts in sizing for hoist duty applications.But for applications of this type basically the wire needs to be sized according to the table in the code book based on hp/voltage/type of motor. Those are about the same as the nameplate ratings on older motors and most import motors. Some motors are higher efficency and use less current, but the wiring is suppose to be sized by the table and not the nameplate.Circuit protection (circuit breaker) is a different story. For motors with overload protection - most 3HP & under motors have built in overload protection and those that done usually have starter with over load protection - the CB is only need used to protect the wiring from faults. And this is a dedicated motor circuit so that you won't have multiple random item pluged in like on a general purpose circuit. Because of that you are allowed to OVERSIZE the CB based on NAMEPLATE current draws. Without looking it up I think that it is 30% and more in some cases.But most home workshop equipment is not hard starting so that is really not needed.However, it might be used for wiring a large air compressor.
Dave/BillThanks for the correction and additional info....I don't know about yours, but my church isn't a hotel for the holy, it's a hospital for sinners
Sojourners: Christians for Justice and Peace
Thanks Bill and 4Lorn,
Based on what you've said here, I'll wire my 220V, 15A device with #12 copper, and put it on a 20A breaker (allowing about 33% "extra" limit for startup, etc.).
Let me know if I've misinterpreted your comments.
Thanks again.
That is perfect.
Getting back to the first post, why is a 2HP motor drawing 15A at 230? That is more in line with a 3HP machine.
That being said, my 15A 3HP cabinet saw does fine on a 30 ft run of 12 ga from the panel to the receptacle, and another 8ft of 15 ga to the machine (as supplied by the manufacturer).
I wonder if the nameplate is indicating the full load amps (FLA) of the motor, or is indicating the size of the branch circuit the motor requires.
At 100% efficiency, you need about 3.1 amps per HP at 240V. 80% efficiency is probably closer to the truth, so make that about 3.9A. However, full-load amps is probably a better way to figure it.You also want low circuit resistance for the start-up surge, which can be several times the full-load current. Depending on whether or not the motor starts under load, the start-up surge may be the bigger issue.
I have never seen a motor, or anything else that I can recall, fail because the supply wire was larger than required. The longer the device is running and drawing current, the higher the wire temperature gets and along with this, the wire's resistance increases. Not a lot at first but in order to do the same work at 220, when the resistance increases, the voltage drops and the current increases. P=IxE Like when a car battery is going dead and the driver is still trying to crank it. You know the cables are going to get hot then.
"I cut this piece four times and it's still too short."
Nick,
The machine (it's a shaper, actually), is identified in the catalogs as 2HP. The nameplate says 15A @ 235 V, but maybe both these ratings are only approximate.
Anyway, I'm glad you posted because I feel more comfortable knowing I'm not venturing off into the land of the unknown. The fact that your 3HP table saw is doing fine on 12ga wire is reassuring.