I am building my future wood shop and making preparations for the electrical wiring. Since I will be insulating the shop and hanging drywall all electrical work will need to be completed before the drywall goes up. Therefore I am planning on wiring for tools that I do not have yet own (I need to pay for the building first!). Here is my question: When wiring for 220volt applications (3hp motors etc.) should I use 3 conductor or 2 conductor wire? I was planning on using 10 gauge wire but am not sure if 10/2 or 10/3 wire would be appropriate. I assume 20 or 30 amp breakers would be the ticket. Any advise would be greatly appreciated.
Happy New Year.
enfrim
Replies
Enfrim: #10 wire would be good upto 30 amps, no more. That would cover most stationary power tools in a home shop. If you needed a 20 amp circuit you could always use a 20 amp breaker on the #10 wire, ie: a lower amp breaker on a larger wire not the other way 'round. Better yet in my experienced opinion would be if there is access above the ceiling use conduit (probably ¾") and then you could pull the proper wire even if you had a machine requiring more then 30 amps. 10/2 would be proper having two line conductors and a ground, either two hots and a ground or a hot and a neutral with ground. 10/3 is more expensive and would not help in most cases. Also if there is only one receptacle on a circuit it must match the breaker and the nameplate on a machine is incorporated in the electric code meaning if it specifies a circuit size it must be followed. Be safe, good luck.
Duke, retired electrician
The Bill of Rights
December 15 1791
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Hey Duke, On my own house I was working on my cable line. (adding a line to a kitchen TV. When I pulled apart the barrel connection outside the house I seemed to get a little shock on the load side, Now the load side feeds a 3-way splitter. Why was I getting a little voltage leak coming back. could it be there maybe a splitter somewhere else in the house that is poorly grounded.
What the heck!!!! Thanx Duke
Could be something coming back out of the cable box? Or some induction from the cable laying next to a power line. Induction is a very important safety issue as fatal voltages can be induced on isolated, ungrounded lines. I don't know much about cable TV stuff. DukeKenneth Duke Masters
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Duke, No cable boxes? (tv's cable ready) Also last night, I touch one of my handles in the shower.and I can feel a very little curant.(this is bad). Can it be @ the panel. and would the local electric power company come out? trying to avoid the cost of bringing someone in. It has to be a bad ground somewhere. could the grounding rod in the ground be bad or done incorrectly? need help
Thanx, Lou in NJ
Lou: Your idea about a bad ground rod or the grounding conductor might be correct. You might have a serious problem there, don't let it go too long before calling for professional help. Look at the clamp on the ground rod if it looks loose shut your main first then clean and tighten it. It could also be in your meter/main or panel where the grounds and ground rod conductor are bonded to the panel, might be loose or corroded. Your local utility might come out to check it. If you do it your self be very careful as disconnecting the ground wires for maintenance is potentially dangerous especially in light of what you are experiencing. DukeKenneth Duke Masters
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A current through the plumbing can be caused by a burned out heating element in an electric hot water heater, I've had the experience in my own home.
A ground will provide a safe path for a current leak to be safely discharged. If you have a bad ground connection the current will find a different and possibly unpleasant path to ground, like through you.
Whether or not you have a good ground, it would also seem that you also have a current leakage and, bad ground or not, you also need to track that down because a leakage is dangerous all by itself and you can't depend on the ground alone.
John W.
Agree 100%. Also, when I did my 220 work the inspector noticed that my three pipe systems (hot water, cold water, and gas) were not interconnected and grounded. That would help in this case... but you definitely want to find out what's causing that voltage!My goal is for my work to outlast me. Expect my joinery to get simpler as time goes by.
John/Lou: Another good place to look, which I forgot, as John suggested is the bonding between hot/cold water and gas piping. If the voltage is an induced one the current will be miniscule and good grounding will take care of it. DukeKenneth Duke Masters
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dont know if i want to ground to a gas pipe
Tommy: Bonding is connecting all metal items that may possibly be energized, no matter how unlikely it is for that to occur. This minimizes any stray voltage and assists in tripping overcurrent devices. Lets say you have a gas wall heater with a fan; something goes wrong with the wireing and the hot wire is touching the metal frame of the heater. If the gas pipe is not bonded to ground the entire gas pieing system and any metal objects connected to it will be at or near line voltage resulting in a hazard to anyone touching a gas drier, stove etc. If the pieing is bonded the breaker or fuse will interrupt the circuit and let you know something is wrong somewhere. That is the reason for bonding. DukeKenneth Duke Masters
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LEAA Life Member
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In general, it's best to ground (earth) through a cold water pipe. One of the problems that can arise when tying things together is the tendency to set up ground loops. If there are multiple routes to ground, then any stray emf can set up noise that can affect radio/tv reception, wireless phones, etc. By grounding to a single point this is avoided... but there is another more important reason to avoid ground loops. By using a single common ground, there is one path to earth for any shorted potential, this reduces the risk of injury. Using your example, if the fan of the gas heater is grounded properly through the cold water pipe to earth, any stray voltage will have a single, direct path to discharge. If the gas pipe is not tied in, the preferential path to ground will be through the cold water pipe, and someone touching a gas pipe will not be at risk, as the will not form a ground path.Glaucon
If you don't think too good, then don't think too much...
Grounding solely to the cold water pipe used to be best practice, but it no longer meets code in the current NEC and, therefore, where I live. The rationale, as I understand it, is that the supply pipe always used to be metal. Nowadays, maintenance and new work often replaces that excellent conductor with nonconductive PVC. This can leave you with an ungrounded system, not good. And while you may be determined to keep metal pipes in the ground, are you sure the previous owner did... or that the next will?
When I put in my 220v circuits a few months ago, I was required to add a pair of grounding rods; this new ground was required to be connected (bonded, I guess) to all three pipe systems.
Maybe it's different when it's not a residential install, or in different communities. I don't know anything about grounding loops. What I'm quite confident in saying is that if you can't satisfy yourself 100% you've got it figured right, paying an electrician or city inspector to check your work can leave you feeling you've adequately protected your family. :)My goal is for my work to outlast me. Expect my joinery to get simpler as time goes by.
John/ Glaucon: Grounding solely to a gas pipe or water pipe has not been code for quite some time but bonding has been required since ? I've been retired from electric work for 5½ years and in that time gas piping, in the street and the feed to the house, has gone to plastic, water piping has been going plastic for a long time both inside and out. Many existing homes and areas still have metal pipe in the ground and in the walls. Bonding is very important to safety anywhere metal piping systems are used. Ground loops may be annoying but do not affect safety. Ground rods have been a code requirement for as long as I've been an electrician and probably much longer. Maybe one of our Knotheads knows the history of ground rods and bonding in the NEC? I'll send a note to the NPFA and see if I can get the dates these items became code requirements. Duke
Kenneth Duke Masters
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All I can say is that my inspector told me I needed to add two ground rods. He said the installation was legal when the house was built (1967 or so), but using the water supply as the ground was no longer conforming. Maybe this helps frame the dates... or maybe my community was behind the times back then, or maybe my installation was wrong then.
In any case, my sons and I pounded in the ground rods and made the required connections!My goal is for my work to outlast me. Expect my joinery to get simpler as time goes by.
Some years ago, you tried to get all the grounds you could get. I recently rewired my place and they didn't tie into any of my other grounds. Two ground rods were laid horizontally out in the yard and that was it. The electric ran to three buildings of which none were grounded. I think it has a lot to do with there being no current flow in the ground system unless there is a fault at which time a ground fault should trip. Under the old system the neutral and the ground were tied together at each building, and before that they didn't even run a ground with the circuits. With current flowing in the system and since all material, even copper, has a given resistance, it would seem that at any point along the system you would have a different ground voltage potential, and a shock hazard. It doesn't take a whole lot of amperes flowing in ones body to be lethal.
Bonding Question: Here is the reply I got from the NFPA re: when did bonding become a code requirement. I guess well never know. Duke
Mr. Masters,<!----><!----><!---->
<!----> <!---->
The library can trace changes in codes. This service is free for NFPA members (up to an hour’s research), but there is a research charge for non-members. Searches are $100 per hour with a half-hour minimum. <!----><!---->
<!----> <!---->
If you wish to have us do the research, please call the library with your credit card information. You can request a maximum amount you want to spend. If we haven’t found your answer by the time we hit your ceiling, we will call you to talk about next steps. If you know the current article numbers in the NEC that the two are found, the search will take less time.<!----><!---->
<!----> <!---->
Sue<!----><!---->
Morgan Technical Library<!----><!---->
617 984 7445<!----><!---->
From: Kenneth Duke Masters [mailto:[email protected]] Sent: Monday, January 23, 2006 8:44 AMTo: <!----><!---->Dunn, Barbara<!---->Subject: Code history<!----><!---->
<!----> <!---->
Hello: Can you help me with a discussion on my woodworker’s forum regarding the NEC? Specifically when did ground rods become required and when did bonding of metal piping systems get added? If you can not help can you suggest some source for this information? <!----><!---->
Thank you, KDM<!----><!---->
<!----><!---->Kenneth Duke Masters
The Bill of Rights
December 15 1791
NRA Endowment Member
LEAA Life Member
CRPA Member
working for the gas company for 30+years we feared any elec ground to gas service line the reason being that if they have to work on the line which would envolve the cutting of the line there is a source of ignition and thats a no no for a gas worker. so you see my concern
Enfrim, Welcome to knots. I finished my shop about a year ago and had some of the same concerns. Not being an electrician, I studied, took the test with the county, earned the homeowners permit and did the wiring myself. I decided, after much thought, to put the wiring in conduit on the surface, which for me, was the right choice. I realized that no matter what plans I had, there would be a time when something would be moved or added that would require changes in the wiring. Since then, I have added one more 240V outlet and am about to add another. Since I'm not a pro I will refrain from offering advice on wiring.
When you say three conductor or two conductor, I want to be sure you mean that plus the ground. A total of two wires would be dangerous because if there is leakage of current then you are potentially the ground. If you have a separate building, you must have three conductors plus the ground for code and maximum protection. They include two hot wires, a neutral, and the ground (a total of four wires). Just two hot wires and a neutral is sufficient for most equipment applications. Some years ago the code only required three but as we proceed in time we become more safety conscious. The sizing of wire was well explained by a previous poster except I find that putting #10 wire on a receptacle or switch designed for #12 can be a real challenge. I usually don't use #14 but it is sure easy to wrap around those terminals. On short distances, use #12 on twenty amp, #10 on a thirty amp breakers. Don't oversize the breaker on a given wire.
I agree with most responders particularly the retired electrician.One thing to add. Some machines require 220 plus a 110 capacity which requires a neutral wire.I have two machines(a drum sander that has one motor to turn the sanding drums an a second 110 motor that runs the adjustable speed feeder and a shaper that also has a cuicuit for a auto feeder) that require a neutral wire. Bottom line is, install the 10/3 then you have it all covered if you someday acquire a machine like I described above. Good luck.
what kind of drum sander do you have and do you like it
I'd favor 12 g, 2 wire plus ground. IMO, the number of power tools that will need 30 amp is pretty low, particularly at 230V. If you are sheetrocking, and thus burying your access, there is a small argument in favor of 10 g. I would bet, however, that few are ever upgraded- and as was pointed out 10 g is significantly more expensive and more difficult to work with. I would run the dc on a separate line as it is likely to be in use with other tools, but in a one man shop, I would not homerun every tool (I've never managed to run my jointer and TS simultaneously). Not an electrician, just my 2p-Glaucon
If you don't think too good, then don't think too much...
I ran all 10g, homerun for each of 5 30A/220v receptacles. The cost of wire just doesn't compare to the effort of running it (at last that was true three months ago -- I heard wire prices were rising), particularly when you include inspection fees and time, etc.
And who knows when you'll need an upgrade. When I ran the juice in, my TS was the only 220v tool I had, and it required a 30A circuit. I decided to run them all as 30A, then lo and behold the 23A heater I ordered had the same plug as my TS. And the bandsaw I'm trying to acquire needs it as well.
in a one man shop, I would not homerun every tool
Check with your inspector before making this decision. Multiple 220v receptacles on a single circuit won't pass inspection where I live. And passing inspection is worthwhile -- first, they may catch a real mistake and prevent a fire; second, your fire insurance may be null and void if a fire is caused by wiring that's not to code.My goal is for my work to outlast me. Expect my joinery to get simpler as time goes by.
Is that a 5 horse saw?
Mike
Yep, 5hp Unisaw, plate says 21A.My goal is for my work to outlast me. Expect my joinery to get simpler as time goes by.
I don't completely agree:
I ran all 10g, homerun for each of 5 30A/220v receptacles. The cost of wire just doesn't compare to the effort of running it (at last that was true three months ago -- I heard wire prices were rising), particularly when you include inspection fees and time, etc.
And who knows when you'll need an upgrade. When I ran the juice in, my TS was the only 220v tool I had, and it required a 30A circuit. I decided to run them all as 30A, then lo and behold the 23A heater I ordered had the same plug as my TS. And the bandsaw I'm trying to acquire needs it as well.
Well why stop at 30A? Why not 8g or 6? Who knows when you might need a bauxite smelter or a Bridgeport milling machine... Seriously, few woodworking tools will need more than 20A, most use less than 15. A 5 hp, 12" TS uses about 25A- but most 10" TS use less than 20A, an 18" BS ~12A, a 3 hp DC ~18A. And most power tools draw their maximum current at start up, not during steady state. A heater is a not a power tool: if you are going to heat your shop electrically, you'll need to make provisons for it separately, on its own circuit.
in a one man shop, I would not homerun every tool
Check with your inspector before making this decision. Multiple 220v receptacles on a single circuit won't pass inspection where I live. And passing inspection is worthwhile -- first, they may catch a real mistake and prevent a fire; second, your fire insurance may be null and void if a fire is caused by wiring that's not to code.
I can comment about this a bit: in the US, there is an assumption that every appliance on a 220V line will draw heavy current, this is because "light" use electrical devices are wired for 110V. So in the US 220V is often reserved for ranges, AC and clothes dryers. But this is not the case in a woodworking shop, and the notion that every 220V device must be on its own circuit is illogical. In Europe and South America, all the mains are 220V- they don't homerun every light and radio circuit. Your safety argument doesn't pass muster either- if each wire is matched to its appropriate breaker (e.g. 12g to 20A, 10g to 30A), there is no safety issue. If too much current is drawn on a particular circuit, the breaker will trip, not explode into flame. One 24A tool running on a 20A line is just as likely to trip as two 12A tools. In fact, a tool wired for 220V rather than 110V will draw less current- since power consumption is generally fairly flat.
I am not recommending that someone go out and violate the electrical code. The trouble is that electricity scares folks into over-designing. Electricity and wiring are really pretty straight forward- they require logical planning, good technique and care, but not a shotgun approach.Glaucon
If you don't think too good, then don't think too much...
All wiring and outlets being the same (instead of one, oops, two 30A outlets and 25A or less for the others) means I can rearrange my shop without rewiring. In any case, I wasn't saying everyone should do it like I did, just pointing out one convenient solution to the problem of shop wiring.
I don't think I'll need any circuits larger than that, so I didn't consider any gigawatt installations.
The heater is plugged into one of the 220v receptacles, so of course it is on its own circuit.
I'm pretty sure I avoided shotguns. I did a homerun for each receptacle because my inspector required it when he reviewed my plans, not out of irrational fear of them magickal electricles.
My "safety argument" wasn't that homeruns are required, it was that as a woodworker dabbling in electricity, it's possible for me to make a mistake that could have nontrivial consequences. Having my plans and my work checked by the inspector gives me confidence that I've taken proper care, and protected my five children and wife to the best of my ability, while still saving nearly the total price of my Unisaw by doing most of it (adding five 220 and two 110 circuits to the shop, and dumping my unsafe old Zinsco panel) myself. I was advocating getting a permit and inspection, because I felt it was the smart thing to do, though I have no beef with others who choose differently.
If I remember right, you're a doctor who has seen people come in badly mangled through lack of care with machinery. I submit that electricity, like our dangerous machines, demands reasonable care. Ever seen a bad electrical burn? I have, and it's not pretty.My goal is for my work to outlast me. Expect my joinery to get simpler as time goes by.
JD:
No offense intended. You're certainly free to do as you like, and it seems very sensible- and flexible.
I am a little surprised at your horsepower requirements. I learned WWing on a 3 hp Unisaw- and I never remember it bogging down- even on fairly thick maple or ash. My sense is if the TS is properly set up with a good blade- 3 hp seems suffcient. I'm not sure what kind of a BS will draw > 20A... seems like a lot. (At this point I am almost afraid to ask what you drive...)
You're right, I am a physician, but I started out in physics, and built a lot of electronic (and high voltage) equipment as an undergrad, actually started out building tube radios as a kid. I think it is important to respect electricity (and fire, and speed...), but what we understand, we can master.
Just my 2p,Glaucon
If you don't think too good, then don't think too much...
I am a little surprised at your horsepower requirements. I learned WWing on a 3 hp Unisaw- and I never remember it bogging down
Well, the best deal I found on a new 3HP was $1749, and the 5HP was $1799. For $50, I figured the extra power could be a good thing. It was certainly not a requirement in my mind!
At this point I am almost afraid to ask what you drive...
A Plymouth minivan ... I have five kids! :)
I think it is important to respect electricity (and fire, and speed...), but what we understand, we can master.
FWIW I agree 100%. I was just glad to have the inspection, even though I do not think most of the changes the inspector required would actually have caused problems. Still, he pointed out two existing issues (no grounding rods, and the hot water, cold water and gas pipe systems needed to be interconnected) that may eventually forestall problems for me or some future owner. I'm reasonably intelligent, but two weeks studying books and the NEC didn't make me an electrician. :)My goal is for my work to outlast me. Expect my joinery to get simpler as time goes by.
I was in the same situation as you a year ago. I run #10 wire with 20 amp breakers. The reason I run #10 wire was that if I ever updated to a 5 hp motor, all I would have to do is change the breaker to 30 amp and update the plug to 30 amp.
Disclaimer: I am not an electrician.
I just had a 220v 50amp line run to a sub-panel in my basement shop by a licensed electrician. It was surface mounted (for most of the run) inside conduit, mostly out of convenience (my basement is finished, so it was run through part of the garage). The electrician used 10/3 cable run to the sub-panel, then piped to new surface mounted twist-lock outlets with 30amp breakers for the new MM BS and Combination Machine.
Clarification: I assume the cable run to the sub-panel was 10/3. I didn't actually examine it closely. But they also made up some cables for me with male/female plugs to connect the machines, and I know that was 10/3. It appeared to be the same as the line run from the main house panel to the sub panel.
I am not an electrician either but I'm sure that your electrician used at least a 6-3 cable from you main to the 50 amp sub panel. The 10-3 would be the minimum for your dedicated 30 amp outlets. Running 50 amps on a 10-3, in my book, would be somewhat hazardous.
Hello,
In general, is a 30 amp 220 volt circuit with 10 ga wire sufficient for a 5hp table saw? I was advised it is, but there seems to be another opinion that it should be 8ga wire and a larger breaker?
Thanks
Generally you take the max draw (in amps) listed on your motor's plate. My 5 hp Unisaw says 21A. Then you increase that number by a factor (I think it's 25% but I'm not at all sure, this memory is fading!) to account for the increased load at startup. Breaker size should be this adjusted value, or the next higher size, 30A in my case.
You cannot use a circuit rated smaller than the breaker, so for 30A you need 10 wire. Some advocate (and the NEC requires, in some situations) running the next larger conductor (8 in this case). The rationale is that in a future maintenance action, you may replace the current motor with one rated at the same HP but with a higher current draw; the larger conductor means you'll only have to replace the breaker, not the wire.
The final issue is distance. All conductors lose voltage over distance. You don't want your voltage to drop more than 2% for motors (IIRC -- it's in the NEC). If you're running further than say 80', you should check out the chart in the NEC and use a conductor size that will maintain your voltage to spec. Undervolting your motor can reduce motor life.My goal is for my work to outlast me. Expect my joinery to get simpler as time goes by.
John, here's a little correction: a) The ampacity of the cable and protective device is based on the horsepower of the motor and Table 430.148 of the NEC in this case. No provision needs to be made for a motor of higher ampactiy since the NEC has already allowed for this. b) Maximum voltage drop in a branch circuit is 3%, total voltage drop feeder and branch circuit combined is 5%.
Horsepower ratings are grossly exagerated by some marketers. Wouldn't motor amperage be more accurate?
If the motor HP is exaggerated you're certain to be safe using the nameplate HP.
Yes, it should be safe but sometimes unnecessarily so. The case of a 7.5 HP air compressor that delivers as only as much air as what a 3 HP would. The difference might be due somewhat to inefficiency of the compressor but also to exaggerated HP ratings. An unwary person would tend to put a larger breaker and unnecessarily large and expensive cable to power the thing.
Edited 1/15/2006 10:04 pm ET by tinkerer2
Pretty close but I think you are confusing start up current with safety factor. When the motor start up it can take several times it running amperage. That is why we have slo blo fuses or breakers. That wire can take an overload for a moment without damage.
A breaker or fuse, on the other hand, may not blow at exactly the rated amperage. An electrician wired my shop and put a fifteen amp circuit to handle some over eighteen amps. It would blow on occasion. I had to change it to two circuits myself. On other instances it might blow at a lower than rated amperage. Limiting a twenty amp circuit to sixteen amps or a fifteen amp circuit to twelve amps gives you a twenty five percent safety margin
I don't have any machines that require 3 conductor wire (that would mean it needs 240 and 120). Even the 240v drum sanders have 240v. feed motors. I ran 2/12 to all the drops. Most of the outlets are on an individual circuit. My dust collector and radial arm saw are the only ones that have 10 ga. If I ever want to change the voltage to a given drop I only need to change the breaker and outlet.
Mike
I am not an electrician, but have just wired my shop prior to installing drywall.
All the 220 volt machines I've got work off 15 amp breakers, which means that any 2 conductor (plus ground) over a reasonable distance should fit the bill. That includes a Unisaw, 8" Jointer, 15" Planer, Dust collector and, no doubt, just about any woodlathe you can get.
However, I chose to run 12 gage cable to a junction box directly above the outlet, and a 10 gage cable from the junction box to the outlet. I then pigtailed 20 gage wire inside the outlet box to the outlet because the electrical outlet is specified for maximum 12 gage wires.
Why did I do it this way? Well, bigger cables are better cables (carry more current with less voltage drop) but they get very expensive very quickly. I happen to have a roll of 10 gage cable, but not enough to do my whole shop. By using 10 gage in the wall, I am sure I woun't have to thread cable through the wall in the future, even if I end up with a 30 amp tool because I will just have to replace the outlet, and run a 10 gage cable to that specific junction box, which is much easier because junction boxes must be accessible.
I made sure the dust collector was on a separate circuit because it will run at the same time as other tools. I also put the table saw on a different circuit that the other tools because if two people are working in the shop, there is a good chance one will be using the table saw. Of course, if I find I need to run two tools at the same time (i.e. jointer and planer), I can just run another cable as noted above.
Irrespective of the cable you use, the breaker must be selected to match the outlet, and the cable must be the minimum size to supply the current rating for the outlet (taking into account distance). In other words, if you are wiring for a typical 15 amp/220 circuit you must use a 15 amp breaker even if your cable can handle 20 amps. The breaker must also be 'ganged'.
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