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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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Two electrical questions, please
Getting things arranged in my new (new for me) shop. It has 3 phase power,
therefore the questions. 1) Do I simply run 3 wires to the machines (lathe, mill, grinder & surface grinder) and let the conduit be the ground, or do I need a seperate ground wire. The existing building has a few 3ph outlets (in conduit), but no ground wires. 2) My machines will be out in the middle of the floor. Do I simply dangle a conduit from the roof framing (15 ft. above), or, do I install a post upon which the conduit will come down? Do I do this once for each machine? Somebody must have a clever solution to this situation. I don't want to cut up my slab and install wires below. Thanks for any and all answers. Ivan, amateur relocated to Oregon. |
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Two electrical questions, please
"Ivan Vegvary" wrote in message
news Getting things arranged in my new (new for me) shop. It has 3 phase power, therefore the questions. 1) Do I simply run 3 wires to the machines (lathe, mill, grinder & surface grinder) and let the conduit be the ground, or do I need a seperate ground wire. The existing building has a few 3ph outlets (in conduit), but no ground wires. Using the rigid conduit (either EMT or the threaded style) as ground does meets code. Code says this is discretionary - run a separate ground wire inside the conduit if the location puts the conduit at risk from corrosion or mechanical damage, or if you feel like it. If part of the conduit is "flex" there are restrictions on the length and the current rating for its use as the grounding conductor. The flex connectors aren't as secure as EMT so it's a good idea to either not use them at all or to run the separate ground wire. 2) My machines will be out in the middle of the floor. Do I simply dangle a conduit from the roof framing (15 ft. above), or, do I install a post upon which the conduit will come down? Do I do this once for each machine? Somebody must have a clever solution to this situation. I don't want to cut up my slab and install wires below. The conduit needs to be fully supported. You'd need a post to drop it all the way down from 15'. The more common thing is to install cord drops. Install a box at the ceiling with a 4 conductor SO cord attached at the top via a cord strain relief, with a L15 twistlock female cord connector at the loose end. If you make the cords long, they can run horizontal some and then drop down wherever. Using the plug and receptacle means you don't need a separate disconnect switch. Bob |
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Two electrical questions, please
Ivan
Two electrical questions, please 1) Run a ground wire at least equal to the phase wires. But at least #6 Bare copper. Conduit does not cut it for ground unless you have some electrical specifications for the conduit and the connectors. Which I have never seen or heard of. A plus for this will be a ground rod at the machine location drivern through a hole drilled in the floor. 2) Run it all in conduit if possible or the code requires it. I don't think the code allows for a 15 foot cord hanging down. Also a conduit has to be supported evry so often. Not sure of the code for this. And above some HP rating a safety switch is required for each machine. A 3 pole safety switch. Securely mounted somewhere within sight of the machine when it is turned off for whatever. Also if there is any use of 110 volts at the machine you will need a neutral wire. And a plus for this would be to simply run the neutral to each machine and provide for an outlef for lighting etc. Additionally. If the machines are in a cluster it is possible to make just one conduit run to the cluster. If you do run conduit make it a size or two bigger to allow for growth or change. Hope this helps Bob AZ |
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Two electrical questions, please
Ivan Vegvary wrote:
2) My machines will be out in the middle of the floor. Do I simply dangle a conduit from the roof framing (15 ft. above), or, do I install a post upon which the conduit will come down? Do I do this once for each machine? Somebody must have a clever solution to this situation. I don't want to cut up my slab and install wires below. I have seen shops which run power to machines right across the floor, and they use sheet metal double-sided "ramps" over the conduit so no one trips. Personally, I'd just run boxes on the walls and run SO cable across the floor in nice neat straight runs. If you have to run machinery over the cabling then place a long 2x4 next to the cable. Grant |
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Two electrical questions, please
On Sun, 28 Dec 2003 04:31:31 GMT, "Ivan Vegvary" wrote:
Getting things arranged in my new (new for me) shop. It has 3 phase power, therefore the questions. 1) Do I simply run 3 wires to the machines (lathe, mill, grinder & surface grinder) and let the conduit be the ground, or do I need a seperate ground wire. The existing building has a few 3ph outlets (in conduit), but no ground wires. That's permissible, but I always like to run a separate grounding wire. That's insurance in case something happens to the conduit, ie a joint comes undone or becomes high resistance, so that it is no longer a good continuous metallic circuit. 2) My machines will be out in the middle of the floor. Do I simply dangle a conduit from the roof framing (15 ft. above), or, do I install a post upon which the conduit will come down? Do I do this once for each machine? Somebody must have a clever solution to this situation. I don't want to cut up my slab and install wires below. You want to support and protect the conduit, so a post would be best. But you can use heavy wall rigid conduit. In effect that *becomes* the post. Gary |
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Two electrical questions, please
"Ivan Vegvary" wrote in message news Getting things arranged in my new (new for me) shop. It has 3 phase power, therefore the questions. 1) Do I simply run 3 wires to the machines (lathe, mill, grinder & surface grinder) and let the conduit be the ground, or do I need a seperate ground wire. The existing building has a few 3ph outlets (in conduit), but no ground wires. 2) My machines will be out in the middle of the floor. Do I simply dangle a conduit from the roof framing (15 ft. above), or, do I install a post upon which the conduit will come down? Do I do this once for each machine? Somebody must have a clever solution to this situation. I don't want to cut up my slab and install wires below. Thanks for any and all answers. Ivan, amateur relocated to Oregon. Ivan, If you like you could run a dedicated ground conductor alongside or inside the existing conduit--bare or insulated copper should be fine..........It then becomes your ground path--at this juncture, the conduit is simply grounded, where this is a requirement in the case of metallic conduit anyways. As to the fifteen foot ceiling drop, not sure it would be to code, but if a plug were installed in the ceiling it would technically be a disconnect at that point. This places the machinery into the "portable " classification........ Personally, I would avoid running power cables across the shop floor. The current trend is to avoid multiple ground paths.......a "star" grounding system is preferred, whereas all grounds lead to a central point--that being the service entrance grounding stake, via the entrance panel grounding bussbar. As such, I would recommend against pounding additional ground stakes in the system other than perhaps those that will be connected only to the service panel ground buss, and only in the event the existing stake is found to be insuffecient. I have taken the liberty of crossposting this thread to the alt.machines.cnc newsgroup, as we have others there, including a resident electricial contractor there who might well be able to answer any further questions you might have. ( Pinging Grampaw Lucas...........) Cheers, -- SVL |
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Two electrical questions, please
On Sun, 28 Dec 2003 01:01:56 -0800, "\"PrecisionMachinisT\"" wrote:
If you like you could run a dedicated ground conductor alongside or inside the existing conduit--bare or insulated copper should be fine..........It then becomes your ground path--at this juncture, the conduit is simply grounded, where this is a requirement in the case of metallic conduit anyways. Always a good plan. As to the fifteen foot ceiling drop, not sure it would be to code, but if a plug were installed in the ceiling it would technically be a disconnect at that point. This places the machinery into the "portable " classification........ Wouldn't be Code. The disconnect has to be in sight and *in reach* of the operator. Unless you're very tall, or have extremely long arms, mounting the disconnect 15 feet in the air wouldn't comply with the requirements. The current trend is to avoid multiple ground paths.......a "star" grounding system is preferred, whereas all grounds lead to a central point--that being the service entrance grounding stake, via the entrance panel grounding bussbar. Yes. Star connection avoids ground loop problems, which can generate EMI problems. Gary |
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Two electrical questions, please
"Gary Coffman" wrote in message ... As to the fifteen foot ceiling drop, not sure it would be to code, but if a plug were installed in the ceiling it would technically be a disconnect at that point. This places the machinery into the "portable " classification........ Wouldn't be Code. The disconnect has to be in sight and *in reach* of the operator. Unless you're very tall, or have extremely long arms, mounting the disconnect 15 feet in the air wouldn't comply with the requirements. Perhaps a drop at ~ seven feet would do the trick then................ -- SVL |
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Two electrical questions, please
From the ceiling come down to the machine with a piece of 4 conductor cable
sized for the machine (10 gauge for 30 amp, 8 for 60 amp) put a recpticale on the end and come out of the machine with a 2 or 3 foot cable with a plug. You didn't say what size machines they where (Power wise not physical size) ""PrecisionMachinisT"" wrote in message ... "Ivan Vegvary" wrote in message news Getting things arranged in my new (new for me) shop. It has 3 phase power, therefore the questions. 1) Do I simply run 3 wires to the machines (lathe, mill, grinder & surface grinder) and let the conduit be the ground, or do I need a seperate ground wire. The existing building has a few 3ph outlets (in conduit), but no ground wires. 2) My machines will be out in the middle of the floor. Do I simply dangle a conduit from the roof framing (15 ft. above), or, do I install a post upon which the conduit will come down? Do I do this once for each machine? Somebody must have a clever solution to this situation. I don't want to cut up my slab and install wires below. Thanks for any and all answers. Ivan, amateur relocated to Oregon. Ivan, If you like you could run a dedicated ground conductor alongside or inside the existing conduit--bare or insulated copper should be fine..........It then becomes your ground path--at this juncture, the conduit is simply grounded, where this is a requirement in the case of metallic conduit anyways. As to the fifteen foot ceiling drop, not sure it would be to code, but if a plug were installed in the ceiling it would technically be a disconnect at that point. This places the machinery into the "portable " classification........ Personally, I would avoid running power cables across the shop floor. The current trend is to avoid multiple ground paths.......a "star" grounding system is preferred, whereas all grounds lead to a central point--that being the service entrance grounding stake, via the entrance panel grounding bussbar. As such, I would recommend against pounding additional ground stakes in the system other than perhaps those that will be connected only to the service panel ground buss, and only in the event the existing stake is found to be insuffecient. I have taken the liberty of crossposting this thread to the alt.machines.cnc newsgroup, as we have others there, including a resident electricial contractor there who might well be able to answer any further questions you might have. ( Pinging Grampaw Lucas...........) Cheers, -- SVL |
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Two electrical questions, please
Should have been more clear, the cable coming down from the ceiling is "SO"
type rubber covered cable "MushHead" wrote in message v.net... From the ceiling come down to the machine with a piece of 4 conductor cable sized for the machine (10 gauge for 30 amp, 8 for 60 amp) put a recpticale on the end and come out of the machine with a 2 or 3 foot cable with a plug. You didn't say what size machines they where (Power wise not physical size) ""PrecisionMachinisT"" wrote in message ... "Ivan Vegvary" wrote in message news Getting things arranged in my new (new for me) shop. It has 3 phase power, therefore the questions. 1) Do I simply run 3 wires to the machines (lathe, mill, grinder & surface grinder) and let the conduit be the ground, or do I need a seperate ground wire. The existing building has a few 3ph outlets (in conduit), but no ground wires. 2) My machines will be out in the middle of the floor. Do I simply dangle a conduit from the roof framing (15 ft. above), or, do I install a post upon which the conduit will come down? Do I do this once for each machine? Somebody must have a clever solution to this situation. I don't want to cut up my slab and install wires below. Thanks for any and all answers. Ivan, amateur relocated to Oregon. Ivan, If you like you could run a dedicated ground conductor alongside or inside the existing conduit--bare or insulated copper should be fine..........It then becomes your ground path--at this juncture, the conduit is simply grounded, where this is a requirement in the case of metallic conduit anyways. As to the fifteen foot ceiling drop, not sure it would be to code, but if a plug were installed in the ceiling it would technically be a disconnect at that point. This places the machinery into the "portable " classification........ Personally, I would avoid running power cables across the shop floor. The current trend is to avoid multiple ground paths.......a "star" grounding system is preferred, whereas all grounds lead to a central point--that being the service entrance grounding stake, via the entrance panel grounding bussbar. As such, I would recommend against pounding additional ground stakes in the system other than perhaps those that will be connected only to the service panel ground buss, and only in the event the existing stake is found to be insuffecient. I have taken the liberty of crossposting this thread to the alt.machines.cnc newsgroup, as we have others there, including a resident electricial contractor there who might well be able to answer any further questions you might have. ( Pinging Grampaw Lucas...........) Cheers, -- SVL |
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Two electrical questions, please
Gary Coffman wrote in
: On Sun, 28 Dec 2003 01:01:56 -0800, "\"PrecisionMachinisT\"" wrote: If you like you could run a dedicated ground conductor alongside or inside the existing conduit--bare or insulated copper should be fine..........It then becomes your ground path--at this juncture, the conduit is simply grounded, where this is a requirement in the case of metallic conduit anyways. Always a good plan. As to the fifteen foot ceiling drop, not sure it would be to code, but if a plug were installed in the ceiling it would technically be a disconnect at that point. This places the machinery into the "portable " classification........ Wouldn't be Code. The disconnect has to be in sight and *in reach* of the operator. Unless you're very tall, or have extremely long arms, mounting the disconnect 15 feet in the air wouldn't comply with the requirements. IIRC, I believe the code says the disconnect must be within 6ft of the appliance/equipment and mounted 4 to 6 ft in elevation from the floor. -- Anthony You can't 'idiot proof' anything....every time you try, they just make better idiots. Remove sp to reply via email |
#12
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Two electrical questions, please
"Gary Coffman" wrote in message ... On Sun, 28 Dec 2003 01:01:56 -0800, "\"PrecisionMachinisT\"" wrote: If you like you could run a dedicated ground conductor alongside or inside the existing conduit--bare or insulated copper should be fine..........It then becomes your ground path--at this juncture, the conduit is simply grounded, where this is a requirement in the case of metallic conduit anyways. Always a good plan. As to the fifteen foot ceiling drop, not sure it would be to code, but if a plug were installed in the ceiling it would technically be a disconnect at that point. This places the machinery into the "portable " classification........ Wouldn't be Code. The disconnect has to be in sight and *in reach* of the operator. Unless you're very tall, or have extremely long arms, mounting the disconnect 15 feet in the air wouldn't comply with the requirements. The current trend is to avoid multiple ground paths.......a "star" grounding system is preferred, whereas all grounds lead to a central point--that being the service entrance grounding stake, via the entrance panel grounding bussbar. Yes. Star connection avoids ground loop problems, which can generate EMI problems. Gary Two different issues here. SAFETY grounding (what the NEC code requires) is all about ground loops, lots and lots of ground loops, the more the merrier. For safety purposes you want to make a ground connection every chance you get. So that ground wire in the pipe is going to be connected at both ends and possibly at several different places. The reasons for all these interconnections is simple. When a big motor running on 3 phase 240 0r 480 volt power suddenly shorts to ground some really interesting **** happens. Look at the circuit breaker feeding that motor. Notice it has an Interrupting Current rating of somewhere between 10,000 and 100,000 AMPS! That's the amount of current that can pass through the breaker in short circuit, and the breaker can open it up without being destroyed by the arc. Those big numbers are NOT speculative, they are easily calculated and demonstrated. You don't want to be near the results during a real demonstration! So what happens to all those amps trying to get back to the source of the power? They flow EVERYWHERE in your grounding system. If it was done right and there are no loose connections, high resistance paths etc, then all that happens is that a fuse blows or a breaker trips. Unless of course the electrical engineer that designed your CNC picked up a couple of different grounds inside the machine while looking for the mythical 'clean ground' If you're feeling real lucky maybe you just gouge a part. If it really ain't your day you may lose your CNC in cloud of smoke. Now inside you CNC is a whole different matter. The ground is used as a zero reference for 24 vdc, 12vdc, 5 vdc, 3.3 vdc etc. For current to flow though you need a complete circuit, a circle or loop. No current can flow, at any voltage, without a complete circuit. By connecting every thing in the CNC, including the external safety ground, to just one ground point (it LOOKS like a star radiating outwards) you ensure that no current can flow from the safety ground THROUGH your CNC. What causes all the problems is all the help we get from the various manufacturers of the parts used to build a machine. Some provide 'convenient' ground points on devices, that just happen to connect to various ground wires in cables and on circuit boards, through different paths. If you go connecting all these without actually checking how they are wired you will inadvertently get ground loops. The ground loops allow current to flow from various sources, say from the enormous surge of that motor which shorted to ground, and then bad things happen. Sometimes people drive ground rods in hopes of getting the mythical 'clean ground'. Sometimes it seems to work, because providing a new path changes the current flowing in other paths. Usually though the relief is temporary. Something big shorts to ground elsewhere in the plant and thousands of amps of current go looking for a new path home. That's when your local part changer earns his big bucks. Now if we could just get the damn electronics engineers to understand the above we could stop fighting this bull****. Gary H. Lucas |
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Two electrical questions, please
"MushHead" wrote in message v.net... From the ceiling come down to the machine with a piece of 4 conductor cable sized for the machine (10 gauge for 30 amp, 8 for 60 amp) put a recpticale on the end and come out of the machine with a 2 or 3 foot cable with a plug. You didn't say what size machines they where (Power wise not physical size) ""PrecisionMachinisT"" wrote in message ... SO is rated differently than romex. With 4 current carrying conductors, 10 Ga is good for 20 amps, 8 Ga. is good for 28 amps and 6 ga is good for 36 amps. Table 400.5 Nate --- Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.544 / Virus Database: 338 - Release Date: 11/25/03 |
#14
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Two electrical questions, please
On Sun, 28 Dec 2003 04:31:31 GMT, "Ivan Vegvary"
wrote: Getting things arranged in my new (new for me) shop. It has 3 phase power, therefore the questions. 1) Do I simply run 3 wires to the machines (lathe, mill, grinder & surface grinder) and let the conduit be the ground, or do I need a seperate ground wire. The existing building has a few 3ph outlets (in conduit), but no ground wires. That used to meet the rules, but all new work should have a ground wire run inside with the rest of the conductors, and you should retrofit everything old that you work on as a safety matter. One loose conduit fitting anywhere in the run (and it happens a lot) and all your equipment isn't grounded anymore. On heavier circuits you can use a reduced size ground, like #8 hots with a #10 ground, as long as the ground wire gauge is heavy enough to pop the breaker on a short circuit without damage. If you have 240V 3-phase Open Delta "High Leg" power (two lines are 120V to ground but one line is 208V to ground) make sure to code the High Leg with Orange wire and tapes, and be very careful not to hook it to the control circuits of the equipment. Or to 120V loads, where the "Magic Smoke" will escape from any device plugged in... And if the machine takes 120V from one of those legs to ground for the work lights or control circuits, you need to run a white neutral wire in the conduit, too. It used to be legal to put parasitic loads like that on the safety ground wire, but no more. 2) My machines will be out in the middle of the floor. Do I simply dangle a conduit from the roof framing (15 ft. above), or, do I install a post upon which the conduit will come down? Do I do this once for each machine? Somebody must have a clever solution to this situation. I don't want to cut up my slab and install wires below. You can drop it from the ceiling, but you should have a vertical 2x4 there for support of the conduit - and that will also give you a place to mount the safety switch & receptacle. You always need a way to lock-out a piece of gear while you're working on it, and a fused safety switch mounted within easy reach of the machine operator is the safest way for hard-wired tools. You could use cord drops from the ceiling, but you need to hang them from strain relief cord grips, the wire basket "chinese handcuff" style, or they'll pull out of the fittings from their own weight. If you use a cord cap as the disconnect & lockout device, you'll need to buy or build the little locking metal plug boxes that physically enclose the machine's plug to prevent the cord being plugged in. For the final word on how it needs to be done, call up your local Building Inspection authority (city, county, state depending on where you are) and have a "Hypothetical" discussion with them about how it should be done in their area to satisfy the codes "if you were going to do it." (Wink, nod...) They may let it slide without an inspection (and the necessary plans, permits & fees) but you still want to do the work right. Don't poo-pooh locking stuff out - ALWAYS as a bare minimum at least tag (paper note "Leave Circuit 3 Off! Working on lathe.") and tape the breaker to the OFF position as a clue for the uninitiated. If you have children (or employees), they sell lock adapters for most modern breaker panels that clamp the breaker handle in the OFF position. The first time someone turns the power back on could be deadly - somebody pops another circuit, doesn't call you, and just goes to the main panel and starts cycling all the breakers back on. While you're out in the shop and have your arms inside the machine up to your elbows... Or worse, you forget that you weren't done with the repairs and you turn the breaker back on & blow it up yourself... -- Bruce -- |
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