| Home |
| Search |
| Today's Posts |
|
|
|
#1
posted to rec.boats
|
|||
|
|||
Flurries
On Thu, 4 Jan 2018 15:23:28 -0500, "Mr. Luddite"
wrote: I definitely agree that not everyone should do this. The best way is to have an automatic transfer box installed to code by a licensed electrician. That said, I've done this several times, including the house we had in Florida after Wilma. I have sufficient knowledge of what I am doing but even so, I stop, check and re-check before firing up the generator and throwing the breaker that it backfeeds through. It's illegal, but safe if you pay attention and know something about house wiring. Here's a little test that I've even tried on licensed electricians to see how knowledgeable they a Your house service is usually 240vac, split phase. Split phase means two "hot" leads, a neutral (used with both hot legs) and a ground (which really is tied to the neutral leg. Across the two "hot" leads you have 240 volts which is used for stoves, large AC units, etc. Between either hot lead and neutral you have 120 volts which is used for your outlets, lighting, refrig and small appliances. Your panel box is supposed to be wired to balance the loads as best as possible. So, here's the question. Let's say: Leg "A" of the 120 volt supply is drawing 40 amps. Leg "B" of the 120 volt supply is drawing 30 amps. How much current is flowing through the common neutral leg that is used for both legs? The answer is 10 amps. Many people assume it is the sum of both current draws or 70 amps in this example and it's amazing how many "electricians" don't know that. They don't realize that the two "hot" legs are 180 degrees out of phase, so the current in the neutral adds algebraically. That's why the neutral feed from the street to your power panel is the same size wire as the two hot leads. It will never carry more than what one hot leg is rated to draw. I can't imagine any real electrician does not know that. In fact with the right engineering, the neutral really only needs to be sized to the maximum unbalanced load. For example You are allowed to use 70% for ranges and dryers in dwelling calcs. OTOH on 3 phase, you may end up actually using a neutral of close to 200% of the ungrounded conductor load because of triplin harmonics. This became an issue with electronic ballasts and switcher power supplies. |
|
#2
posted to rec.boats
|
|||
|
|||
|
Flurries
|
|
#4
posted to rec.boats
|
|||
|
|||
|
Flurries
On 1/4/2018 11:42 PM, wrote:
On Thu, 4 Jan 2018 22:18:24 -0500, "Mr. Luddite" wrote: On 1/4/2018 5:46 PM, wrote: On Thu, 4 Jan 2018 15:23:28 -0500, "Mr. Luddite" wrote: I definitely agree that not everyone should do this. The best way is to have an automatic transfer box installed to code by a licensed electrician. That said, I've done this several times, including the house we had in Florida after Wilma. I have sufficient knowledge of what I am doing but even so, I stop, check and re-check before firing up the generator and throwing the breaker that it backfeeds through. It's illegal, but safe if you pay attention and know something about house wiring. Here's a little test that I've even tried on licensed electricians to see how knowledgeable they a Your house service is usually 240vac, split phase. Split phase means two "hot" leads, a neutral (used with both hot legs) and a ground (which really is tied to the neutral leg. Across the two "hot" leads you have 240 volts which is used for stoves, large AC units, etc. Between either hot lead and neutral you have 120 volts which is used for your outlets, lighting, refrig and small appliances. Your panel box is supposed to be wired to balance the loads as best as possible. So, here's the question. Let's say: Leg "A" of the 120 volt supply is drawing 40 amps. Leg "B" of the 120 volt supply is drawing 30 amps. How much current is flowing through the common neutral leg that is used for both legs? The answer is 10 amps. Many people assume it is the sum of both current draws or 70 amps in this example and it's amazing how many "electricians" don't know that. They don't realize that the two "hot" legs are 180 degrees out of phase, so the current in the neutral adds algebraically. That's why the neutral feed from the street to your power panel is the same size wire as the two hot leads. It will never carry more than what one hot leg is rated to draw. I can't imagine any real electrician does not know that. In fact with the right engineering, the neutral really only needs to be sized to the maximum unbalanced load. For example You are allowed to use 70% for ranges and dryers in dwelling calcs. OTOH on 3 phase, you may end up actually using a neutral of close to 200% of the ungrounded conductor load because of triplin harmonics. This became an issue with electronic ballasts and switcher power supplies. Only on three phase Wye. 3 phase Delta you don't have to worry about the neutral. I've never seen 3 phase service to a residential dwelling. Not saying it doesn't exist, I just have never seen or even heard of it. Both of the facilities I had for my company were 3 phase though, one 208v Wye, the other 480v Delta. I agree the harmonic problem is just on wye but that is the most common configuration, 208 or 480. I think the problem first showed up on 480/277 wye systems where they had a building full of 277v electronic ballasts. Then it started showing up in those 208 systems that were feeding 120v lines in cubicles through the internal wiring with a 5 wire feeder as PCs started replacing terminals with ferro power supplies and space heaters. Delta is always funny stuff, depending on where or even if you land the ground. Corner grounded is probably the easiest to confuse the novice. It will look just like single phase until you get your meter out. (2 pole breakers, white wires etc) Not familiar with that. The majority of the systems we built were designed to run on 480v, 3 phase. All the main breakers, fused disconnects, motor starters, etc. were three pole. Ground was run separately. We used a dedicated control transformer in each power cabinet to generate whatever the low voltage control wiring was ... 120v in the early days but later 24 volt. IIRC, the control transformer on the 120v systems was a 480v/240v step down with a center tap, providing a neutral. |
|
#5
posted to rec.boats
|
|||
|
|||
|
Flurries
On Fri, 5 Jan 2018 05:34:25 -0500, "Mr. Luddite"
wrote: I agree the harmonic problem is just on wye but that is the most common configuration, 208 or 480. I think the problem first showed up on 480/277 wye systems where they had a building full of 277v electronic ballasts. Then it started showing up in those 208 systems that were feeding 120v lines in cubicles through the internal wiring with a 5 wire feeder as PCs started replacing terminals with ferro power supplies and space heaters. Delta is always funny stuff, depending on where or even if you land the ground. Corner grounded is probably the easiest to confuse the novice. It will look just like single phase until you get your meter out. (2 pole breakers, white wires etc) Not familiar with that. The majority of the systems we built were designed to run on 480v, 3 phase. All the main breakers, fused disconnects, motor starters, etc. were three pole. Ground was run separately. We used a dedicated control transformer in each power cabinet to generate whatever the low voltage control wiring was ... 120v in the early days but later 24 volt. IIRC, the control transformer on the 120v systems was a 480v/240v step down with a center tap, providing a neutral. Did you ground your 480 delta at all? If so where did the ground land? I understand your control circuit voltage can be 120 if you want. That is just a class 1 control circuit. Most people are familiar with class 2 but they are both controlled by the same article in the NEC. Class 1 just looks like regular line voltage circuits because it is not voltage or current limited like class 2 and 3. The center tapped 240 delta is commonly called "red leg" or "wild leg"because the corner between the center tapped windings will be 208v to ground. "Red" is a misnomer tho because the NEC requires the wire to be orange. That is very common in places where they want discount 3 phase and have a significant amount of single phase loads like those small industrial bays. The PoCo can do it with 2 transformers, generally the wild leg will be on a much smaller one. One "winding" is actually open. hence another name, "Delta Veep". http://gfretwell.com/electrical/red%...ansformers.jpg 99.99% of the time, if you see 3 transformers on the pole, it will be wye. but I have seen one place in Key West where they had red leg delta with 3 transformers. The only tip off was one was bigger than the other two and it was confirmed by analysing the wiring. http://gfretwell.com/electrical/Tran...%20_breath.jpg Yeah my wife thinks I am crazy too, taking pictures of transformers. |
|
#6
posted to rec.boats
|
|||
|
|||
|
Flurries
On 1/5/2018 11:37 AM, wrote:
On Fri, 5 Jan 2018 05:34:25 -0500, "Mr. Luddite" wrote: I agree the harmonic problem is just on wye but that is the most common configuration, 208 or 480. I think the problem first showed up on 480/277 wye systems where they had a building full of 277v electronic ballasts. Then it started showing up in those 208 systems that were feeding 120v lines in cubicles through the internal wiring with a 5 wire feeder as PCs started replacing terminals with ferro power supplies and space heaters. Delta is always funny stuff, depending on where or even if you land the ground. Corner grounded is probably the easiest to confuse the novice. It will look just like single phase until you get your meter out. (2 pole breakers, white wires etc) Not familiar with that. The majority of the systems we built were designed to run on 480v, 3 phase. All the main breakers, fused disconnects, motor starters, etc. were three pole. Ground was run separately. We used a dedicated control transformer in each power cabinet to generate whatever the low voltage control wiring was ... 120v in the early days but later 24 volt. IIRC, the control transformer on the 120v systems was a 480v/240v step down with a center tap, providing a neutral. Did you ground your 480 delta at all? If so where did the ground land? I understand your control circuit voltage can be 120 if you want. That is just a class 1 control circuit. Most people are familiar with class 2 but they are both controlled by the same article in the NEC. Class 1 just looks like regular line voltage circuits because it is not voltage or current limited like class 2 and 3. The center tapped 240 delta is commonly called "red leg" or "wild leg"because the corner between the center tapped windings will be 208v to ground. "Red" is a misnomer tho because the NEC requires the wire to be orange. That is very common in places where they want discount 3 phase and have a significant amount of single phase loads like those small industrial bays. The PoCo can do it with 2 transformers, generally the wild leg will be on a much smaller one. One "winding" is actually open. hence another name, "Delta Veep". http://gfretwell.com/electrical/red%...ansformers.jpg 99.99% of the time, if you see 3 transformers on the pole, it will be wye. but I have seen one place in Key West where they had red leg delta with 3 transformers. The only tip off was one was bigger than the other two and it was confirmed by analysing the wiring. http://gfretwell.com/electrical/Tran...%20_breath.jpg Yeah my wife thinks I am crazy too, taking pictures of transformers. Ground for the 480 Delta system service was run separately back to the physical (metallic) ground at the panel, usually via a 6 awg wire. Ground was not taken from any of the legs of the 3 phase Delta the way you have described. Many of the systems we built also had a RFI ground consisting of wide, copper flashing to two, 8' copper rods driven through the floor and into the ground. The rods were about 10-15 feet apart and we tried to get close to 1 ohm resistance between them. This often required a copper sulfate solution to be poured into the rod holes. The reason for the exotic grounding had nothing to do with safety. Many of the systems utilized a RF transmitter running at 13 Mhz. The load for the RF transmitter was a plasma (ionized partial pressure gas) generated within the vacuum chamber. We had specially designed "matchboxes" that allowed load impedance matching of the 50 ohm transmitter output to the very low impedance of the plasma. Other systems used an electron beam operating at 10,000 volts. A stream of electrons are emitted from a filament and focused magnetically onto various metals or dielectrics that were vaporized by the beam and deposited on optics in very carefully controlled thicknesses. Anyway, there were often some arcs and sparks within the chamber with either of these deposition methods that would raise hell with some of the very sensitive measurement instruments. The elaborate grounding, using a wide conductor (flashing) is much better at RF and EMI quenching of the arcs. A simple, round ground wire has too much inductive reactance. It's only purpose on these systems was to serve as a safety ground. Sometimes we'd have to chase our tail for a while however because the use of both grounding systems sometimes generated a ground loop which only magnified the RFI problem. |
|
#7
posted to rec.boats
|
|||
|
|||
|
Flurries
On Friday, January 5, 2018 at 12:28:57 PM UTC-5, Mr. Luddite wrote:
On 1/5/2018 11:37 AM, wrote: On Fri, 5 Jan 2018 05:34:25 -0500, "Mr. Luddite" wrote: I agree the harmonic problem is just on wye but that is the most common configuration, 208 or 480. I think the problem first showed up on 480/277 wye systems where they had a building full of 277v electronic ballasts. Then it started showing up in those 208 systems that were feeding 120v lines in cubicles through the internal wiring with a 5 wire feeder as PCs started replacing terminals with ferro power supplies and space heaters. Delta is always funny stuff, depending on where or even if you land the ground. Corner grounded is probably the easiest to confuse the novice. It will look just like single phase until you get your meter out. (2 pole breakers, white wires etc) Not familiar with that. The majority of the systems we built were designed to run on 480v, 3 phase. All the main breakers, fused disconnects, motor starters, etc. were three pole. Ground was run separately. We used a dedicated control transformer in each power cabinet to generate whatever the low voltage control wiring was ... 120v in the early days but later 24 volt. IIRC, the control transformer on the 120v systems was a 480v/240v step down with a center tap, providing a neutral. Did you ground your 480 delta at all? If so where did the ground land? I understand your control circuit voltage can be 120 if you want. That is just a class 1 control circuit. Most people are familiar with class 2 but they are both controlled by the same article in the NEC. Class 1 just looks like regular line voltage circuits because it is not voltage or current limited like class 2 and 3. The center tapped 240 delta is commonly called "red leg" or "wild leg"because the corner between the center tapped windings will be 208v to ground. "Red" is a misnomer tho because the NEC requires the wire to be orange. That is very common in places where they want discount 3 phase and have a significant amount of single phase loads like those small industrial bays. The PoCo can do it with 2 transformers, generally the wild leg will be on a much smaller one. One "winding" is actually open. hence another name, "Delta Veep". http://gfretwell.com/electrical/red%...ansformers.jpg 99.99% of the time, if you see 3 transformers on the pole, it will be wye. but I have seen one place in Key West where they had red leg delta with 3 transformers. The only tip off was one was bigger than the other two and it was confirmed by analysing the wiring. http://gfretwell.com/electrical/Tran...%20_breath.jpg Yeah my wife thinks I am crazy too, taking pictures of transformers. Ground for the 480 Delta system service was run separately back to the physical (metallic) ground at the panel, usually via a 6 awg wire. Ground was not taken from any of the legs of the 3 phase Delta the way you have described. Many of the systems we built also had a RFI ground consisting of wide, copper flashing to two, 8' copper rods driven through the floor and into the ground. The rods were about 10-15 feet apart and we tried to get close to 1 ohm resistance between them. This often required a copper sulfate solution to be poured into the rod holes. The reason for the exotic grounding had nothing to do with safety. Many of the systems utilized a RF transmitter running at 13 Mhz. The load for the RF transmitter was a plasma (ionized partial pressure gas) generated within the vacuum chamber. We had specially designed "matchboxes" that allowed load impedance matching of the 50 ohm transmitter output to the very low impedance of the plasma. Other systems used an electron beam operating at 10,000 volts. A stream of electrons are emitted from a filament and focused magnetically onto various metals or dielectrics that were vaporized by the beam and deposited on optics in very carefully controlled thicknesses.. Anyway, there were often some arcs and sparks within the chamber with either of these deposition methods that would raise hell with some of the very sensitive measurement instruments. The elaborate grounding, using a wide conductor (flashing) is much better at RF and EMI quenching of the arcs. A simple, round ground wire has too much inductive reactance. It's only purpose on these systems was to serve as a safety ground. Sometimes we'd have to chase our tail for a while however because the use of both grounding systems sometimes generated a ground loop which only magnified the RFI problem. I'm familiar with the type of grounding system you're describing. I've working in many equipment rooms over the years with all types of RF and communications equipment, and they almost always have the copper flashing and bars for grounding the equipment. The craziest thing I ever saw was a fire lookout tower on top of an 8k foot mountain in northern CA. It was a 3 story structure with something that looked like a chain-link fence around the roof, with huge cables coming down all four corners, then across the stone mountaintop with rods driven into the stone every so often for maybe 100 feet. This was for lightning protection. It's not the lightning that kills the equipment, it's the difference in potential that kills equipment. So the idea is to get the building, equipment (and ground system) inside the building, and the mountaintop to all rise up to the lightning potential together, then drain back down together. They said it got struck several times every summer with rare losses. Probably pretty exciting for the person inside! It had one other interesting feature... a scuttle hole on the roof with a ladder partially down one side of the building. That was for winter access when they used snow cats to get up there. I was there in the summer.  |
|
#8
posted to rec.boats
|
|||
|
|||
|
Flurries
On Fri, 5 Jan 2018 12:28:51 -0500, "Mr. Luddite"
wrote: On 1/5/2018 11:37 AM, wrote: On Fri, 5 Jan 2018 05:34:25 -0500, "Mr. Luddite" wrote: I agree the harmonic problem is just on wye but that is the most common configuration, 208 or 480. I think the problem first showed up on 480/277 wye systems where they had a building full of 277v electronic ballasts. Then it started showing up in those 208 systems that were feeding 120v lines in cubicles through the internal wiring with a 5 wire feeder as PCs started replacing terminals with ferro power supplies and space heaters. Delta is always funny stuff, depending on where or even if you land the ground. Corner grounded is probably the easiest to confuse the novice. It will look just like single phase until you get your meter out. (2 pole breakers, white wires etc) Not familiar with that. The majority of the systems we built were designed to run on 480v, 3 phase. All the main breakers, fused disconnects, motor starters, etc. were three pole. Ground was run separately. We used a dedicated control transformer in each power cabinet to generate whatever the low voltage control wiring was ... 120v in the early days but later 24 volt. IIRC, the control transformer on the 120v systems was a 480v/240v step down with a center tap, providing a neutral. Did you ground your 480 delta at all? If so where did the ground land? I understand your control circuit voltage can be 120 if you want. That is just a class 1 control circuit. Most people are familiar with class 2 but they are both controlled by the same article in the NEC. Class 1 just looks like regular line voltage circuits because it is not voltage or current limited like class 2 and 3. The center tapped 240 delta is commonly called "red leg" or "wild leg"because the corner between the center tapped windings will be 208v to ground. "Red" is a misnomer tho because the NEC requires the wire to be orange. That is very common in places where they want discount 3 phase and have a significant amount of single phase loads like those small industrial bays. The PoCo can do it with 2 transformers, generally the wild leg will be on a much smaller one. One "winding" is actually open. hence another name, "Delta Veep". http://gfretwell.com/electrical/red%...ansformers.jpg 99.99% of the time, if you see 3 transformers on the pole, it will be wye. but I have seen one place in Key West where they had red leg delta with 3 transformers. The only tip off was one was bigger than the other two and it was confirmed by analysing the wiring. http://gfretwell.com/electrical/Tran...%20_breath.jpg Yeah my wife thinks I am crazy too, taking pictures of transformers. Ground for the 480 Delta system service was run separately back to the physical (metallic) ground at the panel, usually via a 6 awg wire. Ground was not taken from any of the legs of the 3 phase Delta the way you have described. Many of the systems we built also had a RFI ground consisting of wide, copper flashing to two, 8' copper rods driven through the floor and into the ground. The rods were about 10-15 feet apart and we tried to get close to 1 ohm resistance between them. This often required a copper sulfate solution to be poured into the rod holes. The reason for the exotic grounding had nothing to do with safety. Many of the systems utilized a RF transmitter running at 13 Mhz. The load for the RF transmitter was a plasma (ionized partial pressure gas) generated within the vacuum chamber. We had specially designed "matchboxes" that allowed load impedance matching of the 50 ohm transmitter output to the very low impedance of the plasma. Other systems used an electron beam operating at 10,000 volts. A stream of electrons are emitted from a filament and focused magnetically onto various metals or dielectrics that were vaporized by the beam and deposited on optics in very carefully controlled thicknesses. Anyway, there were often some arcs and sparks within the chamber with either of these deposition methods that would raise hell with some of the very sensitive measurement instruments. The elaborate grounding, using a wide conductor (flashing) is much better at RF and EMI quenching of the arcs. A simple, round ground wire has too much inductive reactance. It's only purpose on these systems was to serve as a safety ground. Sometimes we'd have to chase our tail for a while however because the use of both grounding systems sometimes generated a ground loop which only magnified the RFI problem. So you were running ungrounded delta. That is fairly rare and usually only for systems that are very intolerant of faults, like a glass plant where a power failure makes the whole place pretty much trash. I assume you had ground fault indicators since the first ground fault is "free". I have never actually seen ungrounded delta here. The other option is impedance grounding that grounds the system via a resistor, just to stabilize the voltage, not to provide any fault protection. You are right that there is no exception that allows the non current carrying parts of the system to be ungrounded. They are really trying to change that terminology to "bonded" to avoid confusion with the "grounded conductor" that we normally call the neutral and the "grounding electrode" that is your physical connection with earth. Article 250 may be the most misunderstood article in the whole NEC, hence the one I spent the most time studying. They are trying to redefine some of the terms to make it easier to understand because "ground" is such an all encompassing word that it misses the intent about half the time and when you actually start testing, it isn't even the same voltage from one place to another when you actually test with stakes in the dirt. |
|
#9
posted to rec.boats
|
|||
|
|||
|
Flurries
On Fri, 05 Jan 2018 11:37:20 -0500, wrote:
On Fri, 5 Jan 2018 05:34:25 -0500, "Mr. Luddite" wrote: I agree the harmonic problem is just on wye but that is the most common configuration, 208 or 480. I think the problem first showed up on 480/277 wye systems where they had a building full of 277v electronic ballasts. Then it started showing up in those 208 systems that were feeding 120v lines in cubicles through the internal wiring with a 5 wire feeder as PCs started replacing terminals with ferro power supplies and space heaters. Delta is always funny stuff, depending on where or even if you land the ground. Corner grounded is probably the easiest to confuse the novice. It will look just like single phase until you get your meter out. (2 pole breakers, white wires etc) Not familiar with that. The majority of the systems we built were designed to run on 480v, 3 phase. All the main breakers, fused disconnects, motor starters, etc. were three pole. Ground was run separately. We used a dedicated control transformer in each power cabinet to generate whatever the low voltage control wiring was ... 120v in the early days but later 24 volt. IIRC, the control transformer on the 120v systems was a 480v/240v step down with a center tap, providing a neutral. Did you ground your 480 delta at all? If so where did the ground land? I understand your control circuit voltage can be 120 if you want. That is just a class 1 control circuit. Most people are familiar with class 2 but they are both controlled by the same article in the NEC. Class 1 just looks like regular line voltage circuits because it is not voltage or current limited like class 2 and 3. The center tapped 240 delta is commonly called "red leg" or "wild leg"because the corner between the center tapped windings will be 208v to ground. "Red" is a misnomer tho because the NEC requires the wire to be orange. That is very common in places where they want discount 3 phase and have a significant amount of single phase loads like those small industrial bays. The PoCo can do it with 2 transformers, generally the wild leg will be on a much smaller one. One "winding" is actually open. hence another name, "Delta Veep". http://gfretwell.com/electrical/red%...ansformers.jpg 99.99% of the time, if you see 3 transformers on the pole, it will be wye. but I have seen one place in Key West where they had red leg delta with 3 transformers. The only tip off was one was bigger than the other two and it was confirmed by analysing the wiring. http://gfretwell.com/electrical/Tran...%20_breath.jpg Yeah my wife thinks I am crazy too, taking pictures of transformers. === Remind her that it could be worse, like taking pictures of half n'ked babes at the beach. :-) --- This email has been checked for viruses by AVG. http://www.avg.com |
| Reply |
| Thread Tools | Search this Thread |
| Display Modes | |
|
|
Hybrid Mode
