How does one ground the towers if they are being set on ledge?
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Grounding
Started by ski89, May 09 2006 01:59 PM
26 replies to this topic
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Posted 10 May 2006 - 05:22 AM
ski89, on May 9 2006, 01:59 PM, said:
How does one ground the towers if they are being set on ledge?
You can drill holes in the ledge, throw your ground rods in with some Bentonite (to increase conductivity), connect your Grounding Electrode Conductor, and cap off the hole with concrete.
Also, if a snowmaking pipe is nearby, you can bond the tower to the pipe. But, be careful, you might pick up some noise from the pipe.
All of our big transformers all over the hill are bonded to our snowmaking pipes. So, bonding to the pipe is not really an option for us.
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Posted 10 May 2006 - 06:06 AM
How does one ground the towers if they are being set on ledge?
Good question - and it raises the broader question of why do we attach a grounding wire to a steel structure that is rooted in the ground? It's the "belt plus suspenders" approach, that's what.
The main purpose of "grounding" anything is to avoid a possible "potential difference" (read "voltage") between an accessible item and human beings that might come in contact with it. If a lift tower were to somehow be totally isolated from the earth, then any stray (fault) voltage or atmospheric charge could raise its potential with respect to other "earthed" items. This in itself is not a problem - because there is no circuit for current to flow through. If however a person (who is "grounded" by virtue of wet boots or holding on to some item that is grounded) touches this charged tower - that person would provide a current path and might well be injured. Even if the shock itself does not cause injury, the surprise of it can cause a fall from the tower.
So we do our best to keep all accessible conductive parts at the same potential - and since "earth" is pretty much unavoidable, we connect them as best we can to that. It is remotely possible that a tower's foundation does not provide a good path to the earth - so to be sure, we run a copper conductor from it to a suitable, dedicated, grounding electrode near its base.
One of the problems with grounding things to the earth is that "earth potential" is not uniform - it differs from one spot to the next. In fact, lacking a conductor that connects the "grounded" structures of the top and bottom terminals of a lift (the messenger usually), there would exist a very considerable voltage difference between them - with an equally considerable current capability. This is why we not only "earth" each individual tower but also connect them to each other via the comm line's steel support cable. At any given time, there is a current flowing in this cable - attempting to equalize all points "ground".
Now for your "ledge tower". It's probably safe to assume that the rock ledge is at least somewhat electrically isolated from any nearby wet earth and that any potential it picks up (like atmospheric charge) must be dissipated via the messenger cable. This works for the guy sitting on the crossarm who grabs either the messenger or the haul rope, but what about the guy standing on the ledge who is starting up the ladder? Will he experience a current flow when he grabs the ladder? Probably not - since the rock is a very poor conductor. A lightning strike to the tower would be a different story. The insanely high voltage and current capability of an atmospheric discharge should not be conducted solely by the messenger. I would advise that you run a rather large copper conductor from the ledge tower to the nearest good grounding point. If there is not one, then a copper conductor should be run from the ledge tower to both the next tower up the line and the next tower down.
Good question - and it raises the broader question of why do we attach a grounding wire to a steel structure that is rooted in the ground? It's the "belt plus suspenders" approach, that's what.
The main purpose of "grounding" anything is to avoid a possible "potential difference" (read "voltage") between an accessible item and human beings that might come in contact with it. If a lift tower were to somehow be totally isolated from the earth, then any stray (fault) voltage or atmospheric charge could raise its potential with respect to other "earthed" items. This in itself is not a problem - because there is no circuit for current to flow through. If however a person (who is "grounded" by virtue of wet boots or holding on to some item that is grounded) touches this charged tower - that person would provide a current path and might well be injured. Even if the shock itself does not cause injury, the surprise of it can cause a fall from the tower.
So we do our best to keep all accessible conductive parts at the same potential - and since "earth" is pretty much unavoidable, we connect them as best we can to that. It is remotely possible that a tower's foundation does not provide a good path to the earth - so to be sure, we run a copper conductor from it to a suitable, dedicated, grounding electrode near its base.
One of the problems with grounding things to the earth is that "earth potential" is not uniform - it differs from one spot to the next. In fact, lacking a conductor that connects the "grounded" structures of the top and bottom terminals of a lift (the messenger usually), there would exist a very considerable voltage difference between them - with an equally considerable current capability. This is why we not only "earth" each individual tower but also connect them to each other via the comm line's steel support cable. At any given time, there is a current flowing in this cable - attempting to equalize all points "ground".
Now for your "ledge tower". It's probably safe to assume that the rock ledge is at least somewhat electrically isolated from any nearby wet earth and that any potential it picks up (like atmospheric charge) must be dissipated via the messenger cable. This works for the guy sitting on the crossarm who grabs either the messenger or the haul rope, but what about the guy standing on the ledge who is starting up the ladder? Will he experience a current flow when he grabs the ladder? Probably not - since the rock is a very poor conductor. A lightning strike to the tower would be a different story. The insanely high voltage and current capability of an atmospheric discharge should not be conducted solely by the messenger. I would advise that you run a rather large copper conductor from the ledge tower to the nearest good grounding point. If there is not one, then a copper conductor should be run from the ledge tower to both the next tower up the line and the next tower down.
This post has been edited by Emax: 10 May 2006 - 06:09 AM
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Posted 10 May 2006 - 07:39 AM
Emax, on May 10 2006, 06:06 AM, said:
How does one ground the towers if they are being set on ledge?
Good question - and it raises the broader question of why do we attach a grounding wire to a steel structure that is rooted in the ground? It's the "belt plus suspenders" approach, that's what.
The main purpose of "grounding" anything is to avoid a possible "potential difference" (read "voltage") between an accessible item and human beings that might come in contact with it. If a lift tower were to somehow be totally isolated from the earth, then any stray (fault) voltage or atmospheric charge could raise its potential with respect to other "earthed" items. This in itself is not a problem - because there is no circuit for current to flow through. If however a person (who is "grounded" by virtue of wet boots or holding on to some item that is grounded) touches this charged tower - that person would provide a current path and might well be injured. Even if the shock itself does not cause injury, the surprise of it can cause a fall from the tower.
So we do our best to keep all accessible conductive parts at the same potential - and since "earth" is pretty much unavoidable, we connect them as best we can to that. It is remotely possible that a tower's foundation does not provide a good path to the earth - so to be sure, we run a copper conductor from it to a suitable, dedicated, grounding electrode near its base.
One of the problems with grounding things to the earth is that "earth potential" is not uniform - it differs from one spot to the next. In fact, lacking a conductor that connects the "grounded" structures of the top and bottom terminals of a lift (the messenger usually), there would exist a very considerable voltage difference between them - with an equally considerable current capability. This is why we not only "earth" each individual tower but also connect them to each other via the comm line's steel support cable. At any given time, there is a current flowing in this cable - attempting to equalize all points "ground".
Now for your "ledge tower". It's probably safe to assume that the rock ledge is at least somewhat electrically isolated from any nearby wet earth and that any potential it picks up (like atmospheric charge) must be dissipated via the messenger cable. This works for the guy sitting on the crossarm who grabs either the messenger or the haul rope, but what about the guy standing on the ledge who is starting up the ladder? Will he experience a current flow when he grabs the ladder? Probably not - since the rock is a very poor conductor. A lightning strike to the tower would be a different story. The insanely high voltage and current capability of an atmospheric discharge should not be conducted solely by the messenger. I would advise that you run a rather large copper conductor from the ledge tower to the nearest good grounding point. If there is not one, then a copper conductor should be run from the ledge tower to both the next tower up the line and the next tower down.
Good question - and it raises the broader question of why do we attach a grounding wire to a steel structure that is rooted in the ground? It's the "belt plus suspenders" approach, that's what.
The main purpose of "grounding" anything is to avoid a possible "potential difference" (read "voltage") between an accessible item and human beings that might come in contact with it. If a lift tower were to somehow be totally isolated from the earth, then any stray (fault) voltage or atmospheric charge could raise its potential with respect to other "earthed" items. This in itself is not a problem - because there is no circuit for current to flow through. If however a person (who is "grounded" by virtue of wet boots or holding on to some item that is grounded) touches this charged tower - that person would provide a current path and might well be injured. Even if the shock itself does not cause injury, the surprise of it can cause a fall from the tower.
So we do our best to keep all accessible conductive parts at the same potential - and since "earth" is pretty much unavoidable, we connect them as best we can to that. It is remotely possible that a tower's foundation does not provide a good path to the earth - so to be sure, we run a copper conductor from it to a suitable, dedicated, grounding electrode near its base.
One of the problems with grounding things to the earth is that "earth potential" is not uniform - it differs from one spot to the next. In fact, lacking a conductor that connects the "grounded" structures of the top and bottom terminals of a lift (the messenger usually), there would exist a very considerable voltage difference between them - with an equally considerable current capability. This is why we not only "earth" each individual tower but also connect them to each other via the comm line's steel support cable. At any given time, there is a current flowing in this cable - attempting to equalize all points "ground".
Now for your "ledge tower". It's probably safe to assume that the rock ledge is at least somewhat electrically isolated from any nearby wet earth and that any potential it picks up (like atmospheric charge) must be dissipated via the messenger cable. This works for the guy sitting on the crossarm who grabs either the messenger or the haul rope, but what about the guy standing on the ledge who is starting up the ladder? Will he experience a current flow when he grabs the ladder? Probably not - since the rock is a very poor conductor. A lightning strike to the tower would be a different story. The insanely high voltage and current capability of an atmospheric discharge should not be conducted solely by the messenger. I would advise that you run a rather large copper conductor from the ledge tower to the nearest good grounding point. If there is not one, then a copper conductor should be run from the ledge tower to both the next tower up the line and the next tower down.
EMAX,
Ever consider teaching an electrical class?
Say. at RMLA, or something like that?
Sign me up if you do.
This post has been edited by okemopoma: 10 May 2006 - 07:42 AM
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Posted 12 May 2006 - 01:53 PM
Thanks E-MAX, your an electrical encyclopedia. About 50% of the towers will be on ledge but most of that stretch has a cross slope issue and I have to bring fill up to correct where it is a surface lift. How much soil is necessary to provide proper grounding? If I end up with 3' of material on the low side is that enough? And while we are on the subject of electrical....I sat down with my electrician the night before last to talk about layout of panels etc and he seems to be a bit lacking in the motor control and distribution department. The first question is: The previous installation had a small disconnect with slow-blow fuses in it and I was wondering if there are slow blow breakers that would serve the same purpose. I'd like to keep things neat and simple. I have spent hours on square d's web site but.... I am not sure what to get or how to connect it. Any help you would be willing to provide would certainly be appreciated.
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Posted 12 May 2006 - 02:51 PM
ski89:
Ground rods are normally eight or ten feet long and are assumed to be in earth that is at least damp at all times. Your backfill situation sounds like dampness will be a crapshoot. In some shallow earth situations, it is possible to drive several ground rods horizontally from the bottom of the deepest pit that can be created. Since you're backfilling, why not just arrange a grid of interconnected rods before you fill? Again, we'll hope that the earth where the rods end up is damp at all times. Is it utterly out of the question to connect all "ledge towers" together with a #2 bare copper conductor? This method would surely provide good grounding and could be run along the ledge at the bases of the towers prior to backfill.
As for the disconnect, which one are we talking about? If it's the one on the ground near the transformer, a fused disconnect is probably best. In the motor room, nearly any properly sized circuit breaker will work fine (breakers will contain both thermal and magnetic trip mechanisms - sensitivity is adjustable). Both of these current limiters are intended mostly as "catastrophe interrupts", i.e. short circuit protection. Your motor control will come with suitable close-tolerance fast-acting fuses installed.
If possible, use the brand of disconnect and/or breaker that is carried by your favorite local supplier. This makes them a lot easier to repair or replace when you're in a hurry (aren't we always?).
Ground rods are normally eight or ten feet long and are assumed to be in earth that is at least damp at all times. Your backfill situation sounds like dampness will be a crapshoot. In some shallow earth situations, it is possible to drive several ground rods horizontally from the bottom of the deepest pit that can be created. Since you're backfilling, why not just arrange a grid of interconnected rods before you fill? Again, we'll hope that the earth where the rods end up is damp at all times. Is it utterly out of the question to connect all "ledge towers" together with a #2 bare copper conductor? This method would surely provide good grounding and could be run along the ledge at the bases of the towers prior to backfill.
As for the disconnect, which one are we talking about? If it's the one on the ground near the transformer, a fused disconnect is probably best. In the motor room, nearly any properly sized circuit breaker will work fine (breakers will contain both thermal and magnetic trip mechanisms - sensitivity is adjustable). Both of these current limiters are intended mostly as "catastrophe interrupts", i.e. short circuit protection. Your motor control will come with suitable close-tolerance fast-acting fuses installed.
If possible, use the brand of disconnect and/or breaker that is carried by your favorite local supplier. This makes them a lot easier to repair or replace when you're in a hurry (aren't we always?).
There are three roads to ruin; women, gambling and technicians. The most pleasant is with women, the quickest is with gambling, but the surest is with technicians. Georges Pompidou
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Posted 12 May 2006 - 05:15 PM
A #2 bare wire does not sound like a big deal. I guess I pictured something bigger. I can certainly connect the steel support cable for the comm in such a way that it will connect the towers as well.
this is what came with the lift. I left the panel with the fuses in it hoping I could provide that protection in a three phase breaker panel. does the westinghouse controller provide protection?
I was hoping to run 100' from the transformers on the pole at the street to the lift station and into a meter socket. Into a 3 phase breaker panel in the building. Then the westinghouse controller, then the fincor.
Make sense?
this is what came with the lift. I left the panel with the fuses in it hoping I could provide that protection in a three phase breaker panel. does the westinghouse controller provide protection?
I was hoping to run 100' from the transformers on the pole at the street to the lift station and into a meter socket. Into a 3 phase breaker panel in the building. Then the westinghouse controller, then the fincor.
Make sense?
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This post has been edited by ski89: 12 May 2006 - 05:17 PM
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Posted 12 May 2006 - 07:07 PM
OK - this appears to be a Fincor soft starter for an AC motor (correct me if I'm wrong).
1. Yes - the fused disconnect can be replaced by an equally rated circuit breaker - maybe two, since the line side seems to be double tapped.
2. The Westinghouse device is is simply a contactor with overload devices on its output side. Yes - it provides appropriate overload protection.
3. surprisingly, I see no fast semiconductor fuses on the input to the soft starter. This is unusual for Fincor, but if they supplied it that way I guess it's Kosher. Looks like this isn't this cowboy's first rodeo.
4. Please feel free to run a grounding conductor larger than #2. Bigger is better in this case - see if you can find a "deal" on some used wire.
1. Yes - the fused disconnect can be replaced by an equally rated circuit breaker - maybe two, since the line side seems to be double tapped.
2. The Westinghouse device is is simply a contactor with overload devices on its output side. Yes - it provides appropriate overload protection.
3. surprisingly, I see no fast semiconductor fuses on the input to the soft starter. This is unusual for Fincor, but if they supplied it that way I guess it's Kosher. Looks like this isn't this cowboy's first rodeo.
4. Please feel free to run a grounding conductor larger than #2. Bigger is better in this case - see if you can find a "deal" on some used wire.
This post has been edited by Emax: 12 May 2006 - 07:11 PM
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Posted 13 May 2006 - 05:45 AM
The other tap on the line side is a silly outlet for a fan gun. Here's a better picture of the soft start. I did not notice how the brake was connected. Are they tapped off the motor?
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Posted 13 May 2006 - 06:25 AM
"I did not notice how the brake was connected. Are they tapped off the motor?"
I have no way of knowing that - but it could be, I guess. Usually there would be a dry contact available on the controller that confirms motor start - better yet, proof of torque. This contact is available for use by the low voltage controls and can be used as part of the brake release logic. You'll have to look at the drawings to see exactly what was done and decide if that's what you want.
I wouldn't be surprised to learn that someone else on this forum has a setup just like this one. If so, they would be a better source of information than I am.
I have no way of knowing that - but it could be, I guess. Usually there would be a dry contact available on the controller that confirms motor start - better yet, proof of torque. This contact is available for use by the low voltage controls and can be used as part of the brake release logic. You'll have to look at the drawings to see exactly what was done and decide if that's what you want.
I wouldn't be surprised to learn that someone else on this forum has a setup just like this one. If so, they would be a better source of information than I am.
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Posted 13 May 2006 - 06:07 PM
Now it is bugging me that I did not notice how it was connected. I can only assume that it is connected into the motor. I read the installation instructions and they indicated the procedure for physical connection and reccommended to connect electrical connections per instructions...but I do not seem to have them. This is the plate for it. Some of the info is unclear.
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Posted 13 May 2006 - 06:28 PM
This may or may not help - but the brake on our Mueller is off the motor (seen in pic, the small teck cable on the right goes off to the brake). However our T-Bar has a separate contactor for it's brake.
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Posted 13 May 2006 - 08:32 PM
"This is the plate for it. This is the plate for it. Some of the info is unclear."
Well, the data plate says it's a 440v unit. That means it could be tapped from two of the three motor legs - however - the plate also says it's a 120 watt winding - that's about 1/4 amp at 440 volts. Imagine a short in this brake winding - the motor breaker (or fuse) would have to trip to clear the fault. That would be a lot of current for the small brake wires to carry. Also, if you connect the brake winding directly to the motor, you'd be connecting it to the output of the soft starter - that's a time-ramped voltage that I'm sure the brake was not designed for.
You would be better off installing a separate 10 amp circuit breaker in your distribution panel and running it through a separate (small) contactor** that has its coil wired parallel to the motor contactor.
**It's possible that your motor contactor has an auxiliary contact that can be used to switch the brake. If so, just route the 10 amp breaker through that to the brake.
Well, the data plate says it's a 440v unit. That means it could be tapped from two of the three motor legs - however - the plate also says it's a 120 watt winding - that's about 1/4 amp at 440 volts. Imagine a short in this brake winding - the motor breaker (or fuse) would have to trip to clear the fault. That would be a lot of current for the small brake wires to carry. Also, if you connect the brake winding directly to the motor, you'd be connecting it to the output of the soft starter - that's a time-ramped voltage that I'm sure the brake was not designed for.
You would be better off installing a separate 10 amp circuit breaker in your distribution panel and running it through a separate (small) contactor** that has its coil wired parallel to the motor contactor.
**It's possible that your motor contactor has an auxiliary contact that can be used to switch the brake. If so, just route the 10 amp breaker through that to the brake.
This post has been edited by Emax: 13 May 2006 - 08:36 PM
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Posted 14 May 2006 - 05:19 PM
there is a separate feed to the brake as shown in the first picture. I am not sure where it goes and there is no other 3 phase protection in the shed other than whatever is in the panel marked heater that is a fan gun connection.
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Posted 14 November 2006 - 04:39 PM
Making some headway but still trying to figure this one out.
Emax you mentioned.
"Well, the data plate says it's a 440v unit. That means it could be tapped from two of the three motor legs"
The motor is also a 440v unit then why would one tap two of the three legs?
While investigating the brake connection issue I found that the contactor has three wires (ground and two hots) that had been cut when the motor and brake were removed, (see previous picture of contactor) thus supporting the two of the three legs point. They match the wires still connected to the brake.
My limited knowledge of wiring tells me that a 220v motor is connected with two 110v legs. Is that not the case with 3 phase? to get 440v one needs 3 146v legs?
Emax you mentioned.
"Well, the data plate says it's a 440v unit. That means it could be tapped from two of the three motor legs"
The motor is also a 440v unit then why would one tap two of the three legs?
While investigating the brake connection issue I found that the contactor has three wires (ground and two hots) that had been cut when the motor and brake were removed, (see previous picture of contactor) thus supporting the two of the three legs point. They match the wires still connected to the brake.
My limited knowledge of wiring tells me that a 220v motor is connected with two 110v legs. Is that not the case with 3 phase? to get 440v one needs 3 146v legs?
This post has been edited by SkiBachelor: 14 November 2006 - 06:01 PM
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Posted 14 November 2006 - 06:53 PM
I could be wrong, but... I believe each leg of your three phase would be 220v. The brake isn't a three phase motor, so doesn't require the third leg. It was all explained to me at some point, but I can't seem to recall it. But I do know when you measure phase to phase, you get the voltage of your service. If you measure phase to ground you get something like half.
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Posted 14 November 2006 - 07:18 PM
Allan, on Nov 14 2006, 06:53 PM, said:
I could be wrong, but... I believe each leg of your three phase would be 220v. The brake isn't a three phase motor, so doesn't require the third leg. It was all explained to me at some point, but I can't seem to recall it. But I do know when you measure phase to phase, you get the voltage of your service. If you measure phase to ground you get something like half.
You'd have 440v phase to phase (A-B, B-C, A-C)
Divide the 440v by 1.732 (square root of 3) for phase to ground voltage
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Posted 14 November 2006 - 08:15 PM
mikest2, on Nov 14 2006, 07:18 PM, said:
You'd have 440v phase to phase (A-B, B-C, A-C)
Divide the 440v by 1.732 (square root of 3) for phase to ground voltage
Divide the 440v by 1.732 (square root of 3) for phase to ground voltage
That makes sense, I seemed to remember it not being an evenly divisable number. Now you know why I stick to the low voltage!!
- Allan
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