conduit bonding
- Thread starter bwyllie
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russellroberts
Senior Member
- Location
- Georgia
Re: conduit bonding
Dereck, have you thought of teaching/instructor?
You'd make a doggone good one.
Dereck, have you thought of teaching/instructor?
You'd make a doggone good one.
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Re: conduit bonding
Dereck,
Here's another wish for speedy good fortune with your next employment position.
And another question.
Dereck,
Here's another wish for speedy good fortune with your next employment position.
And another question.
I am probably misconstruing your meaning for internal fault, but, it seems to me that structural steel and related conductive members and surfaces can be involved in fault scenarios where the lowest impedance path leads to the GEC before returning to the source. As the fault is on the load side of the service disco, I'd take this as "internal". Ensuring the GEC is not choked keeps the fault circuit impedance lower.
Re: conduit bonding
Al I do not believe the current rise times and supply voltages are high enough on an AC power fault to building steel to be of any concern on a GEC even if choked. Sure enough it would add some impedance, but not enough to prevent a breaker from operating or flashover to nearby grounded objects.
Don't get me wrong, I am not advicating it is OK to choke a GEC. All I am saying is not as serious as we were lead to believe.
The main concern is lightning. Current rise times can exceed 8000 amps in 8 microseconds, and with a high source impedance of lightning is where it can become a problem. The voltage buildup (due to high frequency impedance) at a choke point can be high enough to arc and flashover to other nearby grounded objects.
Al I do not believe the current rise times and supply voltages are high enough on an AC power fault to building steel to be of any concern on a GEC even if choked. Sure enough it would add some impedance, but not enough to prevent a breaker from operating or flashover to nearby grounded objects.
Don't get me wrong, I am not advicating it is OK to choke a GEC. All I am saying is not as serious as we were lead to believe.
The main concern is lightning. Current rise times can exceed 8000 amps in 8 microseconds, and with a high source impedance of lightning is where it can become a problem. The voltage buildup (due to high frequency impedance) at a choke point can be high enough to arc and flashover to other nearby grounded objects.
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Re: conduit bonding
Dereck,
Thanks for sharing the perspective. I take your meaning when comparing the extreme rise times of high speed transients such as lightning, compared to 60 Hz.
Feeling old school,
Al
Dereck,
Thanks for sharing the perspective. I take your meaning when comparing the extreme rise times of high speed transients such as lightning, compared to 60 Hz.
I look forward to the next edition of the Emerald Book.
Feeling old school,
Al
physis
Senior Member
Re: conduit bonding
Hi Bob,
Yeah, Aluminum or plastic should fix that.
Al,
Although amplitude can be increased, passive elements are not generators. And in order to increase amplitude you must have a tuned circuit. Not likely by accident.
As Bennie said. If lightning becomes the issue, none of this matters.
[ May 31, 2003, 03:11 AM: Message edited by: physis ]
Hi Bob,
Yeah, Aluminum or plastic should fix that.
Al,
I'm not trying to challenge you here but I think you're describing an antenna. At 60 cycles the wavelength is 5 million meters. The length of most conduit runs are hardly long enough to reach a harmonic that matters.
Although amplitude can be increased, passive elements are not generators. And in order to increase amplitude you must have a tuned circuit. Not likely by accident.
As Bennie said. If lightning becomes the issue, none of this matters.
[ May 31, 2003, 03:11 AM: Message edited by: physis ]
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: conduit bonding
Beenie
not necessarily the lowest resistance path. Because of the fast rise times with it, the path it might take would be in the window of the resonate frequency of the strike. So this could be the GEC inside of the conduit or something else close by. Remember at high frequency objects not in the window of the resonate frequency will appear to be invisible to the lightning. and it will only strike something it can see.
[ May 31, 2003, 03:27 AM: Message edited by: hurk27 ]
Beenie
Lightning will look for the lowest impedance path.
not necessarily the lowest resistance path. Because of the fast rise times with it, the path it might take would be in the window of the resonate frequency of the strike. So this could be the GEC inside of the conduit or something else close by. Remember at high frequency objects not in the window of the resonate frequency will appear to be invisible to the lightning. and it will only strike something it can see.
[ May 31, 2003, 03:27 AM: Message edited by: hurk27 ]
brian john
Senior Member
- Location
- Leesburg, VA
Re: conduit bonding
Dereck:
One item that has always amazed me in regard to TVSS’s is the requirements set forth by the manufactures on proper installation (which few electricians seem to read from my experience). But when you open the TVSS enclosure one finds loose, (not twisted or bound) factory termination conductors with very sharp bends.
If the TVSS is to perform the job it is designed for, it seems both parties evolved in the manufacture and installation of the product should adhere to the same principles.
The TVSS’s are supposedly designed and built by reputable manufactures, or at least big names in the business. Which does not always make them reputable, AKA Worldcom.
should be ran together in a straight line as possible, nearest the buss as possible, wound in a spiral to closely couple them, and no longer than 12 inches in length.
Dereck:
One item that has always amazed me in regard to TVSS’s is the requirements set forth by the manufactures on proper installation (which few electricians seem to read from my experience). But when you open the TVSS enclosure one finds loose, (not twisted or bound) factory termination conductors with very sharp bends.
If the TVSS is to perform the job it is designed for, it seems both parties evolved in the manufacture and installation of the product should adhere to the same principles.
The TVSS’s are supposedly designed and built by reputable manufactures, or at least big names in the business. Which does not always make them reputable, AKA Worldcom.
should be ran together in a straight line as possible, nearest the buss as possible, wound in a spiral to closely couple them, and no longer than 12 inches in length.
Re: conduit bonding
It is possible for someone to be an engineer with a 'D' average.
It is possible for someone to be a Journeyman and not understand code or theory.
These two factors can combine (and do) to create poor installations (for TVSS's and all other items).
Continually seeking knowledge can significantly reduce the above effects.
My hat is off to those who continually seek knowledge.
Enjoy your day.
It is possible for someone to be an engineer with a 'D' average.
It is possible for someone to be a Journeyman and not understand code or theory.
These two factors can combine (and do) to create poor installations (for TVSS's and all other items).
Continually seeking knowledge can significantly reduce the above effects.
My hat is off to those who continually seek knowledge.
Enjoy your day.
brian john
Senior Member
- Location
- Leesburg, VA
Re: conduit bonding
Scott:
Good point I've always founnd a litle reading goes a long way. The literature that is furnished by the manufacture is a good place to start and the web offers a wealth of information some usable and some BS. Then there is the NEC and........................others
Scott:
Good point I've always founnd a litle reading goes a long way. The literature that is furnished by the manufacture is a good place to start and the web offers a wealth of information some usable and some BS. Then there is the NEC and........................others
Re: conduit bonding
Brian John, the wiring from the circuit breakers to the TVSS unit I am familar with are supplied by the installer, and they go directly to the protector modules. The other wiring inside the units are for indicator lamps, alarms, bells, and whistles. The two best after market manufactures I know of for parallel type TVSS( shunt units) are ACT, and Dihn.
IMHO the best type of TVSS is built into the service switch gear using a "Kelvin" clamp method that uses no leads, rather the modules are bolted onto the bus. Using this method prevents any additional let through associated with lead length.
For any of you who are interested in more info on the subject click on this web site http://www.atis.org/pub/peg/peg2000/reed.pdf It has some good installation info along with some of the math and principles involved.... Dereck
Brian John, the wiring from the circuit breakers to the TVSS unit I am familar with are supplied by the installer, and they go directly to the protector modules. The other wiring inside the units are for indicator lamps, alarms, bells, and whistles. The two best after market manufactures I know of for parallel type TVSS( shunt units) are ACT, and Dihn.
IMHO the best type of TVSS is built into the service switch gear using a "Kelvin" clamp method that uses no leads, rather the modules are bolted onto the bus. Using this method prevents any additional let through associated with lead length.
For any of you who are interested in more info on the subject click on this web site http://www.atis.org/pub/peg/peg2000/reed.pdf It has some good installation info along with some of the math and principles involved.... Dereck
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Re: conduit bonding
Physis,
When a conductor moves through a magnetic field, breaking lines of force, current is created in the conductor.
The motion of field and conductor is relative. If the conductor is stationary, and the field moves, the effect is the same. Current flowing in a conductor creates a circular magnetic field about the conductor. To this magnetic field, the conduit wall will appear as a solid block of metal in between the poles of a magnet, but, because the field is circular, there is no beginning (North) or end (South), only direction. When the current in the conductor increases, the magnetic field density it creates also increases. As the field passing through the conductive conduit metal changes density, eddy currents are generated.
The eddy currents created in the conductive conduit circulate in the conduit, circulate in complete circuits never leaving the conductive conduit.
The faster the rate of change of magnetic field density, the greater the eddy currents.
Dereck is referencing research stating the eddy current induced back EMF in the conductor in the conduit is smaller at 60 HZ fault current rates of change than had been previously understood, at least by me.
Physis,
No, I'm describing basic right-hand rule generator physics (or left-hand, depending on one's definition of what moves as current).
When a conductor moves through a magnetic field, breaking lines of force, current is created in the conductor.
The motion of field and conductor is relative. If the conductor is stationary, and the field moves, the effect is the same. Current flowing in a conductor creates a circular magnetic field about the conductor. To this magnetic field, the conduit wall will appear as a solid block of metal in between the poles of a magnet, but, because the field is circular, there is no beginning (North) or end (South), only direction. When the current in the conductor increases, the magnetic field density it creates also increases. As the field passing through the conductive conduit metal changes density, eddy currents are generated.
The eddy currents created in the conductive conduit circulate in the conduit, circulate in complete circuits never leaving the conductive conduit.
The faster the rate of change of magnetic field density, the greater the eddy currents.
Dereck is referencing research stating the eddy current induced back EMF in the conductor in the conduit is smaller at 60 HZ fault current rates of change than had been previously understood, at least by me.
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Re: conduit bonding
Physis,
Physis,
I'd consider a single lightining stroke to be a collection of many transients. Any one transient in the group can be examined mathematically and represented as a sum of an infinite series of sine waves. (As electricians, we think of each sine wave in the series as harmonics). The shape of the individual lightning transient will result in sine waves of certain frequencies being the largest, and therefore the apparent frequency(ies) of that transient. As the shape of the transient changes, so will the apparent frequency(ies).
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: conduit bonding
Physis
Think of the points on older car ignitions it allows for the transformer (coil) to be able to produce a spark and the fly-wheel effect will produce a full sine wave for one cycle.
Physis
Yes.
Think of the points on older car ignitions it allows for the transformer (coil) to be able to produce a spark and the fly-wheel effect will produce a full sine wave for one cycle.
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