Single ground electrode conductor in raceway

[ohmhead]

Question GEC we normally bond the metal raceway at each end with a bonding bushing and attach it to the bonding bushing .


Why do we do this for what reason ?


Next can the grounding electrode conductor effect in any way under any condition the trip time of breaker under a fault condition any type of fault phase to phase or ground to phase or phase to neutral you pick the one ?


What would be the longest GEC allowed ? Meaning length or distance from service would distance effect its intended use ?


Thanks

 

[raider1]

Question GEC we normally bond the metal raceway at each end with a bonding bushing and attach it to the bonding bushing .


Why do we do this for what reason ?

This is done because lightning induced currents flowing down a conductor encased in a ferrous raceway will induce a magnetic field that will act as a choke and restrict the flow of the lightning induced current. I have heard estimates that the choke effect can be up to 90%. Bonding both ends of the raceway to the GEC will make the raceway part of the conductor and eliminate the choke effect.

Next can the grounding electrode conductor effect in any way under any condition the trip time of breaker under a fault condition any type of fault phase to phase or ground to phase or phase to neutral you pick the one ?

The grounding electrode system does nothing to clear fault current, main bonding jumpers and equipment grounding conductors provide the fault current path to actuate an overcurrent device during a ground fault condition.

What would be the longest GEC allowed ? Meaning length or distance from service would distance effect its intended use ?


Thanks

Distance will affect the performance of the GEC but the code does not have a limit to the length of the GEC. You might want to check out the informational note to 250.4(A)(1).

Chris

 

[ohmhead]

Well lets see if i understand bonding both ends this connects the conduit which now becomes part of the circuit voltage wise .

When a lightning strike hits the service GEC the induce magnetic field from it is now transferrd into the conduit .

We now have a conduit with a high magnetic field applied to it voltage has built up on it .


When it dumps or collapses it returns to the GEC discharging into it like a choke coil .



The GEC shorts out the conduit and discharges it .


If so this would this coil choke effect the current or voltage induced surge from the strike yes .


Now would it be better to use a spark gap on one side and not the conduit meaning install a spark gap to one side of that conduit if one uses a metal raceway if so that the voltage is passed not thur the GEC totally but can pass to ground thur the ground rod system or build steel .

To eliminate voltage passing thur other conduits or systems in the grounding of the electrical system .

 

[bphgravity]

Now would it be better to...

No, you are overthinking the matter. In many cases, the GEC is a single conductor between two points. When that conductor is installed in a ferrous metal raceway or enclosure, addtional bonding is necessary as outlned in Section 250.64(E). An exposed GEC, or one enclosed within a non-metal or non-ferrous metal raceway or enclosure needs no further consideration.

 

[ohmhead]

No, you are overthinking the matter. In many cases, the GEC is a single conductor between two points. When that conductor is installed in a ferrous metal raceway or enclosure, addtional bonding is necessary as outlned in Section 250.64(E). An exposed GEC, or one enclosed within a non-metal or non-ferrous metal raceway or enclosure needs no further consideration.

Yes we are over thinking the matter thats why we asked the question.

What we asked was in a metal raceway only not pvc or exposed GEC conductor .

Does the high magnetic field of a strike induce a current and voltage into the metal raceway were not asking about the NEC code per say what were asking is .

What happens during a strike to that conduit if not grounded or why we ground it