Brian Dang
Member
- Location
- Burbank, Ca, US
Hi everyone,
I am Brian and a new member today. I was so interested in reading this old closed post "250.64 GEC Raceway":
http://forums.mikeholt.com/showthread.php?t=100105
I don't know the reasons why it was closed, but I feel there are unanswered questions and I hope the group don't mind if I am going to dig it up again in order to learn more about the subject.
My understanding of the NEC code about the GEC protection is that if the GEC required to be protected from being damaged, e.g. lawn mover, the code requires the GEC to be protected by an "armor" which can be RMC, intermediate metal conduit, EMT, and even plastic PVC conduit.
The original questions were:
Question 1: Using 250.64(B), is the flexible metal conduit as an enclosure for the GEC permissible?
Question 2: Does the 90 degree connector require a bonding bushing and bonding jumper to the case?
One member's answer:
"
Originally Posted by crossman
Question 2: Does the 90 degree connector require a bonding bushing and bonding jumper to the case?
Connectors must be bonded on each side to avoid a possible choke action in the event the GEC is used.
"
I believe the notion that if a metal conduit is used it must be bonded on each end is incorrect. Only ferrous metal conduit is required to be bonded to the GEC at its two ends due to the effect of the conduit acting as a choke with high frequency (current waveform) lightning , where as non-ferrous metal conduits (aluminum and copper) are not required to be bonded to the GEC.
Another member's answer:
"
Originally Posted by crossman
On question 1, what would be the theoretical reason for not allowing the GEC to be installed in a 3 foot long piece of FMC?
On question 2, the 90 degree connector is bonded to the enclosure by means of the locknut. The GEC is also bonded to the enclosure, either directly, or through the SBJ. So is the bonding bushing/jumper really needed?
1. Who knows. Could be an oversight. Why isn't FNC allowed?
2. I seem to recall a locknut is not allowed to be used for this purpose.
"
Why a locknut is not allowed for bonding the RMC or EMT to the enclosure? I would think the locknut is not allowed only in the case of a concentric knockout.
And here was another answer:
"
Given that there are limitations placed on flexible metal conduit serving as a type of equipment grounding conductor by 250.118,.. I would not want to use it for the grounding electrode conductor ,..bonded or not.
"
The poster missed the point in this case. The flexible metal conduit in this case was not used for conducting ground fault current; it was used for mechanical damage protection only.
So I think the question about bonding the conduit is easily addressed, but is it wrong to use 3 ft of flexible metal conduit to protect the GEC from mechanical damage?
Brian
I am Brian and a new member today. I was so interested in reading this old closed post "250.64 GEC Raceway":
http://forums.mikeholt.com/showthread.php?t=100105
I don't know the reasons why it was closed, but I feel there are unanswered questions and I hope the group don't mind if I am going to dig it up again in order to learn more about the subject.
My understanding of the NEC code about the GEC protection is that if the GEC required to be protected from being damaged, e.g. lawn mover, the code requires the GEC to be protected by an "armor" which can be RMC, intermediate metal conduit, EMT, and even plastic PVC conduit.
The original questions were:
Question 1: Using 250.64(B), is the flexible metal conduit as an enclosure for the GEC permissible?
Question 2: Does the 90 degree connector require a bonding bushing and bonding jumper to the case?
One member's answer:
"
Question 2: Does the 90 degree connector require a bonding bushing and bonding jumper to the case?
Connectors must be bonded on each side to avoid a possible choke action in the event the GEC is used.
"
I believe the notion that if a metal conduit is used it must be bonded on each end is incorrect. Only ferrous metal conduit is required to be bonded to the GEC at its two ends due to the effect of the conduit acting as a choke with high frequency (current waveform) lightning , where as non-ferrous metal conduits (aluminum and copper) are not required to be bonded to the GEC.
Another member's answer:
"
On question 1, what would be the theoretical reason for not allowing the GEC to be installed in a 3 foot long piece of FMC?
On question 2, the 90 degree connector is bonded to the enclosure by means of the locknut. The GEC is also bonded to the enclosure, either directly, or through the SBJ. So is the bonding bushing/jumper really needed?
1. Who knows. Could be an oversight. Why isn't FNC allowed?
2. I seem to recall a locknut is not allowed to be used for this purpose.
"
Why a locknut is not allowed for bonding the RMC or EMT to the enclosure? I would think the locknut is not allowed only in the case of a concentric knockout.
And here was another answer:
"
Given that there are limitations placed on flexible metal conduit serving as a type of equipment grounding conductor by 250.118,.. I would not want to use it for the grounding electrode conductor ,..bonded or not.
"
The poster missed the point in this case. The flexible metal conduit in this case was not used for conducting ground fault current; it was used for mechanical damage protection only.
So I think the question about bonding the conduit is easily addressed, but is it wrong to use 3 ft of flexible metal conduit to protect the GEC from mechanical damage?
Brian
