BlueSky
Member
- Location
- Asheville, NC, USA
It is often stated an Equipment Grounding Conductor (EGC) can be shared
among multiple circuits residing in a conduit or raceway as long as
the EGC is sized to the maximum of all the circuits.
It is also true that over current protection devices depend on low
impedance for proper operation. Low impedance is achieved by
co-locating the conductors (e.g. in the same conduit, raceway, sheath,
etc.).
My question is how does the single EGC allowance in a conduit apply when
portions of the circuits are NOT within the same conduit, sheath,
etc.?
This arises in a fairly common (shop/garage) situation. NM cable runs
to a junction box in the exposed ceiling which drops via EMT conduit
to lower box(es) containing receptacles. The EMT provides physical
protection for the individual THHN conductors running between the upper
and lower box(es).
The single EGC allowance would suggest it's fine to run just one EGC
in the EMT drop. However, because the EMT drop is fed from individual NM
circuits the entire circuit is NOT contained in one conduit, raceway,
sheath, etc.
Does this mean multiple EGC's need to be run through the EMT for each
circuit fed by an individual NM cable instead of just a single EGC connected
to the largest EGC entering the upper box?
P.S.: I do understand the box bonding must be done with the largest
EGC in the conduit).
Pointers the NEC sections would be appreciated (I've read 250.135(b)
but I'm not sure it applies to this situation).
among multiple circuits residing in a conduit or raceway as long as
the EGC is sized to the maximum of all the circuits.
It is also true that over current protection devices depend on low
impedance for proper operation. Low impedance is achieved by
co-locating the conductors (e.g. in the same conduit, raceway, sheath,
etc.).
My question is how does the single EGC allowance in a conduit apply when
portions of the circuits are NOT within the same conduit, sheath,
etc.?
This arises in a fairly common (shop/garage) situation. NM cable runs
to a junction box in the exposed ceiling which drops via EMT conduit
to lower box(es) containing receptacles. The EMT provides physical
protection for the individual THHN conductors running between the upper
and lower box(es).
The single EGC allowance would suggest it's fine to run just one EGC
in the EMT drop. However, because the EMT drop is fed from individual NM
circuits the entire circuit is NOT contained in one conduit, raceway,
sheath, etc.
Does this mean multiple EGC's need to be run through the EMT for each
circuit fed by an individual NM cable instead of just a single EGC connected
to the largest EGC entering the upper box?
P.S.: I do understand the box bonding must be done with the largest
EGC in the conduit).
Pointers the NEC sections would be appreciated (I've read 250.135(b)
but I'm not sure it applies to this situation).