Running equipment grounding conductor outside raceways.

[SuperJohn]

thread238-248237

A previous thread on this subject has been closed, but the question was not answered correctly.

The O.P. had asked if it was ok to run the EGC on the outside of an existing cable, in an existing installation.

The thread ended when someone posted the text of NEC code section 300.3(B), which stated that you can not run an EGC outside of the raceway carrying the circuit conductors.

However, in the O.P.'s case, an EXISTING INSTALLATION, 300.3(B)(2) states "Euipment Grounding conductors shall be permitted to be installed outside a raceway or cable assembly where in accordance with the provisions of 250.130(C) for certain EXISTING INSTALLATIONS".

I believe the wording includes "CERTAIN existing installations" so an AHJ or inspector may still refuse to accept such an install. But, in a case where existing cables are to be used for a new purpose(such as for temporary power), it may be deemed more practical to run an external EGC than pull an entirely new cable, and this section of the code provides a solution for such corcumstances.

 

[waross]

A significant issue is magnetic encirclement. Grounding conductors should be installed within the same ferrous raceway as the circuit conductors. It the ground cable is not enclosed within the same magnetic raceway as the power conductors then fault current will be subject to inductive reactance. The inductive reactance may significantly reduce the fault current and so extend the clearing time. In some instances the inductive reactance of a steel conduit may be enough to reduce ground fault current to less than the trip setting of the breaker.
At one time, steel armoured cables were common. Now cable armour is almost exclusively aluminum. There is less technical reason to have the grounding conductor enclosed in the non-magnetic armour.
You should only consider running a separate grounding conductor outside of non-magnetic armoured cables.
In the case of steel raceways the ground conductor must always be within the same magnetic enclosure as the power conductors. For parallel runs in more than one steel raceway best practice is to include a grounding conductor in each raceway.
As of 2015, the Canadian code requires parallel bonding conductors foe parallel runs.

10-814 Bonding conductor size (see Appendix B)
(.............
(.............
(3) Where circuit conductors are paralleled in separate cables, raceways, or busbars, the bonding conductor
shall be paralleled and the size of bonding conductor in each parallel run shall not be less than that specified
in
(a) Table 16A based on the size of the associated circuit conductors contained in the raceway or cable; or
(b) Table 16B based on the ampacity of the associated busbar.
(4) Notwithstanding Subrules (1), (2), and (3), the bonding conductor shall be permitted to be not larger than
the largest ungrounded conductor in the circuit.

I realize that this doesn't answer your question directly but knowing the reason behind the rule may help.
Check with your local AHJ for a ruling.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[resqcapt19]

250.130(C) is a very specific permission. The heading of that section says "(C) Nongrounding Receptacle Replacement or Branch Circuit Extensions". If you are replacing a receptacle that does not have a grounding connection or if you are extending an existing branch circuit that does not have an EGC, that section applies. If you are not doing one of those two things the section does not apply and the general rule in 300.3(B) applies.

Note that if the existing circuit was installed using a wiring method that does not have an outer ferrous covering, then 300.3(B)(3) would permit the external EGC run with the circuit conductors.