Grounding each metal box when using EMT conduit


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Old 03-16-23, 09:21 AM
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Grounding each metal box when using EMT conduit

Does each metal box in a run need to be grounded via a grounding screw & a ground wire if the run is THHN wires is via EMT conduit & the initial metal box is grounded? Seems redundant since you are connecting all the metal junction/switch/receptacle boxes by the metal conduit if the initial box is grounded aren't they all ultimately continuous via the metal conduit & basically grounded? As well if the wires are grounded in the breaker box aren't they grounded via this contact as well?
 
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Old 03-16-23, 11:53 AM
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No. The various metal outlet boxes joined with rigid metal conduit and properly torqued bushings and fittings do not need ground wires (equipment grounding conductors) running through said conduits and fastened to the backs of said boxes. Here the network of metal conduit and (metal) boxes is the EGC.

The ground screws in the backs of the boxes may be needed to ground receptacles and other devices mounted in said boxes, using appropriate pigtails.

With other wiring methods with EGCs running through the conduits, all EGC ends entering a box together with pigtails as needed from receptacles etc. and from the back of a metal box must be connected together, two bundles of EGCs joined with a/another pigtail are permitted. This interconnection is required even though the EGC going to the panel is grounded in that panel.
 

Last edited by AllanJ; 03-16-23 at 12:12 PM.
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Old 03-16-23, 02:55 PM
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So just to make sure I'm following you correctly:
Assuming I'm using THHN through metal conduit with proper fittings - It sounds like you're saying that if at the first metal box you connect a ground wire to a screw at the back of the box & connect that pigtail to the incoming ground from the breaker box and to any devices in that box (receptacle, switch, light) &/or to any ground wires that continue further down the circuit to any other devices - at each subsequent metal box whether it contains a device or is a pass through - that SPECIFIC metal box DOES NOT require a separate grounding pigtail to the back of it (Obviously whatever device may be in that box - switch, receptacle, light - would be pigtailed to the incoming ground wire). As long as these devices are receiving a ground connection leading back to the original metal box they do not need to be separately grounded to the back of their individual boxes. Being grounded at the breaker panel alone is not sufficient.

When you refer to other wiring methods through conduit in your last paragraph what are you referring to? Are you still referring to metal conduit or PVC?
 
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Old 03-17-23, 05:40 AM
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"Other wiring methods" yes I mean plastic conduit or flexible spiral conduit, or even metal conduit qualified to be the equipment grounding conductor where the installer chose to run a separate EGC inside.

A pass through EGC (no spliced ends, no connection to a receptacle or other device) is not cut and then spliced for the sole purpose of being bonded to the box back. But a device (receptacle etc.) in the box needs EGC back to the panel, either the network of properly installed metal conduit and boxes, or a/another EGC running within.

(correction) Each metal box containing an EGC end including the grounding pigtail from a receptacle unit requires bonding of all EGC ends to the box back usually with an additional pigtail to the latter..
 
 

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