GEC Vs. EGC

[kshah]

Hi all,

I have been questioned from some plan checkers as of late regarding the sizing of the ground conductors on my plans. I need some clarification regarding the use of the equipment grounding conductor and the grounding electrode conductor. There are a few qustions, at the main switchboard, is the ground calculated by the size of the feeders from the utility or the main disconnect? At the panel coming from the main switchboard, is the ground calculated by the size of the main breaker? When a step-down transformer is introduced, is the ground introduced by the transformer for the secondary calculated by the incoming primary feeders of the tranformer, or the secondary? For the branch panel, or distribution panel immediately downstream from the transformer, is the ground calculated by the breaker size of the panel or is it to match that of the ground at the transformer.

Any help would be much appreciated.

 

[augie47]

EGC vs GEC

EGC vs GEC

I think it's safe to summerize that if it has overcurrent protection ahead then the "ground" is an equipment grounding conductor, sized by the overcurrent protection. No overcurrent, such as utility service or SDS transformer secondary conductors, the you size according to the conductors.

 

[iwire]

kshah, I agree with augie47s direct approach.

If there is overcurrent protection ahead of the circuit it is an EGC and sized per all the requirements in 250.122.

If there is no overcurrent protection ahead of the circuit it is a GEC or bonding jumper and is sized per all the requirements in 250.66.

I feel I should mention that if you are going to be working with the NEC you need to take a look at Article 100 Definitions, if you learn the NECs terminology it makes it easer to understand the rest of the NEC.

There are a few questions, at the main switchboard, is the ground calculated by the size of the feeders from the utility or the main disconnect?

For example there is no such thing as utility 'feeders' in the NEC

Feeders have overcurrent protection.

Conductors on the line side of the service disconect are always "Service Conductors"

Also the use of the word 'ground' is not very clear as we have Grounding and grounded conductors in the NEC that have entirely different functions.

Just a quick look at 'ground'

Ground. A conducting connection, whether intentional or accidental, between an electrical circuit or equipment and the earth or to some conducting body that serves in place of the earth.

Grounded. Connected to earth or to some conducting body that serves in place of the earth.

Grounded, Effectively. Intentionally connected to earth through a ground connection or connections of sufficiently low impedance and having sufficient current-carrying capacity to prevent the buildup of voltages that may result in undue hazards to connected equipment or to persons.

Grounded Conductor. A system or circuit conductor that is intentionally grounded.

Grounding Conductor. A conductor used to connect equipment or the grounded circuit of a wiring system to a grounding electrode or electrodes.

Grounding Conductor, Equipment. The conductor used to connect the non?current-carrying metal parts of equipment, raceways, and other enclosures to the system grounded conductor, the grounding electrode conductor, or both, at the service equipment or at the source of a separately derived system.

Grounding Electrode Conductor. The conductor used to connect the grounding electrode(s) to the equipment grounding conductor, to the grounded conductor, or to both, at the service, at each building or structure where supplied from a common service, or at the source of a separately derived system.

And 'Bond'

Bonding (Bonded). The permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and the capacity to conduct safely any current likely to be imposed.

Bonding Jumper. A reliable conductor to ensure the required electrical conductivity between metal parts required to be electrically connected.

Bonding Jumper, Equipment. The connection between two or more portions of the equipment grounding conductor.

Bonding Jumper, Main. The connection between the grounded circuit conductor and the equipment grounding conductor at the service.

As you can see the NEC consistently uses very similar terms for very different functions.