Mike Dolt Enterprises
Mike Dolt Enterprises
User: charlie b, Location: Lockport, IL
Asked on: Wednesday, April 6, 2011 at 4:28 pm EDT
Answered on: Tuesday, May 14, 2024 at 3:52 am EDT
Question: I have struggled with this before, and I am still uncertain. But then, with article 250, I am probably not alone in my confusion.Utility-owned transformer is outside on a pad. Ten conduits will bring the service conductors into the main switchboard. I?ll bond the N&G in the main switchboard, and run a GEC to the ground rods. That part I get. But do I include any ground-thingy (EGC perhaps? or GEC?) or bond-thingy (supply side equipment bonding jumper, perhaps?) in any or all of the 10 conduits? If so, what is it (are they) called, and how is it (are they) sized?The design drawings (that I am reviewing) presently show 10 conduits, each with 5 conductors (500 MCM AL - 3000 amp service), with the conductors described as A, B, C, N, G. This caught my eye because whatever else might be true, the G wire need not be 500 MCM. My belief is that the G wire is not needed at all, let alone in each of the 10 conduits.
Grounding of Utility-Owned Transformer
Yes, you are not alone in your confusion regarding Article 250. The following steps outline the grounding and bonding requirements
1. Transformer Pad:
A grounding electrode system (GES) must be installed at the transformer pad. This typically consists of ground rods or a Ufer ground. The utility-owned transformer must be bonded to the GES using a grounding electrode conductor (GEC).2. Main Switchboard
The neutral (N) and grounding (G) conductors must be bonded together in the main switchboard. A GEC must be run from the bonded N&G point to the GES outside.
3. Conduits
There is no requirement for EGCs or GECs in the individual conduits. The G conductor in each conduit is not necessary, as the GES is provided at the transformer pad and the N&G conductors are bonded in the main switchboard.
Note
The "G" wire in the Conduits may be used for future equipment grounding within the building.
Sizing of GEC:
The GEC must be sized according to Table 250.66. For a 3000 amp service, a 4/0 AWG copper conductor would be required. Flag for review