we ran #4 cu equip ground with 4/0 phase conductors in conduit with steel flex and ground bushing at xformer end; then paralled same for secondary to panel. We plan to run #3/0 system bonding ground (GEC) outside of pipe and tie GEC, equip grounds, xformer frame and XO together at transformer. Any input about whether this will create objectionable current? I thought we should have just run GEC in the conduit thru ground bushing and left out equipment ground but wire is already pulled.
transformer grounding and bonding
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Re: transformer grounding and bonding
It sounds as though you are fine from my interpretation of your post, in fact you are pretty much the same as the graphic and text below from Mike Holts training material below.
To prevent objectionable current from flowing onto metal parts of electrical equipment, as well as metal piping and structural steel, the grounding electrode conductor must terminate at the same point on the separately derived system where the system bonding jumper is installed.
Exception 1: Where the system bonding jumper [250.30(A)(1)] is a wire or busbar, the grounding electrode conductor can terminate to the equipment grounding terminal, bar, or bus on the metal enclosure of the separately derived system. Figure 250?77
Exception 3: Separately derived systems rated 1 kVA (1,000 VA) or less are not required to be grounded (earthed); however, to ensure ground faults can be cleared, a system bonding jumper must be installed in accordance with 250.30(A)(1).
Just be sure to isolate the Equipment Grounding Conductor from the Grounded Conductor down stream of the transformer.
Roger
[ August 27, 2005, 01:10 PM: Message edited by: roger ]
It sounds as though you are fine from my interpretation of your post, in fact you are pretty much the same as the graphic and text below from Mike Holts training material below.
To prevent objectionable current from flowing onto metal parts of electrical equipment, as well as metal piping and structural steel, the grounding electrode conductor must terminate at the same point on the separately derived system where the system bonding jumper is installed.
Exception 1: Where the system bonding jumper [250.30(A)(1)] is a wire or busbar, the grounding electrode conductor can terminate to the equipment grounding terminal, bar, or bus on the metal enclosure of the separately derived system. Figure 250?77
Exception 3: Separately derived systems rated 1 kVA (1,000 VA) or less are not required to be grounded (earthed); however, to ensure ground faults can be cleared, a system bonding jumper must be installed in accordance with 250.30(A)(1).
Just be sure to isolate the Equipment Grounding Conductor from the Grounded Conductor down stream of the transformer.
Roger
[ August 27, 2005, 01:10 PM: Message edited by: roger ]
Re: transformer grounding and bonding
Wonderful topic, I'am currently involved in simliar situation. I have more of a question then a comment. The conductor taken from the ground terminal of the transformer to the overcurrent protection of the panelboard. Is this the Equipment grounding conductor? Therefore is shall be sized per table 250-122. Or is the conductor a bonding jumper and sized per table 250-66. I look forward to any response
Wonderful topic, I'am currently involved in simliar situation. I have more of a question then a comment. The conductor taken from the ground terminal of the transformer to the overcurrent protection of the panelboard. Is this the Equipment grounding conductor? Therefore is shall be sized per table 250-122. Or is the conductor a bonding jumper and sized per table 250-66. I look forward to any response
Re: transformer grounding and bonding
From 250-30
(3) Grounding Electrode Conductor, Single Separately Derived System A grounding electrode conductor for a single separately derived system shall be sized in accordance with 250.66
From 250-30
(3) Grounding Electrode Conductor, Single Separately Derived System A grounding electrode conductor for a single separately derived system shall be sized in accordance with 250.66
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