Transformer Grounding

Status
Not open for further replies.
D

Duuuuug

Member
Existing Installation
800Amp Main Panelboard (MP) with 120Amp breaker feeding a 480-208Y/120 75KVA Transformer
Primary - 3-#1 & 1-#6gnd
Secondary - 4-250mcm & 1-#2gnd
Transformer feeds a 225Amp Main Breaker Panelboard (PB)
The contractor installed a ground rod with a #2-GEC wired to PB.

This does not appear to be right because the ground rod is not connected to anything else.
1. Is this legal?
2. Since building steel is not available can the contractor wire a GEC from PB straight to the 800Amp service electrodes?
 
Re: Transformer Grounding

If I were inspecting, I think I'd want a lil more explanation of
building steel is not available
Click to expand...
that said:


(7) Grounding Electrode The grounding electrode shall be as near as practicable to and preferably in the same area as the grounding electrode conductor connection to the system. The grounding electrode shall be the nearest one of the following:
(1) Metal water pipe grounding electrode as specified in 250.52(A)(1)
(2) Structural metal grounding electrode as specified in 250.52(A)(2)
Exception No. 1: Any of the other electrodes identified in 250.52(A) shall be used where the electrodes specified by 250.30(A)(7) are not available.
Click to expand...

[ October 03, 2005, 03:09 PM: Message edited by: augie47 ]
 
Re: Transformer Grounding

The Electrode is just outside the wall where Panelboard PB is located.

My question is more directed towards whether or not the Transformer's ground rod needs to be connected to the service ground rods.

I am looking at 250.50 and it says that 252(A)1 thru 6 (if available) shall all be bonded together to form the grounding electrode system.

I feel that this ground rod falls under 252(A)5 and must be connected back to the service and not just "Float-Out-There" by itself.

Just want some feedback about my conclusion.
 
Re: Transformer Grounding

Yes, the new grounding electrodes must be bonded to the service grounding electrodes.
 
Re: Transformer Grounding

Don
Does the bonding of the separately derived system electrode(s) to the service electrode system have to be a direct action? Could it be through the path of the equipment grounding conductor that is connected to the separately derived system's supply?
 
Re: Transformer Grounding

Don
Does the bonding of the separately derived system electrode(s) to the service electrode system have to be a direct action? Could it be through the path of the equipment grounding conductor that is connected to the separately derived system's supply?
Click to expand...
Pierre, I was also wondering this, but then I thought the bonding of electrodes had to be through a direct connection. I'm thinking 250.64(C), which states "one continuous length," but does that apply to the bonding conductor between electrodes? Now I see 250.68(B), which mentions only "a permanent and effective grounding path." :confused:
 
Re: Transformer Grounding

The code does not give us any guidance in Article 250 as to how to make this bonding connection. In the Chapter 8 articles, the bonding jumper must be at least #6 copper.
Don
 
Re: Transformer Grounding

So the GEC from the 208Y/120 panelboard to the SDS electrode is #2, sized by Table 250.66 and based on 250MCM coming from the transformer.
The connection from the SDS electrode to the service electrode is based on the 800AMP service conductors (3-Sets of 350MCM) which by Table 250.66 = 3/0 GEC.
Is this right or do you just continue with the #2?

I changed the dual to "3-Sets of" and the 2/0 to 3/0, sorry.

[ October 04, 2005, 05:06 PM: Message edited by: Duuuuug ]
 
Re: Transformer Grounding

Originally posted by don_resqcapt19:
The code does not give us any guidance in Article 250 as to how to make this bonding connection. In the Chapter 8 articles, the bonding jumper must be at least #6 copper.
Don
Click to expand...
250.50 would require the new electrode for the SDS which just became available; to be bonded to the grounding electrode system. A #6 cu, as the sole conductor would be fine.

That being said, I wonder how many people neforce it? We don't. Maybe were the only ones who don't??

The electrode is bonded to the grounding electrode system via the equip. ground with the primary circuit and the water if bonded

As Don said it's a bonding jumper, and there is nothing requiring this to be an unspliced conductor.
 
Status
Not open for further replies.
Top