2 Questions: Grounding and Taps

[ctrane]

I am going to try and get 2 for the price of 1, here goes.

First, after the service entrance ground has been established, and you must ground again for a separatley derived system, like a transformer downstream in the system, is it wise to bond this second ground to the service entrance ground system? If so, do you use a GEC, or size it as a main bonding jumper?

Second, in the taps section, the first 2 are straight forward, the not greater than 10', and 25'. But, in the unlimited length section, there is no ratio between tap and the conductor being tapped. 10' taps are limited by 10:1, 25' is limited by 2/3. What is the ratio for unlimited taps? I got thinking about it because we are working on a existing building, and they have tapped a 2000a feeder with a 15a circuit. This seems a little unreasonable to me, but cannot find code to say it is.

I really appreciate all the return posts, as I have learned so much from all the experience.

 

[iwire]

Iirst, after the service entrance ground has been established, and you must ground again for a separatley derived system, like a transformer downstream in the system, is it wise to bond this second ground to the service entrance ground system?

That is unavoidable if you follow all the SDS rules.

Second, in the taps section, the first 2 are straight forward, the not greater than 10', and 25'. But, in the unlimited length section, there is no ratio between tap and the conductor being tapped.

Unlimited length only applies outside the building, there is no ratio requirement.

they have tapped a 2000a feeder with a 15a circuit.

The tapped circuit does not have a ratio requirement at all.

The tap conductors from the feeder to the over current device may have a ratio requirement.

 

[ctrane]

Something else while I was thinking about it. The 15A tap is on the service entrance conductors. This tap takes place between the utility xfrmr and the point of service. Must this 15A Disconnect be treated as a separate service and grounded at this point? Would you then try and connect the two systems to keep potential the same, or is the neutral doing this by being shared?

 

[cpal]

Something else while I was thinking about it. The 15A tap is on the service entrance conductors. This tap takes place between the utility xfrmr and the point of service. Must this 15A Disconnect be treated as a separate service and grounded at this point? Would you then try and connect the two systems to keep potential the same, or is the neutral doing this by being shared?

This tap sounds more like an additional service allowed by 230.2.
if this is so the GEC may be installed to comply with 250.64

If this answer is not helpful a more detailed description may be in order

 

[ctrane]

one question that may sound silly to the electricians in the field, but I don't know. In the NEC diagrams, they show the system ground being attached to the Neutral bus via the GEC. Is this the physical reality of a panelboard? Or, is there a seperate grounding bar? If so, how do you bond neutral to ground, with a GEC or Main Bonding Jumper? Also, what is the proper way to ground Equipment Grounding Bus to Neutral and/or Ground bar, a GEC or a Main Bonding Jumper? All this is in regards to point of service.

 

[haskindm]

Usually the equipment ground bar and the "neutral bar" are the same in the main service panel. The bonding jumper connects this bar to the panel box (can).
The service neutral and the Grounding electrode conductor(s) are all connected to this bar. IF the panel is to be used as a subpanel, then the neutral barr is isolated from the can and an addition equipment ground bar is installed.
Does that help?