Grounding: Building Addition

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Keri_WW

Keri_WW

Senior Member
Background:
I'm designing an addition to an existing building. The new addition has a separately derived service (I think); however, the main feeder to the exterior transformer that is feeding the addition's switchboard originates from a substation in the existing building.

Questions:
  1. Does the grounding system for the existing building and the new building get tied together?
  2. Does a grounding equipment conductor need to be run between the outdoor switch and the exterior transformer (basically, where is the grounding for the exterior equipment derived?)?
  3. Does the lightning protection have to be tied together between the two buildings (the addition is a bit shorter than the existing, however requires LP past the zone of protection points).

Thanks for the help,
Keri :D:D
 
Keri_WW said:
Background:
I'm designing an addition to an existing building. The new addition has a separately derived service (I think); however, the main feeder to the exterior transformer that is feeding the addition's switchboard originates from a substation in the existing building.



Questions:
  1. Does the grounding system for the existing building and the new building get tied together?
  2. Does a grounding equipment conductor need to be run between the outdoor switch and the exterior transformer (basically, where is the grounding for the exterior equipment derived?)?
  3. Does the lightning protection have to be tied together between the two buildings (the addition is a bit shorter than the existing, however requires LP past the zone of protection points).
Thanks for the help,
Keri :D:D
Click to expand...
Keri i take it the addition is attached to the existing structure. Is there structural steel or metal piping systems in the addition. If there are, they are required to be bonded to the grounding electrode system at the service equipment. If they are bonded to the GEC the new feeder equipment in the addition is required to be bonded to the new addition steel and water.
The outdoor transformer secondary is a feeder and can follow 250.30 rules for grounding to the new outdoor distribution gear. A seperate equipment ground conductor is required to be taken along with the feeder to the addition and bonded to the buildings steel and metal piping.

Attached is a drawing of grounding examples between transformer and first overcurrent device.

Rick

View attachment 4101
 
Since your transformer for the separately derived system is outside this is on time I would recommend utilizing the exception found in 250.30 (A) (1) exception NO. 2

I would bond the grounded conductor to the transformer enclosure drive two ground rods at the transformer location and bond my grounded conductor to the ground rods. Providing protection of lighting strike to my transformer enclosure.

I would use RNC from my Transformer to the distribution of the separately derived system. Bond the neutral again at the distribution panel and treat it exactly like you would a service.
 
I support David's idea but, if you have structural steel in both buildings, I think it would be prudent to bond them together to assure there is no potential.
 
It sounds like the transformer feeds an outdoor switchboard. Maybe the OP can clarify.
  1. Does a grounding equipment conductor need to be run between the outdoor switch and the exterior transformer (basically, where is the grounding for the exterior equipment derived?)?
Click to expand...
 
RUWired said:
It sounds like the transformer feeds an outdoor switchboard. Maybe the OP can clarify.
Click to expand...

Indoor substation -> underground feeder to exterior switchgear -> underground feeder to exterior step-down transformer -> underground feeder to indoor switchboard.

Thanks for all of the suggestions.
 
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