Grounding Electrode Connections for transformers in concrete building

Status
Not open for further replies.

mgardner

Member
I have an existing 6 story all poured concrete building that is being renovated into apartments. We are providing new 480:208/120 transformers on each floor for house power. My main question is how to connect each of these separately derived systems to the grounding electrode conductor system in the building?

Best I can tell, I need to install a continuous CU grounding electrode (wire) up through the building, size of it based on Table 250.66, and provide taps from each transformer to this CU wire. Does this wire need to be in conduit or can it be exposed? How far can I run the tap wires (not all the transformers are stacked)?

Any other ways to do this? Can I connect to the nearest metal water pipe? Does this pipe have to be exposed? If there is rebar in the existing concrete, can we tie into that?
 

ADub

Senior Member
Location
Midwest
Occupation
Estimator/Project Manager
Is there building steel available? Make sure there is a bonding jumper from steel to the water pipe electrode and you should be good just hitting the steel on each floor I believe.


Sent from my iPad using Tapatalk
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Is there building steel available? Make sure there is a bonding jumper from steel to the water pipe electrode and you should be good just hitting the steel on each floor I believe.


Sent from my iPad using Tapatalk

If the steel is a valid grounding electric.

Otherwise there is a rule allowing for a common gec, but it has to be pretty good sized, like 2/0.
 

Smart $

Esteemed Member
Location
Ohio
If the steel is a valid grounding electric.

Otherwise there is a rule allowing for a common gec, but it has to be pretty good sized, like 2/0.
Assuming you meant electrode, building structural steel is not required to be a valid grounding electrode to use it as a GEC extension. See 250.68 and (C)(2) therein. If building steel is not a valid electrode, a bonding jumper to a valid electrode will be required to use it as an extension... but I believe the bonding jumper is required regardless of the building steel being used as an GEC extension
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Yes it in 250.30(A)(6).

250.30(A)(6) Grounding Electrode Conductor, Multiple Sepa-
rately Derived Systems. A common grounding electrode
conductor for multiple separately derived systems shall be
permitted. If installed, the common grounding electrode
conductor shall be used to connect the grounded conductor
of the separately derived systems to the grounding elec-
trode as specified in 250.30(A)(4). A grounding electrode
conductor tap shall then be installed from each separately
derived system to the common grounding electrode con-
ductor. Each tap conductor shall connect the grounded con-
ductor of the separately derived system to the common
grounding electrode conductor. This connection shall be
made at the same point on the separately derived system
where the system bonding jumper is connected.
Exception No. 1: If the system bonding jumper specified in
250.30(A)(1) is a wire or busbar, it shall be permitted to
connect the grounding electrode conductor tap to the equip-
ment grounding terminal, bar, or bus, provided the equipment
grounding terminal, bar, or bus is of suffıcient size for the
separately derived system.
Exception No. 2: A grounding electrode conductor shall not
be required for a system that supplies a Class 1, Class 2, or
Class 3 circuit and is derived from a transformer rated not
more than 1000 volt-amperes, provided the system grounded
conductor is bonded to the transformer frame or enclosure by
a jumper sized in accordance with 250.30(A)(1), Exception
No. 3, and the transformer frame or enclosure is grounded by
one of the means specified in 250.134.
(a) Common Grounding Electrode Conductor. The com-
mon grounding electrode conductor shall be permitted to be
one of the following:
(1) A conductor of the wire type not smaller than 3/0 AWG
copper or 250 kcmil aluminum
(2) The metal frame of the building or structure that com-
plies with 250.52(A)(2) or is connected to the ground-
ing electrode system by a conductor that shall not be
smaller than 3/0 AWG copper or 250 kcmil aluminum

(b) Tap Conductor Size. Each tap conductor shall be
sized in accordance with 250.66 based on the derived un-
grounded conductors of the separately derived system it
serves.
 

mgardner

Member
Copper Piping?

Copper Piping?

So, can we use copper water piping in the vicinity of the transformer? If so, is there a requirement for how big the pipe has to be? The pipe is exposed in the adjacent water heater closet. Also, it is insulated -- is this issue.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
So, can we use copper water piping in the vicinity of the transformer? If so, is there a requirement for how big the pipe has to be? The pipe is exposed in the adjacent water heater closet. Also, it is insulated -- is this issue.


You need to comply with 250.30(A)(4).


250.30(A)(4) 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 of 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 if the electrodes specified by
250.30(A)(4) are not available.
Exception No. 2 to (1) and (2): If a separately derived
system originates in listed equipment suitable for use as
service equipment, the grounding electrode used for the
service or feeder equipment shall be permitted as the
grounding electrode for the separately derived system.
 

Smart $

Esteemed Member
Location
Ohio
So, can we use copper water piping in the vicinity of the transformer? If so, is there a requirement for how big the pipe has to be? The pipe is exposed in the adjacent water heater closet. Also, it is insulated -- is this issue.
Connection has to be within 5' of entrance to building [250.66(C)(1)].
 
Status
Not open for further replies.
Top