Connecting new CEE to exisitng grounding system

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kameele

Member
Location
NH
Greetings all. I have a grounding connection for some newly added equipment that I think I have figured properly, but as with most things grounding/bonding, would like to get some confirmation on.

We are installing a new piece of equipment at an existing plant that will sit on a rebar-reinforced foundation. I have specified a connection point for the EC to bond to the rebar. the EGC for the new equipment will be the cable trays that will carry power and instrumentation to the new equipment from the existing MCC and control panel. They will both be bonded to the plant grounding system at the MCC. because the largest non-grounded conductor feeding the equipment from the MCC will be 2/0 I would make the bonding conductor that size per 250.102 (D). My major question is the size of the conductor from the CEE at the equipment end to the cable trays. 250.66 (B) says it doesn't need to be larger than #4. would this cover both the CEE connection and to the equipment or would the bonding to the equipment frame need to be the 2/0 again?

Thanks for any input.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
The EGC is sized by table 250.122, based on the OCPD.

I am not real sure that the equipment pad you are creating is actually a CEE. If it is, I think it has to be made part of the structure's GES if it is inside an existing structure. Maybe just bond it to a nearby steel column?
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
My view may be questionable, but, if the new footer is classified as a CEE, I would think the #4 (max) specified in 250.66(B) would suffice.
 

augie47

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Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Good question, Bob. When I read the OP, I thought he was installing a conductor as well as the tray. Re-reading, I see that is not the case.
I am stumped as to whether the tray can be an grounding electode conductor. I await more learned input.
 

tom baker

First Chief Moderator
Staff member
If its a CEE per 250.52(A)(3) then the GEC connects to the electrical system per 250.24(A)(1), IE at the service.
If you don't follow 250.24(A)(1) then you are using a auxiliary grounding electrode. However connecting an auxiliary GE to other than the building electrical grounding system can, and has caused problems by a difference of potential in lighting events.
See also 250.54

I would not recommend bonding your CEE to any location but the building electrical grounding system.
 

kameele

Member
Location
NH
As a little bit of clarification, the equipment mentioned is a 4th vaporizer, located outside, that will be sitting on its own reinforced foundation. It will match the 3 exisitng similar units. we did not do any of the original installation and to the best of my knowledge, we do not have a copy of the original grounding plan. Finding a spot to bond to the rest of the plant grounding system will be problematic, so that's why I would make the bond at the MCC which is a pretty much guaranteed connection point.

I seem to remember reading that the EGC could serve as part of the GES if sized properly. (would that be the 3/0 I have in my mind?) but I can't put my hands on it at the moment.
 

kameele

Member
Location
NH
I see several folks were typing along with me. thanks for the info so far.

My foundation has enough rebar to be consdiered a CEE. I guess I'll have to do some more looking on site to see if I can find any pigtails to the exisitng equipment and see if that helps me located the GEC. Lightning problems I don't want :rolleyes:
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
To me, what you describe, based on NEC's definition of a structure, would be a structure. As such, you should follow 250.32 and attach you equipment grounding conductor to the CEE electrode at the "structure" disconnect.
 

kameele

Member
Location
NH
Gus--your quote of 250.32 leads me to what looks like a good solution.

250.32(D) Disconnecting Means Located in Separate Building or Structure on the Same Premises. Where one or more disconnecting means supply one or more additional buildings or structures under single management, and where these disconnecting means are located remote from those buildings or structures in accordance with the provisions of 225.32, Exception No. 1 and No. 2, 700.12(B)(6), 701.11(B)(5), or 702.11, all of the following conditions shall be met:
(1) The connection of the grounded conductor to the grounding electrode, to normally non?current-carrying metal parts of equipment, or to the equipment grounding conductor at a separate building or structure shall not be made.
(2) An equipment grounding conductor for grounding and bonding any normally non?current-carrying metal parts of equipment, interior metal piping systems, and building or structural metal frames is run with the circuit conductors to a separate building or structure and connected to existing grounding electrode(s) required in Part III of this article, or, where there are no existing electrodes, the grounding electrode(s) required in Part III of this article shall be installed where a separate building or structure is supplied by more than one branch circuit.
(3) The connection between the equipment grounding conductor and the grounding electrode at a separate building or structure shall be made in a junction box, panelboard, or similar enclosure located immediately inside or outside the separate building or structure.


My location meets the except. 1 as under single management and there is more than one disconnect feeding the structure. The grounded conductor will not be bonded at the new structure. There will be an EGC (the cabletray) run to the structure that will be bonded to the GEC (in the MCC). And I can bond the CEE pigtail to the EGC at the structure if I do it in a junction box. The GEC will be #4 and the EGC bonding jumper will be 2/0 at each end.

This seems to fit very nicely, so I'm sure that there is something that I've missed. Correct interpretation or WAG?

Thanks again.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
according to my thinking and your post #11, you need to connect your EGC to the electrode.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I don't think it improves the overall grounding, but since it exists, don't I need to bond to it?


If the building already has a CEE then you do not need to use any additional ones. Are you changing the service? If not IMO you do not need to use the new CEE.
 
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