Using service GEC for transformer

Status
Not open for further replies.
W

wawireguy

Senior Member
Lets say your service gear sits in the same room as your transformer. And you used a concrete encased electrode as your service GEC. Can you use the same GEC for your transformer also? Could you in this scenario run a #4 copper from your transformer to your #4 GEC and be code compliant?

If not could you run a properly sized GEC to the panel feeding your transformer as long as it's rated as service gear? 250.30(A)(3) Exception 2 seems to permit it.
 
If you look at 250.30(A)(3) and (A)(7) you will see the structural steel and metallic water are the preferred grounding electrodes fort he SDS, but the CEE should be used if neither of them are available (per the exception).
The GEC should originate from the same point as the bonding jumper and can be at the transformer or the 1st disconnecting means
 
augie47 said:
If you look at 250.30(A)(3) and (A)(7) you will see the structural steel and metallic water are the preferred grounding electrodes fort he SDS, but the CEE should be used if neither of them are available (per the exception).
The GEC should originate from the same point as the bonding jumper and can be at the transformer or the 1st disconnecting means
Click to expand...


I agree, the steel or water electrode first as per 250.30. If either of those 2 are not present, then as Augie stated, another electrode as per 250.52 is acceptable.
 
Am I understanding correctly that if a GEC was established to a water line and brought in to the service gear that I could use this same GEC for my transformer also?
 
That's a fine line...the NEC says the GEC from your transformer will "connect to the grounding electrode" and does not say to another GEC.
I would think to follow NEC your GEC would need to go to the electrode.


(actually I see no problem with your connecting to the CEE as they all bond together...but that's my opinion and not what the NEC says)
 
Last edited:
augie47 said:
That's a fine line...the NEC says the GEC from your transformer will "connect to the grounding electrode" and does not say to another GEC.
I would think to follow NEC your GEC would need to go to the electrode.


(actually I see no problem with your connecting to the CEE as they all bond together...but that's my opinion and not what the NEC says)
Click to expand...
250.30(A)(3) Exception No. 2 seems to say otherwise (with conditions, of course :))...
Exception No. 2: Where a separately derived system originates
in listed equipment suitable as service equipment, the
grounding electrode conductor from the service or feeder
equipment to the grounding electrode shall be permitted as
the grounding electrode conductor for the separately derived
system, provided the grounding electrode conductor is
of suffıcient size for the separately derived system. Where the
equipment grounding bus internal to the equipment is not
smaller than the required grounding electrode conductor
for the separately derived system, the grounding electrode
connection for the separately derived system shall be permitted
to be made to the bus.
Click to expand...

Yet I am curious as to why the necessity for service rated equipment...???
 
Pierre C Belarge said:
Are transformers listed as suitable for service equipment?

That is where the separately derived system originates from, is it not.
Click to expand...

The O.P. SDS does not originate in the service rated equipment, the feeder to the SDS originates from the service rated equipment. Unless the SDS is part there of the feeder or service (service rated equipment), the exception does not apply.
 
Pierre C Belarge said:
Are transformers listed as suitable for service equipment?

That is where the separately derived system originates from, is it not.
Click to expand...
I've not seen any transformer listed as suitable for use as service equipment... even transformers that are used as service equipemnt... but then again, I don't make a habit of noting every transformer's listing...

****

After searching through the UL Whitebook, it appears listed transformers are have no requirement to bear the marking, "suitable for use as service equipment". Additionally, there does not appear to be any blanket statement saying all transformers are suitable for such either... ???

****

PS: As I mentioned in another thread, I don't believe the secondary of the transformer by itself constitutes a SYSTEM, and the requirement says where the SYSTEM originates. You have to have the secondary and secondary feeder(s), and their disconnect(s), and grounded properly before you have a SYSTEM. So at what point does the SYSTEM originate???
 
Last edited:
augie47 said:
Smart$, my understanding has been that the exception you listed is for "modular" (my word) service gear which includes HV & LV panels and a SDS in one component.
(suh as http://www.squared.com/us/products/...A290055669D/$file/unitsubstationsFrameset.htm )
Click to expand...
Perhaps so... but it does not say that specifically, does it?

Regardless, the point is a GEC can be shared among a service and an SDS. What difference is there that if they utilize separately enclosed components to achieve the same end, that separate GEC's must be used?

We already know that multiple SDS's can have a common GEC, right?
 
Last edited:
I think Smart $ summed it up for me. I was just trying to figure out if you could share a GEC, between your service and tranformers if in close proximity to each other. Lets toss the service rated gear part of the question out of the equation and just go with sharing concrete encased electrodes and water GEC's.

Say you put your transformer in the same room with your service gear. No building steel available. Could you run a #4 to your concrete encased electrode and split bolt to it. In addition run a properly sized GEC to your water main service GEC and split bolt to it?

I read through the articles and am unclear if this is ok or not. The gist I'm getting from this thread is that it is ok?
 
I'll refer back to what I said earlier and I may be in the minority with my opinion, but 250.30 says in part: (3) Grounding Electrode Conductor, Single Separately Derived System. A grounding electrode conductor for a single separately derived system shall be sized in accordance with 250.66 for the derived phase conductors and shall be used to connect the grounded conductor of the derived system to the grounding electrode as specified in 250.30(A)(7)

"Connect to the grounding electrode", I take literally and I would look for that direct connection....to the electrode and no to another conductor.
 
wawireguy said:
Could you run a #4 to your concrete encased electrode and split bolt to it. In addition run a properly sized GEC to your water main service GEC and split bolt to it?

I read through the articles and am unclear if this is ok or not. The gist I'm getting from this thread is that it is ok?
Click to expand...

Article 250.30(A)5 refers to 250.64B,C,E for GEC installation. In (C) the conductors can be spliced, but with an irreversible connector only. A split bolt would not qualify.
 
augie47 said:
...
"Connect to the grounding electrode", I take literally and I would look for that direct connection....to the electrode and no to another conductor.
Click to expand...
But the wording doesn't say a direct connection, its equivalent, or nearly identical. And the word connect, in electrical terminology, does not preclude conductor splices and joints in the performance thereof.
 
This gives me some things to research. The exceptions in 250.30 are hard to understand. Parts of the code are written so you can understand it and others are not. Seems like we were able to focus this down to a few articles. I'll re-read them this weekend and try to get back to this if I can.
 
Status
Not open for further replies.
Top