ECN Forum Forums General Topics of the Trade General Discussion Area Service and GEC

Well, let me take a shot at this.

First off, the Grounding Electrode Conductor will need to be sized accordingly to the size of the service entrance conductors on the LINE side of the main disconnect. Refer to Table 250-66 in the 1999 NEC for this [or Table 250-94 in the 1996 NEC]. The equivalent size to use for the paralleled 350 Kcmils' is 1500 Kcmil [350 amps @ 90 degrees X 2 = apx. 700 amps]. I am just quick guesstamating this eq. size here and it should work out OK, but it's really the sum of the total area.
I am figuring as Copper, not Aluminum, so adjust if needed [per Ampacity Table 310-16 in 1996 and 1999 NEC], or just use the resulting Kcmil size applied directly to Table 250-66.
The Minimum Grounding Electrode Conductor size would be 3/0 Copper, or 250 Kcmil Aluminum [yuck!!]. This runs from the one and only point in the system where this service is grounded, to the electrode it's self.
This is done at the designated point [where the "Neutral" or Grounded Conductor's disconnect is at]. If the system does not have dual voltage, like a corner grounded Delta 3 wire system is only one voltage, the grounded conductor will be which ever is grounded at the transformer. Verify with Utility Company, unless a visual and tested verification can be made.

Now for the bonding jumpers [main bonding jumper from grounded conductor's bus to enclosure], plus equipment bonding jumpers for bonding the pull section, CT section and the main switch section together. These would be sized per the rating of the overcurrent device - using Table 250-122 [1999 NEC], or Table 250-95 [1996 NEC]. I know this sounds odd or incorrect, but that's the way to determine the _MINIMUM_ size for ground _BONDING_ conductors.
600 Amp trip setting will need minimum #1 Copper, or 2/0 Aluminum, as shown in both the '96 and '99 NEC.

To get 2 services [under 2 separate KWH meters] on the same single address, the location would need to have 2 different types of services to qualify. That would be either one of high voltage, one of low voltage [one being 480Y/277 VAC 3 phase 4 wire for high voltage, the other being 208Y/120 VAC 3 phase 4 wire for the low voltage].
The other qualification would be 2 different types of serviced power to equipment - one being 1 phase 3 wire, the other being 3 phase 3 wire. This was common in Commercial between the '50s and the mid '70s. One service would be 120/240 VAC 1 phase 3 wire, the other would be 240 VAC 3 phase 3 wire. Each had separate metering, separate gear sections, but were derived from one 4 wire Delta Transformer bank - supplied by the Utility Company.

If there will be individual addresses per customers, each address can get a separate service [under a separate meter].

Let me know how this looks.

Scott SET

Scott,

The two C/T's and meters are the exact same type of service-- 120/208 3phase. The reason for the second meter which I just found out from the utility is the rates charged. One service (or one half of the service, I'm still not sure) will be feeding strictly electric heat and AC load. Our utility gives separate rates if separation of the loads is established, in some instances--probably commercial applications.

So to summarize your opinion-- One service, which means I need to consider all four sets of 350's when I size the GEC, MBJ, and EBJ's. Right?

In reading your part about the connection of the GEC, does it need to be a 3/0 to both MDP's? The neutrals are only connected together at the service drop(supply side), after that they are never connected on the load side(in each MDP)

I see what is going on with the meters now [I think ].
Looks like there's the typical KWH meter, then there's one with a Detent register, possibly along with a KVAR meter for power factor penalty.
Nevertheless, one would be used to measure normal equipment's power [KWHs], while the other measures not only the "heavy machines / loads", but possibly the level of Power Factor over time.
Both readings would be combined to one bill per billing period, to that one customer [or address].
If I have once again missed it, I am sorry. Correct me if you wish to.

The Grounding Electrode Conductor will run only from the place that the grounded conductor [AKA neutral], is bonded to the service equipment - plus has a "Neutral" disconnect -, then to the actual Grounding Electrode system it's self.
The grounding Electrode System would be UFER ground, structural steel, grounding plates, driven rods, cold water, etc.
The Grounding Electrode Conductor connects the[se] items, which make up the Grounding Electrode System, to the main electrical system's ground bonding point for the grounded conductor.
The same goes for Separately Derived Systems - the grounded conductor is bonded to a Grounding Electrode System for that SDS, via the Grounding Electrode Conductor.

I have a hard time explaining this using simple terms, so if anyone can jump in and help out with some analogies that will make sense, please do so!!

Basically, the wire from the neutral bus in the main panel, where the neutral bus is connected to the metallic enclosure - plus has a disconnect - is run out of this panel, then connected to the cold water line and a driven ground rod [for instance], is the Grounding Electrode Conductor.
It bonds the system at the closest point to where it's derived from, in this case, at the same place that the main disconnect would be.

All other grounding would be equipment bonding.

How's this one??

Scott SET

Hi;
i'm reading your comments, flippin' thru codes you've mentioned, and i come to T250-66
check out note #1 under the table....

this is 3 code ref's away from 230, i thought it may provide ammo to your disscussion here.

Scott,
The only thing I don't think I have expressed clearly enough is the fact that there are two separate MDP's.

Each MDP has a parallel set of 350's.

So I have two locations where the grounded conductor is in the main (separate)disconnects.

For a simpler visual but same arrangement, imagine a regular 120/240, 1 phase, 100a single family dwelling, overhead service with a single meter on the rear of the house and the panel immediatley inside the house.

Now imagine this same system twice, placed right next to one another.

1st, is this one service or two?

2nd, if one service, which panel do I attach the GEC to? Panel#1 or #2?

I want to ask a couple other things, but lets start with these two questions.

Thanks for hanging in there with my question, it is a real situation I am currently trying to deal with.

Scott,

I have never installed or seen installed a system where the grounded conductor can be disconnected.(Without loosening lugs and removing it from a terminal.)

Could you elaborate on your meaning of this a little. Maybe I am misinterpreting what you are writing.

Also, if anyone would like to see a diagram of what I am talking about and wouldn't mind receiving a MSWord2000 document with a drawing in it, it may clear things up. But I won't send files unless requested. If interested, send me and email so I can reply and attach the file.

The code loop i see is
#1--230-2
#2--230-40 ex 2
#3--T250-66
#4--note #1 to T250-66

bear with me as i confuse myself on line here

230-2..
number of services,
(d) applies , given different rate schedules.
being OH, not UG it's considered 2 services, note "not connected together @ load end"

230-40
number of service-entrance conductor sets,
EX2- 2 to 6 disco's in separate enclosures, service drop or lateral

Fine & dandy so far..

T250-66, note #1
I think this is saying that, even if i had 6 individual drops, and 6 mains fed from one drop or lateral, that i would need to size the GEC for the equiv. of the combination of all conductors..

So even if you rule that it would be 2 services, you need to supply a GEC for 1 ?

i need a translator here....