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#181120 09/23/08 11:04 AM
Joined: Jan 2004
Posts: 54
A building that I do quite a bit of work on has asked me to give them a price to upgrade the current service (400 amps 3 phase) to 1000 amps 3 phase 120/208.

Presently there are 2 underground 4" rigid conduits run from the pole to the building, 1 supplies the 400 amps and the other supplies the telephone service. The phone company has agreed to provide an overhead service to the building which will allow us to use both 4" conduits to serve the new service. I propose installing paralell 600 kcmil copper to feed a new 1000 amp CB/CT cabinet. To excavate new conduits to the building would be a huge job and the power co has said they will not supply an overhead 1000 A service.

Does this sound reasonable? I'm curious as to how well 4-600 kcmil copper will pull thru the 4" (the total run is approx 125'). I think I will run all of this by an engineer but I would appreciate any opinions.


Joined: Mar 2005
Posts: 1,213
Will your meter be at the pole or the building? The pocos don't have to follow NEC sizing rules, so you may be able to get away with less copper in your service conductors.

Joined: Jul 2004
Posts: 9,950
Likes: 34
There is no logical reason why a poco would run a wire smaller than 310.16 (310.15(B)(6) in residential) in a pipe even if they can. They don't get the break for free air that you have in a drop.

Greg Fretwell
Joined: Apr 2002
Posts: 7,388
Likes: 7
Based on 310.16, never happen.

The pull thru 4" would not be a problem.....but parallel 600's only give you 840 amps for two sets.

Joined: Jan 2005
Posts: 5,457
Likes: 3
Cat Servant
That's quite a service upgrade.

Since you'll need to chat with the PoCo anyway .... why not change over to 480/277?

I'm never really comfortable with parallel feeds ... just my conservatism, or the rarity of my using them.

With wires as big as you're using, I begin to be tempted by aluminum ... the stuff is a lot easier to pull.

Joined: Oct 2000
Posts: 2,723
Likes: 1
Broom Pusher and

I have a couple questions to ask:

Does the Electrical Contractor Provide and Install Service Feeder Ducts (underground ducts) from the Service Equipment to the Pole / Transformer Vault, or does the Utility do this?

Whom Provides and Installs the Service Feeders?
Electrical Contractor or Utility?

Have you discussed this upgrade with a Service Planner?
(i.e.: Service Planner / Design Engineer from the Utility providing Service to the area)

If "Q3" above is "YES", did the Service Planner provide you with the Feeder Requirements and approved installations information?

Have you compiled Load Calcs for the Customer's Existing (to remain)and New loads?

Will there be any issues regarding increased Fault Current Levels for the existing to remain Panelboards + OCPDs?
(the increased system demand will likely result in the Utility increasing Transformer capacity, which will likely also increase available fault current at the Service)

Will you be able to re-use - or even remove the existing Feeders - from the existing GRC Feeder Ducts?

Questions #1 & #2 are in regards to knowing whom will be responsible for Service Feeders & Ducts installations between the Service Equipment and the Utility Pole / Transformer vault.

If the Utility provides & installs the Feeders, then you would not have to do anything ... PROVIDED:
The Service Planner accepts the existing GRC Feeder Ducts for new Feeders to be installed in.
Otherwise, You, as the E.C., will need to install new Ducts, per the Utility's ESRs (Electrical Service Requirements manuals / documents). The Service Planner will (actually "Should") provide you with information - per the ESRs, that they accept.

If the Utility Provides + Installs the Ducts and the Feeders, then you only have to coordinate with the Utility, and provide the Service Planner with the required submittal data (covered below).
This "option" is extremely rare - especially where I am at, but may exist in your area.

Question #3 regards Planning and Design Coordination.

For a Service Upgrade of any size on Commercial / Industrial projects, the Utility Service Planner for the given area should be contacted immediately, to determine their overall requirements + fees.

The Utility will be the AHJ for the Secondary Connections on the LINE side of the Service Disconnect - meaning anything from their existing Transformer or Pole, which will be connected to a Customer's Service equipment, is subject to the Utility's Specifications, Design criteria, and adopted Code(s).

Additionally, the fees may be discussed, with at least an estimated cost projected given to you.

Need to know all this preliminary stuff prior to compiling a Proposal (AKA your "Bid") for your Client to review.
Simply stated; your bid will include:
* the specific materials,
* installation requirements,
* creation of drawings / plans / calculations by you (the E.C.),
* fees required by the Utility,
along with your overhead and profit.

Question #4 is to see what the Utility requires.

Question #5 is something that any Service Planner will want to see for a New or Upgraded Service.

The Load calcs are used by the Utility Planner to determine the Transformer's capacity, Service Feeder size + number of ducts, etc.

They may want to see Panel Schedules, but not likely for your project.

There may be additional plans / calcs / drawings requested, and you may also need to submit specifications for the Service Equipment you plan to install.

Question #6 regards the possibility of increased SCA (Fault Current) at the Service, from an increased Transformer Capacity, larger Service feeders, or both.

The Service Planner will provide you with a fault quote after the Service Design is completed by the Utility.
You should be able to get a quote when you submit load calcs, but the "Quote Letter" will not be issued by the Utility until design is complete.

The "Fault Level Quote Letter" will be required by the Building Department prior to passing Inspection.
Inspection must be passed before the Utility will release the KWH Meter.

Question # 7 is self explaining: Can you actually re-use the GRC, or will the Conductors refuse to come out?

Sorry for the long winded post.

Got to go hit the sheets (sleep).

Will check this thread tomorrow for replies.


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Apr 2002
Posts: 7,388
Likes: 7

Again, your eloquence is outstanding!
That's the basic scenario here in NJ, probably the same in Ma.

800 amps is max OH (from pole mtd pots), larger is pad mount xfr. PSE&G area, layout tech determines locations; EC responsible for pad sub-base; EC installs primary conduit(s)from pad to PSE&G designated location (to PSE&G specs). PSE&G installs and terminates primaries. EC is responsible for all secondary work. CT's & meter pan are supplied by PSE&G; PSE&G wires CT's and meter. All is done to PSE&G Green Book 2005 with amendments (3).

The Green Book, and amendments is available on the internet at PSE&G website.

Joined: Jan 2004
Posts: 54
Thanks for the responses.

I agree the 600s are too small based on 310.16. A previous tennant had originally intended to do this project and had come up with this scenario and I was under the impression it was blessed by the poco, I have a meeting scheduled with a poco engineer to verify this. I was wondering if the conductors might fall under the "jurisdiction" of the poco and could be smaller than what would be required by 310.16.

The main disco and metering will be located at the building, not at the pole.

The responsibility for removing the old conductors and installing the new conductors falls on me.

To answer some of Scott's questions.

I am in the process of doing load calcs. I think 800 is enough, but customer originally wanted 1200 for future expansion.

None of the existing panelboards, equipment will be reused.

The existing conductors in conduit #1 seem to be in good condition as does the conduit that is visible. I'm cautiously optimistic about getting the old conductors out.


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