I plan to install a 400-amp 3-phase service in 4" PVC.
I believe that installing parallel service conductors (2 3/0 Cu THWN/THHN per phase) in the 4" raceway would total 6 current carrying conductors (neutral not counted) and require derating to 80%. Even using the 90 deg. column for derating purposes, the ampacity falls below 400-amps. Would 240.4(B) apply, or would I have to upsize to a pair of 4/0 per phase.

I will probably chech with AHJ, but was wondering what you guys thought about the installation.

Thanks

John

The required ampacity of service conductors is called for in 230.42(A), and is based on the load calculations (125% of continuous loads plus 100% of noncontinuous loads). The ampacity of the conductors is to be determined from 310.15, which includes 310.15(B)(2)(a). As you have stated: 6 current carrying conductors in one conduit needs to be derated to 80%.

230.42(B) also requires the minimum ampacity for ungrounded conductors to be not less than the rating of the service disconnecting means, which you have given as 400 amps.

Assuming 90 degree insulation, paralled 4/0 copper, or 300 aluminum would be the minimum, as 260 amps x 2 x 80% = 416 for copper, and 255 amps x 2 x 80% = 408 amps for Aluminum.

240.4(B) does not come into play on services.

Thanks Early!

I thought about 600 MCM copper, but it would cost 50% more for single conductors than (2) parallel 4/0.

Dean- I'm not in agreement with your post:

"230.42(B) also requires the minimum ampacity for ungrounded conductors to be not less than the rating of the service disconnecting means, which you have given as 400 amps."

This reference only deals with: "Specific Installations" If a person uses conductors that will carry the load (100% Non continuous and 125% Continuous) and the wire is derated due to raceway fill, he can round up to the next size overcurrent device unless he is over 800a. The "Specific Installations" rule doesn't apply to Redsy"s problem because he is over 100a. and less than 800a.

Thanks Guys!

I'll go with 4/0 to be safe.

I appreciate the insight.

Service wires are only required to be sized to the computed load (230.42) not by the breaker since the service wires are up stream of the main breaker. The service wires are protected by the POCO OCPD at the transfomer. OCPD only protects wires down from the device, not up. Your local AHJ may have other restrictions. What is the computed load?

The calculated load is only about 85 KVA (205 amps @ 120/240 3-phase Delta).
The plans, however were drawn by a PE and showed a 400-amp service with 600 kcmil copper.
I have decide to parallel conductors instead and the Camden, NJ plan reviewer wants new drawings to reflect the new installation.

The local cost for 600 kcmil is about $9.50 / ft.
3/0 is $3.30 /ft. ($6.60 for 2)

At about 100' per leg, the savings is around $1,200.00.

Thoughts?

This is a whole new can of worms. You are working off a PE's drawing, you should bounce it off of him/her first. If you are parallelling a pre-sized wire, you must meet the ampacitiy of the original wire. a 600 kcmils is rated at 420 amps at 75 degree rating. 1/2 of that is 210 amps, so a 4/0 would be the minimum which is rated at 230 amps. With the derating of six conductors, you are at 368 amps or 88.3 kva. To meet 100% capacity of the 600 kcmils, 420 x 1.25 / 2 = 263 amps or 300 kcmils. Now you may be looking at a larger conduit(s) In other words, I suggest you contact the PE first. He stamped the drawings so he/she assumes the liability of the design. The PE may have taken in some consideration for some future expansion or some heavy load that you may not be aware of.

Another issue you can run into is whom is paying you to do the work. You are attempting value engineering and the one holding the money may want a piece of the savings.

I may be making mole hills out of ant hills however, I do not know all the details. These kind of things need to be considered prior to deviating from a stamped drawing.

The issue of parallel came up when the original EC decided to run (2) 2 1/2" conduits instead of a 4".

The city plan reviewer told me to have the PE draw it accordingly.

However, the PoCo requires a minimum 4" for a 3-phase 400-amp service, so I have to remove the original pipes and replace with 4".

The Engineering Firm is from out of state and works for the "Family Dollar" store corp. and will re-draw the service based on whatever is required by the locals.

As far as the load calculation, remember it is 3-phase Delta, so 85 kva is only 205 amps at 120/240.

I missed the 3-phase. My bad.

The correct phrasing is 240/120V for a high (wild) leg delta system per IEEE and ANSI. I know saying "120/240 wild leg" is a hard habit to break (heck I still usually say 110/220V) but this method does reduce confusion.

Basically this standard methodology is:
single phase: list the low (line-neutral) voltage first then the high (line-line) voltage - 120/240, 120/208Y, and 277/480Y
three phase: list the high voltage first, then a wye if it is a wye system or nothing if it is delta, and then the low voltage - 240/120, 208Y/120, and 480Y/277.
Including the number of phases and current carrying wires is optional (the ground wire is always infered).

Thanx JBD,

It is important to use proper terminology to convay info. I can not stress that enough. I work with a bunch of engineers of all disiplines, WEEE! Per this post for example the OP did state that the service was 3 phase and I just missed it. We all throw around improper terms daily and without thinking about it. For example: wire nuts, romex, smurf, 110/220, high leg, wild leg, etc. and for the most part we all understand it or know to ask additional questions on what we do not. Not to be picky

Rojo-sy (Redsy):

To me, the 4/0cu THHN looks good, for Parallel runs in the same Raceway.

That being said, I have a few things to mention:

1: Be sure to discuss the Parallel Service Feeders idea with the Utility Service Planner, which is involved with this Project.
This needs to be verified per their compiance before installed - because even if the Building Department accepts it per the EE's drawings, the Utility may not approve it.

To verify compliance, try:

1. Contact the Service Planner for the district / area of the project.
   If unknown, call the Utility and begin the "Hunt" until you find someone with information, who is familiar with your project.
2. Verify minimum compliance via "ESR" documents (Electrical Service Requirements).
   Most Utilities have their ESR manuals + UGS (Underground Structures) manuals available for download via their websites.
   Typically these texts are saved as .PDFs
   Be double sure and verbally verify what the ESR allows, with a Service Planner - then procede with the installation.
3. Contact the Utility Service Inspector whom will be reviewing the installation and approving it, and eventually submitting release for Meter.

After verification of Parallel Service Feeders is obtained, then contact the EE and have that person revise the Single Line, to reflect the proposed Service Feeders + 4" Duct(s).

Lastly, re-submit the revised Planset to the Plans Examination department (Plan Check).

A Bit Of FYI

Out here - in Southern California, Service Feeders are "NORMALLY" installed by the Utility - and we install the Ducts + Pull Ropes.

With a new Pad Mount Transformer installation, we would install Ducts + Pull Ropes for both the Primary side Feeder, and the Secondary side Feeders - along with the Vault and Service Equipment.


A few Utilities - City of Anaheim being one of them, requires the EC to install Service Feeders (Secondary side only), plus terminate them in the Service Equipment.

All proposed Service Designs are per the governing Utility's ESR / UGS manuals, with verifications from the Service Planner - prior to submitting to the building department's plan check.

Typical Duct sizes are 4" Minimum, with 5" ducts sometimes quoted.
Most designs will be minimum of Two 4" ducts for a 400 amp Service.

A typical Service / Utility design for me involves at least Six (6) 4" PVC Ducts, Concrete-Encased; and One (1) 4" PVC Duct - also Concrete-Encased, for the Primary Feeder.

When doing any Service installs in Anaheim, the use of Aluminum makes things much nicer -as opposed to Copper Feeders.
With 12 Parallel Runs, using 750 AL is SOOOOOOO much easier to feed and manipulate, compared to 500 Copper!!!.

Just goes to show the differences each of us face in our trade, per which Ocean you are closest to!

One last thing:

I "Ass-U-Me" you are planning to derate the size of the Grounded Neutral Conductor for this feeder?
Be sure to verify this is OK with BOTH of the AHJs - the Utility Department + the Building Department.

Ohh, one more "Last Thing":

If the 3 Phase load is "minimal", as compared to the L-N 1 Phase load, and therefore the "High Leg" is also being derated in size, verify this with the AHJs too.

Find out if they (the Utility) wants the "High Leg" to be in Position "C" (ØC) at the Meter, or if they do not care anymore.
I am kind of curious what Utilities still want Hot/Cold Sequencing, or still use single stator watt-hour meters on 240/120V 3Ø 4 Wire Delta Services.

Make sure to place that High Leg in Position "B" on the Load side of the Service disconnect + identify it "Orange" - wherever the Grounded Neutral Conductor is also present.

Good luck and have fun!!!

Scott

sparkyinak,

The utility fuse on the line side of the transformer in no way provides any protection for the service conductors...it doesn't even protect the transformer. Its only purpose is to protect the distribution system. That is cut off the supply to the transformer before it takes out the upstream OCPD on the distribution system.
Service conductors are protected from overload by the service OCPD, but they have no protection for ground faults and short circuits.

You are correct. My bad.

Thanks everyone. Thanks Scott.

BTW,

I spoke with the city inspector and he said that in 30+ years, he had never seen parallel conductors in the same conduit.

As long as they are the same length and any possible derating is addressed, does anyone see a problem with this?

The job was bid with parallel conductors because the original EC installed (2) 2 1/2" PVCs.

The utility requires 4" minimum. So, I am replacing the pipes with a 4", but because 600kcmil would cost $1,200.00 more, I want to keep the parallel 4/0. as long as POCO has no issue.

How about you Hotline? This is PSEG and the city of Camden.

Thanks.

John

Redsy:
First...TALK to PSE&G Wiring Inspector/Service Tech!!! Southern District, Moorestown, NJ 856-778-6852
I do not have any contacts there, I'm 60+ miles North

Do you have the PSE&G Green Book??? You need one for all the specs, & it can be a greif preventer!

Why did the 2x2-1/2 get rejected??
Don't make much sense if parallel conductors are OK with PSE&G??

Your 4" with parallel is NEC compliant, based on the above posts......but I have to add....I have not seen a job like this, nor have I personally installed one like that.

Did you price out 750KCMil AL?

I didn't jump in earlier as I thought it was a closed issue.

Need more? Call me on my cell