Running parallel feeders

[burtonboarder84]

Hello,
Does anyone know if you can run parallel feeders through the same conduit?? I can't find anything in the NEC about it. I want to run parallel 400 mcm through schedule 40 pvc, underground. Is this allowed or do I need to run 2 pipes? THanks!

 

[Dennis Alwon]

Yes you can but you must derate according to 310.15(B)(2)(a).

300.3(B)1) Paralleled Installations. Conductors shall be permitted to be run in parallel in accordance with the provisions of 310.4. The requirement to run all circuit conductors within the same raceway, auxiliary gutter, cable tray, trench, cable, or cord shall apply separately to each portion of the paralleled installation, and the equipment grounding conductors shall comply with the provisions of 250.122. Parallel runs in cable tray shall comply with the provisions of 392.8(D).
Exception: Conductors installed in nonmetallic raceways run underground shall be permitted to be arranged as isolated phase installations. The raceways shall be installed in close proximity, and the conductors shall comply with the provisions of 300.20(B).

 

[Dennis Alwon]

Here is another article

310.4 Conductors in Parallel.
(A) General. Aluminum, copper-clad aluminum, or copper conductors of size 1/0 AWG and larger, comprising each phase, polarity, neutral, or grounded circuit conductor shall be permitted to be connected in parallel (electrically joined at both ends).

Exception No. 1: Conductors in sizes smaller than 1/0 AWG shall be permitted to be run in parallel to supply control power to indicating instruments, contactors, relays, solenoids, and similar control devices, or for frequencies of 360 Hz and higher, provided all of the following apply:
(a) They are contained within the same raceway or cable.
(b) The ampacity of each individual conductor is sufficient to carry the entire load current shared by the parallel conductors.
(c) The overcurrent protection is such that the ampacity of each individual conductor will not be exceeded if one or more of the parallel conductors become inadvertently disconnected.
Exception No. 2: Under engineering supervision, grounded neutral conductors in sizes 2 AWG and larger shall be permitted to be run in parallel for existing installations.
FPN to Exception No. 2: Exception No. 2 can be used to alleviate overheating of neutral conductors in existing installations due to high content of triplen harmonic currents.

 

[burtonboarder84]

parallel

parallel

thanks! I had multiple people telling me different things

 

[infinity]

thanks! I had multiple people telling me different things

Will your 400 kcmil's still work with the derating?

 

[burtonboarder84]

400 kcmil

400 kcmil

I am not sure. Need to figure it out. Its a run of about 500 feet so there are voltage drop calculations. I ran 4 inch pipe. Schedule 40 pvc. 400 amp service. This whole system was calculated by an "engineer" at my company for a Photovoltaic system that I believe is wrong. Specifically the nuetral.

He is saying that we do not need to pull a nuetral from the CT cabinet to the subpanel. That we should drive ground rods in and tie the nuetrals from the inverters to ground. Thats rediculous. Don't you have to also run the nuetral to the subpanel, drive ground rods, THEN bond the system? Some inverters don't use a nuetral but these ones do.

 

[Dennis Alwon]

If there are no 120v loads or no loads that require a neutral then you do not need to run a neutral to the sub panel. A neutral needs to be brought into the building but that is as far as the NEC takes us.

Ground rods are only needed if the sub panel is at a detached or separate structure.

 

[Dennis Alwon]

May I assume 400 kcm aluminum? or is it copper? 3 phase or single phase

 

[burtonboarder84]

It is copper and single phase. The inverters are 240v that require a neutral. So I have to run a neutral if the inverters require it right? the voltage from the grid to the inverters must be within 3 or 4 volts to match the output of the inverter. So I think that's why they sized it so large.

If I don't run a neutral or drive ground rods at the subpanel then nothing will be grounded at the subpanel right?? Our engineer told us to run a 4/0 "ground" from the CT cabinet. But its not a ground its actually a nuetral right?

 

[Dennis Alwon]

Well, at 500 feet and a load of 400 amps the VD formula would require a 750KCM. Since you are paralleling 400KCM you would be equivalent to 800KCM so you should be good to go.

Yes, normally your inverter would require a neutral so you must have one.

Is the sub panel at a separate structure? You sub panel would be grounded with an equipment grounding conductor based on 250.122-- a #3 copper. The 4/0 does sound like a grounded conductor.

 

[burtonboarder84]

sub panel

sub panel

yes, it is a seperate structure. I'm confused about the 4/0 that is supposed to be tied to the neutral in the CT cabinet. Shouldn't it be 2 sizes less than the 2 hot legs? (if downsizing the neutral) Then establish a ground at the subpanel with ground rods, water pipe, building steel? Because there is no "ground" established at the CTcabinet yet, right?

 

[Dennis Alwon]

yes, it is a seperate structure. I'm confused about the 4/0 that is supposed to be tied to the neutral in the CT cabinet. Shouldn't it be 2 sizes less than the 2 hot legs? (if downsizing the neutral) Then establish a ground at the subpanel with ground rods, water pipe, building steel? Because there is no "ground" established at the CTcabinet yet, right?

You cannot establish a ground with ground rods. I am not sure what you mean when you say there is no ground established at the CT. What does that mean?

If it is a separate structure then you need to pull 2 hots a grounded (neutral) conductor and a grounding conductor. The neutral does not have to be size 2 sizes less. The neutral, in fact, can be sized as small as the GEC which in this case would be based on 250.66 for whatever the service is of the building.

An example, if you have a 200 amp service and the calculated load for the neutral is say 50 amps then you may size the neutral to whatever the load is except it cannot be smaller than the GEC size-- in this case it would be a #4 copper. If the engineer sized the neutral to 4/0 I will assume that is all you need.

 

[burtonboarder84]

ct cabinet

ct cabinet

The ct cabinet has 2 hots and a neutral from the utility. There's no ground in there right? So from the ct cabinet to the sub panel would be 2 hots and a neutral. Where do I get a ground at the sub panel from? Isn't the ground established inside the builing in the main electrical panel? grounded to water supply pipe.

So I have a 400 amp subpanel, and I can use a 4/0 neutral with parallel 400's for the hot legs? I don't see how that can be legal.

Everything is tied into the CT cabinet. Not the main service panel inside the building.

Sorry if they way I explain it is confusing. I've only been doing PV for about a year. Also our "engineer" has a business degree.

 

[burtonboarder84]

inverters

inverters

Basically, the PV system is putting out roughly 400 amps back into the grid, which in this case is tied into the CT cabinet.

So there is a 400 amp subpanel. Each inverter in terminated on a breaker that backfeeds through the subpanel to the CT cabinet.

 

[Smart $]

Basically, the PV system is putting out roughly 400 amps back into the grid, which in this case is tied into the CT cabinet.

So there is a 400 amp subpanel. Each inverter in terminated on a breaker that backfeeds through the subpanel to the CT cabinet.

What you are calling a 400A subpanel appears to me to be a 400A service panel. So far, you have not mentioned a service diconnect, and I assume the CT cabinet is on the utility side of the main building service disconnect. Is this correct?

Also, if the 4/0 is a grounding conductor, it may be upsized due to the upsizing your ungrounded conductors for voltage drop...

As to no neutral conductor from the PV system, what will happen is the unbalanced neutral current will always travel through the utility transformer, even if powered by the PV system. What I would question is whether the inverter manufacturer recommends, or not, connecting the neutral.

 

[Hameedulla-Ekhlas]

Hello,
Does anyone know if you can run parallel feeders through the same conduit?? I can't find anything in the NEC about it. I want to run parallel 400 mcm through schedule 40 pvc, underground. Is this allowed or do I need to run 2 pipes? THanks!

When installing conductors in parallel in a single raceway, the ampacity adjustment factors in Sec. 310-15(b)(2)(a) apply.

 

[burtonboarder84]

disconnect

disconnect

yes, there is a disconnect between the ct cabinet and the subpanel.

 

[Smart $]

yes, there is a disconnect between the ct cabinet and the subpanel.

Then a GES is connected (bonded) at the [service] disconnect to the grounded conductor (required) and all non-current-carrying parts. A grounding conductor (conductive conduit, wire-type, or optionally both where run in conductive conduit) is required to be run with the circuit conductors (feeder) to the subpanel. With the subpanel being at a separate structure, a GES must be installed there as well, and bonded to the grounding conductor or its terminal but must remain isolated from any grounded conductor.

 

[davedottcom]

Read Article 690

Read Article 690

He is saying that we do not need to pull a nuetral from the CT cabinet to the subpanel. That we should drive ground rods in and tie the nuetrals from the inverters to ground. Thats rediculous. .

Wow! That IS rediculous! & not even close to being NEC compliant.

And are you sizing the panel & feeders according to article 690's 120% rule?

Is this his 1st PV system?