3-phase, 4-wire WYE system 4

[MayorMagna01]

In a 3-phase, 4-wire wye system, such as 208Y/120V system, the neutral conductor is often ground by the utility on the transformer side. It is also a common practice to size and install a grounded conductor from the service entrance connecting transformer's neutral to Main Panel's Neutral Bus Bar to Grounding Electrode.

However, a grounded conductor (on this specific system) is very useful if I have Line-Neutral Loads (120V loads). But what if ALL of my loads are either 208V 3-phase or 208V 1-phase (Line-Line) distributed across each phase..

1. Do I still need to install a grounded conductor (GC)? If so, why?​

2. For North Americans, if I will not going to install GC on this specific scenario, what are my NEC violations?
​

3. With respect to sizing GC on this specific scenario, is Table 250.102(C)(1) the correct table to use?
​

Your expert opinion will greatly help my young mind to understand better this kind of situations.

Thank you.

 

[che12345]

Dear Mr MayorMagna01 (Electrical)(OP)22 Feb 23 06:10
" #1...... It is also a common practice to size and install a grounded conductor from the service entrance connecting transformer's neutral to Main Panel's Neutral Bus Bar to Grounding Electrode."
General: In the US, comply with the NEC in full. It is the LAW.
No. The utility source Neutral shall be connected to the Neutral bb, the ground shall be connected to the ground bar. Only at the source entry point, there shall be a Bonding conductor connected the Neutral and the grounding bar.

" #2. ... what if ALL of my loads are either 208V 3-phase or 208V 1-phase (Line-Line) distributed across each phase.."
In this case, no Neutral is required. Attention: (a) if the three-phase loads are unbalance, the Neutral IS required.. (b) The ground conductor which grounds all the equipments is always required without failed. (c) do NOT use the Neutral to ground the equipments!.

" #3....1. Do I still need to install a grounded conductor (GC)? If so, why? "
Yes, a grounding conductor grounding all equipments IS required without failed . Grounding is for safety to ensure that the equipment conductive parts are NOT charged up in case of an ground fault.
"...2. For North Americans, if I will not going to install GC on this specific scenario, what are my NEC violations? "
See NEC Art 250 for further information.
" 3. With respect to sizing GC on this specific scenario, is Table 250.102(C)(1) the correct table to use?..."
See NEC for detail.
Che Kuan Yau (Singapore)

 

[jghrist]

The grounded conductor to the transformer neutral is required as a path for ground fault current.

 

[LionelHutz]

I would think a grounding conductor is required while the grounded conductor AKA neutral would not be. The utility grounding might not count as the neutral bonding though.

 

[stevenal]

By my read of the NEC:
A neutral (GC) sized per NEC is required to be run to the service entrance, even if it stops there. We have run into this when 480V delta transformers have been replaced with 277/480 Wye units.
Why not future proof the installation? Someone may wish to add a 120V load someday.

 

[cranky108]

I believe a ground is required, and I would carry a neutral, because if at any time someone wants/needs a single phase to ground, it will be harder to add it later.

Here at least, the customer must install two 8Ft ground rods, with a distance of at least 8Ft between them. This is likely because of the poor soil conductivity, or dry conditions. Do not rely on the utility ground. It is likely a good ground, and is usually connected to other grounds, but the ground proximity is the concern of the NEC, and the utility ground will not provide that in many cases.

 

[TugboatEng]

If you are only powering 208V loads you can use a 4 conductor cable (no neutral). If you are powering any 120V loads you'll need a 5 conductor cable (with neutral).

 

[waross]

In a 3-phase, 4-wire wye system, such as 208Y/120V system, the neutral conductor is often ground by the utility on the transformer side. It is also a common practice to size and install a grounded conductor from the service entrance connecting transformer's neutral to Main Panel's Neutral Bus Bar to Grounding Electrode.

Yes, that is correct.
With an aerial feed, no ground conductor is needed, but the utility crew may refer to the bare neutral as "The ground". NEC defines it as a neutral.
The ground path is through the earth.
You must install grounding electrode(s) and ground the neutral at the service entrance.

Here at least, the customer must install two 8Ft ground rods, with a distance of at least 8Ft between them.

I must digress.
The NEC is NOT the law UNTIL it is ADOPTED by a local jurisdiction, usually a state, and empowered by legislation.
It need not be adopted in whole, and some jurisdictions may amend rules or sections to meet perceived local conditions.
In Canada, I have found that grounding is an issue often subject to local amendments.
For grounding it may be prudent to check local practice.

Next issue: grounding conductors with circuit conductors.
The purpose of this rule is to allow bonding of all associated metal parts.
In the event that an energized conductor contacts exposed metal, the grounding conductor serves to provide a low impedance path to trip the breaker and serves to limit the voltage to ground on said exposed metal part.
Even when there are no exposed conductive parts, you must still run a grounding conductor with the circuit conductors.





--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[wroggent]

With an aerial feed, no ground conductor is needed, but the utility crew may refer to the bare neutral as "The ground". NEC defines it as a neutral.
The ground path is through the earth.

waross, is this a Canadian practice or are you saying you think this is allowed by NEC (or NESC)? I think I recall you saying before that it's a common practice (in Canada) to place a neutral only on the last few spans before a transformer station. As far as I know such practices were prohibited by the NESC in 1968.

I think for a grounded system, this is covered by 250.24(D) in the 2023 NEC.

If the service is grounded, a grounded conductor must be brought to the to the service disconnect. I agree with jghrist, this is necessary for as a path for ground fault current.

 

[stevenal]

The question here is not whether 4 or 5 wires is required. NEC is clear that between the service transformer and the service entrance, only four are needed. The question is how to size the fourth wire. It is sized per 250.24(D) using Table 250.102(C)(1). I see MayorMagna01 is in the Philippines. Is this for an NEC installation and who is the AHJ?

 

[bacon4life]

One addition consideration is that section 404.2(C) requires running a grounded conductor to any switch for controlling lighting loads, even if the lighting loads are connected line-to-line. This rule was based on providing power to occupancy controls. When there is no neutral available, folks frequently connect the power supply for the occupancy control to the bare grounding conductor (Thereby creating a safety hazard and code violation-edit).

Certain kinds of surge protection devices also require a neutral conductor.

 

[waross]

Am I to understand that the NEC now requires 5 wires from an overhead feed from the utility transformer to the service entrance?
A quick Google search tells me that all that is required by the NEC for overhead service from the transformer to the house is 4 conductors, three hots and a neutral.
But, I read it on the internet. Has this changed.
Does the NEC now require quadruplex rather than triplex for overhead single phase?

I think I recall you saying before that it's a common practice (in Canada) to place a neutral only on the last few spans before a transformer station.

That was a special case and was the primary, ahead of the distribution transformer.
For single phase feeds to rural farms and ranches, one phase conductor is run to the location. The transformer neutral is by ground return. One ground electrode at the transformer pole and at least one more ground electrode one span back.
It is too dark just now to take a picture of my service.
This is not related to the secondary conductors, overhead from the transformer to the service entrance.

As far as I know such practices were prohibited by the NESC in 1968.

This is on the utility side of the transformer. As far as I know the NEC does not apply.
Sorry for any confusion.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[wroggent]

Am I to understand that the NEC now requires 5 wires from an overhead feed from the utility transformer to the service entrance?

No, this is not the case. It is not 5 nor 3 but precisely 4.

I too apologize for any confusion caused.

 

[stevenal]

If you create a free account at NFPA.org and agree to their terms and conditions, you may view many of the standards for free, including several recent versions of NFPA 70 (NEC).

When there is no neutral available, folks frequently connect the power supply for the occupancy control to the bare grounding conductor.

in violation.

 

[bacon4life]

Thanks stevenal for pointing out my post may not have been clear enough. Section 404.2(C) was added based on observations of too many folks creating safety hazards. I edited my original post to more clearly indicate that connecting a power supply to a grounding conductor is a violation.

 

[MayorMagna01]

" #2. ... what if ALL of my loads are either 208V 3-phase or 208V 1-phase (Line-Line) distributed across each phase.."
In this case, no Neutral is required. Attention: (a) if the three-phase loads are unbalance, the Neutral IS required..

Did you mean that on a 208/120V 3-phase service that serves only Line-to-Line loads, if I got 100A on L1-L2, 100A on L1-L3, and 100A on L2-L3, I don't need to install grounded conductor on my service entrance down to service equipment neutral bus bar? And if I have 100A, 80A, 100A (meaning I have unbalanced loads connected across phases), I need to install grounded conductor?

I believe a ground is required, and I would carry a neutral, because if at any time someone wants/needs a single phase to ground, it will be harder to add it later.

On this given scenario, there will be no chance that the customer will add, even one, Line-to-Neutral (120V) loads.

You must install grounding electrode(s) and ground the neutral at the service entrance.

So supposed I have 100A connected L1-L2, 80A L1-L3, 100A L2-L3 (meaning I have unbalanced loads connected across phases, i.e. Line-to-Line single phase loads), from my service entrance I need to install 3 ungrounded conductors AND 1 ungrounded conductor? If so, is Table 250.102(C)(1) the correct table to use? [The source of my confusion is that I see this table recommends minimum size for grounded conductor for a system with at least one line-to-neutral load while in my question, I have none of it]

The question is how to size the fourth wire. It is sized per 250.24(D) using Table 250.102(C)(1). I see MayorMagna01 is in the Philippines. Is this for an NEC installation and who is the AHJ?

Yes you are right. That is one of the question. But before that, I am confused if do I still need to install ungrounded conductor to the service entrance if I have no Line-to-Neutral load on my system. [The source of this confusion is that in a 208/120V system, if you have various 120V load, most likely you will have an unbalanced system. This unbalanced current will flow through the ungrounded conductor. But what will be the case for a 208/120V system with unbalanced loads? Where will be the unbalanced currents flow?]

I am from the Philippines. Our Electrical Code was inspired from NEC. Our AHJ here is from an Engineering Office of our LGU.

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To all, thank you for giving some time to share your opinions. We are learning from you.

Thank you.

 

[wroggent]

do I still need to install ungrounded conductor to the service entrance if I have no Line-to-Neutral load on my system.

Assuming you meant to say grounded, yes you need to.

 

[stevenal]

If there are no line-neutral loads, any unbalance in the line to line connected loads shows up in the phases. Per NEC, you still need to run the fourth wire and future proof the installation. As a utility representative, I don't want to meter this like a delta, knowing that the first 120V connected load will not be metered properly. Ask the AHJ if you have doubts.

 

[waross]

Metering often requires a neutral conductor at the service entrance.
Wile it is true that primary metering and some types of secondary metering do not require a neutral, the NEC leaves all options open for the utility,
When there are no line to neutral loads, the code allows a reduced ampacity neutral.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[wcaseyharman]

To reiterate what others have said, the utility conductor is the major ground return path. Often a ground rod or two is the sole grounding method for a customer. The resistance to ground of each ground rod could be high depending on soil conditions. The NEC allows up to 25 ohms for a single ground rod. You would not be able to trip a 15 amp 120V breaker on that kind of ground resistance, so the customers ground is linked to the enormous and very low resistance utility grounding system via the utility neutral. Unlike NEC installations, the utility neutral is grounded everywhere - often on every pole, tied to the substation ground grid and tied to every customers ground rods and water pipes.
As I see it, the purpose of the utility neutral brought into the customers site and connected via the main bonding jumper to the customer ground is to ensure a very low earth-ground resistance so grounds faults will clear and the voltage of the grounding conductor stays low for personnel protection, which is why it’s required regardless if there are any Line to neutral loads.