"Ground" wire needed?

[charlie b]

I have struggled with this before, and I am still uncertain. But then, with article 250, I am probably not alone in my confusion.

Utility-owned transformer is outside on a pad. Ten conduits will bring the service conductors into the main switchboard. I?ll bond the N&G in the main switchboard, and run a GEC to the ground rods. That part I get. But do I include any ground-thingy (EGC perhaps? or GEC?) or bond-thingy (supply side equipment bonding jumper, perhaps?) in any or all of the 10 conduits? If so, what is it (are they) called, and how is it (are they) sized?

The design drawings (that I am reviewing) presently show 10 conduits, each with 5 conductors (500 MCM AL - 3000 amp service), with the conductors described as A, B, C, N, G. This caught my eye because whatever else might be true, the G wire need not be 500 MCM. My belief is that the G wire is not needed at all, let alone in each of the 10 conduits.

 

[480sparky]

I've never heard of running a 'ground' wire between the service transformer and the first point of disconnect.

 

[Dennis Alwon]

I don't understand the need for the ground either. The conduits would need to be bonded with an service bonding jumper based on 250.66 based on the size of the conductor in the conduit-- thus 1/0 jumper is needed.

 

[walkerj]

I have seen ground wires run and the utility simply left them un-terminated since they would create a parallel path for neutral current(you know this already).

 

[iwire]

I am in the no EGC needed or wanted camp.

 

[jbt260]

You do not install a ground conductor from the utility transformer to the service entrance equipment. The utility will bond the neutral to ground in their transformer. If you install EGC in conduits between transformer and main switchboard, the ground will basically be in parallel with the neutral conductors and will carry current under normal operation.

 

[charlie b]

Thank you all for alleviating my confusion.

 

[Barndog]

I have struggled with this before, and I am still uncertain. But then, with article 250, I am probably not alone in my confusion.

Utility-owned transformer is outside on a pad. Ten conduits will bring the service conductors into the main switchboard. I?ll bond the N&G in the main switchboard, and run a GEC to the ground rods. That part I get. But do I include any ground-thingy (EGC perhaps? or GEC?) or bond-thingy (supply side equipment bonding jumper, perhaps?) in any or all of the 10 conduits? If so, what is it (are they) called, and how is it (are they) sized?

The design drawings (that I am reviewing) presently show 10 conduits, each with 5 conductors (500 MCM AL - 3000 amp service), with the conductors described as A, B, C, N, G. This caught my eye because whatever else might be true, the G wire need not be 500 MCM. My belief is that the G wire is not needed at all, let alone in each of the 10 conduits.

I am having a little trouble with this. I am thinking along the lines of a 480/208 transformer. You would bond your neutral and ground at the transformer and have your panel wired like a sub panel. Therefore no current on the neutral would would retun on the ground. Also i heard if you Parallel wires in conduit you need a seperate ground in each pipe. But would not have to be the same size as the feeders

 

[OTT2]

I have struggled with this before, and I am still uncertain. But then, with article 250, I am probably not alone in my confusion.

Utility-owned transformer is outside on a pad. Ten conduits will bring the service conductors into the main switchboard. I?ll bond the N&G in the main switchboard, and run a GEC to the ground rods. That part I get. But do I include any ground-thingy (EGC perhaps? or GEC?) or bond-thingy (supply side equipment bonding jumper, perhaps?) in any or all of the 10 conduits? If so, what is it (are they) called, and how is it (are they) sized?

The design drawings (that I am reviewing) presently show 10 conduits, each with 5 conductors (500 MCM AL - 3000 amp service), with the conductors described as A, B, C, N, G. This caught my eye because whatever else might be true, the G wire need not be 500 MCM. My belief is that the G wire is not needed at all, let alone in each of the 10 conduits.

I see this quite often on plans that I have reviewed. I too agree the equipment ground is not required.

 

[charlie b]

I am having a little trouble with this. I am thinking along the lines of a 480/208 transformer.

My question involved a medium voltage primary and a 480/277 secondary, owned by the utility.

You would bond your neutral and ground at the transformer and have your panel wired like a sub panel.

You could do that. Or you could bond the N&G at the location of the first disconnecting means. My example used the later.

Also I heard if you parallel wires in conduit you need a separate ground in each pipe.

That applies only to Equipment Grounding Conductors.

 

[Barndog]

My question involved a medium voltage primary and a 480/277 secondary, owned by the utility.
You could do that. Or you could bond the N&G at the location of the first disconnecting means. My example used the later. That applies only to Equipment Grounding Conductors.

Yes if you were to bond at the panel you would not want to bond at the transformer due to the parallel path on the neutral.

 

[don_resqcapt19]

Yes if you were to bond at the panel you would not want to bond at the transformer due to the parallel path on the neutral.

This is a service and it will be bonded at both locations. Parallel paths are not only permitted on the line side of the service disconnect, in some cases the code rules require them.

 

[tom baker]

Here is how I explain this to my students
On the load side of the service disconnect, we have a white wire and a green wire, at the service they are connected together via the main bonding jumper. On the line side of the service disconnect, we have a white wire with an imaginary green stripe.

 

[volt101]

I'm on the EGC not needed nor required side...

 

[pete m.]

I do not believe that the "EGC" is needed.

I have seen this type of design submitted for review multiple times. It is a bit tricky to flag this as non-conforming due to the fact that there is no prohibition that I am aware of that prohibits this conductor (which I would term as an equipment bonding jumper). The problem comes in, as stated before, when the POCO bonds XO at their transformer and the electrician installs the main bonding jumper at the service disconnecting means putting this conductor in parallel with the neutral conductor.

Pete

 

[steve66]

I also agree: Not needed.

I hope that wasn't intended to be a 200% neutral. IMO, that would probably be a huge waste of copper.

 

[hurk27]

I also agree, see 250.142

 

[walkerj]

Bump

Bump

Today, at the office, I found out that a crew had run a 'green wire' to the utility transformer.

They plan to terminate both on xo in the utility transformer, grounded to the neutral buss in the switchgear, grounding to the ground buss in switchgear.

The equipment bonding jumper will remain in the switchgear.

This will allow current to flow on the 'green wire.'

One solution was to connect the 'green wire' to the case of the transformer

Is this allowed or safe?

 

[don_resqcapt19]

Today, at the office, I found out that a crew had run a 'green wire' to the utility transformer.

They plan to terminate both on xo in the utility transformer, grounded to the neutral buss in the switchgear, grounding to the ground buss in switchgear.

The equipment bonding jumper will remain in the switchgear.

This will allow current to flow on the 'green wire.'

One solution was to connect the 'green wire' to the case of the transformer

Is this allowed or safe?

XO will be connected to the case, so there will still be current on the "green wire".

 

[walkerj]

Thank you, Don.
That is what I said.

I suppose there is no name for this wire?