New Workshop Wiring Question

[BirdHunter]

New Post Truss 30x50
New 100amp panel will be 50 feet from Primary service at the house.
8' grounding rod was driven prior to concrete and tied into rebar.
18" trench has been dug from below the meter to the new shop
Main panel in the house is full and located directly behind the meter inside the garage.
I'm outside city limits but still want to do this the right way.

Here's my plan.

Double lug the primary service on the main panel and route to a disconnect on the outside wall of the house next to the meter.

Run 3 wire #3 direct burial cable from the disconnect, through the trench to the building and up into the new 100amp panel.

Here is my question.
Since the primary coming from the utility has no ground is the 3 wire #3 acting as a primary to the new building? In which case I just ground the new panel to the rod?

Or do I still need to run a ground back through the trench to the main panel ?

 

[wyliesdiesels]

Where are u located? If in the US u need 4-wire feeder to the garage.

Is the garage attached or detached?

A ground rod has a different function than an equipment ground so one doesnt take place of the other.

We need more info. Update your location on your profile...

 

[BirdHunter]

Detached Workshop in West Texas

 

[RickP]

Could you create some room in your main panel by using a couple tandem breakers on lighting circuits? It would be so much easier to add a breaker so this could be a traditional sub panel in the garage. And then you wouldn't need the disconnect on the outside of the house.

 

[BirdHunter]

Unfortunately, no

The main panel in the house is truly maxed out.
House was new construction for us about 8 years ago.
Never would have guessed it was maxed until final walk-through.
By then it was too late.

 

[alfredeneuman]

If the #3 is copper, it's good to go, but requires additionally a #8 copper or a #6 aluminum ground wire.

If it's aluminum, it's only good for 75 Amps. You'd need to use a #1 to be able to use the 100 Amp C/B ....... and you still will need the ground wire

 

[CoopVA]

You can swap out the meter socket to a double lug. Check with your power company and Local Inspectors if it's legal there... It's easier than replacing your main panel with a larger one...


Sent from my iPad using Tapatalk

 

[BirdHunter]

Yes, #3 copper but I have considered 2-2-2-4 aluminum if I need the ground wire.
Where does the ground come back to in the house?

 

[Koobs]

2-2-2-4 al direct burial is correct for the garage feeder. The exterior 100a outdoor disconnect is correct as long as it is clearly marked, and the tap is done in the panel with lugs "listed for the purpose". The #4 ground in the quad-plex needs to be landed in the ground bar in the disconnect. You will also need to pound a ground rod at the garage, and tie it to the ground bar in the panel along with the quad-plex ground. This is the "supplemental" grounding electrode for the detached garage. FYI: I do this for a living.

 

[CoopVA]

2-2-2-4 al direct burial is correct for the garage feeder. The exterior 100a outdoor disconnect is correct as long as it is clearly marked, and the tap is done in the panel with lugs "listed for the purpose". The #4 ground in the quad-plex needs to be landed in the ground bar in the disconnect. You will also need to pound a ground rod at the garage, and tie it to the ground bar in the panel along with the quad-plex ground. This is the "supplemental" grounding electrode for the detached garage. FYI: I do this for a living.

Sounds right to me. Personally, I'd rather tap it at the meter socket, but that's just my personal preference. I see nothing wrong with this as long as the panel can handle the additional lugs and is feed through rated.

I would still consult the Local Inspector and see what they have to say.


Sent from my iPad using Tapatalk

 

[wyliesdiesels]

Lots of confusion here.

Heres the scoop:

Code is 3-wire to first disconnect then 4-wire after that. So if run 3-wire from meter lug to disconnect on house, u will then need 4-wire feeder to go to the garage. I would put the disconnect at the house as u dont want and it isnt legal to have unfused wire going that far.

When the concrete was put in, did the builder do a UFER ground? Its required!

 

[BirdHunter]

2-2-2-4 al direct burial is correct for the garage feeder. The exterior 100a outdoor disconnect is correct as long as it is clearly marked, and the tap is done in the panel with lugs "listed for the purpose". The #4 ground in the quad-plex needs to be landed in the ground bar in the disconnect. You will also need to pound a ground rod at the garage, and tie it to the ground bar in the panel along with the quad-plex ground. This is the "supplemental" grounding electrode for the detached garage. FYI: I do this for a living.

In regards to the grounding.

I have the ground rod driven prior to pouring the slab of the new building. That gets tied to the ground bar in the new panel and runs back through the trench to a ground in the disconnect. Does it end there or does it ground to my main panel in the house too? Or are you saying I need to drive another ground rod at the house, under the disconnect ?

What if I split it at the meter instead of the panel ? Is there a ground in there ?

 

[wyliesdiesels]

2-2-2-4 al direct burial is correct for the garage feeder. The exterior 100a outdoor disconnect is correct as long as it is clearly marked, and the tap is done in the panel with lugs "listed for the purpose". The #4 ground in the quad-plex needs to be landed in the ground bar in the disconnect. You will also need to pound a ground rod at the garage, and tie it to the ground bar in the panel along with the quad-plex ground. This is the "supplemental" grounding electrode for the detached garage. FYI: I do this for a living.

#2 al is only good for 90a in the OPs case!

In regards to the grounding.

I have the ground rod driven prior to pouring the slab of the new building. That gets tied to the ground bar in the new panel and runs back through the trench to a ground in the disconnect. Does it end there or does it ground to my main panel in the house too? Or are you saying I need to drive another ground rod at the house, under the disconnect ?

What if I split it at the meter instead of the panel ? Is there a ground in there ?

If u go to your house panel, then yes u will need 4-wire between disconnect and house panel.

If there is no disconnect at the meter for your house then your house panel should be fed with 3-wire.

If u go to the meter instead, then the EGC from the garage disconnect doesnt need to go to the house panel or the meter UNLESS there is a grounding electrode and its conductor that goes into the meter pan.

The EGC/ground wire would stop at the disconnect as long as there is no breaker at the meter.

Code is 3-wire to first disconnect. This has been since 2008 code cycle and people still havent adjusted to it!

BTW a ground rod or electrode serves a different purpose than a ground wire/EGC...they arent the same thing!

If u could post some pictures it would be easier for us...

 

[Norcal]

2-2-2-4 al direct burial is correct for the garage feeder.

Care to cite the code section allowing you to undersize the conductors?

 

[BirdHunter]

If u go to your house panel, then yes u will need 4-wire between disconnect and house panel.

If there is no disconnect at the meter for your house then your house panel should be fed with 3-wire. This is the case

If u go to the meter instead, then the EGC from the garage disconnect doesnt need to go to the house panel or the meter UNLESS there is a grounding electrode and its conductor that goes into the meter pan. Thus my original plan to use #3 Triplex. I don't understand what purpose the #4 ground in the quadraplex serves in this case

The EGC/ground wire would stop at the disconnect as long as there is no breaker at the meter.

Code is 3-wire to first disconnect. This has been since 2008 code cycle and people still havent adjusted to it! Again, my first thought to double lug the incoming 3-wire feed

BTW a ground rod or electrode serves a different purpose than a ground wire/EGC...they arent the same thing! i think I understand but aren't they all tied together ?

If u could post some pictures it would be easier for us...

walking outside to take pics now

 

[BirdHunter]

At the shop

 

[BirdHunter]

The trench

 

[BirdHunter]

The meter

 

[wyliesdiesels]

Thus my original plan to use #3 Triplex. I don't understand what purpose the #4 ground in the quadraplex serves in this case

I dont think u followed me. U can only use 3-wire to the disconnect at the house. After that u need 4-wire. So the triplex wont work!

The EGC is for providing a low impedance fault path so the breaker can clear ground faults!

Electrodes are grounding lightning, keeping the voltage potential to ground low and for providing a ground reference.

A grounding electrode doesnt and wont provide a low impedance fault path for breakers!

 

[BirdHunter]

The panel

 

[wyliesdiesels]

The meter

Is there a meter tag on the hasp of the meter panel or can u open that? If u can open it, is it just the meter lugs in there and no ground bars?

Where does the grounding electrode at the house or meter terminate/connect at?

Or do u not have a grounding electrode at the house?

 

[CoopVA]

I see were you are going wyliediesel, tap it off the meter socket. That one looks like a double lug meter socket, mount a disconnect next to it and feed your building from that. For a 100 amp feeder to a sub panel, 3-3-3-4 copper SE. That would be your two hots, a neutral and ground.

At the sub panel, you need to take a ground from your ground rod at the new building to the new panel along with the ground from the disconnect.

I would hope he has a ground rod at the meter...


Sent from my iPad using Tapatalk

 

[BirdHunter]

I dont think u followed me. U can only use 3-wire to the disconnect at the house. After that u need 4-wire. So the triplex wont work!

The EGC is for providing a low impedance fault path so the breaker can clear ground faults!

Electrodes are grounding lightning, keeping the voltage potential to ground low and for providing a ground reference.

A grounding electrode doesnt and wont provide a low impedance fault path for breakers!

I obviously don't do this for a living.
So what is the current path when a breaker trips ?

 

[BirdHunter]

Is there a meter tag on the hasp of the meter panel or can u open that? If u can open it, is it just the meter lugs in there and no ground bars?

Where does the grounding electrode at the house or meter terminate/connect at?

Or do u not have a grounding electrode at the house?

Meter is tagged so I can't open it.
I'm assuming the grounding electrode is through the foundation of the house as there is none outside but I can see it attached in the panel.

 

[CoopVA]

Meter is tagged so I can't open it.

They do frown on that...


Sent from my iPad using Tapatalk

 

[wyliesdiesels]

I see were you are going wyliediesel, tap it off the meter socket. That one looks like a double lug meter socket, mount a disconnect next to it and feed your building from that. For a 100 amp feeder to a sub panel, 3-3-3-4 copper SE. That would be your two hots, a neutral and ground.

At the sub panel, you need to take a ground from your ground rod at the new building to the new panel along with the ground from the disconnect.

I would hope he has a ground rod at the meter...


Sent from my iPad using Tapatalk

SE/U or R cant be used underground!

I obviously don't do this for a living.
So what is the current path when a breaker trips ?

When a hot shorts to a metal chassis on say a motor, metal conduit building frame, etc. the fault current flows on the EGC/ground wire!

Meter is tagged so I can't open it.
I'm assuming the grounding electrode is through the foundation of the house as there is none outside but I can see it attached in the panel.

How old is the house? Is the water line metal and if so is it bonded? Should be within first 6' of entering house! Can u take a better picture of your house panel? I could only see where the feeder comes in but the neutral bar was out of view. Take an overall pic and then another zoomed in on the neutral bar.

 

[CoopVA]

You're right... I meant UF...


Sent from my iPad using Tapatalk

 

[BirdHunter]

House is about 9 years old.
The water line is metal and is bonded above the water heaters.

 

[BirdHunter]

SE/U or R cant be used underground!



When a hot shorts to a metal chassis on say a motor, metal conduit building frame, etc. the fault current flows on the EGC/ground wire!

Yes, but what is it grounded to ? The panel ?

 

[BirdHunter]

Neutral bar or ground ?

 

[wyliesdiesels]

Yes, but what is it grounded to ? The panel ?

Neutral and ground are bonded at the main service panel. So in your main disconnect, if u go the double lug route, u would have the EGC and neutral connected to the same bar!

 

[CoopVA]

Yes, but what is it grounded to ? The panel ?

Yes. It's grounded to the panel and to the ground rod...


Sent from my iPad using Tapatalk

 

[wyliesdiesels]

Neutral bar or ground ?

My bad. I wasnt thinking that your house panel IS your main service panel. Out here in California im use to meter/main combos...

So the bar u pictured IS a neutral AND a ground bar. It looks like its insulated from the enclosure. Is there a bonding strip? Odd that theres also a ground bar. Couldve been added to add more room...

Looks like u have double up wires. This is a no no for neutral wires. But u can double up ground wires if the panel is labeled for it. U should separate those that are doubled up.

Where does the larger wire on the righ hand side of the ground bar go?

Hard to tell everything going on in there as the pic isnt too clear or bright....do u have a better pic??

 

[Koobs]

Care to cite the code section allowing you to undersize the conductors?

Sure: 310.15 B (7) (2)

This allows feeders to be sized at 83% of the feeder rating. This was changed in the 2014 code. It was formerly found in table 310.15(B)(7)

Definition of feeder, for those who don't know: circuit conductors Btwn the service equipment, and the final branch circuit over current device.

Service equipment: disconnecting means (house panel)
Final BC over current device (main breaker in detached workshop panel)

 

[BirdHunter]

No idea what the lines on each end are connected to. Everything is behind drywall.

 

[wyliesdiesels]

Sure: 310.15 B (7) (2)

This allows feeders to be sized at 83% of the feeder rating. This was changed in the 2014 code. It was formerly found in table 310.15(B)(7)

Definition of feeder, for those who don't know: circuit conductors Btwn the service equipment, and the final branch circuit over current device.

Service equipment: disconnecting means (house panel)
Final BC over current device (main breaker in detached workshop panel)

Youre misusing that code. Did u read it?

First, its for 3-wire, and the OP needs 4-wire. But thats not the main thing.

If u read it, it says: "These are permitted ratings for Dwelling Unit service and feeder conductors which carry the total load of the dwelling."

A garage is NOT a dwelling!

 

[Koobs]

Explain what a feeder is, diesel dummy? ( maybe you should stick to being a diesel mechanic!!!) lol

 

[Koobs]

If it's three wire, it is still a service entrance conductor. Diesel!

 

[Koobs]

If the workshop (not garage) is on a residentially zoned piece of property, than it falls under dwelling unit premise wiring. Btw

 

[BirdHunter]

So I can use 2-2-2-4 direct burial ?