Wire for main panel

[Wiebster]

Hello, I’ve read through the sticky’s and I don’t believe this applies, and I’m sorry if I missed it. I’m building a new shop, the power company would only run their power 250’ so the meter is 75’ from my shop. I have the 3” conduit ran from the meter to the outside of the shop. I buried a ground rod in the trench for the power company to ground the meter to. What do i need to complete this run to my shop 200 amp panel? I thought 4/0-4/0-2/0 URD. I have a UFER footing ground in my slab. So I thought the two hots to their lugs, neutral to its lug and then my UFER ground to the ground bar. Does this sound correct? The four wire requirement discussed in the sticky has me second guessing myself. Thanks guys.

 

[PCustoms]

Is there a disconnect at the meter?

 

[Wiebster]

Yes, there is a 200 amp breaker below the meter that serves as the disconnect.

 

[mm08822]

The cb enclosure at the meter is considered a main panel and needs 2 grd rods. Neutral block and ground bar must be bonded. In the main panel these may be one in the same.

From that enclosure, a 4 wire feeder is required to the shop. The neutral bar is unbonded from the grd bar.

The shop will also require 2 grd rods.

Conductor sizing of the feeder will depend upon the computed load. Have you done load calcs for the shop?

 

[Wiebster]

Ok, I was afraid I’d need a four wire conductor. I have not done a load calculation nor am I going to. It’s a one man shop with a welder being my biggest draw tool. I’ll go with 4/0-4/0-4/0-2/0. So just to clarify, I need another ground rod at the meter can, even if I’m not using those circuits? And then another rod over at the shop. If I do that and run yet another ground over from the meter can, that will be three ground conductors. They all go to the same bar or grounded to the shop panel?

 

[mm08822]

A one man shop is highly unlikely to need 200a service. Since it is not a residential service, 4/0-4/0-4/0-2 with not be the correct feeder size. Probaly need 250mcm.

The feeder will be composed of 2 hots, 1 neutral and 1 grd . Not sure what else you are reffering to. Grd rods have nothing to do with running a neutral or ground conductor.

 

[Wiebster]

Ok, that makes no sense to me. If 200amp is already overkill, why go with an additional 25 amp wire carrying capability of the larger 250mcm?

 

[Shiftless]

Yes, there is a 200 amp breaker below the meter that serves as the disconnect.

You could use less expensive and easier to pull wire if you swapped out that 200A breaker for a smaller one. As others have already said, a one man shop is highly unlikely to need anything close to 200 amps. How often would you need to charge 2 teslas while you are welding with a big compressor and the AC on ?

 

[PCustoms]

Ok, that makes no sense to me. If 200amp is already overkill, why go with an additional 25 amp wire carrying capability of the larger 250mcm?

Its because the breaker is 200A...

Can you post a pic of the meter and breaker? At least with the door/cover open, even better if you can show the guys on the breaker side

 

[Wiebster]

Yes, but every 200amp service panel I own is fed with 4/0 wires. So why step up to 250mcm for a <75’ run?

 

[PCustoms]

Yes, but every 200amp service panel I own is fed with 4/0 wires. So why step up to 250mcm for a <75’ run?

Because the NEC says 4/0 can only be 200A if it feeds a dwelling.

But a shop is not a dwelling...

Its somewhat irrelevant, as you can add breakers and feed to shop at any value you want. I would suggest 100a or lower.

Will the shop be subject to electrical permit/inspection?

 

[Wiebster]

You could use less expensive and easier to pull wire if you swapped out that 200A breaker for a smaller one. As others have already said, a one man shop is highly unlikely to need anything close to 200 amps. How often would you need to charge 2 teslas while you are welding with a big compressor and the AC on ?

I could but rather have too much than too little down the road. By the time I buy a 100 amp breaker, the money already spent on 3” conduit, small price difference in smaller wire, etc it probably won’t save me much. They probably said the same thing when they were wiring whole houses with 60amp panels

 

[Norcal]

4/0 AL is rated for 180 amperes, because 180A is not a standard size, if the connected load is calculated at 180A or less, a 200A breaker may be used.

 

[PCustoms]

4/0 AL is rated for 180 amperes, because 180A is not a standard size, if the connected load is calculated at 180A or less, a 200A breaker may be used.

For a shop and not a house?

Id run it personally, but I didn't think that was compliant...

 

[Norcal]

For a shop and not a house?

Id run it personally, but I didn't think that was compliant...

The key thing is the load needs to be 180A or less, then it's fine.

 

[Wiebster]

Well just to be on the safe side of passing an inspection then I would need 3 strands of

250 MCM THHN/THWN-2 Aluminum Cable and a 4 ga ground wire?​

Do I still need the second ground rod at the meter panel six feet away from the first one? And then another rod over at the shop? All connected to the ground bar inside the shop panel? I thought the UFER was the shop ground, why the second ground rod?

 

[PCustoms]

The key thing is the load needs to be 180A or less, then it's fine.

And if inspected, would this require a demonstrated load calc?

Again, I'd run it because I know my shop won't go over 180A and I'm not subject to inspection

 

[mm08822]

I missed the ufer at the shop. That covers the need for otherwise 2 rods at the shop.

 

[mm08822]

Now seeing the meter-main panel that you have, there are 2 choices.
Install a 2pole cb (up to 125a) in the panel or use the feed through lugs.

The cb will limit you to 2/0 conductors w/o having to do needless work around.
The feed through lugs probably go up to 300mcm.

Pick a service size and build to it. Cost out wire and breaker vs just wire.

BTW, URD can not enter the building.

 

[PCustoms]

Well just to be on the safe side of passing an inspection then I would need 3 strands of

250 MCM THHN/THWN-2 Aluminum Cable and a 4 ga ground wire?​

Do I still need the second ground rod at the meter panel six feet away from the first one? And then another rod over at the shop? All connected to the ground bar inside the shop panel? I thought the UFER was the shop ground, why the second ground rod?

You should be able to reduce the neutral.


BTW, I have the same meter/main and ran 4/0 to my house (and attached shop).

 

[Wiebster]

Now seeing the meter-main panel that you have, there are 2 choices.
Install a 2pole cb (up to 125a) in the panel or use the feed through lugs.

The cb will limit you to 2/0 conductors w/o having to do needless work around.
The feed through lugs probably go up to 300mcm.

Pick a service size and build to it. Cost out wire and breaker vs just wire.

BTW, URD can not enter the building.

Oh no, the UFER can’t enter the building? Mine does. Yes, the feed through lugs go to 350mcm.

 

[PCustoms]

URD is a type of wire. Since the insulation is toxic when it burns, it cannot go inside a building.

UFER is a style of ground where the ground electrode is encased in the concrete foundation/slab. There has to be a place that this can be tied to the panel.

 

[mm08822]

Oh no, the UFER can’t enter the building? Mine does. Yes, the feed through lugs go to 350mcm.

Not the ufer, but the urd conductors.

Instead of urd consider MHF.

Also consider conduit underground if soil contains sharp aggregate. If choosing conduit then you could use xhhw conductors.

 

[Wiebster]

Oh yeah, underground residential distribution wire. I thought your spell checker got ufer wrong.

 

[Wiebster]

Not the ufer, but the urd conductors.

Instead of urd consider MHF.

Also consider conduit underground if soil contains sharp aggregate. If choosing conduit then you could use xhhw conductors.

I’ve got 3” conduit ran from meter can to the panel in the shop. I thought I would use THHN 250mcm aluminum. MHF 4/0 is quite a bit cheaper than individual strands but still almost $8 a ft

 

[mm08822]

Xhhw is a better choice. Thhn/thwn is code compliant.

Since conduit is in place, don't bother with bundled conductors (mhf).

 

[mm08822]

I’ve got 3” conduit ran from meter can to the panel in the shop. I thought I would use THHN 250mcm aluminum. MHF 4/0 is quite a bit cheaper than individual strands but still almost $8 a ft

Not sure where you are getting pricing but 250-250-2-4 as individual xhhw AL conductors is about $4/running foot. Check wireandcableyourway.

 

[PCustoms]

As long as you're ok defending 180A load if asked, I think you're ok with this:

 

[Wiebster]

Xhhw is a better choice. Thhn/thwn is code compliant.

Since conduit is in place, don't bother with bundled conductors (mhf).

Yeah, I agree. XHHW would be better yet. Ok, so I think I got it all narrowed down except the second ground rod at the meter. Is that required? If so does that just get grounded to the bar in the meter can. Do I need it even if I’m not using any breakers in that meter can panel? Thx

 

[Wiebster]

As long as you're ok defending 180A load if asked, I think you're ok with this:

Doesn’t the aluminum ground need to be at least 2/0?

 

[PCustoms]

Yeah, I agree. XHHW would be better yet. Ok, so I think I got it all narrowed down except the second ground rod at the meter. Is that required? If so does that just get grounded to the bar in the meter can. Do I need it even if I’m not using any breakers in that meter can panel? Thx

Yes it's required.

Space it at least 6' from the first, then you need to connect the 2nd rod back to the first.

 

[PCustoms]

Doesn’t the aluminum ground need to be at least 2/0?

Not if you're able to use the reduced neutral

 

[Wiebster]

Yes it's required.

Space it at least 6' from the first, then you need to connect the 2nd rod back to the first.

Oh yeah, of course! Forgot how that got connected. Unfortunately I buried that first rod horizontally in the trench. Thanks for reminding me how that works.

 

[wyliesdiesels]

The shop will also require 2 grd rods.

He has a UFER in the slab. Wont need 2 rods at the shop.

 

[wyliesdiesels]

4/0 AL is rated for 180 amperes, because 180A is not a standard size, if the connected load is calculated at 180A or less, a 200A breaker may be used.

Too bad he wont be doing a load calc to know what his load will be

 

[mike93lx]

If you haven't yet, **** a string through the conduit, mark the length and pull it out to measure. No need to order extra wire just to clip it off.

 

[wyliesdiesels]

Well just to be on the safe side of passing an inspection then I would need 3 strands of

250 MCM THHN/THWN-2 Aluminum Cable and a 4 ga ground wire?​

Do I still need the second ground rod at the meter panel six feet away from the first one? And then another rod over at the shop? All connected to the ground bar inside the shop panel? I thought the UFER was the shop ground, why the second ground rod?

You need 2 rods at the meter main.

You DONT need any rods at the shop since you have a UFER already.

 

[wyliesdiesels]

except the second ground rod at the meter. Is that required? If so does that just get grounded to the bar in the meter can. Do I need it even if I’m not using any breakers in that meter can panel? Thx

Yes code requires 2 rods at the meter main or service panel unless you can prove 25ohms or less to ground.

The GEC from these rods goes to your bonded neutral bar.

Yes you need it regardless of number of breakers used.

 

[mm08822]

He has a UFER in the slab. Wont need 2 rods at the shop.

Hopefully he means footing. Slabs can be "insulated" from wet earth.

 

[Wiebster]

If you haven't yet, **** a string through the conduit, mark the length and pull it out to measure. No need to order extra wire just to clip it off.

Yep, did that and I have my pull tape in place