Running power to detached garage

[remauto1187]

Ive really got a headache determining all of what I need. So much conflicting info out there.

Detached garage sub panel (100a) will be 150ft from main panel (200a service) fed via a 240vac 100a double pole breaker. According to the charts Ive read I must use 2/0 copper for L1/L2/N to prevent excessive voltage drop. So my questions.

Sizing correct? 2/0?

What size should ground be? #6?

Is sub panel grounded at main panel or seperate ground rod at garage? Ive always been under the impression in my training that only the first disconnect ground bus bar gets grounded to the ground rod (neutral and ground bus bars jumped).

Which conductor type is the most economical since it appears ill be needing a 500ft spool?

 

[wyliesdiesels]

Ive really got a headache determining all of what I need. So much conflicting info out there.

Detached garage sub panel (100a) will be 150ft from main panel (200a service) fed via a 240vac 100a double pole breaker. According to the charts Ive read I must use 2/0 copper for L1/L2/N to prevent excessive voltage drop. So my questions.

Sizing correct? 2/0?

What size should ground be? #6?

Is sub panel grounded at main panel or separate ground rod at garage? Ive always been under the impression in my training that only the first disconnect ground bus bar gets grounded to the ground rod (neutral and ground bus bars jumped).

Which conductor type is the most economical since it appears ill be needing a 500ft spool?

What chart or site is saying 2/0 cu?

That is horribly wrong.

It really boggles my mind how much misinfo there is out there when it comes to the simple task of sizing conductors for voltage drop.

For your scenario all u need is #3 cu or #1 AL for 100a @ 150' to have 3% VD @ full load. Voltage drop just starts coming into play at that distance so its not really a concern.

U need 4 wire which includes an EGC/ground wire which can be #8 cu or #6 al. U will also need ground rods and an isolated neutral bar which may mean purchasing a separate ground bar kit for the subpanel.

 

[lakeroadster]

wyliesdiesels knows his stuff remauto1187. You can trust his counsel on this.

 

[Kaizen]

wyliesdiesels knows his stuff remauto1187. You can trust his counsel on this.

+1

 

[remauto1187]

What chart or site is saying 2/0 cu?

That is horribly wrong.

It really boggles my mind how much misinfo there is out there when it comes to the simple task of sizing conductors for voltage drop.

For your scenario all u need is #3 cu or #1 AL for 100a @ 150' to have 3% VD @ full load. Voltage drop just starts coming into play at that distance so its not really a concern.

U need 4 wire which includes an EGC/ground wire which can be #8 cu or #6 al. U will also need ground rods and an isolated neutral bar which may mean purchasing a separate ground bar kit for the subpanel.

Chart here shows 2/0? http://www.cerrowire.com/voltage-drop-table
Can you reference a different chart?

Why would I need 3 wire with a ground if I need ground rods at the garage? Would not the ground wire run from the sub panel at the garage to the new ground rod? Why is it that I need ground rod at the detached garage instead of running a ground from main panel to the garage ground bus bar? (because of the distance of 150ft between main and sub?

 

[wyliesdiesels]

Chart here shows 2/0? http://www.cerrowire.com/voltage-drop-table
Can you reference a different chart?

Why would I need 3 wire with a ground if I need ground rods at the garage? Would not the ground wire run from the sub panel at the garage to the new ground rod? Why is it that I need ground rod at the detached garage instead of running a ground from main panel to the garage ground bus bar? (because of the distance of 150ft between main and sub?

Aww ok i see whats going on.

That chart is using 120v for the voltage NOT 240v. So that will increase the wire size due to voltage drop.

The size i gave u above will be fine.

U need BOTH the EGC AND the ground rods because they are 2 different animals. It is common for people to confuse the 2 and think they serve the same purpose but they dont.

The EGC is for providing a low impedance path to clear fault current.

The grounding electrodes are for grounding lightning.

Heres a diagram to help visual learners:

 

[pattenp]

You are running a 240V feed, correct? The chart you used is for 120V. Here's a better VD calculator.. http://www.nooutage.com/vdrop.htm

You need the EGC to go from main panel to subpanel for fault current. Rods are for lighting strikes.

Edit: Sorry for the repeat. wylie was posting as I was typing.

 

[Eric29]

Just a comment. That chart is incredibly helpful.

 

[remauto1187]

Outstanding diagram Wylies! I understand what I need now and the why. Appreciate you all taking the time to explain it all even with references. I didnt think about the voltage drop being so less on the 240vac vs 120vac and the chart I had didn't go over 50a for 240vac (which I thought was odd considering most sub panels would be more than 50a). #3 wont hurt near as much as 2/0 when the wallet opens!

 

[pattenp]

For a 150ft run I'd seriously consider using aluminum because of the cost savings.

 

[remauto1187]

Whats the rule on ground rods? When is 2 ground rods required at the garage? 1/2"?

 

[remauto1187]

For a 150ft run I'd seriously consider using aluminum because of the cost savings.

I managed to get TWHN #3 CU for .84 cents per foot per conductor (x3). That wasnt much pain...but the insulation, drywall and insulated garage door bill is going to hurt worse.

 

[wyliesdiesels]

Whats the rule on ground rods? When is 2 ground rods required at the garage? 1/2"?

Need 2 rods unless u can prove u have 25ohms or less of resistance.

I managed to get TWHN #3 CU for .84 cents per foot per conductor (x3). That wasnt much pain...but the insulation, drywall and insulated garage door bill is going to hurt worse.

oouucch

#1 Al wouldve been $189 cheaper

Keep in mind u need 4 wires not 3. The 4th wire, which is the EGC/ground, can be #8 Cu but will need to be green jacketed.

 

[teamextreme]

Whats the rule on ground rods? When is 2 ground rods required at the garage? 1/2"?

No, ground rods are required to be 5/8" minimum. Never understood why they even sell 1/2".