Running wire to detached garage

[Nitpicker]

In the process of budgeting. I need to run wire for 240 to a detached garage. The distance is 88 ft outside of the buildings. the detached garage has a sub panel box already installed. I'm in South Western PA frost line is four feet. Called for cost of wire to run a compressor, plasma cutter and welder. Welder is speced at 180 amp, the plasma at 25-45 amp. and the compressor at 32 amp. I was told that what I require is UF 6/3.
I asked about conduit and was told it was necessary -- even though the wire is stated for underground.
Here's what I need for information/confirmation
1. What size conduit?
2. Can I run three additional 12/3 wires for lights and work bench, door openers as well as the 6/3 in the same conduit at the same time?
3. How deep to bury the conduit?
4. What kind of conduit Schedule 40, 80, metal?
5. How much additional slack wire is required for connection directly opposite to the 200amp house box and connection to the sub panel once through the walls?
6. Electric supplier will cut to length at $2.50/ft. That is close with other local suppliers -- but is that reasonable?
7. What am I missing or what else do I need to ask?

 

[bigb56]

7. What am I missing or what else do I need to ask?

What you are missing is that a detached structure is only allowed one circuit, if you need more than that you install a sub panel. You cannot run multiple feeds to a detached structure. Since it sounds like your present sub panel is either not sufficient for the load or is not yet wired, you need to run a 4 wire feed sufficient for the loads you expect, and a grounding electrode system if one does not already exist.

 

[bigb56]

How big is the sub panel that's out there now? A one man shop with everything you described and no heat or AC could get by with 60 amps. If you have to run new might as well go with 100. It will be easier and cheaper too, than running a bunch of circuits from the house.

 

[Nitpicker]

thanks for the prompt reply. There is a 100 amp sub panel mostly empty. Also a ground rod. What I have now is a single 12 gauge wire buried at 10" deep to run four duplex outlets (one each wall) and one outdoor duplex for little stuff like vacuum, drills, etc.
Door openers, ceiling lighting (new, to be purchased) and additional ceiling outlets for reel lights need connecting. When I do this I want to have the duplex outlets split into two separate breakers. The indoor lights once wired will also have a separate breaker.

 

[bigb56]

If I understand correctly you have a 100 amp 240/120 sub panel in the detached garage? There's everything you need right there. Why do you want to run more power from the house?

 

[wyliesdiesels]

Is the current subpanel powered?

If so what size wire is ran to it?

If it is powered the separate #12 wire feeding the garage is a violation and a big no-no.

Forgetting everything you currently have, and IF this is a one man shop, #2 al MHF will get you by @ 90a.

What is the brand and model of the welder? 180a is the output NOT the input.

What is the HP rating on the motor nameplate of the compressor? Motor circuits are wired based on HP rating NOT nameplate FLA.

If its 32a FLA sounds like a 7.5HP motor. If so, does your PoCo have a limit on HP? Some do...

 

[Nitpicker]

All that is in the sub panel box are two GFI 20 amp breakers. I was wrong about a ground rod at the garage. One was installed only outside the house opposite the main panel when I put in a 240 there.. At present I have only one 12 wire from the house to the garage. I need to run 240 from the main panel to the garage, plus additional 12 wires to divide outlets in the garage for lighting, door openers, and additional four or six duplex at work areas.

 

[Crazyjake8493]

I'm with Wylie, #2 MHF will get you 90 amps which should be plenty, and cheaper ($1.74/ft here) than 6/3 UF or #6 THWN in conduit. I would definitely run conduit regardless of whether your wire is direct burial rated, and run extra conduits for the future. I ran two 1.5" and one 2" and I wish I'd run at least one more. A little extra expense now will save you a headache in the future.

No extra circuits to garage, big no-no, just one feed.

Frost line is irrelevant. Rigid conduit can be 6" deep, PVC at 18", direct burial cable at 24".

 

[bigb56]

I guess I thought the #12 was feeding outdoor outlets in a patio wall, now it makes more sense that it is feeding your 100 amp sub panel, and probably protected at 20 amps, is that correct?

 

[Matt Matt]

From what I read, I will try to summarize

Currently you have

12 gauge line feeding a sub panel. You may only have 15 or 20 A 120 V. You may also have 15 or 20 A at 240 V. Either way, it doesn’t matter. It sounds like you want to bring out an additional 60 A 240 V. If it were me, I would just bring out 100 A and put it into the subpanel you presently have. Then disburse properly from that subpanel. I would remove and replace the 12 gauge wire with the appropriate sized wire for 100 A. I would personally run copper and put it in 1 1/2 - 2” conduit buried to your code. I would bring out two hots, neutral and ground.

 

[wyliesdiesels]

Ok so abandoned then#12.

Pull #2 al MHF in 2" conduit. Breaker at 90a in main service panel.

You will need 2 ground rods at the garage.

Also, you need to make sure the neutral bar in the existing subpanel is isolated. This is imperitive.

While you have the trench open, throw a few more 1.5" conduits in for com wiring, alarm, ethernet, etc.

 

[Nitpicker]

Lincoln 180 dual voltage Input Power 115/208/230/1/60
Rated Output 120V:90A/19.5V/20%
208V: 130A/17.6V/30%
230V: 130A/20V/30%
Input Current 20A
Output Range 120V: 30-140 Amps DC
230V: 30-180 Amps DC
Motor
Compressor:
Ingeroll-Rand
230 Volt
SS3L#
1-Phase
Magnetic Starter
Engine
3HP
PumpCFM
10.3
CFM Rated @
90 PSI
Pump Material
Solid Cast Iron
Pump Type
Single-Stage
Max PSI
135 PSI
Oil Sight Glass
Yes
After Cooler
No
Pump Drive
Belt Drive
Oil Type
Oil Lubricated
Oil System
Splash Lubricated
Tank
Tank Size
60 Gallons
Tank Outlet
1/2 Inch
Tank Orientation
Vertical
Certification
UL/CSA/ASME
Weight 300 Pounds

Plasma Cutter
Waiting for deal
Hypertherm® 200-240 V Powermax45® XP Plasma Cutter

Specifications. Input voltages (±10%). 200–240 V, 1-PH, 50–60 Hz. 480 V, 3-PH, 50–60 Hz. Input current @ 5.95 kW. 200/230 V, 1-PH, 34/28 A. 480 V, 3-PH, 9 A. Output current. 20–45 A. Rated output voltage. 132 VDC. Duty cycle @ 104° F. 50% @ 45 A, 200–240 V, 1-PH. 60% @ 41 A, 200–240 V, 1-PH. 100% @ 32 A ...

 

[Nitpicker]

Yes. #12 is from home panel to garage sub panel. Two GFI 20 amp breakers, One works four indoor duplex outlets and the other the single outdoor duplex.

 

[Matt Matt]

Ok so abandoned then#12.

Pull #2 al MHF in 2" conduit. Breaker at 90a in main service panel.

You will need 2 ground rods at the garage.

Also, you need to make sure the neutral bar in the existing subpanel is isolated. This is imperitive.

While you have the trench open, throw a few more 1.5" conduits in for com wiring, alarm, ethernet, etc.

I agree 100%... but I would probably pull #2 copper or 1/0 aluminum and go for the hundred amp breaker. This is really dependent upon the make and model of your main panel and breakers selection. (I personally don’t like 90 amp breaker’s for sourcing reliably). You should way out all your costs. 90–100 A should accomplish all your needs. You cannot really run two hotlines to the same out building unless one is just for lighting on the outside, or plug outlets from the outside. It’s more trouble than it’s worth.

 

[pattenp]

... but I would probably pull #2 copper or 1/0 aluminum and go for the hundred amp breaker.

All that is needed for 100A is #3Cu or #1Al.

 

[wyliesdiesels]

I agree 100%... but I would probably pull #2 copper or 1/0 aluminum and go for the hundred amp breaker. This is really dependent upon the make and model of your main panel and breakers selection. (I personally don’t like 90 amp breaker’s for sourcing reliably). You should way out all your costs. 90–100 A should accomplish all your needs. You cannot really run two hotlines to the same out building unless one is just for lighting on the outside, or plug outlets from the outside. It’s more trouble than it’s worth.

Where did you come up with those gauges?

 

[sberry]

Number 2 alum can be bought at several stores, its so common and its why they invented this. It also fits in 50 and 60 breakers. I have wired a couple dozen of these, never but never had one come back cause of a trip on a 60.

 

[Matt Matt]

Where did you come up with those gauges?

I use a basic chart similar to this.

http://encorewire.com/wp-content/uploads/amp voltage.pdf

Then I tried to Account for over 100 foot run and then stay on the plus side. I believe the op said 88 feet between buildings.

Please enlighten me if I’m using it wrong. I’ve might have spent a few extra dollars in my last few runs then I needed to. (I consider this 100 to 150 foot run) but I passed.

These are only for buried or conduit runs in the home. (Not air)
0-50’ use Gauge specified. 50 to 100 step up one gauge, 100 to 150 step up 2 gauges.

 

[wyliesdiesels]

Lincoln 180 dual voltage Input Power 115/208/230/1/60
Rated Output 120V:90A/19.5V/20%
208V: 130A/17.6V/30%
230V: 130A/20V/30%
Input Current 20A
Output Range 120V: 30-140 Amps DC
230V: 30-180 Amps DC
Motor
Compressor:
Ingeroll-Rand
230 Volt
SS3L#
1-Phase
Magnetic Starter
Engine
3HP
PumpCFM
10.3
CFM Rated @
90 PSI
Pump Material
Solid Cast Iron
Pump Type
Single-Stage
Max PSI
135 PSI
Oil Sight Glass
Yes
After Cooler
No
Pump Drive
Belt Drive
Oil Type
Oil Lubricated
Oil System
Splash Lubricated
Tank
Tank Size
60 Gallons
Tank Outlet
1/2 Inch
Tank Orientation
Vertical
Certification
UL/CSA/ASME
Weight 300 Pounds

Plasma Cutter
Waiting for deal
Hypertherm® 200-240 V Powermax45® XP Plasma Cutter

Specifications. Input voltages (±10%). 200–240 V, 1-PH, 50–60 Hz. 480 V, 3-PH, 50–60 Hz. Input current @ 5.95 kW. 200/230 V, 1-PH, 34/28 A. 480 V, 3-PH, 9 A. Output current. 20–45 A. Rated output voltage. 132 VDC. Duty cycle @ 104° F. 50% @ 45 A, 200–240 V, 1-PH. 60% @ 41 A, 200–240 V, 1-PH. 100% @ 32 A ...

In your OP you said 32 for the compressor. Where did you get that figure?

You stated here you have a 3HP compressor which would be under 17a...

I use a basic chart similar to this.

http://encorewire.com/wp-content/uploads/amp voltage.pdf

Then I tried to Account for over 100 foot run and then stay on the plus side. I believe the op said 88 feet between buildings.

Please enlighten me if I’m using it wrong. I’ve might have spent a few extra dollars in my last few runs then I needed to. (I consider this 100 to 150 foot run) but I passed.

These are only for buried or conduit runs in the home. (Not air)
0-50’ use Gauge specified. 50 to 100 step up one gauge, 100 to 150 step up 2 gauges.

That chart is horribly wrong. Not sure how you even sized a 100a circuit when they dont list gauges over #6 for 240v circuits. Furthermore, it doesnt list aluminum wire in the VD chart.

That chart is made by a wire manu. who wants to sell more wire so of course they will BS you. Regardless, I wouldnt trust a chart where they cant even get the nominal voltage correct.

I do the calcs myself. here it is

2 x I x Z / 1000 x L / 240 = VD


I = amps
Z= impedance found in table 9 of chap 9
L= length

so:

2 x 100 x .23= 46
46 / 1000 = .046
.046 x 100 = 4.6
4.6 / 240 = 1.9%

.23 is for #3 copper

so in this example if you upsized by one size, you wasted about $30.

I can only imagine the waste for larger and longer circuits...

with #3 on 100a loa, one could go about 157' to stay @ 3% VD...

In the example on that chart, #8 is good @ 100' which would result in 6.9% VD @ full load of 50a...they listed #6 for 100'. Totally wrong...

 

[Matt Matt]

So basically you’re stating that at 100a at 100ish foot run, you would still pull a #3 copper? I’m not arguing your expertise, I just think I am suggesting one size bigger. And I’m OK with being wrong here.

But I think my statement is still OK, yes or no? OR, Am I siding onto, “too” much on side of caution IYO???

 

[pattenp]

So basically you’re stating that at 100a at 100ish foot run, you would still pull a #3 copper? I’m not arguing your expertise, I just think I am suggesting one size bigger. And I’m OK with being wrong here.

But I think my statement is still OK, yes or no? OR, Am I siding onto, “too” much on side of caution IYO???

Your suggestion is okay, the wire size you're suggesting is just not really needed. One thing to remember is if you oversize the current carrying conductors for potential voltage drop you also need to increase the ground conductor at least the same percentage in size. Not sure about what the CEC requires, but is required by the NEC.