Electrical Subforum: 8 Guage 240V 30 amp

[Quads]

How far (feet) can I (safely) run 240V through 8/8/8 wire? I've got a pull from the house to a sub panel in the garage and I need to pull 240V out of the sub panel.

In very basic terms, my diagram looks like this:

200AMP Service into house > Main breaker box > which feeds to Sub Panel A on a 100 amp double gang breaker > From sub panel A I have a 50 amp 8/8/8gauge run to Sub panel B in the garage about 50 feet away > from sub-b, I need to pull 240V and run it to an outlet about 50 feet away. I'll need a 30 amp breaker on the 240V line in the garage.

Am I OK on this, or do I need to upgrade the 8 gauge to sub-b out in the garage? Or will the smoke stay in the wires?

Clear as mud?

[Quads]

oh... that's right.... you want pics... hang on.

[Quads]

Main panel coming into the house:
http://www.pcpotato.com/uploader/files/1/electrical-001.jpg

100 amp breaker feeds sub panel "A"
http://www.pcpotato.com/uploader/files/1/electrical-002.jpg

Sub panel "A" has a 40 amp breaker which feeds sub panel "B"
http://www.pcpotato.com/uploader/files/1/electrical-003.jpg

Sub panel "B" is where I need to pull 240V from.
http://www.pcpotato.com/uploader/files/1/electrical-004.jpg

[Wedge Rock]

How far (feet) can I (safely) run 240V through 8/8/8 wire? I've got a pull from the house to a sub panel in the garage and I need to pull 240V out of the sub panel.

I'd say at least 10 feet, give or take 9'...

[Scuba_Dave]

At 50'with #8 pulling the full 50a you would have a voltage drop of 3.8v which is 1.6% - which is fine
If its 40a you will have less voltage drop:
One sentence you say 40a feeding "B" , another you say 50a ?

Running 30a 240v 50' from that you will have 3.6v drop which is 1.5%
Again that is fine, you want to stay under 3%
And some electricians will exceed the 3% figuring you will not pull the fill amps

Question is what else do you have on the 40a (?) panel
If your load is too much you may keep tripping the breaker
How many amps the wire will handle is determined by the wire type
THWN - individual wires, will handle more then a cable
#8 THWN is good for 50a, #8 cable only good for 40a

[Quads]

Meaning there's currently a 40 amp breaker feeding sub panel B (second to the last pic), which I'm going to change that out to 50 amp. Then, in sub panel B (in the garage), put in a 30 amp 240V circuit.

From all the other research I've done I should be OK. But I'm still limited to 50 amps out in the garage which, come man cave time, I'll be cautious to not overload.

[Scuba_Dave]

Problem is you have a cable feeding sub B, and that cable is only rated for 40a
The sheathing on the cable holds in more heat, so it can carry less amps

You would need #6 cable to go to 55a, or TWHN #8 single wires

[Quads]

No. It's 8-3ga stranded copper. Rated for 50 amps.
Basic Residential Electrical Wiring Circuits Rough In and Codes Guide (http://www.nojolt.com/residential_electrical_wiring_rough_in_guide.shtml )

[Scuba_Dave]

Sub panel "B" is where I need to pull 240V from.
http://www.pcpotato.com/uploader/files/1/electrical-004.jpg


This pic shows a cable ?? Is this the correct pic ?
According to the NEC chart 310.13 that cable is only rated for 40a
You have to use the 75c degree rating, not the 60c rating
Doesn't matter that its #8 wire since its encased in the sheathing
For 50a you need conduit with individual wires
Id' post a pic of the NEC chart but photobucket is down

[Quads]

So to get 50 amps to the garage, I need to pull that out, and string qty 3, 8-gauge or 6-gauge through the existing conduit.

Screw that. I'll leave it at 40 amp.
My biggest issue is the 240V circuit that I need to run my welder and compressor. I can make sure those never run at the same time, but 50 amps would be ideal so they can if / when needed.

Along with 20 amps of neon signs, stop lights, TV, stereo, shop lights, etc. etc.

[Scuba_Dave]

Actually these days you need a 4 wire feed
Hot-Hot=Neutral & ground....looks like there is a ground in the cable ?
And then 2 ground rods are required at a detached structure
With a 50a breaker installed with that wire you may never have a problem.....
But it would not be code & there is the chance it could overheat the wires
Not sure how big of a chance

If that cable is in conduit & the conduit isn't very big it would be a bitch to pull out
I ran #6 wire to my pool cabana for a 60a panel, just in case I ever needed more power
The #6 is actually rated for 65a, so I could install a 70a breaker
But 60a is what HD had in stock.....and I don't need much power out there since the hot tub is solar heated

My garage is attached, so I can run off the 200a main or either of the (2) 100a subs I have installed

[Quads]

Yeah, it's kind of weird the way they did it, but it is what it is.
For now, I'll work with it at 40 amps, and plan to dig up the line later and add a larger piece of conduit as I need to plumb it for natural gas as well, which will go in the same trench.

[huge1s]

Yeah, it's kind of weird the way they did it, but it is what it is.
For now, I'll work with it at 40 amps, and plan to dig up the line later and add a larger piece of conduit as I need to plumb it for natural gas as well, which will go in the same trench.

Ditch Digger attachment for the John Deere?

[Scuba_Dave]

At least you have 40a out there
Some people only run a 20a circuit instead of a sub

[Quads]

Ditch Digger attachment for the John Deere?

I wish. There is a backhoe attachment.... but it's not coming out of my budget.