60 amp subpanel wiring

[TurboTyler]

Hi. New to site, 32 x 26 garage half built. Have a question about the sub panel.

Already have pvc sch 80 conduit buried 4 feet deep from garage to foundation of house. Intending on installing a 60 amp feed to garage. Run from 100 amp panel in house to 60 amp sub panel will be approx. 200 feet.

checked a couple of calculators and some said #6 copper some said #4 copper.
when using these calculators do you put in 60 amps, or what is likely to actually be drawn at once? I doubt I would be drawing more than 30 amps at a time.

 

[sberry]

At 200 ft the acceptable V drop is about half what the wire is good for, in this case right around 30A. This is expensive and limited, a better solution is number 2 alum with a 50 or even 60 on it.

 

[AlwaysFixingSomething]

You should use #4 copper. At 200 feet you will be under the 3% max voltage drop recommended for feeders by the NEC.

Not sure what the guy above me is thinking....

 

[CNGsaves]

Think that Sberry is saying lower cost to use MHF 2-2-2-4 aluminum which is around $1.50 / ft. That mobile home feeder would have no problem with 50A or 60A.

Running copper will be lots 'mo money !

 

[wyliesdiesels]

I got 3.1% VD with #4, still acceptable. #6 would be miserable and yes #2 MHF would be cheaper!

Make sure neutral bar is insulated/isolated from panel enclosure and ground bar. U will need 2 8' ground rods.

 

[AlwaysFixingSomething]

Think that Sberry is saying lower cost to use MHF 2-2-2-4 aluminum which is around $1.50 / ft. That mobile home feeder would have no problem with 50A or 60A.

Running copper will be lots 'mo money !

No he said this "At 200 ft the acceptable V drop is about half what the wire is good for, in this case right around 30A."

makes no sense

 

[sberry]

What I meant was in the case of number 6 it would be good for 30A at that distance. As a rule of thumb and this isn't an exact calc but at 200 ft the acceptable V drop is right around half the rating of the wire. 2 alum is good for 90 or 100 and at 200 ft or so would serve 50A without issues.

 

[AlwaysFixingSomething]

What I meant was in the case of number 6 it would be good for 30A at that distance. As a rule of thumb and this isn't an exact calc but at 200 ft the acceptable V drop is right around half the rating of the wire. 2 alum is good for 90 or 100 and at 200 ft or so would serve 50A without issues.

Ampacity ratings of a wire don't change due to the length of the wire. You can have a wire 1 foot or 1000 feet the ampacity rating is still the same.

The only time the ampacity of a wire changes is when derating is involved.

You are confusing voltage and amperage.

 

[sublimate]

ampacity ratings of a wire don't change due to the length of the wire. You can have a wire 1 foot or 1000 feet the ampacity rating is still the same.

The only time the ampacity of a wire changes is when derating is involved.

You are confusing voltage and amperage.

v = i * r

 

[AlwaysFixingSomething]

Also you don't size a feeder or branch circuit based on the manufacturer listed ampacity. You size the feeder based on many factors. DIYers think sizing a conductor simply by looking at the chart on the wall at home depot.

Derating and temperature ratings of termination points like breakers and lugs are part of what determines the size of a conductor/feeder/circuit.

Most lugs and breakers are listed at max 75 degree temp ratings. Most wire is rated 90 degree but you need to go by the lowest temp rating of termination points throughout the conductors path. So if you have a 90 degree rated wire but a 75 degree rated breaker or lug then you need to size the wire under the 75 degree column in the NEC ampacity table. So a #2 aluminum at max has an allowable ampacity of 90 amps and in lots of cases 75 amps. 75 amps because that is under the 60 degree column in the NEC ampacity table.

 

[woodzie]

I like #2 aluminum if you can fit them in the pipe. probably cheaper than #4 copper and you will have great power for compressor start ups/ welders.

 

[wyliesdiesels]

Also you don't size a feeder or branch circuit based on the manufacturer listed ampacity. You size the feeder based on many factors. DIYers think sizing a conductor simply by looking at the chart on the wall at home depot.

Derating and temperature ratings of termination points like breakers and lugs are part of what determines the size of a conductor/feeder/circuit.

Most lugs and breakers are listed at max 75 degree temp ratings. Most wire is rated 90 degree but you need to go by the lowest temp rating of termination points throughout the conductors path. So if you have a 90 degree rated wire but a 75 degree rated breaker or lug then you need to size the wire under the 75 degree column in the NEC ampacity table. So a #2 aluminum at max has an allowable ampacity of 90 amps and in lots of cases 75 amps. 75 amps because that is under the 60 degree column in the NEC ampacity table.

#2 AL wire can actually be used at 100a if supplying the entire load of a dwelling.

 

[AlwaysFixingSomething]

#2 AL wire can actually be used at 100a if supplying the entire load of a dwelling.

A garage is not a dwelling. You can use #2 sure but with a 90 amp breaker. Again most equipment has 75 degree terminations so you have to go by the 75 degree column in the nec ampacity table.

 

[sberry]

Ampacity ratings of a wire don't change due to the length of the wire. You can have a wire 1 foot or 1000 feet the ampacity rating is still the same.

The only time the ampacity of a wire changes is when derating is involved.

You are confusing voltage and amperage.

I realize this,,, what I am saying is at 200 ft the acceptable voltage drop is somewhere around half the ampacity rating of the wire. You were correct in thinking 6 copper is about 30A at that distance before the V starts heading south.
The 2 alum will perform well to about 50A at that distance, near twice the 6 copper at 1/3 the cost.

 

[TurboTyler]

Wow. Ok that is all a little confusing for a steamfitter, however I think the answer is #4 copper or #2 Aluminum. Also one other question, is using single conductor wires acceptable if run in conduit?

 

[pattenp]

Wow. Ok that is all a little confusing for a steamfitter, however I think the answer is #4 copper or #2 Aluminum. Also one other question, is using single conductor wires acceptable if run in conduit?

Yes you can use single conductors as long as they are rated for wet locations, such as THHN/THWN, or RHH/RHW, or XHHW