Garage Calculation

Status
Not open for further replies.
B

brother

Senior Member
Location
"I have learned, in whatsoever STATE I am, therewi
I have a buddy thats had built his attached garage to the house, He wants a subpanel in it. Hes only going to have general use receptacles, a few light fixtures, and 1 heater 4000 watts, and 3 garage door openers.

Brushing up on my calcs, for the heater I know its calculated at about 21 amps, (4000/240=16.7 X 1.25) . As for the receptacles, lights I forgot you dont have to do the 180volt ampers, since this is residential.

So I just measure the diminsions of the garage and go from there on the 3 VA, or just do a whole house calc on this? Im rusty on my residential add ons. Thanks for the help.
 
brother said:
I have a buddy thats had built his attached garage to the house, He wants a subpanel in it. Hes only going to have general use receptacles, a few light fixtures, and 1 heater 4000 watts, and 3 garage door openers.

Brushing up on my calcs, for the heater I know its calculated at about 21 amps, (4000/240=16.7 X 1.25) . As for the receptacles, lights I forgot you dont have to do the 180volt ampers, since this is residential.

So I just measure the diminsions of the garage and go from there on the 3 VA, or just do a whole house calc on this? Im rusty on my residential add ons. Thanks for the help.
Click to expand...

Bump to the top. ;)
 
Looks Good!

Make sure thats all there going to do, most of the time you should get them to consider a 100 amp service once they go with a good heater! Only a sixty amp is required! They could always have a planer, the vacuum the other big piece of equipment that just have to have like the frig!, or the freezer for the season :)

Give then as little custom design, circuit the bench top switched, motion, three way back to house...
 
cadpoint said:
Looks Good!

Make sure thats all there going to do, most of the time you should get them to consider a 100 amp service once they go with a good heater! Only a sixty amp is required! They could always have a planer, the vacuum the other big piece of equipment that just have to have like the frig!, or the freezer for the season :)

Give then as little custom design, circuit the bench top switched, motion, three way back to house...
Click to expand...

Looking at the code again, I see I really do not have to calculate the heater (fixed heating equipment) at a 125% for a FEEDER, its only 100%. NEC 220.51. Since these garage door openers are about only 5 amps each, and they have intermitted duty, Table 430.22 E, aparrently I calculate them at 110% instead of 125%.

Looks like a 40 amp breaker/ #8 feeder would be ok for this instance. Basically for the subpanel breakers 1, 2-pole 30amp, 1 -single pole 15 amp for lights, 1 single pole 20 amp for garage openers, 1 single pole 15amp for general receptacles. Its an 8 space subpanel.
Check my math, am I right?? Oh the square footage is about, (I'm guessing haven't measured the garage yet) 30ft by 20ft.

Heater 4000
garage openers 5 x 3=15 x 1.10= 16.5 x 120= 1980
general use lights receptacles 30 x 20=600 x 3= 1800
Total 7780

7780/240= 32.42 result 40 amp breaker #8 wire feeder size
 
CadPoint,

You wrote:
""Give then as little custom design, circuit the bench top switched, motion, three way back to house...""

I do like that "Design my own paycheck" approach!

That is one of the perks of doing renovation on older residences.
I always take a few photos of the 'old wiring' and let the H.O. think about it.
I always offer a little "design" suggestions, looking to the future.
I think I'm doing him a favor, and I stand to gain some time on the job.
:)
 
cadpoint said:
Looks Good!

Make sure thats all there going to do, most of the time you should get them to consider a 100 amp service once they go with a good heater! Only a sixty amp is required! They could always have a planer, the vacuum the other big piece of equipment that just have to have like the frig!, or the freezer for the season :)

Give then as little custom design, circuit the bench top switched, motion, three way back to house...
Click to expand...

Huh? 60 required? Care to elaborate? I'ts an attached garage. I was thinking he could get away with a 30.
 
Here I might as well pull off a Wylie Coyote moment, and get cut off from both sides of the limb, I'm out on, and state that:

I don't think you've made the exception of 220 due to this is a garage and your use of 220.52 is incorrect and should be 424.

And that frankly your calculating a total sum of multiple loads to be for one breaker. OK! So you met 40 Amps thats good. Are your going to put all the other devices including the lights and receptacles on the other one circuit?
Go for it... wait you might get two other circuits out of that, and you've totally loaded their new Service Equipment.

The Sixty Amp is looking a lot better to me than that tight of an install... BTJMO

But I'm no paying for it and I don't have to worry about life in a cartoon, either!
 
cadpoint said:
Here I might as well pull off a Wylie Coyote moment, and get cut off from both sides of the limb, I'm out on, and state that:

I don't think you've made the exception of 220 due to this is a garage and your use of 220.52 is incorrect and should be 424.

And that frankly your calculating a total sum of multiple loads to be for one breaker. OK! So you met 40 Amps thats good. Are your going to put all the other devices including the lights and receptacles on the other one circuit?
Go for it... wait you might get two other circuits out of that, and you've totally loaded their new Service Equipment.

The Sixty Amp is looking a lot better to me than that tight of an install... BTJMO

But I'm no paying for it and I don't have to worry about life in a cartoon, either!
Click to expand...

Ok, after reading your post about 4 times, trying to get the understanding from it. You dont feel I meet the requirement for the exception in 220?? why is that?? This is a feeder. I will agree that he wont have much room to expand unless he wants a bigger feeder. What other lights are there that you talking about ?? he actually has a total of 6 light fixtures at a maxium of 480 watts total of all of them. Thats about 5 amps max on any given day, (thats with a continuous load calc. ) They will have their own breaker/circuit and the general use receptacles will have their own circuit, and the garage door openers will have their own circuit.

Seeing that he will NOT being running the garage openers at the same time all the time, hes looking pretty good. Like I said, hes a penny pincher. so, 'BEEEP BEEEP' (Road Runner says to the coyote)!!
 
Ok, I see where another 60 amp requirement that cadpoint might be talking about. Its in NEC 2008 225.39(D).

But 225 deals with OUTSIDE feeders and branch circuits. This is an attached garage not detached. I wonder why they would require a 60 for a detached structure such as garage to have a 60 amp if had ore than 2 circuits.
 
brother said:
Ok, I see where another 60 amp requirement that cadpoint might be talking about. Its in NEC 2008 225.39(D).

But 225 deals with OUTSIDE feeders and branch circuits. This is an attached garage not detached. I wonder why they would require a 60 for a detached structure such as garage to have a 60 amp if had ore than 2 circuits.
Click to expand...

That is the disconnect rating the load is calculated in 220 the circuit conductors are based on the load served.

I did a shed a couple of weeks ago the feed was protected by a fifty amp breaker the shed has a 100 amp Main breaker panel. if you were to use the six swipe rule you can add the rating of each switch / circuit breaker ..
 
M. D. said:
That is the disconnect rating the load is calculated in 220 the circuit conductors are based on the load served.

I did a shed a couple of weeks ago the feed was protected by a fifty amp breaker the shed has a 100 amp Main breaker panel. if you were to use the six swipe rule you can add the rating of each switch / circuit breaker ..
Click to expand...

So from the fifty amp breaker you ran a #6 uf? or conduit with #8?? to feed the 100 amp main. I was wondering what was the reason the code made the disconnecting means at a 'detached' building had be a minum of 60 amps.
any one have an idea?
 
Does the 3 VA per square foot rule even apply to an attached garage? I thought garages and unfinished basements were exempted from a load calculation value. Or do you have to use a value based on actual installed light fixtures to cover that space?

Even if code doesn't require a load value, I'd always assume a 15A 120V load just to handle whatever ends up going into a general use space. But that's just me and not code.
 
suemarkp said:
Does the 3 VA per square foot rule even apply to an attached garage? I thought garages and unfinished basements were exempted from a load calculation value. Or do you have to use a value based on actual installed light fixtures to cover that space?

Even if code doesn't require a load value, I'd always assume a 15A 120V load just to handle whatever ends up going into a general use space. But that's just me and not code.
Click to expand...

as far as I know, there is nothing in the code that require the 3 VA , so long as not 'adaptable for future use' (whatever that means). I just had to have something to go off of, so I chose to use the 3 va rule, I know that works for a house, so it should be no problem working for a garage, (since its residential). just add the heat and the door openers and your good. :)
 
Seems to me it used to be 1/2 VA per foot at some point in time, but the last time I looked I couldn't find it. Too busy to look again (or to read previous posts in this thread. :D )
 
brother said:
.................
...... I wonder why they would require a 60 for a detached structure such as garage to have a 60 amp if had ore than 2 circuits.
Click to expand...

Aaahh ,. one of the great mysteries of the NEC,.. As George could probably tell you ,.. it ain't for expansion. He tried to have the whole section deleted

Panel Meeting Action: Reject

Panel Statement: The title of the section clearly states the ?Rating of
Disconnect?. Simply stated, this is the minimum ampacity rating of the
disconnecting means regardless of type. The fact that it is service rated does
not establish an ampacity rating. Future expansion has nothing to do with this
requirement.
Number Eligible to Vote: 10
Ballot Results: Affirmative: 10
Click to expand...
 
Status
Not open for further replies.
Top