how many amps to make county happy

[777mechanic]

so i have a 200 amp on the house and a 110 feet away is my 1200sqft shop . i have a 3ton a/c unit going in and run a 5hp dust collector with a 5hp planer or a 3hp table saw . i also run a 5hp lathe in vfd and a 2hp mill on a vfd sometimes together . there is aslo 14 more machines ranging from 5hp down to 1/2hp . so when doing load cals how much does the inspector need to know , someone said i need to load cal all machines being turn on at once is this true i'm so confused as to what they look for seems to me that if they want all i'm way over 200amp draw . so help me out on how to do a load calculation for my shop . cant get a electrician to call me back .

 

[dfiler2]

You do not need to add all those machines together, that I'm sure of. I believe you just need to be reasonable and figure out how many amps you might need at any one time. I'm sure one of the knowledgeable, helpful electricians will probably be by shortly.

 

[wyliesdiesels]

Is this a one man shop?

 

[buildyourown]

Is the inspector going to be in the shop when the machines are installed? If this is a new build drop a couple lights and a couple outlets and get it signed off.
I've got a measly 40a feeding my shop and I've never popped the breaker.

 

[sberry]

Number 2 alum to a 100A panel in the garage fed by a breaker from 60 to 90A. You don't add all the machines, you could have 200 of them and run only a couple at a time. My neighbor has a dozen, 2 circuits, 1 used at a time.

 

[ard]

Take the dust collector and two highest loads as a 'highest case' load

Add some lights, heater. THAT should be under 90A.

Do yourself a favor- DO NOT discuss what you are doing in the shop with 'the inspector'. Make your design, draw plans, submit them- build it to the approved plans, inspector signs off. Done. As stated above, get it signed off before you load it with equipment- you do not get some kind of cosmic brownie points for doing it the hard way...

 

[75gmck25]

Good suggestion. Others have found that if you tell or show the inspector everything that is going to be connected, he may decide to go well beyond a normal inspection of the installed wiring. You may find yourself looking for special cutoff switches, UL ratings on old machinery, and all kinds of other details that will complicate your life.

I would even leave the A/C unit completely out of the picture, since some AHJ's have added added requirements for buildings that have conditioned space (have heat/AC). The added requirements are mostly to address a garage that might be converted to living space or an office, but you never know how an inspector will read them.

Just install the main feed, panel, and basic wiring for lights and few receptacles. Then call for inspection.

I used 2-2-2-4 MHF that was rated for burial underground and fire-rated for indoor wiring use. That allowed me to run it underground in conduit and through conduit above ground right up to the panel. I used a 60 amp breaker in the main panel because it was cheaper and easier to find, but could have used a 90 amp breaker.

Bruce

 

[777mechanic]

wyliediesels yes its a one man shop
buildyourown the shop is full of machinery
75gmc25 i want to run 2/0-2/0-2/0 with grd in aluminum wire in conduit .

does anyone have a simple load cal.pdf , the ones on line are so overload with info i don't understand .

 

[ard]

Such an odd response.....People here are trying to help, and you reply as if words cost $100 each.

You can do a load calc with a piece of paper and a pencil.

Why you need a load calc for an inspector is beyond me.

 

[ddawg16]

wyliediesel's question was spot on.

One man shop? You are only going to operate one machine at a time.

I personally don't think the inspector gives a **** as long as you have the proper size wire and circuit breakers

 

[Oldbear]

Our inspectors around here are more concerned that boxes are grounded, the right wires are in the right place in the breaker panel (neutrals connected to neutral bar, etc.) and that the panel is label. No loose or haphazard wiring. No open boxes on final inspection.

I've put a good amount of plugs, including two for my welder. He poked around in a few boxes, looked at my two subpanels (house and shop) and signed off. Total time less that 30 minutes on three visits.

I'm not installing my 4-post lift or forge until the final inspection is done. Everything will be to code (done correctly and by the proper journeyman) but they don't need to know what I do in my garage - and in fact they don't seem to care. They are looking for code violations and shoddy workmanship more than anything.

 

[Falcon67]

Inspectors here are only interested in the code related wiring and service, not the loads. Nobody ask about loads - he just wanted to look at the panel, the feed and bit about the plug runs.

FWIW - I have a 3.5 HP compressor, welder, 3/4HP well pump, big 240V lathe, 240V mill, small lathe, two AC units, 5kW heater and all sorts of misc stuff. Never did a load calc. The run is 2-2-2-4 (90A max) and starts at a 70A breaker. Going into 7th year now and never a trip on the feed.

For fun, at my old 480 sq/ft shop, I did a test - all lights, mill, small lathe, AC, heater, air compressor all running at once. Max measured on the legs at the disconnect on the house was 49A. After that, I never much worried about it.

 

[sberry]

As I have mentioned before, have installed a couple dozen services to small garages with 2 alum from 60 a breakers with the promise that i would come back and install a heavier one should it ever trip. A couple of these have been busy including one of my best Buds who ran a mechanic shop where he had a 5 hp 2 stage, had some greedy lights and even 20A of AC. The AC was rare, I welded from it a few times. 25 years, 2 men working, never a trip. I even moved it to a new service during a remodel. Pulled the breaker from one and moved it to another.