Wire calculation help needed

[wdfifteen]

I have to bury new power supply cables to my shop. The distance is 200ft. The power requirements at a max will be to run some lights and an air compressor (240 volt 100amp at startup 20 amp cont.) What size wire should I budget for? Should I expect to use, Cu or Al? The electrician is coming next week, but I'm trying to do some budgeting this weekend.

[1990C4S]

I think it's 10 gauge, but it might be 8 because of the distance, someone else should confirm, I don't have the 'code' at home.

I would use copper, you will have less trouble getting the right connectors and terminals.

Don't buy it at a big box store, try an electrical supply house.

[slimlynn1]

I think you will need bigger wire than that, more like #1 for 100 amp 240v and a 200 foot run. Here is a calculator for this.
Wire Size Calculator

[Red88Carrera]

The 200 ft is the main problem. From a cost standpoint, I would just install a 100amp sub-panel in the shop. The panels are cheap. You'll then have more than enough to run lights and anything else. Welder?
You can use 2-2-2-4MHF aluminum cable. It is designed as mobile home feeder cable, but can be used in this application. Either direct burial, or in conduit. The 4 wires(2 conductors, 1 neutral, 1 ground) come twisted together. It is relatively cheap at less than $1.50/ft. I installed this in 2" PVC electrical conduit.
The best advice I can give you is to tell the inspector what you want to do, and ask him what he wants to see installed.(Assuming it'll be inspected)
At 200 ft, he may have you upsize the cable.

[wdfifteen]

Originally Posted by Red88Carrera

The 200 ft is the main problem. From a cost standpoint, I would just install a 100amp sub-panel in the shop. The panels are cheap. You'll then have more than enough to run lights and anything else. Welder?
You can use 2-2-2-4MHF aluminum cable. It is designed as mobile home feeder cable, but can be used in this application. Either direct burial, or in conduit. The 4 wires(2 conductors, 1 neutral, 1 ground) come twisted together. It is relatively cheap at less than $1.50/ft. I installed this in 2" PVC electrical conduit.
The best advice I can give you is to tell the inspector what you want to do, and ask him what he wants to see installed.(Assuming it'll be inspected)
At 200 ft, he may have you upsize the cable.

Thanks, this is the information I need. I'll price out the cable and conduit and get a ballpark of what I'm looking at spending.
The deal is, the garage is metered separately and the power company is upping the charge to $29 a month just to have the meter, plus now they want a deposit (after 18 years) - all for $6 or $8 worth of power each month. I want to wire the the garage through my house so I only have one account and one bill. It will save me $390 the first year and $348 every year after that. I'm trying to decide if it's worth doing.

[Red88Carrera]

Definitely worth doing. Just treat it as a sub-panel. Hopefully the inspector will allow the 2-2-2-4 cable. If not, the next size up is about double the price. Still worth doing IMO. Just the additional taxes/fees on the second account should make you want to do it.

[North Coast Cab]

The amperage capacity of AL is much less than CU. If you are installing conduit I would use 1/c 1awg CU THHN. If you are direct buring it I would use 2/0 AL service entrance cable. Think about pulling cable and phone while your're there or at least an extra rope for down the road.
You will be required to have a disconect so as mentioned you are betteroff going with a 100amp sub-panel. 100amp service shoudl be fine.
Now the pther issue is feeding 100amp. Very dependent on your main service, hopefully it is 200amp.

[carambola]

if i'm not mistaken, the detached building has to be grounded there, not bonded to the separate structure. and if you are going to feed off the house the wire needs to be upsized

[wdfifteen]

Originally Posted by carambola

if i'm not mistaken, the detached building has to be grounded there, not bonded to the separate structure. and if you are going to feed off the house the wire needs to be upsized

Which wire needs to be upsized? The one from the transformer to the house, or the proposed one from the house to the garage? I am concerned that if the wire from the transformer to the house was sized for the 200 amp house panel, adding another 100 amps of draw to the garage would overheat it.
A possibility is dropping the service to the garage to as low as 60 amps. It's a long shot that I will ever move my welder or my big air compressor to this shop, so it may never have anything bigger than a 1 hp air compressor and lights in it.

[rick-l]

Originally Posted by slimlynn1

I think you will need bigger wire than that, more like #1 for 100 amp 240v and a 200 foot run. Here is a calculator for this.
Wire Size Calculator

Hmmmm..... type in 120 Volt 20 amps 20 ft and see what it says. (14 when I did it)

[North Coast Cab]

Your house will have a service drop of most likely 100amp or 200amp. Check your main breaker in the main panel. If it is 200amp and assuming you do not run some huge loads in the house all the time you can install a 100amp 2p breaker to feed the shop. If it is only 100amp you should look into upgrading the main service at the same time.
The calculator referenced above factors in the voltage drop for the length of the run.

[slimlynn1]

Originally Posted by rick-l

Hmmmm..... type in 120 Volt 20 amps 20 ft and see what it says. (14 when I did it)

Except he is at 240v 100 amp and 200 ft!

[rick-l]

Originally Posted by slimlynn1

Except he is at 240v 100 amp and 200 ft!

I am thinking that code for that inquiry (120 V 20 amp) would be 12 ga. It must just calculate a wire gauge for an acceptable voltage drop not code requirements.

[Rusty Heap]

Originally Posted by wdfifteen

Thanks, The deal is, the garage is metered separately and the power company is upping the charge to $29 a month just to have the meter, plus now they want a deposit (after 18 years) - all for $6 or $8 worth of power each month. I want to wire the the garage through my house so I only have one account and one bill. It will save me $390 the first year and $348 every year after that. I'm trying to decide if it's worth doing.

You're counterdicting yourself.............if the power company wants to have a seperate meter, then go for it.........put in a whole new 200 amp panel and be done with it with tons of room for expansion.

What size garage? And Unless you have some un-godly huge compressor, (Mine is a 7 horse 80 gallon tank two stage 175SPI) it's only have to have a 50 amp breaker.

Before my big compressor I had 60 amp 240 service, feeding a 30x30 shop, via a 60 amp breaker off the house panel and a ~125 foot run of wire.

But then I added on to that shop with 2100 square feet more, yeah my shop is 3000 square feet. No way I was going to power everything I wanted with researve to spare, so I put in a second meter, second 200 amp 30 circuit panel for the shop addition, and have all the capacity I need plus room to grow.

So once again, what size garage is 200 feet away? how many outlets/lights/welders/compressors/table saws do you want to run, with 25% reserve?

I'm an electrical engineer, and there is no such thing as "too big" of a wire or service. Voltage drop and brown outs is what kills stuff as voltage goes down and amps go up to get the same watts.

for your application, and Alum or Copper, depends on whether you're planning on direct burial or in conduit, there is a difference for heat dissapation. Alum 2/0-2/0-2/0 pre-bundled would be a cheaper choice and the minimum, or copper comes in Triple 6 awg for a 60 amp service for like hot tubs, but at the end of 200 foot, I'd give that a max of a 60 amp sub panel out there.

Go with the full 2nd meter out there run a 200 amp service with a huge 30 circuit panel, and go big with room for growth..........heck the rest is just money. How many compressor motors do you want to go through at $400 each just cuz you're only able to feed it 90-100 volts per leg and running the motor over-amperage verses a solid 120 leg/240 volts total with tons of researve?

You're hiring the electrician, ummmmmmmm this load calculation is what your paying him for? Pull the romex in the shop yourself, put in your own panel and save yourself some money on his labor and put it into your materials.

Buy a NEC (national electrical code book) as they're not that hard to read on what you're doing, or there is on-line help (other than a porsche forum) too.

Electrical Online : Electrical Online Empowering the DIY'er Since 1998


if you want, take a picture and post it of your present home electrical panel, as that gives us an idea of how loaded your present panel is and such.........

[lane912]

this guy doesent phuq around, i like him

Originally Posted by Rusty Heap

You're counterdicting yourself.............if the power company wants to have a seperate meter, then go for it.........put in a whole new 200 amp panel and be done with it with tons of room for expansion.

What size garage? And Unless you have some un-godly huge compressor, (Mine is a 7 horse 80 gallon tank two stage 175SPI) it's only have to have a 50 amp breaker.

Before my big compressor I had 60 amp 240 service, feeding a 30x30 shop, via a 60 amp breaker off the house panel and a ~125 foot run of wire.

But then I added on to that shop with 2100 square feet more, yeah my shop is 3000 square feet. No way I was going to power everything I wanted with researve to spare, so I put in a second meter, second 200 amp 30 circuit panel for the shop addition, and have all the capacity I need plus room to grow.

So once again, what size garage is 200 feet away? how many outlets/lights/welders/compressors/table saws do you want to run, with 25% reserve?

I'm an electrical engineer, and there is no such thing as "too big" of a wire or service. Voltage drop and brown outs is what kills stuff as voltage goes down and amps go up to get the same watts.

for your application, and Alum or Copper, depends on whether you're planning on direct burial or in conduit, there is a difference for heat dissapation. Alum 2/0-2/0-2/0 pre-bundled would be a cheaper choice and the minimum, or copper comes in Triple 6 awg for a 60 amp service for like hot tubs, but at the end of 200 foot, I'd give that a max of a 60 amp sub panel out there.

Go with the full 2nd meter out there run a 200 amp service with a huge 30 circuit panel, and go big with room for growth..........heck the rest is just money. How many compressor motors do you want to go through at $400 each just cuz you're only able to feed it 90-100 volts per leg and running the motor over-amperage verses a solid 120 leg/240 volts total with tons of researve?

You're hiring the electrician, ummmmmmmm this load calculation is what your paying him for? Pull the romex in the shop yourself, put in your own panel and save yourself some money on his labor and put it into your materials.

Buy a NEC (national electrical code book) as they're not that hard to read on what you're doing, or there is on-line help (other than a porsche forum) too.

Electrical Online : Electrical Online Empowering the DIY'er Since 1998


if you want, take a picture and post it of your present home electrical panel, as that gives us an idea of how loaded your present panel is and such.........

[billybek]

I put a 200 amp panel in the garage. Meter is in the alley. House is the sub panel.
Leave room for expansion.
If you use aluminum make sure the panel is tagged to accept it (and the new main breaker). Some are marked for copper only.
There really isn't a problem with aluminum for mains. Just use some NOOXID for the connections and check the lugs for tightness every once and so often.

[dad911]

Originally Posted by slimlynn1

I think you will need bigger wire than that, more like #1 for 100 amp 240v and a 200 foot run. Here is a calculator for this.
Wire Size Calculator

Originally Posted by rick-l

Hmmmm..... type in 120 Volt 20 amps 20 ft and see what it says. (14 when I did it)

This calculator is scary bad. Do 5' and 100 amps... still #14 wire

[Zeke]

Originally Posted by billybek

I put a 200 amp panel in the garage. Meter is in the alley. House is the sub panel.
Leave room for expansion.
If you use aluminum make sure the panel is tagged to accept it (and the new main breaker). Some are marked for copper only.
There really isn't a problem with aluminum for mains. Just use some NOOXID for the connections and check the lugs for tightness every once and so often.

The man breaker should not touch any AL. It's the lugs that touch the AL. Branch circuit breakers will have a wire connected to them.

[wdfifteen]

Originally Posted by Rusty Heap

You're counterdicting yourself.............Blah, blah, blah ...

if you want, take a picture and post it of your present home electrical panel, as that gives us an idea of how loaded your present panel is and such.........

This is all well and good, except I already have a full shop where I do most of my work and the requirements I listed in the OP are the max I anticipate needing in my home shop. Thanks anyway.

[Rusty Heap]

you didn't list much any requirements in your OP.....you asked us to do your budget and design for you...go to your electrician then, go to your county code and kneel and swallow before your inspector, fullfill your mistakes, you didn't list much in your OP...........grins........whiner.

enjoy your 95 VAC line voltage running 12 gauge romex out to the end of the 200 foot run.