Sounds a whole lot like what I went through a few years ago. I bought a house
which had a large 2-car garage below, and planned to use that full-time as my
shop. All good except there was very little wiring down there. There was a 220A
connection for an electric hot water heater which wasn't used, so I cobbled up a
long extension cord and just used my machines one at a time. My house at that
time had a 200 amp service which was absolutely maxed.

After about a year we did a significant addition which doubled my shop space. I
decided to deal with my power issue properly. I had to start by finding out what
was available from my power company. I discovered that 400A services (what I
wanted) are only granted sparingly. I managed to get them to agree, then I had
to get hold of the local electrical inspector and ask him what I'd have to do.
He said I could put in a 400A service which split to two 200A panels, one to my
existing panel, and I could pull the other 200A down to a subpanel in my shop,
but I would have to have a disconnect outside at the service entrance so the
firemen could shut off the power if they had to. You don't have to do this if
the panel is right inside the back door, but if the panel is down through to the
basement, you gotta have it. The meter box (Square D) cost me about $600
wholesale on my electrician buddy's account, another $200 for the adapter it
needed (it was set up for buried power feed and ours is overhead). Then about
another $2800 in electrical labor and parts and I had a nice Square D 200A panel
in my shop.

In my shop, I have a bunch of machines, some 220 single phase, some 220 3-phase
running through a phase converter, and some 110 single phase. Included are 2
welders (one a Millermatic 250) which should by rights have a 60A 220V plug.
They are wired into a 40A circuit, one or the other (never both) and are never
used at anything like full amperage. My philosophy is this is a one-man shop, so
I can run my 30A three-phase power all over the place and as long as I only turn
on one machine at a time nothing bad happens.

You can't realistically do a major electrical move like this without getting a
permit. Think about what happens if something in your shop starts a fire which
does a lot of damage, and the insurance company were to find out you had major
unpermitted uninspected wiring. They could legally refuse to pay. Unless you're
as crazy as friends of mine who own large houses and drive cars without
insurance, you won't go there. So I suggest you do what I did and start by
calling your local building department and talking to the electrical inspector,
then call your power company. What they say is what you will have to pay for.
It's simple, but not cheap.

GWE

sparty wrote:

I have a 150amp panel in my home, which is decently full, but probably
has space for about another 70amps worth of breakers, but only about 4
spots left.

I HAD planned on running a 70 amp breaker, and then 4 gauge wire to my
garage to a new breaker panel. That will probably max out my panel in
my house. I've done all of the math, and I'm pretty sure it can handle
that.

One of the reasons I am doing this is to run some 230V tools in my
garage. Now recently, I may have come across the opportunity to get a
used cheap Millermatic 250 Welder, which is going to pull 44-45 amps vs
the original 20 amps, I was going to pull with a smaller Welder. This
welder all by itself would require a 60 or 70 amp breaker. So now, I
would like to run 100 amps to my garage instead.

Because of this, I'm thinking I need to increase my House Panel from
150amps to 200amps. What all is involved in this? Does the electrical
company usually do this for free? I know I will need to buy a bigger
main breaker, will there be anymore cost involved?

Is 4 gauge NM-B still ok for 100 amps, or is it pushing it too much?
Pushing that much through it, does that present a fire risk, or is 4
still enough? That kind of distance should be a 2% or less drop, which
is ok, just curious about heat.

This will be through my Basement Ceiling Joists, then up a Garage
finished wall, then through the Garage Attic, then to a Breaker Panel.
Should be about 70-80 feet.

Thanks, James