Sub Pannel Help

[firebirdmess85]

After reading a lot of posts by this group over the years I finally decided to join today. First off I just want to say how helpful this group has been by putting a lot of information in understandable terms.

I'm running a new electrical main at 100 amps to my existing circuit breaker. All the breakers are currently used but some are not utilized correctly like the one light I found on one breaker. I"m still tracing all of that but the electrician suggested installing twin breakers to make room for a garage sub panel I want installed.

In the garage I really just need to relocated the wiring from overhead to the garage to underground but I'm trying to think ahead and plan out how many amps I'll need in the garage. The electrician suggested running a 30 amp 6-circuit panel in the garage based off what I told him. I'm running four fluorescent lights, woodworking tools, radio, car battery charger, etc at the moment but may upgrade my gas compressor to a 60 gallon electric at some point. I don't see myself welding anything large scale but small scale would be a possibility.

Based on all this I think I'd probably only run 4 of the 6 breakers and put a 240v outlet utilizing two breaker spots, and one breaker for lights and one breaker for outlets.

My question is would 30 amps be sufficient for all this to make it possible?

 

[ishiboo]

If it's not a long run, I would suggest running 2-2-2-4 SER which is inexpensive and gives you a lot of capacity for future expansion. The need for a single large compressor, welder, or plasma cutter and you would wish that 30A was at least a 60A.

 

[firebirdmess85]

It's about 30 feet to the garage. I'm not sure what wiring they were planning on using as a baseline to see how much extra 2-2-2-4 would cost but I'm assuming they were going to put 10 or 8 gauge ran to the garage. I originally asked him for a 50 amp but he said 30 should be fine. That's why I'm coming to you guys to confirm.

I forgot to state that I'll be using a heater but that'll be gas and may just use electricity for the fan portion.

 

[kd7gab]

Given how cheap 100 Amp panels can be had for, I'd lean towards that option. If you're hiring the install out, your costs would be far higher than those who can DIY most or all of the work. Home Depot has Eaton 100 Amp main breaker panel kits for dirt cheap: http://www.homedepot.com/p/Eaton-10...ack-Includes-6-Breakers-BR2020B100V/100168474

30 amps would be bare minimum for most lower CFM compressors. If you're wanting to run tools and any sort of dust collection, you'll need more than 30 amps. Do yourself a huge favor and plan for more power use than you expect to need in the next year or two. Table saws, planers, shapers, etc can be large power consumers. Even a decent shop vac can draw 10 amps on its own...

In the small shop I built for my dad, we installed a 100 Amp sub panel, which he'll probably never max out. However, he'll never run out of panel space or capacity in that panel. We also went pretty nuts on outlets throughout the space but he's made many comments about how great it is to not need an extension cord when working in/on his shop...



~Jon

 

[firebirdmess85]

The issue with running 100 amp is that I don't have the room on my main breaker panel to do that. I have a 100 amp box after the main right now. If we go with twin breakers i could free up a few spaces but not enough to run 100 amps to the garage.

 

[buddyboy]

i'm not an electrician

you don't really 'run' amps, you draw amps, but I know what you mean.

you only need two spaces on your existing panel to put a double pole 100 amp breaker

this breaker does 2 things, one it can disconnect power to the subpanel, and two it limits the amount of current flowing to the subpanel to 100 amps which protects the wire from burning up

the only time a 100 amps of current would flow from your main panel to your sub panel is when you actually draw 100 amps by running equipment.

a breaker by itself does not draw any power it's only there to protect the wire, that is why it is so important to have correct size wire attached to breakers

the total of all your breakers in your main panel does not have to be less than or equal to your service size

 

[buddyboy]

also,

you can use a 100 amp panel with a 100 amp breaker as your subpanel in your garage.

the breaker in your main panel is the important one, since that breaker will be protecting the wire running to your subpanel

you can use a 30, 50, 60 or 100 amp breaker in the main panel to feed the sub as long as the wire can support it.

the 100 amp breaker in the sub is used as a disconnect, (it doesn't 'pull' 100 amps)

 

[sberry]

Because this is fairly short and demand is not huge this might be a good place for a number 6 copper cable. I agree 30 is a bit short sighted and doesn't really leave any headroom over an air compressor. With a 60 you could hook a full welder circuit to it if yo needed and modern equipment is even less.
One of the main reasons we all pile on 100A is distance and wire cost. I know people witout any choice in warm climes made 30a work but the cost difference here is only for wire.

 

[sberry]

A cable is easy to install in a full panel and basic to route.

 

[kd7gab]

The issue with running 100 amp is that I don't have the room on my main breaker panel to do that. I have a 100 amp box after the main right now. If we go with twin breakers i could free up a few spaces but not enough to run 100 amps to the garage.

You've already posted the solution to dealing with a full panel. Simply replace four of the existing breakers with a pair of twin breakers. The twin breakers only consume 1 space in the panel, so you'd end up with 2 free spaces. As long as these spaces are next to each other, you can put in a 2-pole (240V) breaker of whatever rating you need. A 100 amp 2-pole is the same size as a 15 amp 2-pole breaker...

~Jon

 

[sberry]

Moving the one wire with a single device on it gains a space. Might even be able to find another situation similar for another one.

 

[firebirdmess85]

You have certainly cleared up a bit for me. The only thing I'm confused on is would running the 2-pole 240v to a a 100 amp box in the garage would allow me to run a 240v compressor and lights tools, etc at the same time or just the compressor?

I'm already the one digging the trenching and putting in the gas line so maybe it wouldn't be bad to just run the electrical and conduit to the new sub panel myself and save the cost. I was quoted $1,025 for the 30-amp 6-circuit panel to be ran to the garage with me doing the digging. So really that's the cost of wiring, conduit, and the panel.

I just wasn't wanting to run the electrical myself because I wasn't sure if that was OK with town code.

 

[buddyboy]

do you already have an overhead line coming from your house to the garage?

how far is your garage from your main panel?

your biggest expense (material wise) will prob be the wire running from the house to the garage.

do you already have a subpanel in the garage?

you'll need to run 4 wires from your main panel to your sub panel.

1 will be a ground
1 will be a neutral
2 will be hot

your sub panel will have a ground bar that you hook the ground from the house to, and also hook your ground rods to.

your sub panel will also have a neutral bar that you hook the neutral wire from the house to, and this neutral bar is not connected to the ground or the panel in anyway

also in the sub panel you'll have to bars (where the breakers go) one bar gets one hot the other bar gets the other hot... each hot wire has 120V... if you hook a single pole breaker up you get 120v, a double pole breaker gets you 240v so yes you can have both 120 and 240 at same time in your garage

I would ask your electrician to put 60 amp breaker in your house, size the wire to the garage accordingly and put 100amp panel in the garage with 2 ground rods 6 feet apart

 

[firebirdmess85]

Yes I already have an overhead line to the garage, their old and two separate wires running to the garage. The garage is about 50 feet after re-measuring. I don't have a subpanel in the garage right now.

 

[wyliesdiesels]

Yes I already have an overhead line to the garage, their old and two separate wires running to the garage. The garage is about 50 feet after re-measuring. I don't have a subpanel in the garage right now.

U would have to abandoned the existing feed.

I would go with #2 AL MHF. Its rated for 90a in this application...

 

[theoldwizard1]

The electrician suggested running a 30 amp 6-circuit panel in the garage based off what I told him. I'm running four fluorescent lights, woodworking tools, radio, car battery charger, etc at the moment but may upgrade my gas compressor to a 60 gallon electric at some point. I don't see myself welding anything large scale but small scale would be a possibility.
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My question is would 30 amps be sufficient for all this to make it possible?

Run wire capable of carrying 60A to futureproof your garage.

 

[sberry]

You have certainly cleared up a bit for me. The only thing I'm confused on is would running the 2-pole 240v to a a 100 amp box in the garage would allow me to run a 240v compressor and lights tools, etc at the same time or just the compressor?

Yes, you can run those at the same time.

 

[sberry]

This was the point of getting away from 30A, can only run one major thing at a time. A comp would eat it up.