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Old 09-27-2010, 09:29 PM   #1
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Electrical/wiring concerns


I'm trying to update the wiring in my garage so that I can start using it as a shop. I will be running standard shop tools, nothing that requires high voltage YET. but i will, in the future, be looking into a welder and large air compressor.

This is a diagram of what i have coming from the house to the detached garage. Any help and suggestions would be greatly appreciated. Because of the confusion of the wiring I will be calling an electrician, but I want to get some other opinions before speaking with the electrician.

note for diagram:
Wires change, gauges change... It has 10 gauge in the garage box, but the wiring in the house to the outside seems to be 12 gauge or under. Very worried, and it's been like this since we've moved in the house over 10 years ago. (*i didn't label the junction boxes, but I'm sure they are obvious in the diagram.)

Main Questions:
What gauge wire should be running from house to garage?
What double pole amp would be sufficient for what I want to do in the garage?
What size breaker box/sub panel should I have in the garage?
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Last edited by inlovewithohio; 09-27-2010 at 10:22 PM.
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Old 09-28-2010, 09:34 AM   #2
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Electrical/wiring concerns


Is the garage attached or detached.

The breaker must be sized for the smallest wire on the circuit. So the circuit with the #10 and the #12 must have a 20 amp breaker at most.

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Old 09-28-2010, 09:41 AM   #3
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Electrical/wiring concerns


Your plan is non compliant with the NEC. Article 225.30 prohibits more than one feeder or branch circuit to the detached structure. You should install a sub panel.
Search this site for "sub panels" or any related key word like "wire to shed" wire to garage" and you will be reading for weeks on this subject. The search function is at the very top of the page.
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Old 09-28-2010, 04:36 PM   #4
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Electrical/wiring concerns


It's a detached garage. I want to run a welder and larger air compressor at some point so what gauge wire should i upgrade to? and what amp breaker should i upgrade to?

And I have a sub panel in the garage already.
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Old 09-28-2010, 05:10 PM   #5
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pleace show with diagram heating & cooling unit thormostade diagram for house
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Old 09-28-2010, 05:58 PM   #6
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Electrical/wiring concerns


Quote:
Originally Posted by inlovewithohio View Post
It's a detached garage. I want to run a welder and larger air compressor at some point so what gauge wire should i upgrade to? and what amp breaker should i upgrade to?

And I have a sub panel in the garage already.
What size panel in your main house ?
I'd be inclined to run wire for a 100a sub if you have a 200a feed
What is the distance between the house & garage ?
What is the current rating of the sub in the garage ?
Does it have a main breaker ?

I think you can ignore the post before mine......
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Old 09-29-2010, 09:22 AM   #7
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lol. yeah i was planning on not making the effort to add something to the diagram that has no relevance to this post.

What size panel in your main house ?
- it's a 100 amp in the house. or at least that's what the breaker says! We are getting it serviced to 200amp, not sure how soon.

I'd be inclined to run wire for a 100a sub if you have a 200a feed
-I'd like to run 100amp, but i've heard running a continuous amp feed is not recommended - or safe.

What is the distance between the house & garage ?
it's roughly 30 feet, give or take 5 feet. then about another 8-10 from the inside house wall to the house box.

What is the current rating of the sub in the garage ?
The current rating of the garage panel IS 100amp, and it runs off of a double 20amp from the house.

Does it have a main breaker ?
It's an older box, probably 20 years old... i don't know if that matters, but it doesn't have a main breaker.
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Old 09-29-2010, 09:41 AM   #8
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Since you are upgrading to a 200a main then I'd run 100a to the garage
Use #3 TWHN for copper, in grey electrical conduit
2 hots, neutral & a #6 green ground
2 grounding rods required at the garage
Neutrals & grounds must be on seperate ground bars in the panel
And the neutral bar must not be grounded to the case or the ground bar

Not sure what you mean by continous amp feed
Since you will be upgrading to 200a main a 100a sub will be OK
You need a main breaker OR a shut off ahaed of the panel
Unless the panel will only take 6 breakers or less
Since you need to shut off all power in the garage at the panel w/6 throws (breakers) or less

What Mfg is the 20 year old panel ?
Some older panels its harder to find breakers, other older panels have had problems - only some Mfg
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Old 09-29-2010, 10:23 AM   #9
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Let me add a tibbit or two to Scuba Dave's comment.,,

Be aware that all the 120 volt circuits must have RCD { GFCI } protection to keep the cost down you can use the RCD recetpale instead of breakers.

The 240 volt loads do not need RCD at all unless stated by local code or manufacter equiment requirement.{ only in garage area anywhere else the bet is off }

For the conduit size as SD mention conductor size I will advise you to use the minuim of 1 1/4 inch if you going have more than two 90° Ells.

For burial depth most area will required at 18 inches unless stated otherwise with your local codes.

As far for ground rods you will need 16mm˛ { #6 AWG } bare or green conductor and keep the rods minum of 6 feet apart.

Before you sink the conduit or ground rods make sure you call the digger hotline or simauir to it.
It is a free call and they will check for any buried ulities like phone company ,tv cable , power line etc etc but only thing they will not check is your side that it.

Once that clear the digger hotline or simuar then you are good to go.

For contionous amp.
well.,, for your garage useage with proper sized conductor there will be no load anywhere max setting at all so you will have more than enough load to handle it before the breaker can trip.

The contionuis load it mean if the load is on more than 3 hours like electric baseboard heater or water heater {yeah I know I heard ya on this one } or other load have steady load for 3 hour or more.

Hope that clear up the question you ask for.

Merci.
Marc
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Old 09-29-2010, 10:35 AM   #10
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Quote:
Originally Posted by inlovewithohio View Post
lol. yeah i was planning on not making the effort to add something to the diagram that has no relevance to this post.

The diagram is in itself a violation of the NEC code and therefore useless for any purpose. I guess that's what you mean?

What size panel in your main house ?
- it's a 100 amp in the house. or at least that's what the breaker says! We are getting it serviced to 200amp, not sure how soon.

This will be your priority and the detached garage is not what you need to concern yourself with. Not yet is what I mean.

I'd be inclined to run wire for a 100a sub if you have a 200a feed
-I'd like to run 100amp, but i've heard running a continuous amp feed is not recommended - or safe.

Your sources are wrong and what you have heard is wrong. A 100 amp panel in the garage is perfectly fine and indeed encouraged do to the loads (welders ect) you mention. Theoretically you could run a 100 amp feeder to the garage with the existing 100 amp service that now exists. I would upgrade my service first. See the note at the bottom.

What is the distance between the house & garage ?
it's roughly 30 feet, give or take 5 feet. then about another 8-10 from the inside house wall to the house box.

This short distance poses no issue to wire size.

What is the current rating of the sub in the garage ?
The current rating of the garage panel IS 100amp, and it runs off of a double 20amp from the house.

The double pole 20 amp breaker can be replaced with a 100 amp double pole breaker and a 4 wire feeder can be installed. You would need (3) #4 CU wires and (1) #8 CU green wire. H-H-N-G. PVC conduit would be the best choice.

Does it have a main breaker ?
It's an older box, probably 20 years old... i don't know if that matters, but it doesn't have a main breaker.
Then it must go, or a main breaker must be installed. A disconnect would be allowed in lieu of the main breaker. 100 amp main breaker panels cost around $100.00. I would buy a new one, and trash the old one.

Note: Upgrading the main service is a good idea as you will have much more capability, especially if you use a meter main*. If you have a small house and have gas appliances 100 amp may be sufficient.
Get 3 bids from licensed, insured and bonded electricians or electrical contractors and see what they have to say. It will not cost anything for a quote and you may find it is mush easier and safer to have them do it.
Good luck.

* Meter pan and load center in one enclosure.
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Old 09-29-2010, 10:42 AM   #11
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Quote:
Originally Posted by J. V. View Post
The double pole 20 amp breaker can be replaced with a 100 amp double pole breaker and a 4 wire feeder can be installed. You would need (3) #4 CU wires and (1) #8 CU green wire. H-H-N-G. PVC conduit would be the best choice
I thought #4 THWN is only good for 85a ?
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Old 09-29-2010, 11:07 AM   #12
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J.V.

I just don't want this get missunderstood but I know you mention #4 THHN/THWN conductor size.

Normally I will recommed to use the #3 THHN/THWN conductor that is good for 100 amp breaker.

That is for feeder useage not the Service entrance useage that what it will affect it.

Merci.
Marc
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Old 09-29-2010, 02:01 PM   #13
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All of the replies have been a great deal of help! Thank you. Now to get to the specifics...

I'm going to:

1. Change my house service to 200a. (We have an electrician in the family, he will be doing this when he comes in town)

2. Change the existing breaker in the house panel for the garage from a double pole 20a to a 100a breaker, yes?

3. Use (3) #4 Wire For the hot-hot-neutral and (1) #8 for the ground and run in conduit to the garage, yes?

4. Purchase a 100a sub panel for the garage and pitch the old one. (scuba steve, it's pretty old and more than likely use breakers harder to find, good call)

5. Run my lights on a 15a, outlets on a 15a, and when the welder and larger compressor arrive I'll research more.

Tools/other things I will be running regularly: Table Saw, Router, Power Hand Tools (dremel, power drill, sander, etc.), Miter Saw, Drill Press, Heater, Circular Saw, Shop Vac.

All mentioned above will have sufficient load?
Thanks again!

Cheers!
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Old 09-29-2010, 02:17 PM   #14
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Electrical/wiring concerns


Quote:
Originally Posted by inlovewithohio View Post
4. Purchase a 100a sub panel for the garage and pitch the old one. (scuba steve, it's pretty old and more than likely use breakers harder to find, good call)

5. Run my lights on a 15a, outlets on a 15a, and when the welder and larger compressor arrive I'll research more.

Cheers!
4. Get the same manufacturer panel model for both your new main and garage sub. You can use the same breakers in either panel.

5. For lighting calculate the load and wire the outlets with 12 gauge on a 20 amp ckt.
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Old 09-29-2010, 02:31 PM   #15
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Quote:
Originally Posted by inlovewithohio View Post
2. Change the existing breaker in the house panel for the garage from a double pole 20a to a 100a breaker, yes?

3. Use (3) #4 Wire For the hot-hot-neutral and (1) #8 for the ground and run in conduit to the garage, yes?

Cheers!
Just don't change the breaker until after the new wires are run (of course)

#4 wire is only rated for 85a from what I see
You will need #3 wire for 100a & pretty sure a #6 ground


Last edited by Scuba_Dave; 09-29-2010 at 04:40 PM. Reason: #3 wire needed
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