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Old 09-17-2009, 01:33 AM   #1
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Wiring In a Subpanel


I have a 200Amp Main Breaker Panel in my home I just purchased. Unfortunately the main panel is almost full of breakers and is in a finished basement. I have talked to several electricians to run 220V service to my garage for my welder and air compressor. This is going to require drilling a hole through the block wall, digging and putting in conduit to run to the garage along the side of the house.

In my last home I selected 30Amp breakers for the Welder/ Air Compressor on their specs and wired in one circuit for each.

After talking to electricians and deciding I don't have enough money to pay them, this is the plan: Use Plastic PVC conduit underground and above ground to my attached garage (Do I need to bury the conduit below the frost line?) (25ft between main panel and subpanel). 100 Amp Breaker in the Main panel supplying the Subpanel. 4-Gauge Wire between the sub panel and main panel. This sub panel is a 100AMP unit (with 8 spaces). Installing two 30 AMP breakers for the Air Compressor and Welder on their own circuits. Anything seem incorrect?

The reason I purchased a sub panel with 8 spaces was to allow for the addition of a Hot Tub Breaker and Electrical for a Pool. The chances of me using the hot tub while welding or using the air compressor is almost none.

At some point in my dream world a shop will be built and the compressor and welder will leave the house garage. Then I am sure the pool and hot tub will be fine.

There is a lot of questions and information in this request.

Thanks for your time.

Ben

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Old 09-17-2009, 06:51 AM   #2
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Wiring In a Subpanel


Burying your conduit below the freeze line is immaterial; I believe the code calls for a depth of 18 inches.

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Old 09-17-2009, 08:48 AM   #3
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Wiring In a Subpanel


Just something to think about. Are the welder and compressor 240 volt appliances? If so then you need double wide double breakers for them and you will have commandeered four of the eight slots in your subpanel.

You may need to do a full electrical load calculation for the house, if not now, perhaps when you put in the hot tub. Just guessing about this eventuality since your main panel is filled. A load calculation can point to the need to upgrade the meter and service in order to stay in compliance with code.

If the compressor and welder are cord and plug appliances, you may forestall the need for a new main service by putting in just one "general tool 30 amp" receptacle. Note that a hard wired compressor will cycle on and off, possibly while you are welding, unless you pro-actively turned off its power switch.
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Last edited by AllanJ; 09-17-2009 at 08:53 AM.
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Old 09-17-2009, 09:08 AM   #4
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Wiring In a Subpanel


Quote:
Originally Posted by AllanJ View Post
Just something to think about. Are the welder and compressor 240 volt appliances? If so then you need double wide double breakers for them and you will have commandeered four of the eight slots in your subpanel.

You may need to do a full electrical load calculation for the house, if not now, perhaps when you put in the hot tub.

Just guessing about this eventuality since your main panel is filled. A load calculation can point to the need to upgrade the meter and service in order to stay in compliance with code.

If the compressor and welder are cord and plug appliances, you may forestall the need for a new main service by putting in just one "general tool 30 amp" receptacle. Note that a hard wired compressor will cycle on and off, possibly while you are welding, unless you pro-actively turned off its power switch.
A: Both the Welder and Compressor are 240V. I have 30A Double wide breakers for each.

A: I will hold off on the hot tub for now and just plan on the welder/compressor.

A: How can you do a load calculation?

A: I plan on running both the welder and compressor at the same time. Don't quite understand everything pointed out in this sentence "you may forestall the need for a new main service by putting in just one "general tool 30 amp" receptacle."
Can you explain on this last point?, thank you.
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Old 09-18-2009, 12:39 PM   #5
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Wiring In a Subpanel


Quote:
Originally Posted by benjmatt View Post
I have a 200Amp Main Breaker Panel in my home I just purchased. Unfortunately the main panel is almost full of breakers and is in a finished basement. I have talked to several electricians to run 220V service to my garage for my welder and air compressor. This is going to require drilling a hole through the block wall, digging and putting in conduit to run to the garage along the side of the house.

Since the garage is attached, can you go overhead instead of penetrating a wall and having to trench? Take a look.

In my last home I selected 30Amp breakers for the Welder/ Air Compressor on their specs and wired in one circuit for each.

If they worked in your last home they will work in your new home.

After talking to electricians and deciding I don't have enough money to pay them, this is the plan: Use Plastic PVC conduit underground and above ground to my attached garage (Do I need to bury the conduit below the frost line?) (25ft between main panel and subpanel). 100 Amp Breaker in the Main panel supplying the Subpanel. 4-Gauge Wire between the sub panel and main panel. This sub panel is a 100AMP unit (with 8 spaces). Installing two 30 AMP breakers for the Air Compressor and Welder on their own circuits. Anything seem incorrect?

You need #3 wire for a 100 amp feeder, along with a #8 ground. 4 wires total, H-H-N-G. Since you already have four slots dedicated to the welder and compressor, that only leaves you four more. I would use a sub panel with more spaces. See what happened in your main panel?

The reason I purchased a sub panel with 8 spaces was to allow for the addition of a Hot Tub Breaker and Electrical for a Pool. The chances of me using the hot tub while welding or using the air compressor is almost none.

Once again I would get a panel with more spaces. IMO.

At some point in my dream world a shop will be built and the compressor and welder will leave the house garage. Then I am sure the pool and hot tub will be fine.
There is a lot of questions and information in this request.

Thanks for your time.

Ben
Sounds like you have a handle on the job. Look at the top of this page and see "Stubbies" diagrams. There, look for an attached structure sub panel. There will be a drawing you can look over and even use during installation. Also, if you use the search function on this forum and search "sub panels" you can read literally for days on this subject.

Last edited by J. V.; 09-18-2009 at 12:41 PM.
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Old 09-18-2009, 09:10 PM   #6
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Wiring In a Subpanel


Since you expect to be able to use the welder and compressor at the same time, my idea of one general purpose tool outlet (to be shared) is not applicable. But you might install a general purpose 240 volt outlet anyway, for other tools.

A load calculation is a manual mathematical process that estimates the power requirements of a home and is described in the National Electric Code book. It includes such things as three watts for general lighting and small appliances, per square foot of living space, name plate watts for appliances such as air conditioners that run for long periods (continuous loads) and name plate watts multiplied by various fractions for appliances such as clothes dryers that might only be in use for an hour or maybe less at a time (intermittent loads). When you get a permit and do an electrical project you may be required to perform an up to date load calculation to show that your main panel can handle the final number of watts you computed.

With both the compressor and welder hard-wired in, your load calculation will have an entry for each of them.
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Last edited by AllanJ; 09-18-2009 at 09:22 PM.
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Old 09-18-2009, 09:15 PM   #7
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Wiring In a Subpanel


Quote:
Originally Posted by benjmatt View Post
The chances of me using the hot tub while welding or using the air compressor is almost none.

To the above I saw why not, you can sit in the hot tub relax have a cold one and do some welding.
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Old 09-18-2009, 09:21 PM   #8
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Wiring In a Subpanel


My hot tub (pumps) kick on every 12 hours to circulate the water
The heat also kicks on & off as needed
So if those 2 events coincide they pull quite a bit of power
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Old 09-23-2009, 05:21 PM   #9
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Wiring In a Subpanel


Thanks for your input. This is mostly complete now. I used #4 wire on the two hots and #6 for the neutral and ground. Do I need a (5th wire) ground wire off the subpanel like the main panel has that goes to a rod in the ground?

The toughest part was digging the hole along my house and drilling through the block wall.
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Old 09-24-2009, 01:54 PM   #10
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Wiring In a Subpanel


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Originally Posted by benjmatt View Post
Thanks for your input. This is mostly complete now. I used #4 wire on the two hots and #6 for the neutral and ground. Do I need a (5th wire) ground wire off the subpanel like the main panel has that goes to a rod in the ground?

The toughest part was digging the hole along my house and drilling through the block wall.
You were not paying attention. #4 wire is too small for a 100 amp sub panel. You needed (3) #3 Cu for the 2 hots and neutral and a (1) #8 for the ground. Why did you derate the neutral? It's a current carrying conductor. You will need to pull out the #6 neutral and pull in a #4. Then use a 90 amp breaker instead of a 100 amp for the feeder.

Sub panels in attached structures require no ground rod, so no grounding electrode conductor is required.

Note: Article 310.15 allows a #4 wire for a 100 amp three wire service. Is this why you used #4? If you did, it is wrong. This article is only for 3 wire services, not sub panels.

Ps......Derating neutrals are allowed in some cases. I do not think it is allowed in this case. I will check.

Last edited by J. V.; 09-24-2009 at 01:56 PM.
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Old 09-24-2009, 04:41 PM   #11
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Originally Posted by J. V. View Post
You were not paying attention. #4 wire is too small for a 100 amp sub panel. You needed (3) #3 Cu for the 2 hots and neutral and a (1) #8 for the ground. Why did you derate the neutral? It's a current carrying conductor. You will need to pull out the #6 neutral and pull in a #4. Then use a 90 amp breaker instead of a 100 amp for the feeder.

A: I didn't realize the Neutral was a current carrying conductor, just thought the two hots were supplying power

Sub panels in attached structures require no ground rod, so no grounding electrode conductor is required.

Note: Article 310.15 allows a #4 wire for a 100 amp three wire service. Is this why you used #4? If you did, it is wrong. This article is only for 3 wire services, not sub panels.

A: Didn't read Article 310.15, I figured incorrectly.


Ps......Derating neutrals are allowed in some cases. I do not think it is allowed in this case. I will check.
Reply: Can you please check on this for me?


I will just go down to a 90 AMP feeder, #2 wire was just too big to feed through the conduit. There are too many bends. I didn't want to fight it the whole way.

I can add a 3rd Neutral at #4 instead of the #6. I didn't realize I needed #4 for the Neutral as well. Thank you for pointing that out!

Now when I wire out to my welder/ compressor outlets (2 30AMP circuits) I was planning on running 2 #6 wires for the hots and and 2 #8 for the Ground and Neutral. Does the Neutral need to be #6 as well on these?

I don't have this all hooked up yet, the wires are just hanging loose at the main panel end (away from the breakers of the main panel of course. Don't want them to touch something and ground out) The Subpanel is mounted in the garage and I have secured down the wires on that end. That is as far as I have gotten. Had planned to finishing this up this weekend.


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Old 09-24-2009, 05:36 PM   #12
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Wiring In a Subpanel


Your 30 amp circuits would only need to be #10.

If they are straight 240 you would not need a neutral.
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Old 09-25-2009, 01:21 PM   #13
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Wiring In a Subpanel


Quote:
Originally Posted by benjmatt View Post
Reply: Can you please check on this for me?

This will be a call your inspector will have to make. I would just pull out the #6 and pull in a #4.


I will just go down to a 90 AMP feeder, #2 wire was just too big to feed through the conduit. There are too many bends. I didn't want to fight it the whole way.

Yes, You use a 90 amp breaker in the main panel instead of a 100 amp.
If you had to fight it, you were doing something wrong. What size conduit did you use and how many bends did you make? What kind of wire did you use?

I can add a 3rd Neutral at #4 instead of the #6. I didn't realize I needed #4 for the Neutral as well. Thank you for pointing that out!

Your inspector can answer the question on using a smaller wire for the neutral. If he passes the inspection with a #6 neutral, you are good to go. I seriously doubt he will pass it. So pull out the #6 and drag a #4 in using the #6. Get some wire lube and rub down the new wire good as you are pulling it in. The lube would have helped you on the first pull too.


Now when I wire out to my welder/ compressor outlets (2 30AMP circuits) I was planning on running 2 #6 wires for the hots and and 2 #8 for the Ground and Neutral. Does the Neutral need to be #6 as well on these?

30 amp circuits only require #10 wire for a 30 amp circuit.
No neutral required for 240 volt circuits. But it does not hurt to have a spare neutral. Could come in handy some day.

I don't have this all hooked up yet, the wires are just hanging loose at the main panel end (away from the breakers of the main panel of course. Don't want them to touch something and ground out) The Subpanel is mounted in the garage and I have secured down the wires on that end. That is as far as I have gotten. Had planned to finishing this up this weekend.


You will have trouble pulling out just the #6 wire, so you may need to pull it all out. Make sure you have some wire lube to pull it back in. It makes it so much easier. Like night and day. Put it on heavy.
Or call the inspector and ask him if he will allow it. This is the best way to go. Might save you alot of work. Might?



Last edited by J. V.; 09-25-2009 at 01:23 PM.
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Old 09-27-2009, 01:13 PM   #14
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The #6 neutral must be removed. I just got it verified. But you might have some luck with your inspector, depending on the type of loads you have. Try him out on this.
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Old 09-28-2009, 02:22 PM   #15
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The #6 neutral must be removed. I just got it verified. But you might have some luck with your inspector, depending on the type of loads you have. Try him out on this.
I pulled the wire out of the conduit. Ran (3) #4 wires and (1) #6 for ground. Installed a 60A breaker in the main panel for the subpanel. I would have gone bigger but the next jump at Lowes/Menards was 100A breaker. Got the rest installed and everything is working.

The 220 runs in the garage (from the subpanel) I used (3) #6 wire and (1) #8 for the ground.

Thank you for your help.

Ben

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