Another Sub Panel Question

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  #1  
Old 04-08-06, 09:06 AM
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Another Sub Panel Question

I need to install a 100amp subpanel for my workshop/garage for my stick welder, table saw, dust collector, air compresser, beer fridge etc. It will be 60 feet from the main(200 amp) panel. My research reveals that I should use 2 #3 copper(hots), 1#6 copper (neutral) and 1 #8 copper (ground). I realize that I could get away with smaller wire (#4 copper ) but I prefer to not cut any corners. A few questions: Can this wire be purchased as a cable or am I stuck buying individual wires and running conduit? If using conduit, can I run it perpendicular to my floor joists? Any preference on a main lug versus a main breaker panel?
Thanks to all have replied to other threads. I have learned a huge amount reading this and the other forums.
 
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  #2  
Old 04-08-06, 10:55 AM
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Originally Posted by simp6216
I need to install a 100amp subpanel
Are there any electricians in your area?


> My research reveals that
Where did you do this "research"?


> I should use 2 #3 copper(hots), 1 #6 copper (neutral)
That's bad information you got. The neutral must be no smaller than #4.


> and 1 #8 copper (ground).
the bare minimum.


> I realize that I could get away with smaller wire (#4 copper )
> but I prefer to not cut any corners.
You are cutting a corner by using a reduced neutral.


> Can this wire be purchased as a cable?
Probably not.


> or am I stuck buying individual wires and running conduit?
Stuck? I think that's a great idea.
100A ar 200A SER might be an alternative.


> If using conduit, can I run it perpendicular to my floor joists?
Yes.


> Any preference on a main lug versus a main breaker panel?
Main breaker panels are usually larger which I think is preferable.
With a main lug, you can instead backfeed and fasten a 100A breaker.

If you need to kill power in a hurry you will instinctively go for the MAIN as would anyone who came to your rescue if something bad happens in the workshop.

Therefore, I recommend a MAIN breaker of some sort in your panel and that the panel be in plain sight - and hope it's never used.
 
  #3  
Old 04-08-06, 12:16 PM
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You can reduce the neutral to 6ga or even smaller, but only if the 'maximum unbalanced load' is less than the ampacity of the 6ga conductors. Using this 6ga neutral will probably safely meet your present needs, but will reduce your flexibility since it will reduce the number of 120V circuits you can install in this panel. I recommend against reducing the neutral in this fashion.

A main breaker panel is quite likely cheaper than a main lug panel, simply because of economies of scale.

A suitable cable assembly, eg type SE-R cable, will likely have a full size neutral.

-Jon
 
  #4  
Old 04-08-06, 04:59 PM
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Originally Posted by bolide
I should use 2 #3 copper(hots), 1 #6 copper (neutral)
That's bad information you got. The neutral must be no smaller than #4.
Can you cite a code reference for this statement?

Simp6216, is this a detached building, or a part of your house?

If this is part of your house, I would use a main lug panel, and consider using 2/0 AL SER for the run. You'd have ample room for expansion, and aluminum is less expensive than copper. (Aluminum SE-R is service entrance cable, in a gray outer sheathing, that would consist of two hots, a neutral and a ground. It's commonly used between the meter (or meter/main breaker combo) and the panel inside. It can be used for feeders to sub-panels, too.)

If you're looking to do this as inexpensively as feasible and don't foresee your needs increasing, I would simply run #2 AL SER and put in a 90A feeder. I imagine #2 SER would be more readily available (and less expensive) than #1 SER (for a 100A feeder), but I've never looked for #1 SER, myself.

You can secure a cable this large to the underside of your joists, but I would recommend installing something to prevent it from being used as a clothesline, such as a run of 2x4's or something along those lines. Along the wall of your basement might do the trick.

Can you list off the nameplate ratings of all the appliances you'll have as permanent residents of your shop? The welder is my main concern. I doubt it would exceed the needs for a 90A feeder, but I'd like to know.
 
  #5  
Old 04-08-06, 09:57 PM
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My workshop/garage are attached to my house.
table saw 1560
dust collector 1380
planer 1800
jointer 1440
air compressor 1800
all wattages at 120 vac

welder is a Miller: nameplate shows 230 volts 45.5 amps

My needs might increase as time goes. Keep in mind that I have been using all of the equipment above except the welder on 2 20 amp circuits without any problems. I only run the dust collector and one other tool at a time. I could run a line just for the welder, but I thought that I might as well do a sub panel now because one never knows what the future holds. The cost of the material for this work isn't the issue. I just need to know what to use. Thanks for your help.
 
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Old 04-08-06, 10:16 PM
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If cost is not an issue, Go with copper, The difference is not all that much for what your looking for, anyway. (the price thing is over rated, larger wires ,larger pipes, etc. it all works out in the end. everything has a trade off. I Digress)

2ndly, Check your equipment. can you change any of it to 220v?
This would reduce your power needs, And copper would still be best.

*welder is a Miller: nameplate shows 230 volts 45.5 amps*

I'm sure you won't use all of that(amps).




*
 
  #7  
Old 04-08-06, 11:02 PM
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My table saw and dust collector can be changed to 220. That was also one of the reasons I going with a sub panel. Thanks
 
  #8  
Old 04-09-06, 04:29 AM
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Switching your tools to run from 240 volts instead of 120 volts will not save you any power. Your table saw still needs 1560 watts, and your dust collector still needs 1360 watts.

What does change is the current they draw, At 240 volts they draw half as much current. This can save you money by allowing you to use smaller wire, but that is only an issue with larger power draw devices. There is also less voltage drop, but again less of an issue here.
 
  #9  
Old 04-09-06, 07:05 AM
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In many areas a #2 AL (2-2-2-4) or #4CU (4-4-4-6) SER cable is acceptable for a 100 AMP sub panel. You should see if this is the case in your area by checking with the electrical inspector. This is strictly an interpretation issue.

The same sizes would work with conduit, upsizing if table 310.15(B)(6) isn't allowed for sub panels in your area.
 
  #10  
Old 04-09-06, 10:23 AM
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I realize that switching tools to 220 doesn't save any power. I believe that they run more efficiently on 220. Since there will be plenty of room in the sub panel, why not.
 
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Old 04-09-06, 10:39 AM
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*I realize that switching tools to 220 doesn't save any power*

Correct, But you now run your table saw AND dust collector for the same money it would cost for one or the other.
And you can run them on the same ckt(Wire) and breaker.
2-runs a 30' of 12/2 , 2 20A breakers.Or 1 run @30', And the 2-pole breakers aren't that much more expensive.
 
  #12  
Old 04-09-06, 12:05 PM
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run for your money

Originally Posted by lectriclee
But you now run your table saw AND dust collector for the same money it would cost for one or the other.
What do you mean "run" and "money"?
Are you talking installation costs or operating costs?
The kWh usage is about going to be 99.9% on 240V compared to 120V for the same equipment.
 
  #13  
Old 04-09-06, 01:07 PM
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Lets see..... 1 peice of equipment, drawing 15 amps , or 2-peices drawing the same 15 Amps.

Not sure what your power co. charges you for. But mine charges by the KWH.
So am I that wrong thinking that 2 peices @ 15 amps total, is better(cheaper,less expensive,more cost effective.... add what you like) than 2- peices @ 15 amps each?

Sorry, should have worded it as "operate".
RELAX!
 
  #14  
Old 04-09-06, 01:17 PM
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When you change from 120 volts to 240 volts, you do indeed cut the current in half. However, since the voltage doubles, the amount of power remains the same.

With the exception of the slight advantage that 240 volts holds over 120 volts, the power used will be the same, as will the cost.
 
  #15  
Old 04-09-06, 01:18 PM
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Lee, Bolide's correct. There's no difference in the electric bill when using 240V over 120V appliances of the same wattage.

RELAX!
Now, that I can agree with!
 
  #16  
Old 04-09-06, 01:30 PM
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Thank you.
So in essance the only TRUE savings would be on materials? That is how I understand what you both have said.
 
  #17  
Old 04-09-06, 03:12 PM
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Originally Posted by lectriclee
So in essence the only TRUE savings would be on materials?
That's what we're saying... or else we'd run just about everything on 540V.

There is a small savings from power not wasted heating up the conductors.

Pretty much this same effect can be created by using larger conductors.
If you run your A/C off 12 AWG, you are paying extra to remove the heat given off by the interior portion of the wiring. 8 AWG will run much cooler, give off less heat, and reduce kWh usage.

This is true regardless of 120V or 240V or any other voltage.
Upsizing the conductor or cutting the current mean less transmission loss.

Switching 120V to 240V is a good way to cut current. Upsizing the conductor cuts electrical resistance. This can reduce your electric bill -- but not by even 5% -- unless you are actually seeing a voltage drop with the light gauge conductors.


The more apparent advantages (other than cost of installation) of 240V motors versus 120V can be faster starts and less dimming of lights.
 
  #18  
Old 04-09-06, 03:33 PM
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The more apparent advantages (other than cost of installation) of 240V motors versus 120V can be faster starts and less dimming of lights.

genrally yes this is very true.

the instering fact that some poco do have limit [ load ] of electric motor size majotry of them will like to ask the owner of machainery to wired on 240 much as possible due as what the quote say above :

that espcally more noteable with very large single phase motor ueseally like 5 hp and larger [ myself i did see few single phase motor can be big as 15 hp the current drawage is about same as some larger house main breaker rating { 100 amp } ]

thanks

Merci , Marc
 
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Old 04-10-06, 08:43 PM
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Thank you bolide,

*Pretty much this same effect can be created by using larger conductors*

So in theory, I could run #8s to my dryer @240 vac- and #6s or up to my range @ the same 240vac(+-) and Then should I up the sizes of the conductors to my AC and such.

Not being wise here, just want to know, coz it wouldn't be a big deal.

And how substantial would the savings be?
 
  #20  
Old 04-10-06, 11:02 PM
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> So in theory, I could run #8s to my dryer @240 vac and
> #6s or up to my range @ the same 240vac and then
> should I up the sizes of the conductors to my AC and such.
> Not being wise here, just want to know, coz it wouldn't be a big deal.

Well, if the wire is already installed, I'm not saying to replace it.

> And how substantial would the savings be?

You can figure I^2 x R losses the same as I can.

Let's take an a/c run 100' from panel to compressor.

Current draw is 20A for 5 hours per day, 100 days a year.
Electric is $0.10/kWh.

(Sorry about this little secret: with smaller wire, there will be a voltage drop, less current draw, and the unit will runs a little slower and a little longer. But it doesn't change the math by much, so I'll disregard it.)

I^2 = 400 A^2
I^2 x T = 200,000 A^2·hr
I^2 x kh = 200 A^2·khr


R = ___ ohms; ___ kWh; $__/year
#12 Cu: 0.201; 40.2; 4.02
#10 Cu: 0.126; 25.2; 2.52
#8str Cu: 0.081; 16.2; 1.62
#6str Cu: 0.051; 10.2; 1.02

So the answer is that upgrading from #10 solid to #6 stranded would save you $0.015 per hour that is wasted heating up the cable.

It would take a long time to pay for new conductors.

But when first installing the conductors, it can pay for itself on certain loads.

Obviously larger, longer, and more distant loads pay off more.


Because loss is proportional to the square of the current, changing from 120V to 240V cuts heat loss to 1/4. That's why I said that there is some savings on your utility bill by making the conversion (but we're talking a penny a month or something for a hobby workshop).
 
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