Sub-panel - Electrical - DIY Chatroom Home Improvement Forum


Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Electrical

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Display Modes
Old 02-17-2010, 08:01 PM   #1
Newbie
 
Join Date: Feb 2010
Posts: 12
Rewards Points: 10
Default

Sub-panel


Quote:
Originally Posted by Stubbie View Post
What you have is service equipment located at the house and workshop both have 3 wire service entrance. Probably have a 200 amp service I can't imagine the utility would have ran 100 amp service to the meter in your situation but let us know if they did.

Assuming 200 amp service what is the main breaker size in the shop panel?

What you want to do is determine what tools and loads you have in the shop and list them by individual load requirements. This information is on the nameplates. Then determine the load that the main breaker in the shop panel will need to handle calculating in the expected load being used at the sub-panel. The main breaker needs to hold the demand from both panels. I think you understand that quite well.

The key in a shop is how many tools or pieces of equipment and lights etc will be operating at one time. Usually if a one man shop this is generally no more than two tools plus lights and heat/ac etc. If more than one man shop where multiple tools then you may have to be more aware of load management to keep from tripping breakers .... common sense really.

What I'm saying is if the shop main panel has a common demand of 30 amps per hot leg and it has a 100 amp main breaker then I have 70 amps per hot leg in reserve. So my sub panel cannot have a load of over 70 amps on one hot leg of its feeder from the shop main panel or I will trip the shop panel main breaker. If I run a welder at max output setting placing 50 amps on the two hot legs of the sub-panel feeder then my main breaker in the shop panel is 20 amps from its maximum rating. So I think you see the thinking.

There is a calculation called demand load that you can do but frankly you likely will only get confused having never done one. So just stick with real load figures from what you operate in the shop at one time..

From your description your wanting to move your main 120 and 240 volt power tools to the sub-panel. So you need to determine what the max. load those tools will place on the sub-panel after considering how many will operate at the same time. Once you know that in amps of load then you can determine your wire size for the feeder to the sub -panel. Example .. if at the most I am having a hole drilled by the 120 volt drill press with a helper and that drill press has running amps of 12 amps shown on the nameplate. In the meantime you are welding a steel plate and using 35 amps from your 240 volt stick welder. One leg of your feeder to the sub is 47 amps and one is 35 amps. Your also operating 30 amps per hot leg from your main shop panel .. heat, lights etc. so the 100 amp main breaker is holding 47 + 30 = 77 amps on one leg and the other leg is 35 + 30 = 65 amps.

Your sub-panel feeder is going to have to have an ampacity that will carry the load you calculate. In this case 47 amps is your highest load on one leg of the sub panel feeder. Your going to need at least #6 awg to carry the load. And you would likely install a 60 amp breaker in the shop panel to protect your sub-panel feeder. Voltage drop should not be any issue at 80'. You also want to consider giving yourself some extra ampacity if possible for added equipment in the future.

So if you can get us the main breaker information of your shop panel and the figures you feel will be the highest loads the sub panel and shop panel will be using we can get on with wire size and how to wire your sub-panel. Use the 'rated input current' for your welders and plasma cutters. Remember this is a calculated loadof what you feel will be the maximum load at any given time not a sum of all your tools operating at once. Don't forget that air compressors come on and off as they cycle.

BTW this is absolutely doable as a DIY project. Being handy and having wiring experience this should not pose any problem for you. Several of us here can answer any questions you have and we will help get that sub-panel installed safely.

On more thing .. since your not adding more load to the shop just moving tools to a different location there really isn't any issue with the service capacity but I would just like to know what it is so you can plan for the future.
I am planning to run a 240V circuit from my main panel (400amp) to a new sub panel (60amp 12/24 bus) in a remote garage. i need the voltage to run a Delta 3hp tablesaw (pulls about 15 amps). I may have other 240 tools in the future, but for now that is it, thus the 60amp 12/24. Also, I am unlikely to be running more than one 240V appliance at a time. The distance of the pull is 125 feet through PVC laid underground. I am in Los Angeles, so no cold climate. Sounds pretty simple, but I have a couple of questions that I hope you will answer:
1. Since i plan to use a 60 amp sub panel, i am assuming that #6 awg wire is sufficient. Considering the distance (line drop) and any other factors, is that correct?
2. Does the ground have to be the same size wire as the 2 hots? Using #6 or #4 hots, could I run #12 or #10 as the ground to save $ and make the pull easier.
3. If I want to run 120V circuit off of the new sub panel, would I have to run a 4th and 5th wire (hot and neutral) through the conduit for that circuit, or could I just run it off of one of the buss bars catching one of the hots? If yes, what do I use as a neutral wire?
4. I have been planning on using THHN for this. Is that the correct type of wire or is there a better choice.
5. Finally, wire seems to be MUCH cheaper on the web than in Home Depot or even the local electrical supply houses. Is the stuff offered online (like from Hardware and Tools.com) any good? Do you have a favorite online source.
Thanks very much for your help.

Advertisement


Last edited by selewis; 02-17-2010 at 08:05 PM. Reason: typos
selewis is offline   Reply With Quote
Old 02-17-2010, 09:27 PM   #2
Just call me Andrew
 
Join Date: Mar 2009
Location: Albany, NY
Posts: 2,258
Rewards Points: 1,012
Default

Sub-panel


1. Since i plan to use a 60 amp sub panel, i am assuming that #6 awg wire is sufficient. Considering the distance (line drop) and any other factors, is that correct?

#6 Is appropriate for 60 amps, but i'm not sure about voltage drop over 125 feet.

2. Does the ground have to be the same size wire as the 2 hots? Using #6 or #4 hots, could I run #12 or #10 as the ground to save $ and make the pull easier.

You can use #10 ground, but again, not sure about voltage drop.

3. If I want to run 120V circuit off of the new sub panel, would I have to run a 4th and 5th wire (hot and neutral) through the conduit for that circuit, or could I just run it off of one of the buss bars catching one of the hots? If yes, what do I use as a neutral wire?

You only need the two hots that feed your panel. You just run off one buss bar, like you said, for a 120v circuit.

4. I have been planning on using THHN for this. Is that the correct type of wire or is there a better choice.

Underground in conduit is considered a wet location, you need to use THWN. Most wire at your local store is rated for both purposes. Look at the wire for the THHN/THWN marking. The sign may not say it is rated for both but the wire itself will.

5. Finally, wire seems to be MUCH cheaper on the web than in Home Depot or even the local electrical supply houses. Is the stuff offered online (like from Hardware and Tools.com) any good? Do you have a favorite online source.

Not sure, I don't see much about pricing discussed on these boards. It might be frowned upon

Here is an online calculator you can use to calculate voltage drop:
http://www.csgnetwork.com/voltagedropcalc.html

It says at 125 feet, 6AWG wire, 240 volts, you would lose 7.1 volts, leaving you with 232.9 at the subpanel. The experts here can say if that's enough of a loss to go with a bigger wire.

Advertisement

__________________
Andrew


Last edited by secutanudu; 02-17-2010 at 09:30 PM.
secutanudu is offline   Reply With Quote
Old 02-17-2010, 09:33 PM   #3
Member
 
Join Date: Jan 2009
Location: South of Boston, MA
Posts: 17,248
Rewards Points: 2,000
Default

Sub-panel


Voltage drop is only 3% at that distance - 7.1v for 240v sub

http://www.csgnetwork.com/voltagedropcalc.html

2 #6 hots, #6 neutral....#10 ground
2 grounding rods connected with #6 min

Yeah...wire may be cheaper on the web
Wait til you see the shipping charges
Scuba_Dave is offline   Reply With Quote
Old 02-18-2010, 04:48 PM   #4
Newbie
 
Join Date: Feb 2010
Posts: 12
Rewards Points: 10
Default

Sub-panel


So, if I ever intend to pull a 120 off of one of the hot buses in the sub panel I need a neutral running back to the main that is the same gauge as the 2 hots (#6 in this case)?? If I don't ever pull a 120 off of the sub panel, then I don't need a neutral running back to the main, right? Then I would just have the 2 #6 hots and a #10 ground running back to the main. Is that correct?
I'm thinking of the difficulty of pulling 3 #6 wires through 1 1/2" conduit. In your experience would I be better off pulling #12 hot and #12 neutral from the main if I want to provide for a 120amp circuit? (#12 big enough?)
selewis is offline   Reply With Quote
Old 02-18-2010, 05:03 PM   #5
Member
 
Join Date: Jan 2009
Location: South of Boston, MA
Posts: 17,248
Rewards Points: 2,000
Default

Sub-panel


I doubt an Inspector will accept a sub with just 2 hots & ground
I pulled (3) #6's & a #10 in 1" conduit, 1.5" would be a breeze

No #12 is not big enough
Run the 3rd #6 neutral & do it right

You are going to have a garage with 240v lights ?
Scuba_Dave is offline   Reply With Quote
Old 02-18-2010, 05:10 PM   #6
Licensed electrician
 
Join Date: Sep 2007
Location: Maryland
Posts: 7,994
Rewards Points: 2,786
Default

Sub-panel


Since this is in a remote building you can only run a feeder to the panel. You cannot run multiple circuits to the outbuilding.
__________________
Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.
Jim Port is offline   Reply With Quote
Old 02-18-2010, 05:26 PM   #7
Newbie
 
Join Date: Feb 2010
Posts: 12
Rewards Points: 10
Default

Sub-panel


No. Actually, there is already 120 v power there from another subpanel. Alright, so I gotta pull 3 #6s (hot, hot, neutral) and 1 #10 (ground)

By the way. Nice hat.
selewis is offline   Reply With Quote
Old 02-18-2010, 05:28 PM   #8
Newbie
 
Join Date: Feb 2010
Posts: 12
Rewards Points: 10
Default

Sub-panel


Quote:
Originally Posted by Scuba_Dave View Post
Voltage drop is only 3% at that distance - 7.1v for 240v sub

http://www.csgnetwork.com/voltagedropcalc.html

2 #6 hots, #6 neutral....#10 ground
2 grounding rods connected with #6 min

Yeah...wire may be cheaper on the web
Wait til you see the shipping charges
Quote:
Originally Posted by Jim Port View Post
Since this is in a remote building you can only run a feeder to the panel. You cannot run multiple circuits to the outbuilding.
Got it. So the third #6 is essential if I ever want to run a 120 circuit or two from the new sub panel? Right?
selewis is offline   Reply With Quote
Old 02-18-2010, 05:39 PM   #9
Newbie
 
Join Date: Feb 2010
Posts: 12
Rewards Points: 10
Default

Sub-panel


Ok guys, now's where I get really dumb. Once I've got my new 120 and 240 sub panel fired up, I'll want to install at least one 240 circuit with a receptacle(or 2) for the table saw. If I run one around the walls of the garage, let's say 25 feet or maybe 35 feet, or both, I'm gonna bring my two hots (one off each bus through a 240 breaker) + my ground (off the grounding bar in the panel -- which will be separate from the neutral bar in case I ever need to run a 120) to the receptacle. Right? What gauge does the circuit wire have to be? Can I use Romex (NM) or do I have to install flex or thin wall? If the circuit is a 30 amp circuit, then the breaker has to be no greater than 30 amps. Right? If it were a 20 amp circuit -- a 20 amp max breaker??
selewis is offline   Reply With Quote
Old 02-18-2010, 06:27 PM   #10
Just call me Andrew
 
Join Date: Mar 2009
Location: Albany, NY
Posts: 2,258
Rewards Points: 1,012
Default

Sub-panel


From your subpanel, you can install circuits the same way you would in your main panel. The guage for your branch circuit wire has to be appropriate for the breaker you choose. What size breaker to choose is dictated by the equipment you will be plugging in.


For NM (romex) cable, use the 60c column, for THHN in conduit, use the 75c column.

For example...on a 30 amp circuit, you can use 10AWG romex or THHN in conduit, but with the THHN in conduit you could theoretically push 35 amps (which is obviously not possible with a 30Amp breaker). I think, you COULD use a 40 amp breaker with 10AWG thhn in conduit as long as your calculated load does not exceed 35 amps.

__________________
Andrew

secutanudu is offline   Reply With Quote
Old 02-18-2010, 06:53 PM   #11
Member
 
Join Date: Jan 2009
Location: South of Boston, MA
Posts: 17,248
Rewards Points: 2,000
Default

Sub-panel


Quote:
Originally Posted by selewis View Post
No. Actually, there is already 120 v power there from another subpanel. Alright, so I gotta pull 3 #6s (hot, hot, neutral) and 1 #10 (ground)

Ok guys, now's where I get really dumb. Once I've got my new 120 and 240 sub panel fired up, I'll want to install at least one 240 circuit with a receptacle(or 2) for the table saw.
Already 120v from a sub in the Main building ?
Or an existing sub in the garage ?

You can only have one Feeder to the detached garage
So you need to disconnect the 120v from the sub in the house & run from the new sub in the garage

OR if there is an existing sub in the garage you need to upgrade it or eliminate it


What does the table saw require for power ?
Scuba_Dave is offline   Reply With Quote
Old 02-21-2010, 01:28 PM   #12
Newbie
 
Join Date: Feb 2010
Posts: 12
Rewards Points: 10
Default

Sub-panel


i just bumped into another unknown: "Whip." What is Whip and can it be used in conjunction with PVC conduit or instead of PVC conduit? How do you connect it up with PVC conduit if used together?
selewis is offline   Reply With Quote
Old 02-21-2010, 02:20 PM   #13
Newbie
 
Join Date: Feb 2010
Posts: 12
Rewards Points: 10
Default

Sub-panel


here's another question. Can I use 6/3 NM W/G in pvc conduit. Home Depot has it for $1.56/ft (that's about 52/ft per conductor or 49 if you include the ground). Altogether that's cheaper than pulling individual wires (because I only need about 125-140' and with the cutting fee, its 89/ft.)
selewis is offline   Reply With Quote
Old 02-21-2010, 02:54 PM   #14
Member
 
Join Date: Jan 2009
Location: South of Boston, MA
Posts: 17,248
Rewards Points: 2,000
Default

Sub-panel


You can't use NM in conduit underground, must be UF
Its a pain to pull cable thru conduit so you would need to oversize the conduit - 2" would be needed for 6-3 UF per conduit fill
Scuba_Dave is offline   Reply With Quote
Old 02-21-2010, 03:28 PM   #15
Newbie
 
Join Date: Feb 2010
Posts: 12
Rewards Points: 10
Default

Sub-panel


Got it. Thanks Dave

Advertisement

selewis is offline   Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Multiple Panel Question theatretch85 Electrical 5 12-12-2009 06:26 AM
100 -> 200 amp panel upgrade questions philipjcaputo Electrical 1 10-30-2009 04:35 AM
Replacing 2 Sub Panels with 1 Larger Panel GuitarJack Electrical 7 08-25-2009 09:43 PM
Replacement Meter Panel leonard_voet Electrical 19 04-09-2008 11:27 AM
Installing new (service?) breaker panel and generator panel Nhrafan Electrical 6 04-01-2008 04:03 PM




Top of Page | View New Posts