240v duplex recepticle help

Reply

  #1  
Old 12-14-13, 09:34 PM
Member
Thread Starter
Join Date: Dec 2013
Location: USA
Posts: 8
240v duplex recepticle help

I want to have 2 tablesaws (13 amp each) and a router (no more than 8 amp) running off of one box that hangs from the ceiling in the middle of the garage.

Here's my plan, is it to code?

In the sub-panel I have a 30 amp 240v breaker

From the box I am running 10/3 romex to an octagon box screwed to a rafter in the ceiling. 2 hots a neutral and a ground

From the center of the box cover (3/4" knockout) I install a wire mesh cable strain relief and run a 10/4 sjoow wire down to about 2 feet off of the floor.

At the end of the wire I add another strain relief and run the sjoow wire into a deep metal square box.

In the box, I use 2 hots on a DUPLEX 240V 20 amp receptacle and pigtail a hot to a standard 120v duplex receptacle, adding the neutral. Ground both and shazam!

I know it will work but is it code AND the real question is,

can a 240v 20 amp duplex receptacle handle 2 13 amp tablesaws running at the same time, as long as the feeder line is 30 amp and the breaker is 30 amp.

Really it comes down to, when an outlet says it's rated for 20 amp is that 20 amp per outlet or combined. Yes, occasionally the tablesaws may run at the same time.

Also, is there a better way to hang an outlet?

Thank you so much. I love this forum.

Hillel

items in question:
250v duplex Leviton 5822-I 20-Amp, 250-Volt, Narrow Body Duplex Receptacle, Straight Blade, Commercial Grade, Self Grounding, Ivory - Amazon.com

strain relief: Leviton L7504 3/4-Inch, Straight, Male, Steel Body, Wide-Range Strain-Relief, .520, .730 Cord Range - Amazon.com

or mixed voltage recpticle:
Leviton 5842-I 20 Amp, 125/250 Volt, Narrow Body Duplex Receptacle, Straight Blade, Commercial Grade, Self Grounding, Dual Voltage, Ivory - Amazon.com
 
Sponsored Links
  #2  
Old 12-14-13, 11:43 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,374
I am not an electrician but I have done a whole lot of electrical work over the last fifty-plus years. Your mechanical installation sound okay but I do not think that the electrical portion masses muster. I think that it is not allowable to have the 20 ampere duplex receptacle on a 30 ampere circuit no matter what the load on the individual receptacles.

Using two single 30 ampere receptacles would be compliant but would require changing the plugs on the saw motors. Each saw would be required to have overload protection as a 30 ampere circuit breaker is too high to provide overload protection on a one-horsepower motor.

I think a 10/5 drop cable would be better as you could then have the 240 volt and 120 volt circuits separately protected. Protect the 120 volt circuit at a maximum of 20 amperes.
 
  #3  
Old 12-15-13, 02:11 AM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,362
Fued is correct about the maximum ampacity for a general receptacle being limited to 20 amps.

Also the octagonal box is too small.
 
  #4  
Old 12-15-13, 06:54 AM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 9,221
I want to have 2 tablesaws (13 amp each) and a router (no more than 8 amp) running off of one box that hangs from the ceiling in the middle of the garage.
Considering the 13 amps each, these table saws sound more like they are 120 volt machines and not 240 volt. Are you sure that at 240 volts they draw 13 amps each??
 
  #5  
Old 12-15-13, 10:02 PM
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,374
Joe, NEC standards for a 2 horsepower 240 volt single phase motor is 12 amperes so these saws may very well be 13 amperes at 240 volts. Two, or even three, horsepower would not be excessive for a commercial table saw with a ten inch or larger blade.

Ideally each saw should have its own circuit with short-circuit protection at 25 to 30 amperes. In addition, each saw should have a manual reset overload protection.

A third issue is the power from a ceiling drop, I would think that drop cable would get in the way when sawing larger panels. Floor (or underfloor) conduit makes more sense to me.
 
  #6  
Old 12-16-13, 03:31 AM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,362
Good point about the hanging cord getting in the way.
 
  #7  
Old 12-16-13, 07:30 AM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 9,221
Joe, NEC standards for a 2 horsepower 240 volt single phase motor is 12 amperes so these saws may very well be 13 amperes at 240 volts. Two, or even three, horsepower would not be excessive for a commercial table saw with a ten inch or larger blade.
Very true, Furd, but I was thinking that it would be unusal to find commercial table saws in a residential garage. When you get into commercial saws, 2 HP would be on the small side, many are 5 HP.
 
Reply

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


Thread Tools
Search this Thread
Display Modes
'