Wire size for a 60 amp circuit

Reply

  #1  
Old 11-22-03, 06:30 PM
BuzzHazzard
Visiting Guest
Posts: n/a
Wire size for a 60 amp circuit

I am wiring a subpanel for a workshop. I will have a 2HP Dust Collection system on a dedicated circuit, lighting on a dedicated circuit, and two 20 amp receptacle circuits for now. I may want to expand to a 240V circuit for a 3HP table saw at some point as well, and perhaps add an air compressor.

Anyway, a 50 Amp circuit will probably be enough and I know that I should use 6-3 w/G to feed the subpanel and isolate the neutral bus bar from the ground bus bar in the subpanel.

But if I choose to go with a 60 Amp subpanel feed instead, what size wire do I use? I know 6 AWG is good to 55 Amps. Yet I have a furnace with two backup strip heaters on 60 Amp circuit breakers. Each looks like the electrician used 6-2 cable for the circuit although I can't find any writing on the sheath that I can tell for sure. And I've never seen any 4-3 NM-B cable.

I have a number of very good books on the subjecdt, but none address this issue beyond stating that I should use SER cable to feed subpanels at or above 100A and NM-B 6-3 for a 50 Amp.

Thanks in advance.

Rob

Oh, BTW, in Lowes today, I purchased a subpanel with a 125 amp rating. The guy in that department said that I was "supposed" to use cable consistent with that rating even though I plan to feed the panel with a 50 (or 60) Amp circuit. That didn't sound right at all. Am I confused or was he?
 
Sponsored Links
  #2  
Old 11-22-03, 07:26 PM
Member
Join Date: Sep 2000
Location: United States
Posts: 18,497
6/3 supports either a 50-amp or a 60-amp subpanel (using the next larger standard size rule in 240.4(B)).

The information you got at Lowes is certainly not the stupidest thing I've ever heard coming from a home improvement store, and at least it isn't dangerous, but the advice you got was both stupid and wrong anyway. He's confused. You're not.
 
  #3  
Old 11-22-03, 07:34 PM
BuzzHazzard
Visiting Guest
Posts: n/a
Thanks John.

As an "advanced amateur," I am aware of the 240.4B rule as it was mentioned in one of my books, but I wanted to make sure I wasn't misapplying it in my case.

Rob
 
  #4  
Old 11-23-03, 01:48 AM
noxx
Visiting Guest
Posts: n/a
You can go ahead with the #6 cable for the load you have planned at this time. Personally I would run #2 to allow for expansion of your shop in the future up to a 100A feed. Wire's pretty cheap, saves running it over a few years down the road if your projects take off.
 
  #5  
Old 11-23-03, 07:36 AM
brickeyee
Visiting Guest
Posts: n/a
A dust collector and a 3 HP table saw may have a problem starting on only a 60 amp line. Even if you start one and wait for it to come to speed, the second may trip the main in the sub-panel. 100 amp is more usefull in a full up wodd shop.
 
  #6  
Old 11-23-03, 07:47 AM
Member
Join Date: Jun 2002
Location: Brethren, Mi
Posts: 1,648
I have a 3 hp and a 5 hp compressors on a 60A sub with a total of 42 run amps, it stars them just fine and the 5 is the secondary. Never have a problem, but of course bigger is always better.
 
  #7  
Old 11-23-03, 08:57 AM
brickeyee
Visiting Guest
Posts: n/a
I have a 3 HP unisaw installed on a 60 amp panel for a while. It need 45 amps to start repeatedly, and even after it was up to speed the dust collector would trip the breaker about 25% of the time. A lot depends on the motor quality. Better quality motors have a higher kVA locked rotor code and take more power to start up. The unisaw motor would be >60 HP using the 'maximum developed' method. It will also cut through 3 inches of hard maple, or even ironwood without slowing.
 
  #8  
Old 11-23-03, 10:09 AM
BuzzHazzard
Visiting Guest
Posts: n/a
Thanks guys.

Thanks guys. I got the 6-3 cheap and will go with that for now. In my old house, I had a 40 amp subpanel, and never had a problem with the same equipment I plan to use now.

However, I will always have access to the run between the Service Entrance (Two 200 Amp panels) and my workshop subpanel, so if necessary I can replace the subpanel feed and buy a new breaker. As I stated earlier, my subpanel is rated at 125A.

Rob
 
  #9  
Old 11-23-03, 11:27 AM
Member
Join Date: Feb 2002
Location: port chester n y
Posts: 2,117
Art. 430.63 allows the rating of the Feeder C-B to exceed the rating of the Feeder conductors where the Feeder supplies a "combination" load consisting of motors, liting fixtures, and appliances. It's possible to have a 100 amp C-B protect Feeder conductors rated at 60 amps if the Feeder is supplying motors.

The 40 amp "difference" would be the full-load current of the largest motor mutiplied by a factor of 250% (Table 430.52).

The FLC of a 240 volt, 3-HP, single-phase motor is approx 20 amps. If this motor was supplied by a Feeder with a 30 amp liting/appliance load, the rating of the C-B would be (250% X 20 )+ 30 = 80 amps. The ampacity of the Feeder would be (125% X 20) + 30 = 55 amps.
 
  #10  
Old 11-23-03, 07:05 PM
bubinga1
Visiting Guest
Posts: n/a
Thanks guys. I got the 6-3 cheap ............................
Where did you get a good price on the 6/3.

I think when I got about 10 feet at lowes, it was about $1.00 a foot.
Thanks, Tony D.
 
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