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

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

Reply
 
Thread Tools Search this Thread Display Modes
Old 01-17-2013, 04:07 AM   #16
Member
 
Join Date: Oct 2010
Location: Cairns Australia
Posts: 2,366
Share |
Default

What size circuit do I need.


Quote:
Originally Posted by Toller View Post
For bonus points, if someone wants to explain how a 3hp motor can draw 20a, I would like to know. I thought maybe that was with no load, but it is 20a while working the machine. Seems really really high.

Sounds about right !
1 hp = 750w.
3 x 750 = 2250w.
2250w / 120v = 18.75a.

Close enough !

dmxtothemax is online now   Reply With Quote
Old 01-17-2013, 04:49 AM   #17
MEASURE ONCE, CUT TWICE
 
123pugsy's Avatar
 
Join Date: Oct 2012
Location: MARKHAM, ON
Posts: 467
Default

What size circuit do I need.


Quote:
Originally Posted by Toller View Post
Thats interesting. I can use #12 and a 40a breaker if I hardwire. There would only be about 25' for cable, so the voltage drop would be trivial. I think a 40a breaker is overkill; I can use a 30a breaker can't I?
I know I can't just run the romex to the switch box; I would have to run romex to a junction box and run some sort of whip to the switch box. What are the requirements for that?

I take it that everything changes if I go to a plug. What do I need then?
I appreciate the help.
Last time I checked, #12 needs to be protected by a maximum 20 amp breaker.
I would use emt if surface mounting, from the panel to a box and cabtyre for your "whip" to the motor.
123pugsy is offline   Reply With Quote
Old 01-17-2013, 07:01 AM   #18
Master Electrician
 
Join Date: Nov 2008
Location: Northern Virginia
Posts: 463
Default

What size circuit do I need.


Quote:
Originally Posted by 123pugsy View Post
Last time I checked, #12 needs to be protected by a maximum 20 amp breaker.
What did you "check" to find that? That is a common misconception among DIY'ers who don't read the ENTIRE code.

Mark
__________________
Licensed Master Electrician
Commonwealth of Virginia
busman is offline   Reply With Quote
Old 01-17-2013, 12:21 PM   #19
MEASURE ONCE, CUT TWICE
 
123pugsy's Avatar
 
Join Date: Oct 2012
Location: MARKHAM, ON
Posts: 467
Default

What size circuit do I need.


Quote:
Originally Posted by busman View Post
What did you "check" to find that? That is a common misconception among DIY'ers who don't read the ENTIRE code.

Mark
Thanks for pointing out my error.

Enlighten us DIY'ers as that's why we're here.

Thanks.
Pugsy
123pugsy is offline   Reply With Quote
Old 01-17-2013, 12:50 PM   #20
Semi-Pro Electro-Geek
 
Join Date: Jul 2009
Location: Arizona, USA
Posts: 2,531
Default

What size circuit do I need.


Quote:
Originally Posted by 123pugsy View Post
Thanks for pointing out my error.

Enlighten us DIY'ers as that's why we're here.

Thanks.
Pugsy
Stickboy's post #9 above cites the code sections and includes a diagram.
__________________
I am a lawyer, but not your lawyer. And who cares anyways? We're here to talk construction. This is DIY advice, not legal advice.
mpoulton is offline   Reply With Quote
Old 01-17-2013, 01:47 PM   #21
Lic Electrical Inspector
 
electures's Avatar
 
Join Date: Dec 2009
Location: The Great Police State of New Jersey
Posts: 1,617
Default

What size circuit do I need.


Quote:
Originally Posted by stickboy1375 View Post
You size the OCP and min. branch circuit wiring off the HP rating...

3 HP @ 240 v. = 17 AMPS

17 AMPS X 250% = maximum breaker size, = 40 Amp breaker

17 AMPS x 125% = minimum branch circuit wiring, = 21.25 #12AWG is good for 25 amps in this scenario,

This of course is for hard wiring the motor.
THHN/THWN in conduit yes. Romex is only good for 20A 60C. 2011 NEC.
__________________
All responses based on the 2011 NEC.
If you live in New Jersey click here. All other states click here.
Please check with local, county and state officials as laws may vary.
Sizing motors here. Online motor calculator here. Online calculators here.

Last edited by electures; 01-17-2013 at 01:53 PM.
electures is offline   Reply With Quote
The Following 2 Users Say Thank You to electures For This Useful Post:
frenchelectrican (01-19-2013), stickboy1375 (01-17-2013)
Old 01-17-2013, 02:09 PM   #22
Member
 
Join Date: Jan 2013
Posts: 550
Default

What size circuit do I need.


Quote:
Originally Posted by electures View Post
THHN/THWN in conduit yes. Romex is only good for 20A 60C. 2011 NEC.
Is MC considered to be in conduit?
Toller is offline   Reply With Quote
Old 01-17-2013, 03:46 PM   #23
Semi-Pro Electro-Geek
 
Join Date: Jul 2009
Location: Arizona, USA
Posts: 2,531
Default

What size circuit do I need.


Quote:
Originally Posted by Toller View Post
Is MC considered to be in conduit?
Nope. MC is MC - it's a specific type of cable assembly, like NM or UF. THWN in FMC may seem almost identical to MC, but according to the code it's completely different.
__________________
I am a lawyer, but not your lawyer. And who cares anyways? We're here to talk construction. This is DIY advice, not legal advice.
mpoulton is offline   Reply With Quote
The Following User Says Thank You to mpoulton For This Useful Post:
electures (01-18-2013)
Old 01-17-2013, 04:59 PM   #24
Member
 
Join Date: Jan 2013
Posts: 550
Default

What size circuit do I need.


I have a 25' length of 10/3 romex. Can I just ignore the unneeded wire? I don't expect to ever use it for any thing else, so I might as well use it here. I would run it from the panel box to a junction box above the cyclone.

Also I have a 12' length of 10/3 SOOW. Can I run that from a junction box to the switch box on my cyclone? I used it to connect a generator to a transfer switch, but don't have either of them anymore.

Now I just have to decide on the breaker. My understanding is that I could use either a 30a or a 40a. I think a 30a will be adequate, but mfg. recommends a 40a presumably to avoid nuisance trip on startup, but I have pretty much determined that is not a problem. Would a 40a be any more dangerous? Just about anything dangerous that would trip a 30a would trip a 40a also. It is all so confusing, but I think I am almost there.
Toller is offline   Reply With Quote
Old 01-17-2013, 05:52 PM   #25
Semi-Pro Electro-Geek
 
Join Date: Jul 2009
Location: Arizona, USA
Posts: 2,531
Default

What size circuit do I need.


30A on #10 wire is definitely fine for this installation. Since that does not rely on the motor's thermal cutout for overcurrent protection (#10 wire is rated for 30A), you can install a receptacle and put a plug on the dust collector if you want. I would install a 4-wire 30A dryer receptacle next to the machine, and put a standard dryer cord on it. Leave the white wire unconnected (taped off) at the machine.
__________________
I am a lawyer, but not your lawyer. And who cares anyways? We're here to talk construction. This is DIY advice, not legal advice.
mpoulton is offline   Reply With Quote
Old 01-18-2013, 07:37 AM   #26
Lic Electrical Inspector
 
electures's Avatar
 
Join Date: Dec 2009
Location: The Great Police State of New Jersey
Posts: 1,617
Default

What size circuit do I need.


Quote:
Originally Posted by Toller View Post
I have a 25' length of 10/3 romex. Can I just ignore the unneeded wire? I don't expect to ever use it for any thing else, so I might as well use it here. I would run it from the panel box to a junction box above the cyclone.

Also I have a 12' length of 10/3 SOOW. Can I run that from a junction box to the switch box on my cyclone? I used it to connect a generator to a transfer switch, but don't have either of them anymore.

Now I just have to decide on the breaker. My understanding is that I could use either a 30a or a 40a. I think a 30a will be adequate, but mfg. recommends a 40a presumably to avoid nuisance trip on startup, but I have pretty much determined that is not a problem. Would a 40a be any more dangerous? Just about anything dangerous that would trip a 30a would trip a 40a also. It is all so confusing, but I think I am almost there.
Yes, you can use the 10/3 and abandon the un used wire. Just cap it off. As for the SOOW cord, splicing it in a JB makes it a permenant wiring method. That's a no no.
__________________
All responses based on the 2011 NEC.
If you live in New Jersey click here. All other states click here.
Please check with local, county and state officials as laws may vary.
Sizing motors here. Online motor calculator here. Online calculators here.

Last edited by electures; 01-18-2013 at 10:08 AM.
electures is offline   Reply With Quote
Old 01-18-2013, 02:01 PM   #27
Member
 
Join Date: Jan 2013
Posts: 550
Default

What size circuit do I need.


Quote:
Originally Posted by electures View Post
Yes, you can use the 10/3 and abandon the un used wire. Just cap it off. As for the SOOW cord, splicing it in a JB makes it a permenant wiring method. That's a no no.
Geez, just when I thought I had it settled.
What material is proper from the junction box to the tool?
Is MC acceptable?

I know I can use a 40a with the #10 wire if it is permanent. Is that true for the plug/outlet also?
Toller is offline   Reply With Quote
Old 01-18-2013, 02:40 PM   #28
MEASURE ONCE, CUT TWICE
 
123pugsy's Avatar
 
Join Date: Oct 2012
Location: MARKHAM, ON
Posts: 467
Default

What size circuit do I need.


Quote:
Originally Posted by Toller View Post
Geez, just when I thought I had it settled.
What material is proper from the junction box to the tool?
Is MC acceptable?
A power tool or machine is not a part of a structure. Does that not mean that the cord is OK to use? Isn't the only part of this run considered permanent, the run from the panel to the JB?

Or if splicing into the JB does make it permanent and unaccepable, would adding a recepticle in the JB and a plug on the end of the cord be good?
123pugsy is offline   Reply With Quote
Old 01-18-2013, 04:39 PM   #29
Semi-Pro Electro-Geek
 
Join Date: Jul 2009
Location: Arizona, USA
Posts: 2,531
Default

What size circuit do I need.


Quote:
Originally Posted by 123pugsy View Post
A power tool or machine is not a part of a structure. Does that not mean that the cord is OK to use? Isn't the only part of this run considered permanent, the run from the panel to the JB?

Or if splicing into the JB does make it permanent and unaccepable, would adding a recepticle in the JB and a plug on the end of the cord be good?
The cord is fine if it's plugged into a receptacle, but not if it's wired in. But if you use a receptacle, there is a good argument that the breaker and wire size must match (i.e. 30A for #10) since it is now a general-purpose receptacle circuit and not a motor load circuit.

__________________
I am a lawyer, but not your lawyer. And who cares anyways? We're here to talk construction. This is DIY advice, not legal advice.
mpoulton is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
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
proper calculation for circuit size withoutlicense Electrical 19 02-16-2012 09:15 AM
Can someone help me size my lighting circuit? Alan Electrical 12 01-19-2012 09:01 AM
Need a wiring diagram Mooreski Electrical 46 03-12-2011 03:25 PM
Just for fun Andy in ATL Electrical 56 10-20-2009 09:33 AM
Circuit breakers and wire size stan 41943 Electrical 19 03-06-2008 02:29 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.