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 01-16-2013, 05:05 PM   #1
Member
 
Join Date: Jan 2013
Posts: 552
Share |
Default

What size circuit do I need.


I just bought a dust collector. The vendor says it draws 20a and requires a 40a circuit. I asked around and most users put in a 30a circuit and never have a problem.

I wired it up temporarily and found it draws 140a for less than a second and then quickly drops to 20a.

I looked up Square D's trip curve. They say that 5x the rated load will trip a breaker between 4 and 12 seconds. So my 140a is less than 5x the 30a rating, and only occurs for a split second. So, a 30a breaker ought to be okay, right? Even if my meter is reading low, it will take 210a for 2 seconds; and it couldn't possibly draw 210a.

140a seems like a lot of current and I am a little surprise they design breakers to stay open that long. Since it sounds odd to me, I just want to check to see that I am understanding it right.

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.

Toller is offline   Reply With Quote
Old 01-16-2013, 05:11 PM   #2
E2 Electrician
 
stickboy1375's Avatar
 
Join Date: Apr 2012
Location: Litchfield, CT
Posts: 4,723
Default

What size circuit do I need.


Is this hard wired or cord and plug connected?

If its hard wired, take a picture of the motor name plate and we can size it accordingly.

if its cord and plug, you must match the cord configuration to the proper receptacle and circuit breaker.

stickboy1375 is online now   Reply With Quote
Old 01-16-2013, 05:47 PM   #3
Member
 
Join Date: Jan 2013
Posts: 552
Default

What size circuit do I need.


They put the plate on the back of the motor, so my picture of it isn't very good.
3hp, 60hz, 220v, 22a, 3450rpm, 1 phase, continuous, 40C, Class F.

It came without a cord. For testing it I hardwired it, but planned on putting cord and outlet in. It is only 15' from the breaker box; I suppose hardwiring might be an option. What material is suitable for a whip to the control box?

I swapped the 40a breaker out for a 30a and started it 3 times without any problems. Oddly it only drew 19.2a on the 30a breaker compared to 20.4 on the 40a breaker; same cable. Maybe it was a bit more broken in?
Attached Thumbnails
What size circuit do I need.-griz.jpg  
Toller is offline   Reply With Quote
Old 01-16-2013, 05:51 PM   #4
Member
 
Join Date: Sep 2008
Location: Massachusetts
Posts: 263
Default

What size circuit do I need.


The breaker size has nothing to do with what the unit is drawing for amperage. If you are going direct to the panel there are lots of options depending on what is allowed by the authority having jurisdiction in your area.

Last edited by teamo; 01-16-2013 at 05:54 PM.
teamo is offline   Reply With Quote
Old 01-16-2013, 05:59 PM   #5
Licensed Electrician
 
k_buz's Avatar
 
Join Date: Mar 2012
Location: SE Wisconsin
Posts: 4,336
Default

What size circuit do I need.


If the manufacturer states it must be on a 40A circuit, it must be on a 40A circuit.
__________________
__________________________________________________ ______________
Answers based on the National Electric Code. Always check local amendments.


k_buz is offline   Reply With Quote
The Following 2 Users Say Thank You to k_buz For This Useful Post:
jbfan (01-16-2013), Missouri Bound (01-16-2013)
Old 01-16-2013, 06:21 PM   #6
Member
 
Join Date: Sep 2008
Location: Massachusetts
Posts: 263
Default

What size circuit do I need.


What model # dust collector is this? The motor nameplate says 22 amps continuous so I believe the minimum branch circuit wiring for a single motor @ 125% is 27.5 amps.
teamo is offline   Reply With Quote
Old 01-16-2013, 06:31 PM   #7
E2 Electrician
 
stickboy1375's Avatar
 
Join Date: Apr 2012
Location: Litchfield, CT
Posts: 4,723
Default

What size circuit do I need.


Quote:
Originally Posted by teamo View Post
What model # dust collector is this? The motor nameplate says 22 amps continuous so I believe the minimum branch circuit wiring for a single motor @ 125% is 27.5 amps.
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.
stickboy1375 is online now   Reply With Quote
Old 01-16-2013, 06:37 PM   #8
Member
 
Join Date: Jan 2013
Posts: 552
Default

What size circuit do I need.


Quote:
Originally Posted by teamo View Post
What model # dust collector is this? The motor nameplate says 22 amps continuous so I believe the minimum branch circuit wiring for a single motor @ 125% is 27.5 amps.
I wasn't aware there was a rule like that. Thanks.

Grizzly G0441
http://www.grizzly.com/products/3-HP...ollector/G0441

The same motor is used in the Shop Fox W1816. There they call for a 30a circuit. They used to sell the identical cyclone, and that was on a 30a circuit also.
http://pics.woodstockint.com/specsheets/w1816_ds.pdf

I can't see how the breaker could affect the current also, but it was consistant. I guess I should go back to the 40a and see what happens. Actually, now that I think of it, I measured the 40a at the circuit box, and the 30a at the machine; but that couldn't possibly matter.
Toller is offline   Reply With Quote
Old 01-16-2013, 06:43 PM   #9
E2 Electrician
 
stickboy1375's Avatar
 
Join Date: Apr 2012
Location: Litchfield, CT
Posts: 4,723
Default

What size circuit do I need.


Quote:
Originally Posted by teamo View Post
What model # dust collector is this? The motor nameplate says 22 amps continuous so I believe the minimum branch circuit wiring for a single motor @ 125% is 27.5 amps.
You are not allowed to use the nameplate to size the branch circuit wiring, you have to use the NEC.

Last edited by stickboy1375; 01-16-2013 at 06:49 PM.
stickboy1375 is online now   Reply With Quote
The Following 3 Users Say Thank You to stickboy1375 For This Useful Post:
electures (01-17-2013), frenchelectrican (01-19-2013), Speedy Petey (01-16-2013)
Old 01-16-2013, 07:55 PM   #10
Member
 
Join Date: Dec 2011
Location: Huntsville, AL USA
Posts: 229
Default

What size circuit do I need.


Quote:
Originally Posted by k_buz View Post
If the manufacturer states it must be on a 40A circuit, it must be on a 40A circuit.
You know this, buz, but it's worth saying for others: What buz says is true for sizing the conductors; you must comply with the code for wiring the circuit that the nameplate says it requires. It's nearly always OK to underfuse a circuit, though. So you must wire a circuit sized for 40A. However, you can then put a 30A breaker on the circuit, and if it'll start on that without tripping, no harm done.
fa_f3_20 is offline   Reply With Quote
Old 01-16-2013, 07:57 PM   #11
Licensed Electrician
 
k_buz's Avatar
 
Join Date: Mar 2012
Location: SE Wisconsin
Posts: 4,336
Default

What size circuit do I need.


Quote:
Originally Posted by fa_f3_20 View Post
You know this, buz, but it's worth saying for others: What buz says is true for sizing the conductors; you must comply with the code for wiring the circuit that the nameplate says it requires. It's nearly always OK to underfuse a circuit, though. So you must wire a circuit sized for 40A. However, you can then put a 30A breaker on the circuit, and if it'll start on that without tripping, no harm done.
Except voiding the warranty.
__________________
__________________________________________________ ______________
Answers based on the National Electric Code. Always check local amendments.


k_buz is offline   Reply With Quote
The Following User Says Thank You to k_buz For This Useful Post:
electures (01-17-2013)
Old 01-16-2013, 08:03 PM   #12
Member
 
Join Date: Dec 2011
Location: Huntsville, AL USA
Posts: 229
Default

What size circuit do I need.


Quote:
Originally Posted by k_buz View Post
Except voiding the warranty.
Really? I'm not saying they wouldn't, but how would they know? As long as the breaker doesn't trip, the circuit should behave exactly the same.
fa_f3_20 is offline   Reply With Quote
Old 01-16-2013, 09:09 PM   #13
Member
 
Join Date: Jan 2013
Posts: 552
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.
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.
Toller is offline   Reply With Quote
Old 01-16-2013, 09:22 PM   #14
Electrical Contractor
 
rrolleston's Avatar
 
Join Date: Oct 2011
Location: Granville, NY
Posts: 1,941
Send a message via AIM to rrolleston Send a message via Yahoo to rrolleston
Default

What size circuit do I need.


I would be sure to hard wire it. You will need to run some sort of conduit to the dust collector I would run mc wire or liquid tight. And I would also do a 40 amp circuit to the dust collector.
__________________
With Electricity there is the right way to do it and the dead way. Just because it works does not make it safe.
rrolleston is offline   Reply With Quote
Old 01-16-2013, 09:38 PM   #15
Member
 
Join Date: Jan 2013
Posts: 552
Default

What size circuit do I need.


Quote:
Originally Posted by rrolleston View Post
I would be sure to hard wire it. You will need to run some sort of conduit to the dust collector I would run mc wire or liquid tight. And I would also do a 40 amp circuit to the dust collector.
Do I run MC from the panel to the switch box, or can I run romex to a junction box and MC from the junction box to the switch box?

When you say a 40a circuit, are you saying #8, or the #12 that stickboy says is adequate,with a 40a breaker?

Toller 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.