BT3Central Forums

Go Back   BT3Central Forums > Discussions > Tool talk

Tool talk This forum is for discussions about any and all power tools. Whether you are looking to buy a new tool or you have a question about the usage of a tool, this is the place to be!

Reply
 
Thread Tools Display Modes
  #1  
Old 12-30-2006, 10:06 PM
LCHIEN's Avatar
LCHIEN LCHIEN is offline
Internet Fact Checker
 
Join Date: Dec 2002
Location: Katy, TX, USA.
Posts: 16,737
LCHIEN will become famous soon enoughLCHIEN will become famous soon enough
Send a message via AIM to LCHIEN Send a message via Yahoo to LCHIEN
Circuit Breaker Tutorial-why you should not use a 20A breaker.

Seems to me like Circuit breakers are commonly used by everyone and little understood by most. I will explain Circuit breakers and why you should not use a 20A breaker with your BT3x saw.

Technical basis for this tutorial comes from the Square-D company that makes circuit breakers used in their panels for industrial and residential uses. These are designed to the same guidelines of the National Electrical code as other manufacturers' breakers so the operation should be the same.

I think the typical person thinks circuit breakers are black and white devices. That is, for a 15A breaker that if the current is 14.9 amps it will continue to conduct and if the current rises to 15.1 Amps it will open up and disconnect the circuit.

But in reality, circuit breakers are both time and current sensitive. This is a very useful thing because it allows us to use devices which vary in current pull so that the average is 15 amps and have peaks (say when your saw encounters a knot, or when a motor or light bulb turns on) very much in excess of 15 amps.

If you look at the end of the reference document, it has trip-point curves for the breakers , time vs. normalized current (e.g. the rated, or handle current is considered to be "1"). The curves and the text say that the circuit breaker should conduct the rated "handle" current (e.g. the value marked on the handle) pretty much forever if the ambient temperature is less than 40°C (~104°F). If the current is over about 1.5 times the rated current for longer than 10-100 seconds the breaker will eventually trip.

The curves approach the rated current when the time exceeds 10-100 seconds, this is because one trip mechanism is a bimetal element that is heated by the current flow. The element takes time to heat up to the trip point, allowing brief overcurrent surges since the heating takes time. And, devices shifting quickly from 10-20 amps and back but averaging 15 will also work forever.

The other feature of the curve is that around 9-10 times the rated current (about 135 Amps in this 15A breaker example), the breaker trips within one AC cycle (a few milliseconds) due to the electromagnetic trip element based solely on current. This is sufficient to let motor and light bulb starting curges through.

Between the two portions of the curve, like from 1.5x to 9x the rated current, the time it takes to trip decreases from 10 seconds to less than .3 of a second.

Thus you see that circuit breakers will trip immediately on gross overcurrent levels starting around 9x the rating, but allow brief, surges in the 1-10 second or more range. this is consistent with motors which can stand brief surges without overheating due to the thermal mass of the motor.

If you understand how these work, the people who put a 20A breaker on their dedicated circuit for their BT3100/BT3000 are just fooling themselves and taking a risk that the saw will melt down when overloaded. A 15A breaker for the BT3100/BT3000 is more than sufficient, given the leeway designed into the breakers. A 15A breaker is more than sufficient, allowing current surges consistent with startup and brief surges in operation associated with knots and feeding inconsistencies and other short term irregularities which do not exceed 15A on average. It will also protect the 15A-rated motor properly since the saw itself does not use any current overload protection.


Reference:
http://ecatalog.squared.com/techlib/...01&action=view
__________________
Loring in Katy, TX USA
If your only tool is a hammer, you tend to treat all problems as if they were nails.
PM me (with your e-mail address) for a copy of the BT3 FAQ current vers 4.13

Last edited by LCHIEN; 12-30-2006 at 10:12 PM.
Reply With Quote
  #2  
Old 12-30-2006, 10:30 PM
Stormbringer Stormbringer is offline
Platinum Patron
 
Join Date: Feb 2005
Location: Floral Park, NY
Posts: 1,387
Stormbringer is on a distinguished road
Valuable information Loring. Thanks for taking the time.

Greg
Reply With Quote
  #3  
Old 12-30-2006, 10:47 PM
lcm1947's Avatar
lcm1947 lcm1947 is offline
Veteran Member
 
Join Date: Sep 2004
Location: Austin, Texas
Posts: 1,490
lcm1947 is on a distinguished road
OK you got my interest Loring. So then with that knowledge am I correct in thinking all my circuits for my tools like my DeWalt chop saw, band saw, drill press, etc should be on a 15 amp breaker? How about the HF DC? It's suppose to be rated at 20 amps so I assume that's really the only tool where I should use a 20 amp breaker then right?
__________________
May you die and go to heaven before the Devil knows you're dead. My Best, Mac
Reply With Quote
  #4  
Old 12-30-2006, 11:00 PM
Ed62 Ed62 is offline
The Full Monte
 
Join Date: Oct 2006
Location: NW Indiana
Posts: 6,021
Ed62 will become famous soon enough
Good post, Loring. Thank you.

Ed
__________________
Do you know about kickback? Ray has a good writeup here... http://www.bt3central.com/articles/l...p?ArticleId=85

For a kickback demonstration video http://www.metacafe.com/watch/910584...demonstration/
Reply With Quote
  #5  
Old 12-30-2006, 11:01 PM
maxparot's Avatar
maxparot maxparot is offline
Cookin' in the Dry Heat
 
Join Date: Jan 2004
Location: Mesa, Arizona, USA.
Posts: 1,421
maxparot is on a distinguished road
Send a message via ICQ to maxparot Send a message via AIM to maxparot Send a message via MSN to maxparot Send a message via Yahoo to maxparot
A bit of additiional info for optimizing your dedicated circuits.

Although Loring's info on breakers is quite correct there is a couple of things that can help support a high draw device on a circuit:

Increase the gauge of wire you use to run your circuit. Even though a 15 amp circuit calls for 14 awg cables using 12 or 10 awg lowers circuit resistance. Likewise running conduit and using stranded thhn wire instead of solid wire will lower resistance. Using the combination of a larger gauge and stranded wire will insure you never choke your tool.
__________________
Opinions are like gas;
I don't mind hearing it, but keep it to yourself if it stinks.
Reply With Quote
  #6  
Old 12-30-2006, 11:49 PM
Sawatzky's Avatar
Sawatzky Sawatzky is offline
Established Member
 
Join Date: Apr 2005
Location: CA
Posts: 355
Sawatzky is on a distinguished road
I had my saw plugged into a 15 amp circuit. It was always tripping, especially in hot weather. I used no extension cord either. Even if I had other devices plugged into the same circuit (the circuit powered additional plugs in my garage) but did not turn them on, the circuit still tripped when I ran my BT. I added a 20 amp circuit because of advise on this forum. I now plug my BT and miter saw (both with 15 amp motors) into this outlet. I have not had any problems. Will I really damage my tools? If so, how do I avoid tripping the breaker all the time?
Reply With Quote
  #7  
Old 12-30-2006, 11:59 PM
and207 and207 is offline
Forum Newbie
 
Join Date: May 2006
Location: Repentigny,Québec,Canada
Posts: 10
and207 is on a distinguished road
Thanks

Hi!
Thanks.
Your posts are always informatives.

Andre
Reply With Quote
  #8  
Old 12-31-2006, 12:16 AM
cgallery cgallery is offline
Veteran Member
 
Join Date: Sep 2004
Location: Milwaukee, WI
Posts: 4,501
cgallery is on a distinguished road
Quote:
Originally Posted by Sawatzky View Post
I had my saw plugged into a 15 amp circuit. It was always tripping, especially in hot weather. I used no extension cord either. Even if I had other devices plugged into the same circuit (the circuit powered additional plugs in my garage) but did not turn them on, the circuit still tripped when I ran my BT. I added a 20 amp circuit because of advise on this forum. I now plug my BT and miter saw (both with 15 amp motors) into this outlet. I have not had any problems. Will I really damage my tools? If so, how do I avoid tripping the breaker all the time?
Did you try replacing the original 15a breaker before adding the 20a circuit?
Reply With Quote
  #9  
Old 12-31-2006, 02:59 AM
LCHIEN's Avatar
LCHIEN LCHIEN is offline
Internet Fact Checker
 
Join Date: Dec 2002
Location: Katy, TX, USA.
Posts: 16,737
LCHIEN will become famous soon enoughLCHIEN will become famous soon enough
Send a message via AIM to LCHIEN Send a message via Yahoo to LCHIEN
Quote:
Originally Posted by cgallery View Post
Did you try replacing the original 15a breaker before adding the 20a circuit?
That would be my question - perhaps your 15A breaker was bad.

My point is that a 15 Amp breaker will allow at least 15amps average to be delivered to those motors for a long time. A 20A breaker will allow 20 Amps average to be delivered to those devices for a long time, it has no conscience.

If you push a 15A motor to draw 19Amps it will burn out quickly. Because the magnetics of the motor will be saturated and the current will just end up heating the motor rather than doing mechanical work. The 20Amp breaker will allow it to self destruct.
__________________
Loring in Katy, TX USA
If your only tool is a hammer, you tend to treat all problems as if they were nails.
PM me (with your e-mail address) for a copy of the BT3 FAQ current vers 4.13

Last edited by LCHIEN; 12-31-2006 at 03:29 AM.
Reply With Quote
  #10  
Old 12-31-2006, 03:03 AM
LCHIEN's Avatar
LCHIEN LCHIEN is offline
Internet Fact Checker
 
Join Date: Dec 2002
Location: Katy, TX, USA.
Posts: 16,737
LCHIEN will become famous soon enoughLCHIEN will become famous soon enough
Send a message via AIM to LCHIEN Send a message via Yahoo to LCHIEN
Quote:
Originally Posted by lcm1947 View Post
OK you got my interest Loring. So then with that knowledge am I correct in thinking all my circuits for my tools like my DeWalt chop saw, band saw, drill press, etc should be on a 15 amp breaker? How about the HF DC? It's suppose to be rated at 20 amps so I assume that's really the only tool where I should use a 20 amp breaker then right?
A 20 Amp breaker would simply be to protect the dwelling from fire due to overcurrent in the wiring, caused by a fault (likely catastrophic short) in one of the loads or perhaps the wiring itself.

It (15 Amp breaker used with single tools) should be adequate and provide maximum protection. You would want to use a larger breaker if you were running several loads on a single circuit, whose total was more than 15A but less than 20A. But the possibility exists, unless the individual loads were fused or protected by internal circuit breakers, any device on the line could be damaged by overcurrent.


I believe you are incorrect about the HF 2HP DC. It is rated to draw 14 or 15 Amps and I have confirmed mine draws 14.7 amps (67 Amps on startup) when running with no hoses attached - pretty much the maximum airflow condition and hence maximum current condition. I run mine on a 15A circuit without tripping any breakers.

from the HF webpage:
Powerful 2 HP dust collector creates a dust free working environment. Develops over ten times the suction of most shop vacuums. Works with a 4'' hose to pick up large chips from jointers, saws, shapers and planers. Hose sold separately.
  • Locking casters
  • Lockable on/off toggle switch
  • Motor: 2 HP, 110V, 14 amps, single phase
  • Bag capacity: 70 gal.
  • Air flow: 1600 CFM
  • Single stage
  • Filtration: 30 micron
  • Hose inlet: 4''
  • Overall dimensions: 75-1/2''H x 33''L x 22''W
  • Shipping weight: 145 lbs.
  • CSA-US certified

ITEM 45378-7VGA
__________________
Loring in Katy, TX USA
If your only tool is a hammer, you tend to treat all problems as if they were nails.
PM me (with your e-mail address) for a copy of the BT3 FAQ current vers 4.13

Last edited by LCHIEN; 12-31-2006 at 03:14 AM.
Reply With Quote
Reply

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
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

Forum Jump


All times are GMT -4. The time now is 01:18 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Copyright 2002-2014 - BT3Central, LLC.