Chop saw popping breaker

Status
Not open for further replies.
R

reyamkram

Senior Member
Location
Hanover park, il
I have this chop saw (attached picture) it is on a 20 amp circuit and there is only 3 to 5 amps on that circuit, now when I start the chop saw it keeps popping the 20 amp breaker, OK, so, I installed a new 20 amp breaker, it still pops the breaker, now why when I plug the chop saw into a 16 gauge 6 foot extension cord, and the breaker will not pop. Why is that??? Thank you for all and any information.

Resized_20221128_021343.jpg
 
Is the breaker GFCI, AFCI or dual function GFCI/AFCI or just a simple thermal/magnetic breaker?
If it is one of those specialized types the opportunities (causes) for false or unexpected tripping are much more varied.
At first glance it seems there is a very substantial startup surge when the chop saw is turned on. So large that it activates the magnetic trip of the breaker. With that high a starting surge, the resistance of a 6' 16ga cord is apparently enough to limit that excess current. Either the chop saw motor is very poorly designed or the saw is defective.

See also the discussion in https://forums.mikeholt.com/threads/arc-fault-tripping-causes.2569827/ for AFCI tripping.
 
Last edited:
GoldDigger said:
Is the breaker GFCI, AFCI or dual function GFCI/AFCI or just a simple thermal/magnetic breaker?
If it is one of those specialized types the opportunities (causes) for false or unexpected tripping are much more varied.
At first glance it seems there is a very substantial startup surge when the chop saw is turned on. So large that it activates the magnetic trip of the breaker. With that high a starting surge, the resistance of a 6' 16ga cord is apparently enough to limit that excess current. Either the chop saw motor is very poorly designed or the saw is defective.

See also the discussion in https://forums.mikeholt.com/threads/arc-fault-tripping-causes.2569827/ for AFCI tripping.
Click to expand...
It is just a simple Square D-20 amp breaker, it is in an industrial plant, we use it for cutting hoses and 80-20.
 
My Milwaukee chop saw did the same thing on a standard QO 20A breaker. Sq-D makes these breakers in a “high-mag” version for these applications. Mine hasn’t tripped since replacing the breaker with the high mag version.

Previous thread about this:
https://forums.mikeholt.com/threads/why-a-high-magnetic-breaker.1912/

b9e7b3ffb3d7d19d057764bffd442155.jpg
 
reyamkram said:
It is just a simple Square D-20 amp breaker, it is in an industrial plant, we use it for cutting hoses and 80-20.
Click to expand...
The issue is the QO breaker, change it to a HACR breaker and it will work fine.
 
acrwc10 said:
The issue is the QO breaker, change it to a HACR breaker and it will work fine.
Click to expand...
All breakers, built to UL489, are HACR since the early 90s. The HACR rating has nothing to do with tripping points.

As was mentioned, by retirede, use a high magnetic device or one rated for HID loads.
 
Last edited:
I thought that was true as well about HACR breakers. Had a building department comment the other day to make sure certain breakers were HACR. I checked and all the breakers were indeed hacr type. Did I luck out due to manufacturer used. Do they need specified still?
 
Charged said:
I thought that was true as well about HACR breakers. Had a building department comment the other day to make sure certain breakers were HACR. I checked and all the breakers were indeed hacr type. Did I luck out due to manufacturer used. Do they need specified still?
Click to expand...
Some building departments live in the past and so ask to see a label. You can special order breakers with an HACR label, but the UL standards do not require it.
 
Yea when I got the comment I did a little research and saw the ul testing reasoning why it wasn’t a thing anymore. Thanks for the reply. I’m curious about this high magnetic type though. Seems like they could have some good applications.
 
Charged said:
Yea when I got the comment I did a little research and saw the ul testing reasoning why it wasn’t a thing anymore. Thanks for the reply. I’m curious about this high magnetic type though. Seems like they could have some good applications.
Click to expand...
When they were introduced in the late 50's QO breakers tripped at 10X rating which is typical for most residential breakers.
In the 60's(?) the Qwik-Open feature was added, only to the 15 and 20A single pole QO breakers, which opens the breaker in 1/60 of a second.

The QO product line is not named for the Qwik-Open feature. It replaced the XO breaker which replaced MO breakers
 
Last edited:
jim dungar said:
All breakers, built to UL489, are HACR since the early 90s. The HACR rating has nothing to do with tripping points.

As was mentioned, by retirede, use a high magnetic device or one rated for HID loads.
Click to expand...
I did not know that. We had a 30 amp air compressor that kept tripping on start up, on a SQ D panel, about 15 years ago. We changed the breaker and it worked fine, I thought we changed it to an HACR style, maybe not?
 
steve66 said:
Does it have a starting capacitor? Have you checked it?
Click to expand...
This saw (Dewalt D28175) has a Universal (brushed) motor.

Universal motors are known to have an inrush of about 300%, so a 15A universal motor would be 45A inrush, not typically enough to trip a 20A QO breaker. But a universal motor with bad brushes or commutator will draw a lot more current than normal. So chances are that your saw needs some attention.

By using the 16ga extension cord, you are creating a severe voltage drop, basically doing what a soft starter would do. But that is a continuous VD, not temporary, so you are also robbing your saw of speed and torque, plus heating up that extension cord to the point of failure. It’s also likely that by using too small of an extension cord and running at lower voltage, the blade speed is lower, making it take longer to cut, so it has been straining your brushes and may have caused an earlier than normal demise.

Change the brushes and get yourself a 12ga extension cord.
 
Status
Not open for further replies.
Top