Slow blow circuit breaker

[Rick Levine]

I installed a Woodtek 3 hp DC which, according to the specs draws 19A. I had the electrician install a 20A circuit breaker on a dedicated 10ga drop. The problem is that when I try to run the DC the circuit trips. I replaced the 20A with a 30A and it works fine. I'm not sure this is the best solution. It was suggested that I replace the 30A with a 20A slow blow breaker. Is that the correct solution?

[Steven Triggs]

If it is rated for 19 amps, it should be on a 30 amp breaker anyway. A dedicated machine load shouldn't pull more than 85% of what the circuit is rated for. Since you have 10 gauge wire, it is sufficient for 30 amps.

[Howard Acheson]

If your tool draws 19 amps when running, it draws considerably more on start up. Also, is good wiring practise to only load a circuit to 80% of it's capacity. In other words, a 20 amp circuit should not be loaded with more than 16 amps.

Your 10 gauge wire will be fine for 30 amps. Change the breaker and also change the outlet and plug on your tool to 30 amp devices.

[Steve knight]

a dc really sucks power when starting up far more then any other tool.

[Andrew Williams]

From the Baldor website I looked up some performance characteristics on a 5HP motor with 19.5 amp nominal draw. At 150% of rated load it draws 29.9 amps! Since this data is included on the chart it makes sense that 150% is a load that could occur in a real-world situation, such as spinning up a motor with a huge load of resistance on it. Interesting that your 3HP motor appears to have similar characteristics to the Baldor 5HP.




http://www.baldor.com/products/perfd...40C+AMB%2DCONT

[Bill Turpin]

All motors that start from a dead stop pull locked rotor amps (LRA). This is SIX times full load amps (FLA). Your name plate should list these values. Motors that are properly sized, in good repair, and with proper voltage will pull this for much less than a second on start-up. As any of the above three items go south the LRA time increases. Breakers and motor starter overloads actually trip at about 115% of load rating. This allows for normal motor starting without tripping. Dead shorts (instantaneous infinite amps) will over-ride this built in time delay. So your motor pulls at least 100 amps for about a quarter of a second. Fans must start moving the air before reaching full speed, consequently the time is much longer before amps drop. Once the motor's magnetism is balanced by full speed, the amps drop to FLA.

The breaker protects the wire, not the motor. Thirty amp breaker is perfectly safe and to code.

Bill in WNC mountains

[Tim Malyszko]

a dc really sucks power when starting up far more then any other tool.

My Delta dust collector pops the 20 A circuit just about every time I start it up "cold" on a chilly day. In days above 50 degress, it isn't a problem and starts up fine. Also, on cold days, once it's running for a few minutes, I don't have the problem of tripping the breaker when I shut it down and start it up again.

[Rick Levine]

Here's the question. I discovered that the line is yellow (new construction Romex) and is 12ga. It is a home run of about 40 feet. The DC is and will be the only piece of equipment ever on the line and according to the specs, draws 19A. During the initial startup it peaks somewhere above that figure and the 30A circuit breaker handles it. Will a 20A slo blo circuit breaker work, if there is such a beast? I know they are available in fuses but I can't seem to find one by Square D, HOM version.

[Charlie Velasquez]

There are many more knowledgeable people on this list that can probably give you more information...and I am wrong more than I am right.... but... I think... you need to look for the
Square D HOM120HM the HM stands for high magnetic. I believe it will allow up to 20X the rated amperage for a few milliseconds.... Please confirm with a "knowledgeable" salesperson (the salesperson at our local BORG didn't know the difference between this and a GFCI) or an electrician to verify. But maybe this is at least in the right direction

(FIRST EDIT): Never mind, I just noticed that this is for 240 VAC, but I think they make them in 120 VAC... I wil do a quick search.....

(SECOND EDIT) http://ecatalog.squared.com/catalog/.../17401013.html sure looks like they have them in the 120 VAC... but....

[Bill Turpin]

A thousand cubic feet of air at 50°F weighs 78 pounds, 72 # at 90°F. The motor has to get all that weight moving before LRA goes away. That extra six pounds is the difference in whether it tripps or not.

Bill

[Rick Levine]

Charlie,

Actually, I need a 240v 2 pole breaker. I'll call them on Tuesday and see if they carry them.

[Bruce Wrenn]

Go to electrical supply house and get a HVAC rated breaker. They are made to stand momentary inrush of current. I have a heat pump compressor that will kick a 20 amp breaker in an instant, but has never blown 20 carteridge fuses. Finally had to up grade to a thirty amp breaker and wire, but kept 20 amp fuses, No more problem.

[Ryan Myers]

You need to to use an HACR type breaker which is a time delay CB. Your wire ampacity should be rated 125% larger than the FLA of the motor. Then you could use a larger overcurrent device, such as a 25 amp circuit breaker. The electrician should have installed 10 guage wire, but maybe he didn't know the actual nameplate data when he installed the wiring. If he did I would question his abilities.