Tripping Breaker ??


Old 10-21-04, 08:57 PM
Thread Starter
Join Date: Oct 2002
Location: USA
Posts: 44
Question Tripping Breaker ??

When we wired my workshop we added two new 20 amp circuits for outlets around the perimeter of the shop- They run together from the panel to a fused shut off switch in the shop (child safety).

I have been having problems with the breaker tripping when I start a saw. Either the miter saw or the table saw. There can be nothing else running at all on the circuit and still have problems. It has been happening more recently. After I reset the breaker, it will generally be fine for the rest of the day.

All the wiring was done by a pro.

I heard something about problems with motors starting if they are on the wrong wave of the 60 hz cycle, but was not sure what it was all about and what you do about it.

Any Thoughts??

Thanks so much in advance for your help and wisdom - I'm stumped.

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Old 10-21-04, 10:01 PM
Join Date: Sep 2000
Location: United States
Posts: 18,497
Eventually the breaker will break. But that might be quite a while from now.

You could try replacing the breaker. It might or might not help, but it's only a five buck experiment.

If you try to start your saw under load, this is more likely to happen.

Is the breaker a GFCI breaker? Maybe it's not an overload.
Old 10-22-04, 07:52 PM
Join Date: Aug 2004
Location: USA
Posts: 31
It may be caused by the in-rush current that happens when a motor is first turned on. The motor is cold and sitting at rest. Voltage is applied when you push the switch. It strains to overcome the weight of the rotor and the drag of the cold oil or grease. This initial effort causes a lot of current to be drawn. The current draw goes up and the voltage goes down. You may even notice lights dimming for a moment. As it starts to spin it builds up heat which thins the lubrication. The rotor is now spinning and is easier to keep spinning. The current goes back down to the rated value on the dataplates on your saws and the voltage goes back up to normal. This happens every time you start it but it is most severe when totally cold.

If the saws are getting old then they may need to be cleaned and relubricated. Also as previously mentioned, make sure no extra load is on the saws such as sawdust in the bearings, the blade touching the wood, or maybe a string wrapped around the shaft.

Check that all electrical connections are tight and enough wire is under the screws.

If you are using extension cords make sure they are also rated at 20A or they can become the weak point in the circuit and cause high current draw.

If a "Pro" installed the circuits then either the Circuit Breakers or recepticles should be GFCI type since that is required in all garages.

Have you looked at the breakers with your own eyes to make sure they are 20A?

Are you sure there are two separate circuits?

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