My home is 18 years old. Around 4 to 5 years ago, the GFI breaker to the garage began tripping when I turned on certain power tools. I replaced the breaker and everything was fine. Recently the breaker began tripping again, when I would turn on one of two power tools ( a table top belt sander or the table saw). There are three outlets on the circut and one or two overhead lights. The table saw is connected to one of the outlets and the belt sander to another. If I do not turn on either of these two items, I can run a radio a small drill press, a small compressor. However, as soon as I turn on one of the two items mentioned, the circut trips. I repalced the GFI breaker last week and it still trips. Any suggestions on what it might be and how I might run down the problem?

 

Are you talking about a GFCI circuit breaker in your panel or a GFCI receptacle?

 

John, the circut breaker in the panel.

 

Is the breaker tripping on overload or tripping on ground fault? If it is just tripping, you may have too many or too large tools on that circuit.

 

Sounds like a simple overload. You need a second circuit for your workshop. Add a new 20-amp breaker to the panel and wire a new circuit with 12/2 cable.

 

594, how do I determine if it is tripping on overload or on ground fault.

John, I just did a bit more testing, here is what I found. There are no lights on the circut, just four four wall outlets around the wall. I turned everything off and took an electric drill and pluged it in to each outlet and it ran on all outlets without tripping the circut. Then with everything off, I turned on the table saw and the circut tripped. I reset the circut breaker and I turned on the belt sander and again the circut breaker tripped. The belt sander and the table saw are plugged into different outlets.

 

How far and wide did you check for other things on the circuit? Front porch? Back porch? Each and every bathroom? Basement? The other stuff on that circuit could be anywhere so you have to look around.

If there really is nothing else on the circuit (which I consider very unlikely), try temporarily as an experiment only try replacing the GFCI breaker with a regular breaker.

 

The symptoms you describe are consistent with problems I have cleared up before by eliminating a high impedance fault on the grounded current carrying conductor that most of us call the neutral. Such a fault will not conduct enough current to trip the GFCI breaker when the load is light but when the voltage drop on the neutral rises do to the high starting current of the larger tools then the voltage at the fault rises to a level sufficient to conduct the six or more milliamperes that will trip the GFCI's detection circuit. If you disconnect both the neutral and the ungrounded current carrying (hot) conductors at the panel that supplies them you will be able to test both sides of the circuit for it's resistance to ground. Any measurable resistance is unacceptable. Both wires should read infinite resistance to ground when tested with a good meter. In one case I had to apply a megger to a circuit to demonstrate to the owner that it did in fact have a fault between neutral and ground.
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Tom H

 

John, you are correct, I have checked the entire house and what I have found is that the outlets in all of the bathrooms are on the circut. So, I turned everything off in the entire house and re tested the circut by turning on the saw ( the circut breaker tripped) and then the sander ( circut tripped). What I don't understand is that for most of the fourteen years I have been able to run these powertools with no problem and now I can not. As I have installed a new circut breaker ( GFIC), is is likely that the problem is in the wiring or one of the outlets? Thanks for all of yout help.

 

Perhaps you've dropped these tools one too many times (or it happened due to age) and they have developed a ground fault. Try your vacuum cleaner (or a hair dryer) on the garage circuit. Also, try plugging the sander into the bathroom receptacle and see if the circuit trips there too. And don't forget my earlier suggestion of temporarily using a non-GFCI breaker.

 

I tried a couple of more test. I plugged in my circular saw to one of the outlets and it ran fine, so I plugged in an angle grinder and started both the circular saw and the angle grinder at the same time and the circut tripped. I reset the circut and plugged in a 1hp hand sander ( not the sander originally mentioned) and it tripped the cricut by itself. Does this add anything to solving teh puzzle?

John I am not ignoring your other suggestion to try a non GFCI breaker, but it will be next week before I get to town. If I ran an extention cord attached to the table saw or the table top sander to another outlet on a non GFCI circut would that tell anything?

Just tried something else. The overhead lights in the garage are on a circut by themsleves ( non GFCI ). I ran an extention cord from one of the light sockets and both the table saw and the table sander ran fine from the extention cord. Does this help isolate the problem.

Once again, thanks to everyone for their help.

 

Is the breaker tripping or the GFCI tripping? The tools could have developed a fault that trips GFCI.

 

I'd suggest re-reading what hornetd wrote above. I believe that his hunch is most likely correct.

Power is supplied to a receptacle by two conductors, the 'hot' and the 'neutral'. Both of these conductors are equally important in carrying the current.

The neutral conductor in residential wiring is also the 'grounded conductor'. That means that it is the current carrying conductor that is electrically connected so as to be close to '0' V. The 'grounded conductor' is to be distinguished from the 'safety ground wire''; which is supposed to be at '0'V but is not supposed to carry current when everything is working properly.

If you have a 'neutral to ground' fault, then the amount of current flowing through this fault will be quite low, much lower than if you had a 'hot to ground' fault. But enough current can flow through a 'neutral to ground' fault to cause a GFCI to trip.

The amount of current that flows through a neutral to ground fault can depend upon the total current flowing through the circuit, and it may be that you have a minor neutral to ground fault that is only sufficient to trip the GFCI when high startup currents flow to the larger power tools.

If the power tools work when plugged into a _different_ GFCI circuit, then you know that the problem is with the circuit.

If the power tools trip a different GFCI breaker, then you have localized the problem the the tools.

If any other large loads trip the GFCI that you are having problems with, then it probably localized the problem to the circuit.

-Jon

 

joed, it is the circut breaker that is tripping. The cricut breaker was a GFCI and began tripping, so I replaced it with a new GFCI 20 amp. As you will see by my previous post, I have tried these tools on another circut and they run fine. Also, until recently they ran fine on the circut in question.

 

Jon, from my test, it would seem to me as though the problem is in the circut. If so, does that mean it is either a wire or a receptical? Could it be a loose wire attached to a recptical?

 

If this is a neutral to ground fault and only trips the GFCI on the higher amperage tools try disconnecting the ground wire of this circuit at the panel. Then run the table saw or belt sander and see if the breaker holds.

 

Roger, is that the load neutral wire going to the circut breaker?

 

No, leave it connected I'm talking about the bare ground wire that is connected at the neutral/ground bar from the cable supplying this circuit. If the breaker holds with this bare ground wire disconnected and trips with it connected then you have the neutral (white wire) and ground touching somewhere. Leave both the pigtail white wire that goes to the neutral/ground bar and the gfci and the neutral from the cable that goes to the gfci connected.
The neutrals (white wires) are current carriers....the bare grounds are not unless of a fault as we suspect here. If we eliminate the fault path on the bare ground wire by disconnecting it at the panel, then all the current will have to flow on the neutral and the gfci should hold if there is a fault to ground.
I'm not so sure that since you only have a few outlets that it wouldnt be quicker to just pull those outlets and make sure you dont have a neutral receptacle screw or bare part of white wire touching either the metal box (if thats what you used) or bare ground wire.

 

If the circuit will carry the load with the Equipment Grounding Conductor disconnected it would be a strong indication of a neutral to ground fault. One way to isolate the problem is to use an extension cord to walk the load back in the circuit. You have to know how the circuit is laid out for that to be effective. The idea is that if the circuit will carry the load on one outlet and not on another the problem is between those two outlets.

There are other ways to isolate the fault. One involves disconnecting receptacles and measuring resistance to ground in each direction until you find which two outlets are on either side of the fault.

Another way is to rent a circuit tracer and trace the faulted wire until the signal disappears. This occurs at the fault point.
--
Tom H

 

Roger & Hornetd, I'm a little slow, as I'm sure you have figured out. I think I am starting to understand. Is this correct?

The electric cable that runs form the circut breaker to the recepticals has three wires, one black ( power), one white ( neutral) and one bare ( ground ). You are saying that somewhere between the breaker and the last receptical, there may be a neutral and ground touching.

Disconect the copper wire (ground) form the electrical cable and if the circut breaker doesn't trip when I use the power equipment, it is a neutral to ground fault. Meaning the white wire is touching the ground wire or perhaps a receptical somewhere along the line.

 

Yep, you are a quick learner. Reasoning here is there is no current on the neutral until you operate a load (table saw). So is pretty certain that you have a neutral to ground fault. With the gfci at the panel it monitors the entire circuit start to finish. So as soon as it detects a change in the current on the neutral (because some of it is flowing on the equipment ground) when it compares it to the hot wire (black) and "sees" this difference between the two it trips the gfci.
Example: 10 amps flowing on the hot wire (black) and 10 amps flowing on the neutral (white) everything is fine gfci wont trip.......Now 10 amps flowing on the hot wire and 10 amps on the neutral......a ground fault occurs because the equipment ground (bare wire) contacts a neutral screw on a receptacle or any metal on the grounding path. Now lets say that ground fault is allowing 2 amps to flow on the equipment ground. Now you have 10 amps on the hot wire 8 amps on the neutral and 2 amps on the equipment ground. Since there is a difference of 2 amps between the hot wire and the neutral the gfci trips.
What is somewhat strange with your situation is that an electric drill wont trip the circuit but your higher amperage tools will.

 

Thanks to all replys. I will give this a try tomorrow evening and give a you an update. Thanks again.

Jay E