GFI Puzzle

[John K Jordan]

Hi, I made a longwinded explanation of how it works, how to wire it, and apparently hit the wrong button because it isn't here. ...

Yikes, that's frustrating. I've had SMC mysteriously forget message text I've spent a lot of time on, especially if I switch briefly to another tab in the browser or use another application. For protection, I've learned to hit Ctl-A/Ctl-C to quickly select and copy the text to the Clipboard before doing ANYTHING else or clicking on any buttons, even the Post or Preview buttons. If I use another tab to find a link or text to copy and paste in a message it would overwrite what I have in the Clipboard so I open Notepad, paste the message so far there, then get my link. That way if the message disappears I have a copy at hand.

BTW, the dumbest mistake I've made (dumb because I've done it twice) is compose a message then for some reason click the "+Reply to Thread" button instead of the Post. Sometimes "back" doesn't. The second dumbest thing I've done to make a message disappear is do a preview then get distracted and forget to actually post it. :-( Later I wonder, where is that message!

JKJ

[Doug Hepler]

Sean and Artie -- yes, that's what makes SMC special. I actually started out on another forum but I got tired of the trolls. The mods here do a much better job of keeping the discussions on a professional level.

BTW Artie you're a prince

Doug

[Arthur Fleming]

Well last night as I was in the basement, doing laundry (I'm not that nice a guy, the Missus is recuperating from some surgery, stairs are still offlimits) (I did learn that they are less than happy if you put their bra's in the dryer LOL) I was thinking about the problem, and it dawned on me that the remote controlled switch part of the equation is probably a nonstarter. I sincerely doubt that the on/off switch on the dust collector is a two pole switch either, so if you turned off the DC using it's switch, there should still be a wind down, inducing back fed currents. Like Bill said previously the click sound is most likely the centrifugal switch opening, sending the induced current through the starting windings (more powerfull), instead of the running windings. This would send a larger current back to the gfi. This is why there are time delay fuses for motors. The relay should still eliminate this, but it would seem that this should happen regardless of whether the remote controlled receptacle is used. So Doug apparently you and your DC are the going to be the main part of this science project LOL. How often does the DC usually trip the gfi? 50% of the time? 25% of the time? Just often enough to be an irritation? Wondering how long it will need to go without tripping before we judge this a success. Maybe I should just stop laundry LOL. Artie

[Doug Hepler]

Artie,

It happens just often enough to be a nuisance, but it seems the intervals are random. It will go for 10 or more cycles without tripping the breaker and then trip the breaker every other cycle for a while, and so on. As far as I can recall (aging brain) this did not happen once for the months that I was operating the switch on the DC itself. It started after I installed the remote. At first, I blamed the remote and got a replacement, but that did not correct the problem.

I can't tell, but the switch on the DC is heavy-looking. Maybe it is a DP switch. I can ask Jet customer service.

Your original theory is still worth a try. If making a contactor becomes more trouble than it's worth for you, I'll be glad to buy one if somebody will tell me what product to ask for. I was confused by the lower voltage for the coil on the ones I saw. It sounded as if they needed a secondary 12- or 24-V external circuit to operate the coil in addition to the main 115V circuit being switched. As I said before, I understand the theory but not the practical realities.

Happy laundry. You still have a lot to learn, I see.

Doug

[Rick Christopherson]

I've avoided commenting on this until now, but I think this needs to be clarified as to the cause before someone starts chasing money.

The reason the GFI is tripping is not because there is a single pole disconnect. If that were the case, it would do it all the time, and as soon as the switch was opened.

The reason this occurs when he hears the centrifugal switch re-engage, is because the start winding in the motor has stored magnetic energy, and the switch closes to permit this to suddenly drain back into the system. It is an unexpected current that did not originate from the mains.

A GFI uses a differential amplifier to detect the imbalance in lines, which is extremely sensitive to a difference between its lines. A sudden phase shift will cause an inexpensive GFI to trip. The easiest solution is to use a higher grade GFI, or remove the GFI completely from the particular receptacle. While installing a 2-pole contactor would fix the problem regardless of cause, it does over complicate the issue.

[Arthur Fleming]

Doug, making this is easy, and actually will be a little fun, also I'm curious to see if this fixes the problem. I'm hoping to get it completed tomorrow, but with that being election day (thankfully!) things could get busy (We're responsible for the voting booths staying powered). This sounds like a circumstance that could occur somewhat often so I'm interested in seeing if this works. If you're game to using it, and letting us know what happens, I'm game for making it, and getting it to you. Does your DC have the option to be wired for 220 volts? If so, there is a much greater chance the on/off mechanism/switch is a two pole type. As for the laundry, my experience as a husband is, if you are real good at something, you will always have to do it . Artie

[Arthur Fleming]

Rick I'm thinking we're saying the same thing, but differently. Yes it would seem that it should happen all the time. He has a gfi breaker (I believe he said in the first post) these are usually a better gfi than the receptacles in my experience. Swapping the breaker out for a regular breaker should indeed solve this issue, but it is probably removing gfi protection that is code mandated. (Here in Mass. they pass the state Code as law, so it is actually illegal to do so). Making an isolating relay seems to be a pretty easy fix, if I'm correct on what's happening. I may not be, but this will give certain proof of that if it doesn't work. Various factors that could affect why it's an intermittent condition could be voltage drop, other machines running on the same circuit while the DC is being shut-off, absorbing any induced back current. I think I can scavenge the parts, and get them to Doug, cheaper than the cost of a new gfi breaker (and maybe the cost of an electrician to install it, depending on Dougs electrical skills. They are more difficult to install than a standard breaker). On forums I am very loathe to give any electrical advice unless I am sure it can't make the situation any worse. I can't see this fix adding anything negative to Dougs situation. If I'm wrong the DC should continue to operate as it's currently doing so, and if I'm right, should stop the nuisance trips. I'm guessing the panel is not in the same room as the equipment. Not having any knowledge of Doug's work shop, a simple test could be to plug a drop light into the same outlet as the remote controlled receptacle is plugged into, and leaving it on while the DC is in operation, and only turning it off after the DC motor has completely stopped turning. I would guess that the light bulb would absorb any back feeding currents. On a separate note, I'm about to go down to the basement and add a sub panel for my (hopefully) forthcoming workshop

[Mike Henderson]

The reason this occurs when he hears the centrifugal switch re-engage, is because the start winding in the motor has stored magnetic energy, and the switch closes to permit this to suddenly drain back into the system. It is an unexpected current that did not originate from the mains.

To clarify Rick's comment just a bit, it's unlikely that the starting winding has any stored magnetic energy. A coil cannot store energy for any appreciable length of time. As soon as current stops flowing in the coil, the magnetic field collapses and can self induce continued current flow. But that happens very quickly and the starting coil has been disconnected from the circuit for a very long time by the time the motor is turned off.

However, in the starting circuit is a capacitor, which can store energy for a very long time. If that discharges (somehow) when the centrifugal switch closes, it can send current someplace.

But that someplace is a problem. For current to flow, you must have a complete circuit. So if you have a capacitor and you touch one pole of the capacitor, you will not be shocked because the current must flow from that pole, through you, to the other pole.

Since the black line has been broken by the time the centrifugal switch cuts in, the only way current could flow in the white line is if there's an arc across the black line switch points, or if the current flows between the white (neutral) and ground.

We're always warned about handing a starting capacitor if disconnecting it shortly after running the motor because it could still have a charge. That's because when the motor is turned off (one line or two) the capacitor may not be able to discharge.

Mike

[Doug Hepler]

Artie, There is "always" at least one lamp on the same branch as the DC and remote switch to illuminate whatever I am doing. [Edit: Yes the DC can be wired for 220V.]

Rick, I'm game to try the DP contactor solution that Artie has proposed. If that does not work, I will explore a new breaker as the solution. I am not up to swapping the breaker myself and would not know what to get, anyway. So trying a contactor would be the cheaper alternative at this point. GFCI in garages is code in Golden AFAIK and I won't ask an electrician to violate it.

Doesn't this theory make sense if the built-in switch on the DC is DP? Then when the DC is turned off with that switch the induced current would not feed back into the mains, but with that switch always closed, the nature of the remote switch becomes the issue. Does that make sense?

I spoke to Jet Tech support and the tech did not know whether the switch on the DC is SP or DP. He said that my problem "happens sometimes." (It was on the phone so I could not see the mechanics shrug that went with it.) Big Help.

To keep this in perspective, this is a nuisance issue. It has become more interesting as time goes on, but I can live with it. The entry panel is across the room. I just don't feel comfortable having to reset it so frequently. The switch on the DC is very hard to reach and also is often across the room from where I am working. A remote switch is a great convenience but not that huge a deal in the great scheme of things.

This is interesting. I appreciate the input.

Doug

[Arthur Fleming]

I will plead complete ignorance about capacitors, think I have replaced maybe three in the past 35 years. My thought was where Doug had said this seems to occur at the same time as a click sound comes from the DC motor, the centrifugal switch is switching back to the starting windings as opposed to the running coils, creating a stronger induced current into the circuit, the armature is still turning, so it will induce a voltage/current. Whether this can trip a gfi, I don't know, only guessing. The neutral line being tied into the ground at the main panel, may be giving the induced voltage/current a place to go. I am still thinking that a small wattage, incandescent bulb plugged into the same circuit, and on, would absorb this, and stop the nuisance trips. WE HAVE A SCIENCE PROJECT! Artie

[Mike Henderson]

I will plead complete ignorance about capacitors, think I have replaced maybe three in the past 35 years. My thought was where Doug had said this seems to occur at the same time as a click sound comes from the DC motor, the centrifugal switch is switching back to the starting windings as opposed to the running coils, creating a stronger induced current into the circuit, the armature is still turning, so it will induce a voltage/current. Whether this can trip a gfi, I don't know, only guessing. The neutral line being tied into the ground at the main panel, may be giving the induced voltage/current a place to go. I am still thinking that a small wattage, incandescent bulb plugged into the same circuit, and on, would absorb this, and stop the nuisance trips. WE HAVE A SCIENCE PROJECT! Artie

Just a note, Artie. An induction motor only has power to the field coil. When you remove the power, the magnetic field of the field coil disappears, and when it disappears, the magnetic field of the rotor disappears (it's called an "Induction motor" because the field "induces" current in the rotor, which provides the magnetic field of the rotor). So the rotor cannot induce a voltage/current in the starting coil, or the field coil, once power is removed.

There are ways to electrically brake a motor but most of them require that you put a voltage into the field coil. For example, putting a DC current into the field will provide a brake effect on the rotor. But if you just turn off a single phase motor, the rotor will not generally induce any voltage/current in any of the field coils.

But even if you could induce a voltage/current in the starting circuit, you have the problem of no longer having a complete circuit (since you opened the hot wire). The current has to go somewhere and there's no such thing as single wire current.

Mike

[Malcolm McLeod]

Doug,
Just to be clear, are you sure this is GFCI breaker? Could it be AFCI? Or, combo AF/GFCI?

The intermittent trip just makes me think it might be an arc fault issue....

[Doug Hepler]

Malcolm,

I don't know. The question had not occurred to me. I just know the facts I described. The breaker has a yellow "test" button on it.

Doug

[Arthur Fleming]

So Mike, care to throw a guess in on what's causing the the gfi breaker to trip on the DC winding down, after it's been turned off? Cause I'm out of idea's if an induced current can't bleed back to the neutral/ground. GFI's generally trip on an imbalance between the hot and neutral. I would think a capacitor could also discharge back to the neutral. I'm still planning on making an isolation relay and see what happens. Artie

[Rick Christopherson]

To clarify Rick's comment just a bit,......

Mike, you need to bone up on your reactive component background. I'm not interested in arguing about it, which is why I didn't enter this thread when it started, but pretty much everything you wrote following my post is wrong. For simplicity, I'll hit the simplest one: Both capacitors and inductors are energy storage devices. You throw in a rotating core, and it becomes even more pronounced. ELI the ICE man.