220V dryer sparked on startup (3 wire) What to test?

[Danny D'Amico]

The wife said the dryer was sparking "in the back". I moved things around, but didn't see anything so I tell the wife not to worry.

A week later, I turn on the 220v 3-wire dryer, and a single bright white spark snaps in the back, between the dryer and the 4-foot 6-inch diameter aluminum corrugated lint pipe connect to the outside vent.

Huh?

Could it be static electricity? Could it be the dryer frame is hot? What do I test?

The only connection to the wall is the three-pronged 220v dryer cord, which looks perfectly fine when I remove it from the wall outlet.

There is no specific "ground" wire from the dryer to anything (should I have put a ground wire in to the 120 volt outlet nearby?).

What would you test? If you need pictures, just ask.

[Stormin Mormon]

My gut sense, is that something is loose inside the dryer. Something (sounds like) is touching the case of the dryer, and charging it.

I'd pull the plug, check for continuity between power and ground prongs of the plug. I'd also open up the case, and look for bare, burnt, or loose wires.

Do you have any friends with electrical skills?

[Ralph Mowery]

It could be static electricity. Is the 4 foot long vent pipe seperated from the dryer by some material that does not conduct electricity ? If so you may want to connect a wire between the pipe and dryer. It does not have to be very large as almost no curent is going through it, just high voltage.

You may also want to look at the dryer where the power wire is. As this is only a 3 wire cord make sure there is a strapgoing from the neutral wire to the frame of the dryer. This should be factory installed so it can be used for 3 wires or bent out of the way if a 4 wire cable is used.

While it may not trip a breaker, I would think it might if there was an intermittant short in the power wiring.

[Tony Hwang]

Hi, What is your multi-meter doing? How about measuring things between vent pipe and dryer body for a starter? 220V can kill.....

[Danny D'Amico]

This is the 3-pronged 220 volt cord connected to this dryer:

I think, IIRC, two of the prongs are 120 volt hot wires, 120 degrees out of phase (that's the 220 volts); while the third, I think, is a neutral wire.

So, I think, IIRC, the 120V circuitry in the dryer (e.g., the light bulb and the controls and perhaps even the motor) run off one of the hot wires and the neutral; while the heater runs off the full

220 volts from the two hot wires and the neutral.

So, there is no ground that I know of, if I understood this correctly. That's why I asked if you guys ADD a ground wire in this situation?

[Danny D'Amico]

I'm not sure HOW static electricity could build up, but, that's the only thing, at the moment, that makes sense to me.

Here's a picture of what the vent hose looks like when it's all in place:

Here's a front view:

[Danny D'Amico]

Hmmm... There is no *external* 'strap" going to the steel frame of the dryer. Are you saying there should be an *internal* strap that I can look for?

[dpb]

On 11/14/2013 7:25 PM, Danny D'Amico wrote: ...

No, you misunderstood (or the reference you looked at was wrong; I didn't check it) -- the third wire is the ground but NEC until relatively recently allowed the ground to also be the neutral in specific instances, the household dryer likely the most prevalent followed closely by electric range.

The "blinding flash" _may_ have been one of the two heater coils failing

-- does the dryer still reach full temp and otherwise function properly as far as you can tell? If it's now taking a lot longer for things to dry, likely you did lose an element.

If, as somebody else noted, it didn't trip the breaker the likelihood of a short other than the element is minute. In 60 yrs in a dry climate I've never seen a static electricity flash from a dryer vent or even got a shock so don't say it's not possible but surely sounds far-fetched hypothesis to me.

OTOH, when wife sewed a lot or when were many cloth diapers so that straight or safety pins accidentally getting in the dryer caused fair number of element shorts when one would finally manage to get thru the vent holes in the rear of the drum and land across a heater coil. Or, they do eventually fail on their own...

[Ralph Mowery]

This looks like a 3 wire power cord. You need to unplug the dryer and open up the back where the wire goes in. Look and there will be 3 terminals the power wire hooks to. It will probably be the middle wire that is the neutral and there should be a strap going from there to the frame of the dryer.

While the dryer is open look around for any black or burnt areas near wires or the internal electrical parts.

[Danny D'Amico]

You seem to understand this better than I do.

The way *I* understand a "ground" is that a ground wire carries no current (unless there is a problem). The "neutral" wire, on the other hand, *always* carries current.

That's a pretty big difference (as I understand it anyway).

More specifically, the way I understand a ground wire, is that it goes from the receptacle in the wall to the main breaker panel, where it literally is driven directly into the ground (usually by some kind of bar).

In contrast, the neutral wire, as I understand it, goes to the same breaker panel, but then it goes from there to the power pole, and then from that pole it may travel hundreds of feet to a few more power poles, but eventually, it too is driven straight into the ground.

The difference, as I understand it, is that the ground never carries current (unless there is a fault), while the neutral is always carrying current (and therefore it might have a potential on it).

Given that they're not at all the same thing, I then have trouble understanding the statement that the ground is "also" a neutral.

Again, you seem to understand better than I do, but, the way I described it above, a ground and a neutral are totally different things.

So, I don't understand how a ground can 'also' be a neutral.

[Danny D'Amico]

As far as I know, the dryer works just fine.

My wife said it was making static sounds in the back, when she turned it on about a week ago, which I had dismissed until I saw the bright spark at the aluminum vent hose when I turned it on.

The spark happened quickly, so, I'm not exactly sure *where* it was, but, it was *OUTSIDE* the dryer.

The white spark *appeared* to be between the dryer frame and the aluminum vent hose, as shown in this picture in a RED mark:

[Danny D'Amico]

This is good to know, since the static electricity idea was the only one I could come up with that was benign.

I would agree that static electricity isn't likely, so, let's forget about that.

But, if it's not something benign, then I need to figure out WHAT is making that spark, and why.

The whole fact that there is no explicit ground is part of what confuses me.

I'll check to see if the body of the dryer is hot with respect to ground.

[Danny D'Amico]

Just to confirm, there is a breaker in the laundry room and it has not tripped.

So, whatever it is, it isn't pulling enough current for a long enough time to overheat the breaker switch.

[Ralph Mowery]

The power comes into your house by 3 wires. At the pole is a transformer that has a wire on each end of a coil and one from the center. If you only used 240 volt devices there would be no need for the neutral wire. If the power usage on each side of the 120 volt lines were exectally the same there would not be any need for the neutral going to the pole. As the sides are not exectally ballanced and often not ballanced very well at all, the neutral carries the unballanced current. In the house the 120 volt circuits use one of the hot wires and the neutral for the return.

At your breaker box the neutral is bolted to the frame of the box and it also goes to the recepticls and other parts of the house. The ground wire goes to a rod outside the house that is driven into the ground. It is bolted to the frame of the breaker box. It then also goes whever the power wires goes to such as the recepticals. In effect the neutral and ground wire are the same wire, but perform differant functions. Often the neutral or ground wire may be a differant size than the two hot 240 volt wires. If the neutral and ground wires are the same size, there is no electrical reason that you could not use either of them for the ground or neutral. YOu do not want to do this as it can create great confusion to the people doing the wiring. That is one reason the neutral is insulated and white and the ground is either bare or green.

The two hot wires may be red and black or maybe just two black wires as it does not usually mater which wire is hooked to which side of the 240 volt device.

YOu are correct, there should not be any current on the ground wire unless there is a problem. If one of the hot wires shorts to the frame of the dryer and there is no ground or neutral (on a 3 wire plug) connected to the frame, it becomes 120 volts to ground and if you or anything conductive gets between the frame and the real ground or another device that has its frame grounded, there will be current flowing and could shock or kill.

If in the 3 wire circuit the neutral becomes disconnected down line of the dryer, the frame of the dryer will become hot with 120 volts minus a small ammount. That small ammount could be the timmer and light bulb in the dryer that is still connected to one side of the 240 volt line. That is the reason for using the 4th wire that is only connected to the frame of the dryer in later years.

[Stormin Mormon]

You're out of your field of training, here, my friend. I'd suggest you find someone you can trust, who knows some about electricity.

Two hots, and a ground. No neutral wire.

[Stormin Mormon]

Please be careful listening to this person. Three wire dryer connection has two hots and a ground. No neutral. And, you'd never deliberately connect a neutral to the frame or case.

[Stormin Mormon]

Three wire cord doesn't have a neutral. Two hots and a ground.

[Stormin Mormon]

Both go to the Earth. Small loads like a timer, can flow a small enough current, that it doesn't noticeably raise the electrical potential of the ground line.

[WW]

Hi, What is your multi-meter doing? How about measuring things between vent pipe and dryer body for a starter? 220V can kill.....

Tony,,, You can only get the one leg of voltage to ground on a 220 volt system on a dryer. However that also is dangerous. The OP may have a sagging heater coil that is touching the case. If he is not handy on this stuff, time to get an appliance repairman to check and repair it. WW

[Ralph Mowery]

Hate to inform you, but in a 3 wire dryer socket there are 2 hots and a neutral. There is no ground. Go here and learn.

Also notice the picture where the frame of the dryer is attached to the neutral wire.