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Old 12-09-2011, 12:18 AM   #1
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Default Buzzing from dishwasher breaker and weird current draw?

I had a power quality meter hooked up to my house's panelboard to get an idea of how much power I was using at certain times of the day (yes, it was overkill). As I was getting ready to disconnect it and return it to my work, out of curiosity, I checked the scope function. I noticed the dishwasher appeared to be dragging the voltage down for a millisecond or so near the drop of each peak. Is this to be expected or does this indicate a problem with my dishwasher?

Here are pictures of the voltage and current waveforms: http://imgur.com/a/tDxqC (note that the color coding on the amp reading is reversed from voltage - I must've had the CTs swapped).

Also, since I was close to the panelboard when disconnected this, I noticed that there was a faint buzzing sound coming from my expansion subpanel. It went away whenever the dishwasher momentarily shut off between its cycles, so I assumed it was from the dishwasher's breaker. I tried gently pressing on the breaker and didn't notice a difference. My ammeter read about 7.5A for that circuit (it's a 15A breaker). After taking my clamp off the wire and the wire snapped back, I did notice a slight change in volume/pitch (probably volume). Any ideas?

Thanks in advance!
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Old 12-09-2011, 08:08 AM   #2
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It sounds like the stabs behind that breaker are bad
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Old 12-09-2011, 05:25 PM   #3
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Quote:
Originally Posted by mcclary's electrical View Post
It sounds like the stabs behind that breaker are bad
?????????????? Kidding right??

This buzzing is what we used to refer to 60 cycle hum, but in reality it was the vibrating of the mechanical fingers inside of the breaker, which is usually caused by dust/etc and not making complete contact. When you snapped the wire back it moved those fingers a bit from the lug ,changing the sound a little. It's almost like pushing on a buzzing contactor.........
Replace the breaker.

Last edited by mrmike; 12-09-2011 at 05:30 PM.
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Old 12-09-2011, 06:24 PM   #4
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Quote:
Originally Posted by mrmike View Post
?????????????? Kidding right??

This buzzing is what we used to refer to 60 cycle hum, but in reality it was the vibrating of the mechanical fingers inside of the breaker, which is usually caused by dust/etc and not making complete contact. When you snapped the wire back it moved those fingers a bit from the lug ,changing the sound a little. It's almost like pushing on a buzzing contactor.........
Replace the breaker.


60 cycle humm is what gets induced onto phone lines that are too close. A piece of metal vibrating is not 60 cycle hum. Look at the guys scope pics. 60 cycle hum causing that too? I worked on a few thousand panels and they should not be buzzing.
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Old 12-09-2011, 09:51 PM   #5
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I am going with MR. Mike- change the breaker and take a new reading.

Everything now has some type of switching for the motors. I am not sure how that meter records a VFD waveform, but its possible that is what you are looking at.

As far as the spikes, see what happens when you change the breaker before you get too concerned.

Is the dishwasher a pretty new model? Like I say, I don't know much at all about dishwashers, but most everything has a form of VFD of some kind today.
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Old 12-10-2011, 07:04 AM   #6
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Quote:
Originally Posted by mcclary's electrical View Post
60 cycle humm is what gets induced onto phone lines that are too close. A piece of metal vibrating is not 60 cycle hum. Look at the guys scope pics. 60 cycle hum causing that too? I worked on a few thousand panels and they should not be buzzing.

Please read my post again! I did not say it was........... and your definition of 60 cycle hum is very vague.............
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Old 12-10-2011, 07:08 AM   #7
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Originally Posted by lefleuron View Post
I am going with MR. Mike- change the breaker and take a new reading.

Everything now has some type of switching for the motors. I am not sure how that meter records a VFD waveform, but its possible that is what you are looking at.

As far as the spikes, see what happens when you change the breaker before you get too concerned.

Is the dishwasher a pretty new model? Like I say, I don't know much at all about dishwashers, but most everything has a form of VFD of some kind today.


That's what I said, change the breaker.
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Old 12-10-2011, 10:44 AM   #8
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That's what I said, change the breaker.
Sorry, I was trying to Multi-task. I cant do it, I can barely "single task" anymore.
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Old 12-10-2011, 09:45 PM   #9
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Quote:
Originally Posted by cerfsud View Post
I had a power quality meter hooked up to my house's panelboard to get an idea of how much power I was using at certain times of the day (yes, it was overkill). As I was getting ready to disconnect it and return it to my work, out of curiosity, I checked the scope function. I noticed the dishwasher appeared to be dragging the voltage down for a millisecond or so near the drop of each peak. Is this to be expected or does this indicate a problem with my dishwasher?

Here are pictures of the voltage and current waveforms: http://imgur.com/a/tDxqC (note that the color coding on the amp reading is reversed from voltage - I must've had the CTs swapped).

Also, since I was close to the panelboard when disconnected this, I noticed that there was a faint buzzing sound coming from my expansion subpanel. It went away whenever the dishwasher momentarily shut off between its cycles, so I assumed it was from the dishwasher's breaker. I tried gently pressing on the breaker and didn't notice a difference. My ammeter read about 7.5A for that circuit (it's a 15A breaker). After taking my clamp off the wire and the wire snapped back, I did notice a slight change in volume/pitch (probably volume). Any ideas?

Thanks in advance!
Everyone here knows that the electric meter will not correct for low power factor; Your dishwasher is doing the best that it can do.
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Old 12-10-2011, 09:55 PM   #10
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Can you get a current draw with the same time period? I wonder if you're seeing a sag caused by some sort of load in the dishwasher, and would be interested to see what the peak current was.

-John
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Old 12-11-2011, 08:09 PM   #11
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OT: is that a 435 you are using?
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Old 12-11-2011, 09:59 PM   #12
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I replaced the breaker, but the noise still persists. The bus bar behind the breaker looked fine. I didn't check tightness on the neutral, though, so I'll do that when the dishwasher is finished (it's running right now).

There were two images in my link, btw, but people seem to be skipping over the second, so here they are:

Voltage: http://i.imgur.com/wnVpf.jpg
Current: http://i.imgur.com/JRJZE.jpg
(these are for my whole house, not just the dishwasher, but the current spike and resulting voltage sag are definitely from the dishwasher - they disappeared whenever the dishwasher cycled off momentarily)

Yes, the meter is a Fluke 435.
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Old 12-12-2011, 10:49 PM   #13
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your scoping your dishwasher - and i cant get a scope to check the noise on a single phase to three phase conversion from my VFDs -

I just dont know what to make of that.

1. Does your dishwasher work?
2. Is the buss behind the offending breaker bad?
If 1 is yes and 2 is no then close the panel and put the meter up.
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Old 12-12-2011, 11:02 PM   #14
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i herd the same thing from a front load washer today. New sub panel i just put in. IDK.
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Old 12-14-2011, 08:35 AM   #15
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Hi: Try tightening the Neutrals in the panel & metering box, as for your Dishwasher it's probably working fine. When your scoping the AC supply you can get some unusual traces when you've got appliances running & switching loads on / off continually.
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