sharing a neutral

[ohm]

I am still going with the coffee pots. If you have an impedance tester, you should be able to see the circuits layout even behind the walls.

There was a thread from the day before yesterday on a breaker tripping when the phone rang. People kept writing in with suggestions after the question was answered. Thing here is, the problem hasn't been solved.

I have several questions on this. I was waiting for someone else to ask before me.

-Has there always been coffee pots at this location?
-If so, are the 2 that fried a different type?
-How big and what type of pots are these?
-How many shifts are run there? Are these pots electronically controlled?
-Are there other things plugged into this recep, or just the one pot?
-I apologize, I can't see a pot frying with a supply of, what did you say, 112V's?
-What about make and model so we can see specs?

I am willing to bet if you open up these pots, you'll find the TCO fried.


Always curious,...........ohhhhh the suspense!:grin: :grin:


More questions after your response to come:wink:

Since circuit #6 supplies two relatively low wattage loads and shares the neutral with six other computers that are doing fine I now cast my vote w/ 76 Nemo!

The coffee pots are GUILTY !:grin:

Got to make popcorn be right back!:grin:

 

[76nemo]

If we had the pots opened up, the answer would be much more clear. I don't know if these are electronic coffee pots, or the older 20-30 cup tanks, they have no electronics. The new and older models all have TCO's. If the pots were electronically controlled, we could learn much more to the story by seeing just what failed in the pots themselves.

 

[76nemo]

Where are you GAR or ELA on this?

 

[ptonsparky]

I vote cheap coffepots and could venture a WAG as to where they are made.

 

[ELA]

76nemo,

I am more of a data driven person and not very good at guessing what the cause of a problem might be. I would agree that the coffee pots should be examined for what the defect is.
Could the circuit in question be monitored with a recording voltmeter over a few days time.
It would also be nice to see more voltage readings taken from each phase - with changing loads on the various phases.

 

[mxslick]

I vote cheap coffepots and could venture a WAG as to where they are made.

Jeeze, all those pages of posts to get to the definitive answer.


Seeing as the computers, etc. are all much more sensitve to power issues than the coffee pots, it doesn't matter which phase they are on, if there was a bad neutral the electronics would have been affected, voltage high or low, or more importantly, unstable.

And did anyone consider that maybe the pots were from a defective production run? It has happened you know.

This is a literal example of a tempest in a (coffee) teacup.

 

[Billy_Bob]

...did anyone consider that maybe the pots were from a defective production run?

This has happened to me a LOT about the past couple of years. I have purchased many things which don't work out of the box and need to be repaired to get them to work. Or they don't last very long before they break - sometime a few months.

Luckily I know how to fix and/or modify many different types of things to get them to work.

Companies used to have quality control. These days they ship products working or not.

 

[LarryFine]

It's also very possible that the circuit with the coffeepot that went bad was subject to too-high a voltage, not only too low. Nobody says it was heating when it went bad, and even if on, other circuits may have had a greater total load.

 

[duhhuh]

sharing a neutral

I appreciate everyone's comments and thoughts:

I have used an Ideal 61-165... what I have found with regards to the coffee pot issue: when a 12a load is applied, the vd is 3%... from 121.7V to 118V. the lady in the office has her printer (which draws approx 2A when in use) plugged into the same outlet as the coffee pot (which is a programmable coffee pot), which being rated at 900W, draws 7.4A... also, it would only be on during the day while the gal is in her office.

Practically speaking, the offices in question will never see a 15 amp load on their particular circuit... Except for the gal wanting the coffee pot in her office... it will be a strain to get a 7amp load at any given time.

Also: we found the imepedence of around .2 and slightly lower, on average on all circuits coming out of the same panel. At the panel, amp draw on the neutral matched the load applied by both the 61-165, as well as a little 1500 space heater (which we used for an actual load to verify the simulated load of the 61-165).

On an initial assessment, it was discussed that we may need to increase the size of the neutral to the point of splice closest to the offices to account for potential unbalances that can't be controlled such as someone plugging in a unexpected loads. However, the confounding thing is, is that the electrical contractor installed an oversized neutral (a #10). They did this with all multi branch circuits sharing a neutral, at least to some point of junction where they seperated it out to go to the offices.

It would seem that a loose neutral would have registered a higher impedence wouldn't it?

It was also theorized that as the neutral is shared, it is covering more distance than the individual branch circuits, and as result this could allow some of the unbalance current to bleed off to outlets that may have a better ground path, creating a spike at that particular device. While an "ebb & flo" theory sounds somewhat plausible, I still cannot quite get my arms wrapped around this theory... especially with the size of the neutral being a #10.

bottom line: I'm still perplexed on this one...

mjr

 

[duhhuh]

Since circuit #6 supplies two relatively low wattage loads and shares the neutral with six other computers that are doing fine I now cast my vote w/ 76 Nemo!

The coffee pots are GUILTY !:grin:

Got to make popcorn be right back!:grin:

1- no, not until this gal moved into her office. (inccidently no-one else has one in their office)

2- I would have to check on the previous make. I cannot say it is the same.

3- One coffee pot, a Mr. Coffee 12 cup, with clock and auto preset.

4- only day shift, 7a to 4p

5- in the specific outlet, the printer is also plugged into it. However, on the same circuit, different outlets is the phone, computer, computer screen, and a paper shredder.

6-supply is actually 121.7V. The voltage with an applied 15A load, was 112
(8% vd) with the pots 900w load, is actually 118V (3% vd).

thanks

 

[duhhuh]

My apologies, my previous post was meant to answer nemo76s questions.

 

[ohm]

This has happened to me a LOT about the past couple of years. I have purchased many things which don't work out of the box and need to be repaired to get them to work. Or they don't last very long before they break - sometime a few months.

Luckily I know how to fix and/or modify many different types of things to get them to work.

Companies used to have quality control. These days they ship products working or not.

Right on Bill-Bob
I once got a defective VCR. It was a top of the line 4 head unit (good stuff then). I returned it and before I left the counter opened the box up & tested it. It too was bad. So I had the clerk bring out another, and another etc. All 76 of the units they had in stock could not stay on! I selected another brand.

One definition of stupid is doig the same thing over & over again and expecting different results. Like duplicating a poorely designed coffee pot.

 

[76nemo]

1- no, not until this gal moved into her office. (inccidently no-one else has one in their office)

2- I would have to check on the previous make. I cannot say it is the same.

3- One coffee pot, a Mr. Coffee 12 cup, with clock and auto preset.

4- only day shift, 7a to 4p

5- in the specific outlet, the printer is also plugged into it. However, on the same circuit, different outlets is the phone, computer, computer screen, and a paper shredder.

6-supply is actually 121.7V. The voltage with an applied 15A load, was 112
(8% vd) with the pots 900w load, is actually 118V (3% vd).

thanks

The printer places a large non-linear load on the circuit. Rid of the printer and rerun the coffee pot cycle. You already stated the neutral is one size over. I really want you to prove me wrong on this. I truly believe the pots are not being fried with a supply of 118V's.

What gripes me the most, is I can not be there with you to do your study with. I still don't feel the branch is the problem, but at this point, after your conclusion, I am a little baffled.

I would need to see the pot's power supply after it failed to draw conclusion.

I'll bet if you had a 20-30 cup brewer in place, you would have no problems. Something is easily being overlooked here, and I don't think your branch circuit is in question.

 

[ohm]

Mr. duhhuh does the pot or any of the branch circuits have working TVSS or surge protection? Was there any lightning activity in the area before the failures? Have you performed an autopsy on the dead pots yet? A pix might be useful.

 

[Besoeker]

wrong because it's now a series circuit and the current stays the same. look at the powerpoint presentation and learn.

Although it says that in the PPT presentation, it isn't shown as a series circuit.
For it to become a series circuit, the supply neutral would have to be disconnected.
Normally, there should be current flowing in the neutral to ground connection so opening it would have no effect on the distribution of voltages round the circuit.

 

[76nemo]

It's also very possible that the circuit with the coffeepot that went bad was subject to too-high a voltage, not only too low. Nobody says it was heating when it went bad, and even if on, other circuits may have had a greater total load.

If these pots are new consumer type, there will be a MOV right at line coming in on the PCA. If it's that high of an over-voltage issue, it's going to take out the MOV.

Send me the dead pots dh:grin: I am still baffled on this. The reason I am so intrigued is because if it wasn't the coffee pot's issue, I really have something to learn here. I still don't see how it could of been the branch circuits fault when nothing else was/is affected:-?

 

[steelersman]

Although it says that in the PPT presentation, it isn't shown as a series circuit.
For it to become a series circuit, the supply neutral would have to be disconnected.
Normally, there should be current flowing in the neutral to ground connection so opening it would have no effect on the distribution of voltages round the circuit.

You are wrong also.
If you actually bother to look at the entire presentation you will see that it does turn into a series circuit by opening the neutral. So maybe you should go back and look again!

 

[76nemo]

Easy now,......

 

[steelersman]

Easy now,......

just saying. when you're wrong you're wrong. Facts are Facts.

 

[76nemo]

just saying. when you're wrong you're wrong. Facts are Facts.

I know, just :grin: :grin: :grin: 'ing.