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Wierd voltage readings on a 240 volt plug  Rate Topic 
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 Posted: Mon Mar 24th, 2008 08:03 am
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Budget Appliance Repair
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I ran into something strange on a job this weekend and would like some feedback.

I was working on a built-in GE double oven that the control board was fried from a dropped neutral line.

The oven was at a hospital work shop in storage and that is were I was to work on it.

The pigtail whip is the hardwired conduit type and there was a 240volt plug near by so I grafted a pigtail on the the conduit pigtail whip to plug into the 240volt socket to test.

Before testing I needed to make sure the socket had power becuase the circuit breakers were off to the 240volt plugs and the guy that let me in didn't know what circuit breakers went to what plugs so we had to turn the breakers on and test the plug.

This being a hospital they have 3 phase circuits in the same box as the 2 phase. There are circuit breakers with with 3 breakers ganged together.

Anyway, when I tested the plug, this is what I got:
L1 to Neutral=119volts
L1 to L2 =238volts
L2 to Neutral=206volts

L2 to Neutral if I had hooked the clock power circuit to this power leg I would have fried the new clock.

I made sure the clock power circuit was on the L1-Neutral line to test the oven when I was done and all worked ok.

I would like to know what would cause the strange voltage reading on the L2 to Neutral side, but L1 to L2 still reads the correct voltage. Would this be something to do with the 3phase power circuit and maybe the breaker for this 240volt line is feeding off the wrong power line phase for the L2 side.

Also, should something be done about this? The oven won't be installed were I worked on it and I would have to assume this power setup has been this way all along and they haven't had any problems that anyone knew of.



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 Posted: Mon Mar 24th, 2008 04:09 pm
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when did the dropped neutral occur / and repaired ?

recently or the dryer has been sitting in storage for a while ?

what type of outlet was this ?  

3 or 4 prong dryer OR some type of 3phase outlet ?

is the power to this outlet shut off with one of the double breakers or one of the  triple breakers ?

check the voltages again to GROUND to see what they read, there may still be something wrong with an open neutral SOMEWHERE.

 

 



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 Posted: Tue Mar 25th, 2008 07:27 am
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when did the dropped neutral occur / and repaired ?

ANSWER: At the house where the oven was orginally hooked up, yes it was repaired and oven replaced with new one.

recently or the dryer has been sitting in storage for a while ?

ANSWER: It's not a dryer, it's a built-in GE double oven, only been at the hospital storage/shop for a couple weeks.

what type of outlet was this ?
3 or 4 prong dryer OR some type of 3phase outlet ?

ANSWER: A standard looking 240volt 3prong range outlet

is the power to this outlet shut off with one of the double breakers or one of the triple breakers ?

ANSWER: A standard double 240volt breaker, I didn't notice the amp rating of the breakers.

check the voltages again to GROUND to see what they read, there may still be something wrong with an open neutral SOMEWHERE.

ANSWER: Where I was working on the oven, (Hospital storage/shop), wasn't were the dropped neutral happened, and I carefully hooked up the oven making sure the L1-Neutral that had the 119volts went to the circuit that runs the ERC and cooling fan. The oven tested fine on this setup when I tested it. It will not be installed in this location, it will be going to another house to be installed, (not the original house where the dropped neutral happened).



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 Posted: Tue Mar 25th, 2008 10:53 am
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Budget Appliance Repair wrote:

Also, should something be done about this? The oven won't be installed were I worked on it and I would have to assume this power setup has been this way all along and they haven't had any problems that anyone knew of.


Not necessarily. There could be a problem with that particular feeder line. A good test would be to see if you could do another voltage measurement at a different location, fed by a different feeder line.



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 Posted: Tue Mar 25th, 2008 12:49 pm
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OK, sorry about the "dryer" reference...

The oven sounds OK, but I still think there may be someting wrong with that outlet wiring.

You're right, the L2 voltage sounds like it may be one leg of a 3 phase circuit.

For their safety and to put our minds at ease, I'd still check all (3) voltages (L1, L2, & neutral) to ground to try to determine if there's something wrong, and mention the results to an electrician or someone else at the hospital.

 

 

 

 



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 Posted: Wed Mar 26th, 2008 07:03 am
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Thanks, I will call the guy I was contracted to fix the range for, he is the contractor, (I think), for the hospital and explain to him what I found and leave it up to him to take it from there.

I'm not an electrician, and wasn't in anyway responsible for the hospital wiring, but will let him know in case he wants to follow-up on it.

Thanks again,



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 Posted: Fri Mar 28th, 2008 01:36 pm
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Was the glow stick the same color on the L1 as the L2 or did it seem a little brighter on one leg??:cool:

 Samurai has a valid point of checking it to a different opposite potential.  I would bet if you checked the neutral to a good ground that you would of found stray voltage sitting on on the neutral from a feed somewhere. 



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 Posted: Sat Mar 29th, 2008 09:58 am
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Didn't and don't use a glow stick, used my digital meter and I haven't had any problems with said meter.



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 Posted: Sat Mar 29th, 2008 03:10 pm
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Glow stick reference was humor Willie :(.  I have seen stray voltage on neutrals as high as 65-70 volts.  Usually something else in the home, shop, etc. is the cause.  Somewhere, something was bleeding back through from the L1 side.  You did not read the increase on the neutral to L1 because the L1 you were testing and the bleed through were the same potential.  That is whey it only showed up on the L2.  I've always confiscated glow sticks from my techs unless they use them to look for breaks in L1 wires, or quick verifications of L1 potentials such as outlet polarity.  Usually I take it out of the pocket and ask what they use if for.  If they tell me voltage tests, I snap it or confiscate it.  The kids like rubbing them on their shirts and making them blink!! 



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 Posted: Sun Mar 30th, 2008 02:24 am
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Keinokuorma
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Is the hospital using automatic inductance compensation? If that malfunctions (overcompensation) it can give you excess voltage.



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 Posted: Sun Apr 6th, 2008 04:51 pm
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I've seen two-phase configurations (for sewer pumps) that provide a voltage of 208.  I think this is what you're experiencing.  In residential it's normally not a problem as most homes don't have more than one phase connected.  Having a standard 240V plug set up like that sounds a bit dicey.

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 Posted: Sun Apr 6th, 2008 09:46 pm
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Chesterfoxes wrote: I've seen two-phase configurations (for sewer pumps) that provide a voltage of 208.  I think this is what you're experiencing. 
That would be two phases out of three, 208V between, 120V from each to Neutral...   25% less power to a device designed for 240V, but should be in the acceptable range for most devices.

Or are you talking about a 3x208V sewer pump?

If I read it right, B.A.R. had normal looking readings from L1 to N and L1 to L2, but an abnormal reading of 208V between N and L2... if it was a 208V two phase feed, it would have read 208V between live legs.

We never came to know if the voltages normalized when under load. There apparently was a good Neutral hookup.

Last edited on Sun Apr 6th, 2008 09:47 pm by Keinokuorma



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 Posted: Mon Apr 7th, 2008 08:42 am
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Keinokuorma wrote:

If I read it right, B.A.R. had normal looking readings from L1 to N and L1 to L2, but an abnormal reading of 208V between N and L2... if it was a 208V two phase feed, it would have read 208V between live legs.

We never came to know if the voltages normalized when under load. There apparently was a good Neutral hookup.



You read correct Keinokuorma, And I don't know if for sure there was a good NEUTRAL hookup. I never went back out on it.

The hospitals wiring wasn't my job, I was there to fix the built-in oven that was just in storage at the maintenance shop and had to power it up to check and make sure all repairs were successful.

At the time I never thought to check each leg to ground, (the plug box or conduit). Just did my normal checks at the plug to see if it was a 240volt plug before tryng to hook the oven up to it and make sure there was power to the plug since the guy that let me in didn't know what breakers went to the plug and it had no power when I started until we found the breaker for that plug and turned it on.



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 Posted: Sun Apr 27th, 2008 05:52 am
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glad to be here

http://www.appliancemidwest.com

hope to help somebody



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 Posted: Mon May 5th, 2008 01:17 pm
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Midwest,

If (and apparently when) you are an appliance tech, contact the Samurai about upgrading your status from Grasshopper to Master Appliantologist. That way you can start your own topics, you'll later on upgrade to Sublime Master after posting enough, etc. You probably even get a free upgrade, while a "layman" upgrade to an Apprentice costs $5. Grasshopper and Apprentice statuses will not upgrade.

Also I'd like to note to you that by the Netiquette it isn't exactly advisable to post your company advertisements in an unrelated thread. You may post your ad here: http://applianceguru.com/forum18/ where people are pointed to look for local servicers.

EDIT: That forum appears to require the Sublime status, but I think it only takes 50 to 100 posts as a Master to obtain.

Last edited on Mon May 5th, 2008 01:26 pm by Keinokuorma



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 Posted: Mon May 5th, 2008 01:21 pm
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Not sure how a grasshopper is posting in this thread but I am closing it down...



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 Posted: Mon May 5th, 2008 02:09 pm
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Our friend, Midwest, has joined the ranks of the Grasshoppers and so, sadly, we will no longer enjoy his spammy posts. However, it is my fervent hope and prayer that by re-opening this topic, we can all, somehow, get over the collective grief that I'm sure we all feel at the loss of our dearly departed friend, Midwest. :moon:



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 Posted: Mon May 5th, 2008 02:37 pm
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Blessed A. :dude:



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 Posted: Mon May 5th, 2008 02:42 pm
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Thanks, was not figuring out how the dude was posting in new threads...so better safe than sorry.....:poison:



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 Posted: Mon May 5th, 2008 09:59 pm
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I ran into a similar situation in an HVAC scenario in Atlanta where I was expecting 208 VAC on all 3 lines of the 3 phase system.  I got 208 208 and 242.  Asked my tech school instructor and he advised that it was the type/configuration of the transformer serving the location.  Cant remember how exactly it went; however, a particular Wye or Delta configuration at the step down transformer to the building's panel will give you the 1 line that is over and above the other 2 legs and outside of the 10% tolerance for motors and 2% tolerance between legs. 



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