A Phase 124Volts B Phase 128Volts

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Mets978

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Friend called me about his Keurig coffee maker burning out. Apparently a few days ago he noticed it stopped working so he purchased a new one. The next day the new one burnt out. He asked me to check the outlet. Outlet was fine but when I took a voltage reading I noticed the voltage to range between 126-129 Volts. I went to the panel the A phase was reading 124Volts and the B Phase 129Volts. What could the problem be?


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It may be the result of a high resistance neutral and therefore be dependent on current in circuits on the opposite phase.
On the other hand, I find it hard to see 129 volts burning out a heating appliance.
Possibly the voltage is sometimes higher at the time the coffee maker is in use.
 
Although my work is normally in the commercial/ industrial environment, I think the theory also applies here. This smacks of either a loose or missing neutral/ ground connection as GoldDigger pointed out. I recall a time being called out where the lab equipment plugged into some 120V receptacles was burning up. Even the receptacles where the plugs were showed burnt marks. Turned out the wye point of the 208/120V supply transformer was never grounded (in service for 5 yrs!) When the currents in the phase conductors vary due to the single phase loads the electrical center-point shifts causing the voltages on the other phases to skyrocket, puncturing the insulation and damaging equipment/ wiring. These high voltages are usually intermittent and unless there is a monitoring instrument connected, it will go undetected.
The XO terminal was grounded: problem solved.
 
ATSman said:
Although my work is normally in the commercial/ industrial environment, I think the theory also applies here. This smacks of either a loose or missing neutral/ ground connection as GoldDigger pointed out. I recall a time being called out where the lab equipment plugged into some 120V receptacles was burning up. Even the receptacles where the plugs were showed burnt marks. Turned out the wye point of the 208/120V supply transformer was never grounded (in service for 5 yrs!) When the currents in the phase conductors vary due to the single phase loads the electrical center-point shifts causing the voltages on the other phases to skyrocket, puncturing the insulation and damaging equipment/ wiring. These high voltages are usually intermittent and unless there is a monitoring instrument connected, it will go undetected.
The XO terminal was grounded: problem solved.
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Usually the unbonded wye neutral shows up when a piece of equipment goes to ground, and energizes the ground to neutral, blowing surge suppressors. I’ve ran across systems that have been that way for 15-20 or more years. Looking at a system tomorrow that just had a new transformer and panel installed, and the facility is having computer issues. First thing I check.
 
ptonsparky said:
What is the line to line with no load?
Now load up one line. Plug in an iron, electric heater or hair dryer.
Line to line?
Line(s) to neutral?
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good question. 124 + 129 = 253, which is what line to line likely would have read if OP checked it. That starting to get to point of being POCO regulation problem and not an on site issue for customer. Is still potentially the mentioned neutral issue on top of a regulation problem though.
 
kwired said:
good question. 124 + 129 = 253, which is what line to line likely would have read if OP checked it. That starting to get to point of being POCO regulation problem and not an on site issue for customer. Is still potentially the mentioned neutral issue on top of a regulation problem though.
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Good chance, but it sure helps if you take the time to test properly. A set of test lamps would work.
 
ATSman said:
Although my work is normally in the commercial/ industrial environment, I think the theory also applies here. This smacks of either a loose or missing neutral/ ground connection as GoldDigger pointed out. I recall a time being called out where the lab equipment plugged into some 120V receptacles was burning up. Even the receptacles where the plugs were showed burnt marks. Turned out the wye point of the 208/120V supply transformer was never grounded (in service for 5 yrs!) When the currents in the phase conductors vary due to the single phase loads the electrical center-point shifts causing the voltages on the other phases to skyrocket, puncturing the insulation and damaging equipment/ wiring. These high voltages are usually intermittent and unless there is a monitoring instrument connected, it will go undetected.
The XO terminal was grounded: problem solved.
Click to expand...
Voltage to neutral would remain pretty stable, voltage to ground will shift as loading changes though.
 
It's interesting how many threads in the forum that involve troubleshooting of some sort, someone will eventually bring up a bad or dropped neutral. Is there really that many neutral issues going on that it is a "go to" check almost always being brought up?
It also would be nice to hear what a resolution to the issue is when an OP makes an inquiry, it is a nice learning tool if we hear how issue was fixed vs just it could be this or that. I do realize sometimes you don't get one, the problem is transient and can't be replicated or it is simply given up on to just start over, that too would be good to hear.
 
The frequency with which a poor neutral is mentioned in troubleshooting could just be an example of survivorship bias. The other troubleshooting issues get resolved without posting to this forum so all we see are the "tricky" troubleshooting issues.
 
Fred B said:
It's interesting how many threads in the forum that involve troubleshooting of some sort, someone will eventually bring up a bad or dropped neutral. Is there really that many neutral issues going on that it is a "go to" check almost always being brought up?
It also would be nice to hear what a resolution to the issue is when an OP makes an inquiry, it is a nice learning tool if we hear how issue was fixed vs just it could be this or that. I do realize sometimes you don't get one, the problem is transient and can't be replicated or it is simply given up on to just start over, that too would be good to hear.
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There are a lot of those questions and they could be a compromised neutral connection, especially when an item 'burns up'.
Given only the limited voltage checks of the OP and others like it, there could be excessive VD on that one leg. We don't know if its a poor connection, undersized wire
 
d0nut said:
The frequency with which a poor neutral is mentioned in troubleshooting could just be an example of survivorship bias. The other troubleshooting issues get resolved without posting to this forum so all we see are the "tricky" troubleshooting issues.
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I second this notion.

A bad neutral can introduce a variety of symptoms that can mislead a fairly competent troubleshooter, especially the first time he/she encounters one.
 
If this is on a 120/208 network system(like a large apartment complex) it could simply be a POCO regulator way too high.
It happens more than one thinks..
 
Hv&Lv said:
If this is on a 120/208 network system(like a large apartment complex) it could simply be a POCO regulator way too high.
It happens more than one thinks..
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That is why I mentioned it earlier, the voltages OP mentioned add up to too much line to line volts which is pretty much never an customer problem if you have no customer transformation going on.

Long marginal sized service conductor or feeder can also mislead you to thinking about bad neutral, particularly if load severely unbalanced and it wouldn't take much to get the five volts of imbalance that the OP is seeing, but on split single phase source you still can't add line to neutral voltages at the load and end up with more than the line to line input from the source (at least not without a boost coil somewhere in the circuit).
 
kwired said:
That is why I mentioned it earlier, the voltages OP mentioned add up to too much line to line volts which is pretty much never an customer problem if you have no customer transformation going on.

Long marginal sized service conductor or feeder can also mislead you to thinking about bad neutral, particularly if load severely unbalanced and it wouldn't take much to get the five volts of imbalance that the OP is seeing, but on split single phase source you still can't add line to neutral voltages at the load and end up with more than the line to line input from the source (at least not without a boost coil somewhere in the circuit).
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I have only saw this one other time where the voltages didn’t add correctly as you stated.
We had a single phase transformer that served a house doing about this same thing. Electricians came by multiple times. Yes, our guys said bad neutral in the house also. The guys resqueezed everything outside.
Finally had the guys pull the service leads out of the XF and check the XF by itself with nothing on it.

Same voltage readings. 124 on one side, 130 on the other side. 254 across..
(I just used those numbers, I can’t remember exactly what the voltages were)

Took the XF down and changed it out. All was well.
We TTR the XF and one coil was off just enough to give higher voltage. Junked that unit, (think it was a 15kVA) even though it was within the 10% tolerance.
 
Hv&Lv said:
I have only saw this one other time where the voltages didn’t add correctly as you stated.
We had a single phase transformer that served a house doing about this same thing. Electricians came by multiple times. Yes, our guys said bad neutral in the house also. The guys resqueezed everything outside.
Finally had the guys pull the service leads out of the XF and check the XF by itself with nothing on it.

Same voltage readings. 124 on one side, 130 on the other side. 254 across..
(I just used those numbers, I can’t remember exactly what the voltages were)

Took the XF down and changed it out. All was well.
We TTR the XF and one coil was off just enough to give higher voltage. Junked that unit, (think it was a 15kVA) even though it was within the 10% tolerance.
Click to expand...
254 still a little on high side, but then if primary was high your replacement unit probably also would be high. Maybe a turn to turn short somehow occurred?
 
kwired said:
254 still a little on high side, but then if primary was high your replacement unit probably also would be high. Maybe a turn to turn short somehow occurred?
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Yes. last paragraph of my post.
 
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