I am STUMPED!!!HELP ME !! (please)

[grab1]

I have been an electrical contractor for 8 years, in the business for almost 20 yrs, today I got stumped. I have a 120/240 v single phase panel, there is a 2 pole main breaker on the top of the panel. When I turn on one of the branch breakers, the a phase of the main breaker drops to 20 volts. I spent hours troubleshooting this and I cant get a grasp on what is happenening. When I turn the branch breaker back off, I get 120 v on the a phase, lwt me know what you think before I quit the business and become a plumber!

 

[jumper]

Bad/broken neutral is my first guess.

 

[Volta]

It might be that the A leg is not energized from the line side of the main.

Have you read 240 across the main?

It may be the voltage from B leg through the water heater or similar restive load.

Welcome to the forum.

 

[luckylerado]

Bad neutral. That is my guess too.

 

[jim dungar]

What are all of your voltages?
L1-L2
L1-N
L2-N
L1-G
L2-G
N-G

 

[growler]

I have been an electrical contractor for 8 years, in the business for almost 20 yrs, today I got stumped. I have a 120/240 v single phase panel, there is a 2 pole main breaker on the top of the panel. When I turn on one of the branch breakers, the a phase of the main breaker drops to 20 volts. I spent hours troubleshooting this and I cant get a grasp on what is happenening. When I turn the branch breaker back off, I get 120 v on the a phase, lwt me know what you think before I quit the business and become a plumber!

Well I'll take a stab at it and if I'm wrong it won't be the first time.

I would assume that when you turn on one of the branch circuit breakers you are putting a load on the phase that drops to 20 volts. If that's what happening then I would assume there is a really poor connection somewhere on the line side of the main breaker ( meter base or weather head ). This would act as a resistor and there would be a huge voltage drop under a load. I am thinking this because a meter doesn't put a load on the circuit and when you do possibly put a load on the circuit you read almost nothing.

 

[grab1]

Neut

Neut

Thats what i am thinking too, im going to check it out tomorrow

Bad/broken neutral is my first guess.

 

[grab1]

I do have 240 across the main,

 

[don_resqcapt19]

I do have 240 across the main,

With or without a load?

 

[grab1]

without a load, as soon as i turn the branch breaker on it drops the voltage down

 

[hurk27]

When testing this type of loss, always turn off all 240 volt loads or you can be reading back fed voltage from the other leg, but since you have stated you have 240 volts which wouldn't be the case if this was happening I would suspect you have a bad connection if the service is overhead, or maybe a damaged latteral if underground or somthing inbetween, it could even be at the transformer, so a call to the POCO might be in order if you are not allowed in the meter to test.

also test before and after the main to make sure its not a bad main contact or buss stab if it applies, if this voltage drop is before the main then its somewhere on the POCO's side, if when you turn on this circuit breaker and the voltage drops on A leg, check B leg to neutral to see if it rises above 120 volts, if it does then that is a bad neutral and can damage equipment and or cause a fire, if the voltage between both legs drop from 240 to 140 then you have a bad leg in this case A leg.

 

[hillbilly1]

without a load, as soon as i turn the branch breaker on it drops the voltage down

99% chance it's a bad or open neutral. Could be in the meter, service drop, out at the transformer or the service lateral. (Very common for the POCO to have a bad neutral in the service lateral, especially if its been there quite a few years.)

 

[GUNNING]

Magic smoke everywhere but in the wires.

Magic smoke everywhere but in the wires.

If it was a bad neutral there would be voltage spikes to 800 volts. Smoking DVR's and 60 inch flat screens with walls of flame shooting up out of them.

I'm thinking loose connection too or maybe a bad transformer.

Call the POCO in the morning. Meter base might be bad or any of the connections out to the distribution. Look for smoking glowing wires, its a dead give away.

When the magic smoke leaves the wires everything stops.:roll:

Check with the neighbors and see if they have blinking lites, if they do its at the transformer.

 

[hurk27]

99% chance it's a bad or open neutral. Could be in the meter, service drop, out at the transformer or the service lateral. (Very common for the POCO to have a bad neutral in the service lateral, especially if its been there quite a few years.)

Not disagreeing with you but to me not enough info was given to determine this, a 100 volt drop would be very rare with a bad neutral, and only if all grounding electrodes were non existent, and the fact only one breaker on the "A" leg cause this 100 volt drop in voltage.

If it was a bad neutral there would be voltage spikes to 800 volts. Smoking DVR's and 60 inch flat screens with walls of flame shooting up out of them.

Not sure where you would get 800 volts in a 240 service, the max unbalanced voltage you could ever get with a lost neutral is 240 volts, the output of the two hots, but even with that yes I have seen smoking DVRs, TV's, and fires caused by sending 240 volts through equipment rated for 120 volts.

 

[don_resqcapt19]

without a load, as soon as i turn the branch breaker on it drops the voltage down

If the line to line voltage drops with a load, it is a problem with the ungrounded conductors or the transformer, not the neutral. Neutral problems do not change the line to line voltage.

 

[Twoskinsoneman]

What does the voltage on the main do if your turn on a 240v load?
What is the current on GEC?

 

[220/221]

let me know what you think before I quit the business and become a plumber!

You might want to consider that option.:lol:

Seems like 101 stuff to me. You should know that testing without a load means nothing sometimes. Even on a 200 amp breaker, one tiny strand will read full voltage. You must put a load on it to see whats up.


My guess is burned buss/breaker, not neutral but, to diagnose, I'd really have to go thru all the steps to isolate the problem.

 

[K8MHZ]

You might want to consider that option.:lol:

Seems like 101 stuff to me. You should know that testing without a load means nothing sometimes. Even on a 200 amp breaker, one tiny strand will read full voltage. You must put a load on it to see whats up.

With care.

Realize that loading a 120 volt circuit down to 20 volts is going to create some heat somewhere.

I wouldn't do it for too long, or at all if there were other means to locate the area of high resistance.

 

[grab12]

Problem Solved!

Problem Solved!

Thanks a lot guys for your replies, I really appreciate the help. It turns out the neutral was fine. When I did my megger test on the feeders there was some leakage to ground. It wasnt a dead short but the wire wouldnt clear at 250 volts either. We re-fed the panel from another source and now we are dancin! This might be basic to some but it was very odd to me, as I have not come across this yet in my career.

Thanks again guys!

Go Dolphins!

and Yankees!!

:thumbsup:

 

[luckylerado]

I have had a similar experience. The cause was when the utility made the connection at the service drop they did not use oxide inhibitor. Cut the splice out back about 6 inches on both sides, re-spliced and the problem went away. The chunk that was cut out looked perfectly fine but when you tried to read continuity through it you got many thousands of ohms. The problem started out with dimming lights and a burning smell from electronics in the house.