Main CB tripping before subpanel breaker, possible short in feeder

Status
Not open for further replies.
L

Leeworm

Member
Location
Houma, LA
Good day all,

Please excuse this post if this has already been addressed and, if so, could someone provide a link to the thread addressing it.

I recently installed a subpanel to service an addition to my house. When I try to energize the subpanel the main breaker trips. There are no loads presently on the subpanel as the branch circuits haven't been terminated yet so it is essentially just the feeder connected to the busses. I checked for shorts at the subpanel lugs and, when checking for continuity between the lines and ground, I had a short between my black and ground. I pulled the breaker feeding the subpanel, checked continuity between black and ground, and showed a short as to be expected. I did loosen the connection on the cable connector at the subpanel and then loss tone when checking for continuity and have never been able to get a continuity tone since.

However, I have tried several different things and the results are still the same; the main CB trips immediately:
Turned off all remaining breakers in the main panel so that the only possible draw in the subpanel, which has no loads currently on it.
Connected the feeder to a different breaker.

I could be wrong but I think that I have a short in the feeder cable and that cable will have to be replaced but I am more concerned about why the main trips before the branch breaker does.


Thank you in advance for any advice.
 
Are you an electrician? Your profile seems to indicate maybe not. If you are, then we can help you, however this forum is not for DIY and those not in the electrical field.
 
The best advice is to call an ec.

As said above, the rules here do not permit us to help you perform your own DIY electrical work.
 
Last edited:
Leeworm said:
Good day all,

Please excuse this post if this has already been addressed and, if so, could someone provide a link to the thread addressing it.

I recently installed a subpanel to service an addition to my house. When I try to energize the subpanel the main breaker trips. There are no loads presently on the subpanel as the branch circuits haven't been terminated yet so it is essentially just the feeder connected to the busses. I checked for shorts at the subpanel lugs and, when checking for continuity between the lines and ground, I had a short between my black and ground. I pulled the breaker feeding the subpanel, checked continuity between black and ground, and showed a short as to be expected. I did loosen the connection on the cable connector at the subpanel and then loss tone when checking for continuity and have never been able to get a continuity tone since.

However, I have tried several different things and the results are still the same; the main CB trips immediately:
Turned off all remaining breakers in the main panel so that the only possible draw in the subpanel, which has no loads currently on it.
Connected the feeder to a different breaker.

I could be wrong but I think that I have a short in the feeder cable and that cable will have to be replaced but I am more concerned about why the main trips before the branch breaker does.


Thank you in advance for any advice.
Click to expand...
You are in way over your head. Get some professional help. Spend the money.
 
You do need some professional help.
But I will say this, it depends on the trip curve of the breakers as to which one will trip first. Sometimes it's a "crap shoot" as to which will trip.
You're situation needs attention sooner rather than later!
 
To everyone who took the time to reply, I appreciate the advice and do truly understand the protocols of this forum. I probably should have been more detailed when I filled out my profile information so that I wouldn't have come off simply as a DIY homeowner. For the sake of clarity, I am not an licensed electrician but I do work with them everyday as a Project Manager for a large mechanical contractor. I was simply looking for some feedback on a Sunday morning because, at the time, I was somewhat po'd that a feeder cable appeared to have a short in it and it did.

Again, thanks to everyone that replied.
 
Leeworm said:
To everyone who took the time to reply, I appreciate the advice and do truly understand the protocols of this forum. I probably should have been more detailed when I filled out my profile information so that I wouldn't have come off simply as a DIY homeowner. For the sake of clarity, I am not an licensed electrician but I do work with them everyday as a Project Manager for a large mechanical contractor. I was simply looking for some feedback on a Sunday morning because, at the time, I was somewhat po'd that a feeder cable appeared to have a short in it and it did.

Again, thanks to everyone that replied.
Click to expand...

Im sure its redundant asking this, but in your words, how are you related to the electrical industry?
 
How was your feeder cable installed?

Cables just don't get a short.

What kind of feeder?
 
Leeworm said:
Good day all,

Please excuse this post if this has already been addressed and, if so, could someone provide a link to the thread addressing it.

I recently installed a subpanel to service an addition to my house. When I try to energize the subpanel the main breaker trips. There are no loads presently on the subpanel as the branch circuits haven't been terminated yet so it is essentially just the feeder connected to the busses. I checked for shorts at the subpanel lugs and, when checking for continuity between the lines and ground, I had a short between my black and ground. I pulled the breaker feeding the subpanel, checked continuity between black and ground, and showed a short as to be expected. I did loosen the connection on the cable connector at the subpanel and then loss tone when checking for continuity and have never been able to get a continuity tone since.

However, I have tried several different things and the results are still the same; the main CB trips immediately:
Turned off all remaining breakers in the main panel so that the only possible draw in the subpanel, which has no loads currently on it.
Connected the feeder to a different breaker.

I could be wrong but I think that I have a short in the feeder cable and that cable will have to be replaced but I am more concerned about why the main trips before the branch breaker does.


Thank you in advance for any advice.
Click to expand...

Sounds like your feeder cable has some damage,
You will have to pull it out and look at the damage
then you will be able to work out what caused it

As for the main tripping first !
this is a known phenominuim
especially under bolted shorts
it is caused by the fact that the main is closest
to the main supply so it cops the most current
The main breaker, buss bars, and more breakers
all add more resistance to the system so they receive
a little bit less current.

PULL YOUR MAIN FEEDER !
 
I agree with the others, you need to contact an EC to help you with this problem.

With that said I am closing this thread in accordance with the forum rules.

This site is designed for:


  • Contractors
  • Electricians
  • Engineers
  • Inspectors
  • Instructors
  • Other electrically related individuals
* This NEC Forum is for those in the electrical and related industries. Questions of a "How-To" nature by persons not involved in the electrical industry will be removed without notice.
Click to expand...

Roger
 
Status
Not open for further replies.
Top