1200 Amp Main wear

[Wireman300]

Hello all....client experiencing repeated outages due to corrosion of feeders at transformer vault (per utility). 1200 amp 3 phase 4 wire fed with 3 runs of 750 kcmil aluminum. Question I have is this......if we're going to upgrade feeders to copper, should we consider replacing main breaker as well? Dozens of outages tripped main every time. Am I correct in my assumption so many trips may have weakened main? Service was installed in 2005. Thoughts?

 

[Ragin Cajun]

What, if any, preventative maintenance, testing, etc. has been done on the breaker?

 

[petersonra]

Why change to copper?

 

[ptonsparky]

What is causing the corrosion? Improper termination?

 

[Wireman300]

What, if any, preventative maintenance, testing, etc. has been done on the breaker?

None.....

 

[Wireman300]

Why change to copper?

Utility informed them repeated outages are caused by corrosion of aluminum feeders in vault, and while they keep coming out and reterminating, they are "running out of good wire to splice on to". They told my customer that solution is to upgrade to copper.

 

[Wireman300]

What is causing the corrosion? Improper termination?

I believe storm water runoff filling transformer vault plays a role.....

 

[jim dungar]

None.....

Is this an electronic trip breaker?
Why does this breaker open if the fault is on its feeder cables?
Breakers, this large, can probably handle hundreds of mechanical one-off operations. However, the number of fault operations it can handle depends on the amount of current being interrupted.

 

[petersonra]

What makes them think that aluminum is any more susceptible to corrosion than copper?

I'm not convinced that corrosion could cause enough extra current that it would trip the breaker.

I am suspicious that you may end up with an expensive fix that doesn't actually solve any problem you have.

If they are just running out of spare wire to Make terminations to, it seems to me you could just splice in some tails of copper to the ends of the existing aluminum conductors. You can get waterproof splice covers that would prevent any corrosion at the splice points.

 

[Wireman300]

Its a Cutler Hammer ND 50K with Digitrip 310 trip unit.....short delay set at 8, ground fault settings are 1 at pickup and INST. Settings haven't been changed from original build 2005.

 

[Wireman300]

What makes them think that aluminum is any more susceptible to corrosion than copper?

I'm not convinced that corrosion could cause enough extra current that it would trip the breaker.

I am suspicious that you may end up with an expensive fix that doesn't actually solve any problem you have.

 

[Wireman300]

I agree....and believe problems are caused by utility not able to keep vault from filling up with water. Was told the owners weren't interested in pointing fingers....just solving the problem. And could I just price replacing feeders with copper......

 

[electrofelon]

Everything in UG vaults is made to be submerged. Nearly every vault in Seattle I have seen is completely full of water year round. Not sure why these connections keep failing. It also doesn't make any sense that the breaker would trip from an upstream fault. There's got to be something else going on here.

 

[ptonsparky]

I would certainly try crimping on a pin first.

 

[jim dungar]

Its a Cutler Hammer ND 50K with Digitrip 310 trip unit.....short delay set at 8, ground fault settings are 1 at pickup and INST. Settings haven't been changed from original build 2005.

I believe those breakers should be tested/maintained every 5 years, especially if the company follows NFPA 70E for arc flash.
Has anyone reviewed the settings? The ground fault looks like they would not coordinate with much more than a 50A branch breaker.

 

[Wireman300]

I'm just getting involved and gathering info......plan on speaking with engineer from build to find out why settings are what they are and also CH rep for their input beginning of the week.

 

[Ragin Cajun]

None.....

I personally would recommend as a minimum complete testing to determine it it's worth keeping. Which likely it's not worth keeping depending on the environment it has been in.

 

[ATSman]

First, record the load over time to make sure the breaker is not tripping on an over-current condition, i.e. doing what it's suppose to do.
Most likely, in such a moist environment and electronic trip unit on the main breaker, my thoughts are that the breaker is nuisance tripping from the ground fault feature of the trip unit. Sometimes the moisture gets into the circuit board of the trip unit, shorts out the traces, causing erratic mis-firing/ breaker tripping. Other times, often due to age, the trip unit trips for no reason and needs to be replaced. We have replaced the trip unit of a 4000A breaker (SS trip unit) due to GF miss-fire (GF trip LED indication on the trip unit) and this was a dry environment!
Was there any Trip Light indications (if they exist) on the trip unit when it tripped?
Primary Testing with high current or Secondary Injecting testing with a test set is a waist of money as Ragin Cajun suggested. Testing only tells you that it will trip if the thresholds are exceeded, not that the trip unit WON'T trip due to it just being defective.
Try raising the GF trip settings (Pickup and Time) to maximum. If it still trips, see if the trip unit is replaceable and replace it with the same or the thermal-magnetic equivalent.
According to this link it is:
https://www.google.com/search?q=cut...MTDABHZ8WDhYQ9QF6BAhIEAE#imgrc=0pICK2rs_JJHxM

If not then replace the breaker.
Lastly, I never liked aluminum cable but changing to copper cables will not stop the tripping and is only a waist of money. The moisture problem has to be addressed and corrected (change enclosure to NEMA 3R ?) otherwise other problems will occur down the road.