Message Board Thread - "Causes for 1 phase hotter"

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Causes for 1 phase hotter NEVERLATE 6/30/2009
Take a look at this image. The conductors on the top of the breaker are the load side of the breaker. The breaker is a 350A 277/480V breaker feeding a 150A continuious load across all phases. I am going to do a shut down and check the connections. Upon a rescan if the issue is still there, I assume the only thing to do is replace the breaker. Ideas?
 
Re:Causes for 1 phase hotter IRJay 6/30/2009
Looks like the front conductor has the problem. My first quess is missing strands or too large of a lug for the wire and it has slipped to the side of the box connector, meaning has no pressure from the lug.

A side shot of the breaker will help determine if this is a breaker problem. Also get a millivolt read across contact.
 
Re:Causes for 1 phase hotter NEVERLATE 6/30/2009
IRJay wrote:
ike the front conductor has the problem. My first quess is missing strands or too large of a lug for the wire and it has slipped to the side of the box connector, meaning has no pressure from the lug.

A side shot of the breaker will help determine if this is a breaker problem. Also get a millivolt read across contact.
I should have specified, there is only one conductor per a phase. You are seeing the conductors reflection in the can.
 
Re:Causes for 1 phase hotter BVT 7/2/2009
NEVERLATE wrote:
I should have specified, there is only one conductor per a phase. You are seeing the conductors reflection in the can.
It appears that the heat is coming from the connection. If it were load the conductor would be hot the length of the conductor. During shutdown, inspect connection and conductor for corrosion/dirt/oil, etc, replace as necessary. You may have to trim off some of the conductor, looks like you have a little to spare.
If no damage is present on either, re-seat conductor,tighten, and re-check.
 
Re:Causes for 1 phase hotter BVT 7/2/2009
BVT wrote:
It appears that the heat is coming from the connection. If it were load the conductor would be hot the length of the conductor. During shutdown, inspect connection and conductor for corrosion/dirt/oil, etc, replace as necessary. You may have to trim off some of the conductor, looks like you have a little to spare.
If no damage is present on either, re-seat conductor,tighten, and re-check.
I should have mentioned clean conductor and connection throughly, before re-seating, if foreign substance is present.
 
Re:Causes for 1 phase hotter Herk 7/2/2009
The lug in the breaker may be loose or the pressure holding the contact closed may be weak,(long shot), and last, over torque of the lug can cause cold flow leading to a loose connection. You probly will catch all of the suggestions on shut-down.
 
Re:Causes for 1 phase hotter zury 7/2/2009
Herk wrote:
in the breaker may be loose or the pressure holding the contact closed may be weak,(long shot), and last, over torque of the lug can cause cold flow leading to a loose connection. You probly will catch all of the suggestions on shut-down.
The picture shown only one phase was hot.They could be the termination not tight enough or the lug was not fited to cable size.By cut the cable a bit shoot and replace new lug will help to reduce the hot at the phase.
Or might be one of phase load was higher due to coil unbalance ohm reading.
 
Re:Causes for 1 phase hotter BDL 7/6/2009
NEVERLATE wrote:
look at this image. The conductors on the top of the breaker are the load side of the breaker. The breaker is a 350A 277/480V breaker feeding a 150A continuious load across all phases. I am going to do a shut down and check the connections. Upon a rescan if the issue is still there, I assume the only thing to do is replace the breaker. Ideas?
My input is this image is inconclusive but it lends itself to the heat source coming from the breaker using the information already provided. I suggest re-scanning the breaker from multiple angles to attempt to determine if the heat source is within the breaker. If it seems it is it will be radiated heat which means the T inside is much higher. But is it really out of tolerance? Check the specs on the breaker. Thermographers are smart to notice things unevenly heated but sometimes they are still okay. If not within tolerance and the load is critital I suggest planned replacement. If the loads are not critical it may self correct or it may operate for years. I have seen this myself and have recommended replacement too but the corrections have not been made and it has been over a year since I found them.
 
Re:Causes for 1 phase hotter BDL 7/6/2009
I forgot to suggest to attempt to view the wire housing and the terminals visually for discoloration. This may require shut down upstream for safety.
 
Re:Causes for 1 phase hotter Ice Cream Man 7/13/2009
This is more than likely a loose or corroded connection. If it were load you would see the even thermal distribution the whole length of the conductor. We correct several of these twice annually. In some of our cases, one lug is not torqued as tightly as the others, reducing the amount of suface contact area between the conductor and the lug, causing the temperature increase. We have also seen instances where the insulation jacket is not cut back far enough and partially compressed within the lug causing a reduction of cantact surface area also.
 
Re:Causes for 1 phase hotter NEVERLATE 8/26/2009
UPDATE: I scheduled a shutdown with the client and sent my guys in to check the connection. They found that the C phase lug was a little loose and they tightened it to spec. I went back to the site and did a re-scan under the same load conditions and I am seeing the same thermal signature. Again, all three phases have the same exact load +/- 8A. The only solution I see is replacing the breaker. This is a critical load as this feeds the chiller pump that circulates water for the entire buildings heat and air. If they loose this breaker, they will loose climate control.
 
Re:Causes for 1 phase hotter TDLIR 8/26/2009
Hi NEVERLATE:

I think you should not rush into replacing the breaker. The condition seems as if it is a connection problem, but you need to get a better view of the terminals. Go on a step ladder and look at all 3 phases from the top in one image making sure you see the cables and termination point in the field of view.

If you are contemplating breaker replacement, I would suggest you use the absolute acceptance criteria to determine if the temperature is above the corrected load value.

From what you explained with regards to the repair work done, your electricians made the common mistake of simply retightening the connection. The proper way to address a connection problem is to disassemble the connection, inspect the breaker lugs for signs of damage and contamination; Inspect the cable properly (frayed strands, crimps, insulation, discoloration, contamination, or any other damage); Properly clean both breaker lug assembly and cable; Make sure the cable fits properly into the breaker lug and when retightening make sure that there is proper contact between the breaker lug and cable.

Note that from this view of the Cables:
A Phase = 39C
B Phase = 41C
C Phase = 48C
 
Re:Causes for 1 phase hotter Dnicejr1 8/27/2009
On some of these larger breakers the lug that the wire goes into is actually bolted to the buss bar in the back of the breaker. The loose connection may actually be within the breaker itself and not the wire connection. If you pull the breaker out you can easily see if this is a bolted lug from the back in most cases.
 
Re:Causes for 1 phase hotter jimS3 9/15/2009
you might try performing a voltage drop test across the breaker poles to see if there is a higher resistance on the "C" phase leg.
 


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