1600A Chiller Breaker Tripping

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Nebben242

Nebben242

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Location
Denver
Occupation
Electrician / Project Engineer
I have a 1600A 480V Breaker in a Control Cabinet that powers a Chiller. A few years ago Carrier replaced components in the chiller to correct the tripping issue, but it has persisted. The building has multiples and it has not crippled them, but they want answers.
I was asked to investigate:
The Plastic Fin on the Line side Shroud was burnt and melting on the C-Phase side of the lugs, with les discoloration on the B-Phase (Middle). But the Breaker Tripped on the Load Side of the Lugs, not the Main up stream.
The breaker was swapped out and tested, the New (used) Breaker also tripped and old one passed NETA testing and was re-terminated. all connections have been checked for tightness.
I installed an logging meter on Line and Load and found no issues on all three phases, yet the breaker tripped at around 750A, about 2 hours after start up.
The Thermal Scope shows a temp of about 174deg F. on the lugs.
I noticed the 1/2 of Output wires to the Chiller pass between A-Phase and B-Phase, should this be causing a magnetic/heat issue - ultimately tripping the breaker?
Pic - Chiller 6
 
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
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EC - retired
Nebben242 said:
I have a 1600A 480V Breaker in a Control Cabinet that powers a Chiller. A few years ago Carrier replaced components in the chiller to correct the tripping issue, but it has persisted. The building has multiples and it has not crippled them, but they want answers.
I was asked to investigate:
The Plastic Fin on the Line side Shroud was burnt and melting on the C-Phase side of the lugs, with les discoloration on the B-Phase (Middle). But the Breaker Tripped on the Load Side of the Lugs, not the Main up stream.
The breaker was swapped out and tested, the New (used) Breaker also tripped and old one passed NETA testing and was re-terminated. all connections have been checked for tightness.
I installed an logging meter on Line and Load and found no issues on all three phases, yet the breaker tripped at around 750A, about 2 hours after start up.
The Thermal Scope shows a temp of about 174deg F. on the lugs.
I noticed the 1/2 of Output wires to the Chiller pass between A-Phase and B-Phase, should this be causing a magnetic/heat issue - ultimately tripping the breaker?
Pic - Chiller 6
Click to expand...
IDK if that's the cause, but it sure stands out.
 
T

topgone

Senior Member
Ughhh. . . That's an ugly wiring! The output conductors should have been ran in a single wire duct to make the installation nicer or the conductors belonging to the same phase as a group.
 
P

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Nebben242 said:
I have a 1600A 480V Breaker in a Control Cabinet that powers a Chiller. A few years ago Carrier replaced components in the chiller to correct the tripping issue, but it has persisted. The building has multiples and it has not crippled them, but they want answers.
I was asked to investigate:
The Plastic Fin on the Line side Shroud was burnt and melting on the C-Phase side of the lugs, with les discoloration on the B-Phase (Middle). But the Breaker Tripped on the Load Side of the Lugs, not the Main up stream.
The breaker was swapped out and tested, the New (used) Breaker also tripped and old one passed NETA testing and was re-terminated. all connections have been checked for tightness.
I installed an logging meter on Line and Load and found no issues on all three phases, yet the breaker tripped at around 750A, about 2 hours after start up.
The Thermal Scope shows a temp of about 174deg F. on the lugs.
I noticed the 1/2 of Output wires to the Chiller pass between A-Phase and B-Phase, should this be causing a magnetic/heat issue - ultimately tripping the breaker?
Pic - Chiller 6
Click to expand...
A thermal magnetic breaker could certainly trip on thermal if the ambient temperature went up.

Is there any way you could move the wires so that they're more conventionally routed? I don't think it's going to make a whole lot of difference, but one never knows.

Without being able to see what's going on and look more closely it is very hard to troubleshoot something like this.

Perhaps a sketch of what you are talking about would help.

What size and qty of wire?

I seem to recall you mentioned something about DLO cable being used. This kind of cable requires special connectors or you can get very hot connections. I have seen it happen if the wrong connectors are used.
 
4x4dually

4x4dually

Senior Member
Location
Stillwater, OK
Occupation
Electrical Engineer/ Ex-Electrician
I would guess heat from terminations.

From Anixter:


How to Terminate Diesel Locomotive Cable​

The major lug manufacturers offer special lugs for finely stranded cable, called flex lugs. These lugs are required for DLO cable, welding cable, Type W, G, G-GC and SHD-GC cable. Section 110.14 of the 2017 NEC requires that conductors more finely stranded than ASTM Class C be terminated in specially identified connectors. Care should be taken by users when stripping the cable in preparation for termination to not allow the fine stranding to become frayed. Most barrel-compression lugs sized for DLO cable have a chamfered barrel to help guide the conductor into the barrel. Be careful to not break off any of the strands when stripping the insulation and jacket or allow any of the strands to bend back on themselves.
 
P

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
ptonsparky said:
One would hope that if the DLO is factory installed, it was done correctly. Hope' being the key word.

Hopefully the new used breaker came with new, appropriate lugs.
Click to expand...
Most circuit breaker lugs are not rated for fine stranded cable.

I would be totally unsurprised if a manufacturer shipped a unit with DLO terminated with regular connectors, especially if it was done years ago. It takes a while for the problem to show up most of the time. Like decades in some cases.

One could just wrap the copper cable ends with heavy duty copper foil and re-terminate them. Not exactly a UL listed way of handling things but it appears that it works.
 
augie47

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I wouldn't be surprised. We have a local manufacturer of modular buildings complete with MCCs, drives etc.
I inspected one of theirs (initially flagged for no NRTL) and they had used DLO throughout with standard "set-screw" terminals on all the breakers.
In most cases not many of the strands were even under the screw.
 
Nebben242

Nebben242

Member
Location
Denver
Occupation
Electrician / Project Engineer
petersonra said:
Most circuit breaker lugs are not rated for fine stranded cable.

I would be totally unsurprised if a manufacturer shipped a unit with DLO terminated with regular connectors, especially if it was done years ago. It takes a while for the problem to show up most of the time. Like decades in some cases.

One could just wrap the copper cable ends with heavy duty copper foil and re-terminate them. Not exactly a UL listed way of handling things but it appears that it works.
Click to expand...
I agree here, I have purchased and installed ferrules in the past for temp "DLO" RHW-2 Fine Strand, as the correct Lugs are hard to get.
These have NEITHER.
 
Nebben242

Nebben242

Member
Location
Denver
Occupation
Electrician / Project Engineer
The Big Head Scratch here is that the Melted Lug Shroud on the Line Side of the Breaker in the picture, is where the bulk of the heat build up is. This to me, is generally where the issue should lie, but that doesn't explain it away, as we have replaced and re-termed these lugs.
Unless it was "Another" Issue, but not the cause of the breaker tripping.
 
E

Eddie702

Licensed Electrician
Location
Western Massachusetts
Occupation
Electrician
It would seem the cabinet should have been fed from the bottom. I am assuming the line side are the two sets of parallel conductors coming in the top and splitting down to the bottom? And the wire from the breaker on the top left go into the chiller.....or am I backwards
 
Nebben242

Nebben242

Member
Location
Denver
Occupation
Electrician / Project Engineer
Eddie702 said:
It would seem the cabinet should have been fed from the bottom. I am assuming the line side are the two sets of parallel conductors coming in the top and splitting down to the bottom? And the wire from the breaker on the top left go into the chiller.....or am I backwards
Click to expand...
Yes, you are backwards.
The line side hits the OCPD first. The load is what is splitting.

Sent from my SM-G988U using Tapatalk
 
Jraef

Jraef

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San Francisco Bay Area, CA, USA
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Electrical Engineer
There is a Benshaw soft starter in there, and with 6 sets of leads out to the motor, it must be set up for what's called an "inside the delta" configuration. If you have never encountered it before, it can be confusing, but they do it because the soft starter can be smaller / cheaper. They are SUPPOSED to have another contactor in there for an inside-the-delta configuration in order to isolate the motor windings if there is a fault, however I don't see one. Could it be in another cabinet next to this? If not, it's a dangerous situation in that a short in any one SCR and the motor will fry...

UNLESS, they put a Shunt Trip in the breaker, and it DOES appear to have one (two small black wires going to the back of the breaker on the right side). So what might be happening is that SOMETHING is making those SCRs misfire occasionally and that would NORMALLY cause that extra contactor to open, but because they are not using one, the only thing th3e soft starter can do it to energize the shunt trip on the breaker. SCRs can misfire as a result of a voltage spike, like from another large with a 480V coil opening or closing nearby. I have had this happen with just a little 25HP air compressor starter with a 480V coil in a nearby room causing SCRs to "self-commutate", meaning turn themselves on briefly. But because of the lack of that isolation contactor, that could conceivably be causing the soft starter to react in the only way it can; tripping the breaker. I believe that soft starter will have a log of the last trip, maybe even the last 3 or so. You should look at their manual and see if you can find that.
 
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