Good morning all. I need your help. My company wired a 200+ unit apartment complex two years ago. Last month, we got a call from the on site maintenance tech called and asked us to provide him with (50) replacement 50-amp, two pole breakers for the electric furnaces. Of course, we asked why and he said that the furnace breakers were overheating and melting.
We IMMEDIATELY sent out a crew and began unit by unit inspections. In approximately (50) of the unit panels (125A MLO's with aluminum bussing), we found the furnace breakers in various states of meltdown and damage to the bussing where they snap in.
The wiring method and spec's were as follows:
Cutler Hammer BR series - 125 amp MLO's with aluminum bussing
Furnace overload protection: Cutler Hammer BR 2-pole 50A breaker
Conductors: #6 Aluminum SEU
Inhibitor: Ilsco De-Ox
Terminations at breakers we tight
Furnace loads: 9,700 VA
Voltage: 240
Phase: Single
Furnace field amp read at furnace startup, 41 amps.
The ranges were also wired with #6 SER aluminum with 50A, 2-pole BR breakers. There were no problems with these circuits.
Worth noting (as we are chasing our tails):
The furnaces were set after the electrical rough was completed. After the furnaces were set, we were able to read the decal on the furnace J-cover "terminate copper only." As the furnace had a pull out disconnect, inside the mechanical area of the furnace, we installed insulated dual rated AL/CU butt splices ahead of the furnace disconnect to transitioned from aluminum to copper (#8 THHN, rated at 50A, like the wire). There was no damage to these butt splices or terminations.
We contacted Cutler Hammer and they now have the damaged bussing and breakers at their laboratory. There is visible latex paint overspray on the bussing and the breakers (painters obviously pulled panel covers off when they were painting). They feel this is the most likely cause. I.e. Latex paint on the bussing doesn't allow the breakers to seat against the bussing 100% and this created arcing. Our customer feels this explaination is BS.
Also of note, in many cases, the wire melted off the furnace breaker in the panel. However, the breaker did not trip.
Does anyone have any experience with this sittuation or any idea what could be causing this sittuation?????
Could it be a furnace issue? A voltage drop issue at the utility primary causing amperage to increase? I.e.:
If the incomming voltage was too low (say 180V phase to phase) divided by 9,700 W furnace load = 54 amps
If the incomming voltage was OK (240V) divided by the furnace load of 9,700 = 40 amps - withing parameters
Thank you very much for your replies!!!!
We IMMEDIATELY sent out a crew and began unit by unit inspections. In approximately (50) of the unit panels (125A MLO's with aluminum bussing), we found the furnace breakers in various states of meltdown and damage to the bussing where they snap in.
The wiring method and spec's were as follows:
Cutler Hammer BR series - 125 amp MLO's with aluminum bussing
Furnace overload protection: Cutler Hammer BR 2-pole 50A breaker
Conductors: #6 Aluminum SEU
Inhibitor: Ilsco De-Ox
Terminations at breakers we tight
Furnace loads: 9,700 VA
Voltage: 240
Phase: Single
Furnace field amp read at furnace startup, 41 amps.
The ranges were also wired with #6 SER aluminum with 50A, 2-pole BR breakers. There were no problems with these circuits.
Worth noting (as we are chasing our tails):
The furnaces were set after the electrical rough was completed. After the furnaces were set, we were able to read the decal on the furnace J-cover "terminate copper only." As the furnace had a pull out disconnect, inside the mechanical area of the furnace, we installed insulated dual rated AL/CU butt splices ahead of the furnace disconnect to transitioned from aluminum to copper (#8 THHN, rated at 50A, like the wire). There was no damage to these butt splices or terminations.
We contacted Cutler Hammer and they now have the damaged bussing and breakers at their laboratory. There is visible latex paint overspray on the bussing and the breakers (painters obviously pulled panel covers off when they were painting). They feel this is the most likely cause. I.e. Latex paint on the bussing doesn't allow the breakers to seat against the bussing 100% and this created arcing. Our customer feels this explaination is BS.
Also of note, in many cases, the wire melted off the furnace breaker in the panel. However, the breaker did not trip.
Does anyone have any experience with this sittuation or any idea what could be causing this sittuation?????
Could it be a furnace issue? A voltage drop issue at the utility primary causing amperage to increase? I.e.:
If the incomming voltage was too low (say 180V phase to phase) divided by 9,700 W furnace load = 54 amps
If the incomming voltage was OK (240V) divided by the furnace load of 9,700 = 40 amps - withing parameters
Thank you very much for your replies!!!!
