I just replaced a 400a breaker. It was in a VFD sized for a 125 hp moter 480v 3p. 200a fuses and 3/0 copper thhn fed this VFD.Line side connections are ok. Load side phase 1 ok, phase 2 got very hot the insulation was brittel falling off and copper wire had color distortion for about 12in. phase 3 almost as bad as phase 2. The connections seemed tight, this vfd is only 18 months old. After repair amp draw was equal less than 90a each leg. What could cause this? john
Bad breaker
- Thread starter jociha
- Start date
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james wuebker
Senior Member
- Location
- Iowa
Re: Bad breaker
It could have been loose wires. I've came across these before. The termials seem to be tight but from the heat that was on them it made them seem tight. I hope it works fine now. Might want to check the connections on the motor also. Good luck.
Jim
It could have been loose wires. I've came across these before. The termials seem to be tight but from the heat that was on them it made them seem tight. I hope it works fine now. Might want to check the connections on the motor also. Good luck.
Jim
bphgravity
Senior Member
- Location
- Florida
Re: Bad breaker
I hope you torqued the terminations on the new breaker per the manufacturer's instructions?
I hope you torqued the terminations on the new breaker per the manufacturer's instructions?
Re: Bad breaker
John, I have run into this before so I'm assuming a few things that may be the cause of your problem.
One of the challenges when putting all this stuff in an enclosure is the connection from the breaker to the drive. Common 3/0 builders cable is made of of?19 strands and is somewhat flexible but can be all but impossible to use when interconnecting between components in the confines of and enclosure. As an alternative they opt for the finer strand locomotive cable of welders cable which has excellent flexibility and does meet the temperature and ampacity that is required. Locomotive cable has a mere 450 strands where welders cable can be up to 1591-4180 strands for 3/0 cable and neither has been listed by UL to be used in the standard terminal that breakers are supplied with. I must pass a heat rise and pull test in the terminal. Matter of fact there are none that I know of. I illustrated to P-H for an overhead crane application the fact that no matter what you torque the terminal to the cable will never be tight, the inside strands will remain loose. The terminal will heat and cool as the load cycles and will lossen and propagate the failure. I keep an example of a 250a frame breaker illustrates the failure of the terminal which eventually arc to ground and escalated to the adjacent phase.
If this describes your installation and failure, the only answer is to use crimp on ring tongue terminals and bolt the connections.
I this is the problem you may become a hero when you point this out and correct it.
John, I have run into this before so I'm assuming a few things that may be the cause of your problem.
You didn't say if this was an assembly, breaker and drive, that was assembled by either a panel shop or the drive manufacturer themselves. But I'm assuming that it was.
One of the challenges when putting all this stuff in an enclosure is the connection from the breaker to the drive. Common 3/0 builders cable is made of of?19 strands and is somewhat flexible but can be all but impossible to use when interconnecting between components in the confines of and enclosure. As an alternative they opt for the finer strand locomotive cable of welders cable which has excellent flexibility and does meet the temperature and ampacity that is required. Locomotive cable has a mere 450 strands where welders cable can be up to 1591-4180 strands for 3/0 cable and neither has been listed by UL to be used in the standard terminal that breakers are supplied with. I must pass a heat rise and pull test in the terminal. Matter of fact there are none that I know of. I illustrated to P-H for an overhead crane application the fact that no matter what you torque the terminal to the cable will never be tight, the inside strands will remain loose. The terminal will heat and cool as the load cycles and will lossen and propagate the failure. I keep an example of a 250a frame breaker illustrates the failure of the terminal which eventually arc to ground and escalated to the adjacent phase.
If this describes your installation and failure, the only answer is to use crimp on ring tongue terminals and bolt the connections.
I this is the problem you may become a hero when you point this out and correct it.
charlie tuna
Senior Member
- Location
- Florida
Re: Bad breaker
was the motor fully loaded when you checked the amperage draw? we come across problems like this during infrared scanning. maybe the breaker had an internal problem and caused the current draw on the damaged line conductors to be unbalanced--almost like a partial single phasing incident due to resistance across one phase inside the breaker. we have also seen factory problems within magnetek drives. almost like the contactors are under sized. twelve inches of damaged insulation on a 3/0 copper wire means the problem has existed for some time or is very serious! you really can't determine if the original connections were tight at this point because if the terminal connection got hot enough to melt the insulation back twelve inches it is distorted out of shape and may feel like it is tight. if these drives are operating close to full load for long periods of time they cannot handle the least bit of a poor connection! use knowlox on all connections and also lubricate the connection threads with it before torquing! then retorque it after operating the first day...
was the motor fully loaded when you checked the amperage draw? we come across problems like this during infrared scanning. maybe the breaker had an internal problem and caused the current draw on the damaged line conductors to be unbalanced--almost like a partial single phasing incident due to resistance across one phase inside the breaker. we have also seen factory problems within magnetek drives. almost like the contactors are under sized. twelve inches of damaged insulation on a 3/0 copper wire means the problem has existed for some time or is very serious! you really can't determine if the original connections were tight at this point because if the terminal connection got hot enough to melt the insulation back twelve inches it is distorted out of shape and may feel like it is tight. if these drives are operating close to full load for long periods of time they cannot handle the least bit of a poor connection! use knowlox on all connections and also lubricate the connection threads with it before torquing! then retorque it after operating the first day...
Re: Bad breaker
Charlie, Interesting, Magnetek was my account some years back and the 250a breaker I referred to came from there which I still keep as an example. I pointed out their sin that they made ammends by using crimp on ring tongue terminals bolted to the breakers.
Maybe they went back to their old ways again.
I should post a picture of it.
Dave
Charlie, Interesting, Magnetek was my account some years back and the 250a breaker I referred to came from there which I still keep as an example. I pointed out their sin that they made ammends by using crimp on ring tongue terminals bolted to the breakers.
Maybe they went back to their old ways again.
I should post a picture of it.
Dave
Re: Bad breaker
Thanks for all the advice, was it fully loaded not sure, i am going to wait a week and go back for a good check out, sorry its not a magnatek, it is a complete factory assembled cutler hammer HV 9000. Charlie, what you say sounds true to what i have, i may have fixed the wire connection problem by accident i replaced the bad wire with THHN. john
Thanks for all the advice, was it fully loaded not sure, i am going to wait a week and go back for a good check out, sorry its not a magnatek, it is a complete factory assembled cutler hammer HV 9000. Charlie, what you say sounds true to what i have, i may have fixed the wire connection problem by accident i replaced the bad wire with THHN. john
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: Bad breaker
Jociah, simple take a look at table 400.4, you won't find it listed there. Welding cable is often misused for portable power cable, there is a product intended for the use, its a Type W cable
Jociah, simple take a look at table 400.4, you won't find it listed there. Welding cable is often misused for portable power cable, there is a product intended for the use, its a Type W cable
Re: Bad breaker
jociha,
I did some research of the UL testing of terminals and rated wire a number of years ago. After all that messing around and finding out how UL conducted the tests and with what wire I don't know if I have that file anymore.
It's interesting, the wire has to be UL, then the terminal is listed with a specific wire with basically a high rise and pull test, then the terminal is installed on the breaker and then the terminal is listed and tested with the breaker.
jociha,
I did some research of the UL testing of terminals and rated wire a number of years ago. After all that messing around and finding out how UL conducted the tests and with what wire I don't know if I have that file anymore.
It's interesting, the wire has to be UL, then the terminal is listed with a specific wire with basically a high rise and pull test, then the terminal is installed on the breaker and then the terminal is listed and tested with the breaker.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: Bad breaker
A quick search of the Thomas and Betts website shows they have specific compression lugs for standard "stranded" wire, navy stranded, and welding stranded but they have no special mechanical lugs.
A quick search of the Thomas and Betts website shows they have specific compression lugs for standard "stranded" wire, navy stranded, and welding stranded but they have no special mechanical lugs.
- Status