Motor T-Lead Sizing
Motor T-Lead Sizing
(OP)
What is the basis for large motor t-lead sizing? We have a 7000HP, 4000V, 900FLA motor that had to be rewound. During the repair, parallel 4/0 conductors were used per phase. The motor originally had 3/0 conductors. This seems like it would but a large thermal load on termination lugs for the guy used to sizing such things per NEC.





RE: Motor T-Lead Sizing
You may not have a problem
respectfully
RE: Motor T-Lead Sizing
4/O AWG---- 275 Amperes
3/O AWG---- 235 Amperes
2/O AWG---- 203 Amperes
1/O AWG---- 176 Amperes
According to above values, for 900 Amperes you should have 4 cables 3/O in parallel or any other practical combination per phase.
RE: Motor T-Lead Sizing
The motor has been sent to a different repair facility and is ongoing complete lead replacement. I want to specify a larger lead size or more than 2 parallel 4/0 per phase, but didn't know what the manufacturer used as the basis for sizing. I asked, but wasn't given this information.
The last lug failure resulted in the catastrophic destruction of the terminal box; after the lug burned off, the open ended lead contacted a grounded component in the box.
RE: Motor T-Lead Sizing
Ussually in our Shop for 4160 Volts motors we use EPDM Class F - 7500 V manufactured By BELDEN for this manufacturer wire the 3/0 Ampacity is 457 and 4/0 wire: 529 Amps.(Maximum values for single conductor in free air @ 30 C) If the motor was designed by the maufacturer with parallel 3/0 per phase, I think this could be a short design. If the motor was rewound with two Parallel 4/0 and failled maybe the motor´s temperature is too high and this could be derrating the wires.
the shops could use 13.2 KV 250KCMIL wire.
Regards
Petronila
RE: Motor T-Lead Sizing