I am sizing hookup wire for a impulse heater using NiChrome ribbon for a multi PVC layer sealing tool running at a low 6.4VAC but at 50+ amps for less than 5 seconds in a 30 second machine cycle time. Are there specific NEC codes that can be applied for such a short duration so that I would not need to use a 8AWG wire or larger?

If I use the correct size circuit breaker for a size 12AWG or 10AWG MTW that I would like to use for its flexibility and installation constraints, the wire will never get hot enough and the breaker will never trip at that load and duty cycle. Any possible code violations here?

 

Kedgamatic... while RMS equivalent is low, I believe you should be more concerned with voltage- drop.

Regards, Phil Corso

 

Voltage drop is present but not significant since the lead lengths are less than (3) feet. Watts to the load is sufficient for a fast seal with the smaller gauge wire. I may even run a larger gauge wire for all but the last 6" where I would like to drop down to a smaller gauge to provide for greater conductor flexibility and ease of termination at the load.

 

Kedgamatic... if you are altering/modifying another manufacturers’ commercially available equipment/device without their permission, you are liable for any consequence related to your modification!

Wiring, terminal-connectors, crimp-connectors, solder-lugs, step-down transformer... anything in the circuit up to the point of fault... are dependent on the fault-duty available at the point of failure. Therefore, I suggest you look into the current-withstand capabilities (at 50A) of the devices/components mentioned.

Regards, Phil Corso

 

Kedgamatic... what is the waiting time between cycles? Phil

 

Don't believe NEC applies for a machine component like this.

Fundamentally, the NEC is a part of the NFPA (fire protection codes) and governs circuit protection for fire prevention and safety.

 

Kedgamatic, Dave... my point is that a step-down transformer is probably being used to supply the 50A, 6.3V "Sealer" load. Unlike a 3-phase power transformer, a single-phase control-type transformer has a lower impedance!

If a short-circuit occurred down-stream of the #8 AWG wire, the current could be as high as 25-30 times the xfmr's nominal secondary rating. Thus, the smaller wire's temperature-rise, during the fault's duration, could exceed the permissible insulation temperature causing failure.

Furthermore, if the protective device (fuse or breaker) is not properly chosen, the wire can even reach its fusing (melting) temperature.

Wht's the "Old Saw" about accidents... they don't just happen, they are caused!

Regards, Phil