Then along comes the June, 1995 issue of my favorite trade magazine with an article on Protecting High Efficiency Motors with a long drawn out discussion on the 700 per cent rule and the 1300 per cent rule for instantaneous trip circuit breakers. After discussing time-delay fuses and inverse time circuit breakers, the conclusion of the article was that "we think" one of the code devices should allow the motor to accelerate without tripping . Then after the end of the article there was a note on the 1996 NEC that said Article 430-152 will have 800 % replacing 700% and 1700% replacing 1300% for the instantaneous trip circuit breakers used with Design E motors, the type for most high efficiency motors. Like I said, "Stay around long enough and the Code will catch "up" (or should that have been "on?")

But let's not stop here. Let's go right to the source, the 1995 Report On Proposals, proposal 11-108 by Larry Miller of the National Mfrs. Association. His substantiation states it very well:

"This is a companion proposal to other proposals to define and add Design B, C, and D and Design E to the Code. Design B, C, and D motors are basically the present motors addressed in the Code and Design E are energy efficient motors. Changes are in [proposed] Table 430-152 to accurately reflect the motors being manufactured today."

"Instantaneous trip circuit breakers are only used as part of a listed combination controller as allowed in 430-52(a) and only provide the short circuit protection for the circuit. Ideally, the setting of these breakers is as low as possible to allow the motor to start without tripping. The motor manufacturers have stated that the peak inrush current on starting is in the range of 1.8 to 2.8 times the Locked Rotor Current. These peak currents must be converted to rms currents to determine the setting of the circuit breakers. Since the LRC/ FLC ratio is approximately 6, an initial setting of 800% of the FLC (rms current) would more closely match the low end of this peak current range and would eliminate some of the nuisance tripping that occurs. For the Design E motors, the LRC/FLC ratio is approximately 8. Using the same process, this converts to an initial setting of 1100% of FLC (rms current) and an upper setting of 1600% of FLC (rms current."

In the preprint of the 1996 NEC, Exception No. 1 to 430-52 states that for Design E motors the instantaneous trip setting may be raised to 1100% of FLC, and where the need has been demonstrated by engineering evaluation, this may be raised to 1600% of FLC. The Code is catching up!