See if you can figure this one out.....

[testtech]

Linden--Drives generate odd multiple harmonics and their corresponding magnetic fields. That is, 1x 60 Hz, 3x 60 Hz, 5X 60 Hz etc. Any frequency that is an even multiple of 60 Hz will not be produced by the drive. I simply provided an example at 240 Hz which is 4x 60 Hz. The drive harmonic amplitudes will typically diminish as frequency increases. However, PWM drives can produce interference at fairly high frequencies. Again, this problem is probably best approached with very narrow band filtering set to an even multiple of 60 Hz. By the way, the exception to all of this is if you have DC motors. The DC drives will produce fields at 360 Hz and a few multiples beyond that. It is unlikely that the chiller and related equipment use DC motors. Waste water plants, particularly older plants, could have DC drives for some of their equipment. These days, AC drives will be more likely in most industries.

[Linden Riddle]

No problem understanding your original post. The information makes sense but in a limited way. Tell me how 240 hz would be beneficial for locating lines situated underneath the electric duct?

[beyond help]

It's an alien. Oh crap!!!!!

[testtech]

Linden: If your utility is beneath electrical conductors associated with a VFD and you used a tracer frequency of 240 Hz, then you would be unlikely to be interfered with by the electrical conductors. This assumes your receiver has very narrow band filters.