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There's got to be some kind of interesting explanation behind that weird specification!

At that frequency, the grinder motors would really be hauling. But 300 is a wierd value to settle on. Maybe 400 Hz was too fast?

Hi,

I have been told that the frequency was chosen to reduce vibration white finger. No one is old enough to remember when it was installed but it has a rotary frequency convertor connected to it which burned out, that is what caused us to notice it.
The box with the contactor contains the motor starter. The grinders plug in using some bizarre metal socket with a metal sprung lid.
No one knows what happens to that SY cable. I shudder to think
In the last pic, the earth has been disconnected. When it was re-connected, the breaker wouldnt stay on. That has all been re-wired since, we didnt even bother to find a fault.

Is that a contactor installed on the door in the one pic?(with the hanging connectors) That looks pretty scary to me. So what did you do? Convert to more conventional wiring techniques with VFD(s)?
Joe

[This message has been edited by JoeTestingEngr (edited 01-10-2006).]

That on the door is the on/off switch for the voltage/frequency set, there is a start and stop button on the door to. I will try and get a pic of that later. It is a mechanical one. It is still in use today, with no plan to upgrade it - "if it works, it must be ok" thats our motto. I work in IT so dont get directly involved with that side of maintenance.