Ground Detection Help

[gabany]

We are installing a 12K # mobile column lift. This unit features a main panel with all integral protection for the motors, control, etc. This main panel is fed via a 20 foot cord (30A, 480VAC 3 phase + ground). Our plant features an ungrounded ("floating") 480VAC service.

I would like some type of detection ensuring the main panel (attached to the mobile lift) still has a good frame ground connection, thus ensuring a phase to ground fault with the equipment will not result in the equipment frame being energized but instead will open the circuit.

Any ideas? I few of the items I looked at for ground fault detection require a 3 pole grounded whye source.

Thanks

 

[charlie]

Re: Ground Detection Help

I would recommend some outside professional help. The "floating" service is just that and the reason is to maintain service if and when a ground fault were to occur. The plant grounding system will ground the frame of your equipment but no overcurrent device will operate with a single ground fault. Upon the completion of a second ground fault, the overcurrent device to one or the other or perhaps both circuits will open.

With all that said, you have a few choices. First you can install ground detectors if you have not already done so. Second you can install a zig zag transformer in order to derive a neutral. Third, you can install a small three phase delta/wye transformer for this piece of equipment.

I am sure there are other options but most are not low cost.

 

[don_resqcapt19]

Re: Ground Detection Help

I would like some type of detection ensuring the main panel (attached to the mobile lift) still has a good frame ground connection, thus ensuring a phase to ground fault with the equipment will not result in the equipment frame being energized but instead will open the circuit.

If the system is ungrounded, a phase to ground fault will not open the overcurrent protective device.

few of the items I looked at for ground fault detection require a 3 pole grounded whye source.

I don't understand. Ground dectection equipment is not used on grounded wye systems.
You could use this device along with a shunt trip breaker to kill the power in the event of a ground fault.
Don

 

[gabany]

Re: Ground Detection Help

Perhaps I am trying to provide unnecessary personell safety, but what I was envisioning was some type of "frame ground loss" detection at the lift panel.

In other words, if I have a phase to frame fault somewhere on the lift, and I have lost that solid frame ground connection, the mobile lift metal frame will then become energized.
If I do have a solid frame ground connection and a phase to frame connection accidently occurs, there is no problem (assuming it is the only location).

However it is that rare instance that I have lost my solid frame ground connection and a phase to frame connection accidently occurs that I am trying to avoid.

A typical ground fault monitor which measures all three phases and operates on the imbalance between them will not work in this application.

 

[don_resqcapt19]

Re: Ground Detection Help

If you add an additional conductor in your power cable maybe you could use something like this. this looks like it is only for use on impedance grounded systems, but they may be others for ungrounded systems.
Don