GFI and VFD?

[DennisCNC]

Hi,

I need to put a GFI breaker on a VFD driven motor because it will be used around water. How is this done? The VFD is single phase.

Would this work:
LINK

Thanks

[Al_The_Man]

It looks like a double pole GFI breaker, but it does not appear to be stand-alone, if it is not you would need the compatible GE panel to use it in, as the input clips on to the Supply panel bus.
Al.

[gar]

060403-1407 EST USA

DennisCNC:

If your VFD has input filtering connected to safety ground, or if there is enough capacitive coupling for high frequency noise from the VFD to ground, then you will not be able to use a GFI at your input.

A GFI looks for a small current in the safety ground wire. If this current exceeds a threshold limit, then the breaker trips.

Why do you want a GFI?

.

[DennisCNC]

This motor is used on a edge router for granite and water will be all over the place. Water + electricity =

Or what about making one of the inputs on the vfd connected to the frame of the router and configure the input to be e-stop and when something goes wrong it will kill the power to the motor ( I think) and mabe kill the VFD and not me?

What are some other options?

[HuFlungDung]

Perhaps an isolation transformer (one sized appropriately for the motor current) could be used to feed the VFD.

[2muchstuff]

I second the isolation transformer.

[DennisCNC]

So use a isolation transformer to isolate the noise from the VFD so the GFI dosen't see it?

Or did I get it all wrong?

[HuFlungDung]

No, the isolation transformer creates an isolated power system, with no connection to earth ground. The primary side of the transformer carries the current from your power company, but the current induced in the secondary side really has no circuit connection to the primary side.

Since the power company conductors do have a potential to ground, this is why if an insulation fault occurs, and you happen to help make the connection to ground with your body, that the current flows through you. This is what the GFI detects and stops by tripping open.

So on the secondary side of the isolation tranformer, none of the induced currents really has any potential to ground, so the danger is lessened in that regard.

You should consult a real industrial electrician about doing the hookup in an approved and safe manner.

Edit: in clarification, an isolation tranformer is simply two identical windings, there is no change in voltage. Its sole purpose is to create a seperate power system with no physical conductor joining the two systems.

[Al_The_Man]

This is rather attacking it from the wrong end, the code recommends that the motor be selected for the service it is going to be used in, There are Wash-Down & TENV (totally enclosed non-ventilated) type.
Just as sump and coolant pumps are designed to be submerged.
I would recommend you obtain the code requirements for running an isolated motor, for example, if you do, make sure that both feed conductors have protective devices, unlike a neutral supplied system which is a non-fused conductor.
Plus all conduits etc should be liquidtight as well.
Apart from the NEC code I use the NFPA-79 for ref. which is Electrical Standards for Industrial Machinery.
Al.

[DennisCNC]

Got it about the isolation transformer!

The motor is a power wash down TENV (totally enclosed non-ventilated) type.
I just wanted to be sure about not getting shocked.