What vfd do you buy?

The makers manual should have a typical connection drawing showing the incoming 1ph supply with their recommended protection devices and whatever is shown on the outgoing side to the motor. Following their installation recommendations should suffice in terms of meeting any protection requirements.

Typically, fused protection or rated mcb on the input and direct connection to the motor on the outgoing side with maybe a filter.

There is certainly no need for anything too complicated.

For your own protection there should be an nvr switch on the primary side.

Presumably this contactor is to go in the supply line to the VFD as normally a VFD is connected direct to the machine and its controls superset the machines own.

In the home workshop the primary reasons for a contactor are to provide a "No Volt Release" so that the circuit is broken if power is lost so the machine cannot self restart when power is restored and to provide overload protection if the motor draws to much current, e.g. when stalled. A properly set up VFD automatically provides both functions so no need for a contactor in the supply to the VFD.

Some VFD boxes can be configured for automatic restart when power is restored but, usually, the option is safely buried inside the standard incomprehensible detail part of the manual.

However I would fit a nice clear lever operated switch in the power line to the VFD so you can clearly see whether or not things are turned on and ready to go. I like the Lewden MW single phase **LINK** and ISO three phase **LINK** ones as they are fairly small and can be see all the way across the shop. Can be a bit hard to find.

Clive

The VFD can provide many of the functions of a contactor (overload and no-volt release) if configured appropriately – note it is possible to configure in ways that would not provide these expected protections.

Does your VFD include STO functionality? If it does (and if the STO circuit is wired correctly) that may well satisfy even requirements for safe working on the machine.

Provision of a manual isolator switch, or removable plug for the supply to VFD would be sensible.

The contactor is a safety feature and no-one today can tell you it's OK not to fit one. It's down to you to assess the risks, and these have to be taken much more seriously if someone else is involved. Do you ever have visitors in the workshop? Is there an insurance problem if you burn the house down due to a home-made electrical installation?

That said, many older machine tools have unacceptably poor safety features by modern standards and people use them privately without ending up in hospital, being persecuted by the HSE, or getting sued by the neighbours. Exposed gears and belts whizzing round on machines with dodgy 1925 electrics and no interlocks are manageable provided the owner takes reasonable care. Although the hobby has it's risks, I think they're relatively small. Model Engineering is considerably safer than Amateur Radio where chaps get killed and maimed falling off masts and roof-tops, or having heavy aerials land on them, plus the odd RF burn, electrocution, and lightning strike. Let's not mention microlights, horse-riding, or motor-bikes!

I would definitely build Mitsubishi's recommended circuit if your machine already has safety interlocks because deliberately rendering interlocks ineffective to save money isn't smart. Conversely, if an older machine doesn't have safety interlocks, adding a contactor is likely to be a waste of time.

For H&S and commercial reasons Mitsubishi are unlikely to recommend anything but the very best contactor. There are plenty of cheaper alternatives available: prices start just below £14 on Amazon, other suppliers available.

Dave

Two buttons (one make and one break) and a 10k pot are all you need for basic control of this VFD.

If the volts disappear from the device it will need a start command to run again so NVR is sorted anyway!