VFD aux contact

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ptonsparky

ptonsparky

Tom
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NE (9.06 miles @5.9 Degrees from Winged Horses)
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EC - retired
Customer recently asked us to interlock a piece of equipment with another. One of the machines had 480v for power & control including the interlock utilizing the drive's aux contact. It is not rated at 480v either on the device itself or in the installation instructions for that drive. The equipment had been mfgd for a specific purpose and had an Idaho inspection sticker on it.

Is this an oops in an otherwise well designed system or normal?
 
ptonsparky said:
Customer recently asked us to interlock a piece of equipment with another. One of the machines had 480v for power & control including the interlock utilizing the drive's aux contact. It is not rated at 480v either on the device itself or in the installation instructions for that drive. The equipment had been mfgd for a specific purpose and had an Idaho inspection sticker on it.

Is this an oops in an otherwise well designed system or normal?
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I'd call it an oops.
We'd normally fit an external interposing relay for any interlocks that are not specifically part of the VSD system.
Apart from any rating limitations, there is the safety aspect to consider. If you are using the contact to switch anything that gets its supply elsewhere you will potentially have that voltage present at the drive even with the supply to the drive switched off.
 
Another thing to consider is that the aux contacts are usually derived form a teeny-tiny board-mount relay on the drive. My soldering iron and I have spent many hours replacing them...

Even if they say they are rated for 5 or 10 amps, I would drive nothing but a control signal with those relays and nothing over 120v.


My 2?
Doug S.
 
I don't know of any VFD on the market with output relays rated for any more than 250VAC (if even that).

The spacing on the terminals is probably the best visual clue if you have nothing else to go by. 480V requires at least 1" if total surface area between live terminals. So that usually results in some sort of vertical barrier between terminals on things like control contacts.
 
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