Help on system with multiple safety contactors to power up

[fwagner5]

I have a customer requesting safety contactors on the load side if a VFD (I know that this is not good, but this is what they want). My question for anyone is I have 14 safety contactors that I need to power up and was going to use a contact off of the safety relay, but looking at the contactor of pulling almost .5A x14 is a lot of the safety relay. Any suggestions on how to do this right looking at adding a 120VAC output card for them but then would require an expansion module for the safety relay since the all the contacts are used. Presently, this is a 24VDC system.

 

[LJBMatt]

have the safety relay fire 2 24vdc force guided relays (with 8 N.O contacts) to handle firing your other power contactors. I would advise against using an output card for safety reliable control.

 

[parky]

you could feed the positive guided contactor into the common of the plc card & use this to sequence the contactors.
We have done this in the past, feed the main safety contactor from the safety relay, this feeds 110v to the plc card & then fire the outputs in sequence.
We also series a spare contact off each of the contactors (normally closed) back to the safety relay so if one of the contactors welds in you cannot energise the safety relay this is common practice with the use of a main safety contactor on the 3 phase supply, this way you have double safety one main contactor feeding all the inverters (or drive contactors) & one contactor on each output of the inverters, the feedback (n/c) off the main & aux contactors if broken (one contactor welded in)will stop the safety relay energising.
The use of contactors on the output is not a problem on most new type inverters, indeed we have an inverter with three contactors on the output driving two motors so we have contra rotating, both forwards & both backwards.
This system has been in for 9 years & never had an inverter fail yet.

 

[504bloke]

have the safety relay fire 2 24vdc force guided relays (with 8 N.O contacts) to handle firing your other power contactors. I would advise against using an output card for safety reliable control.

And over here depending on the level of safety we would put 2 of the NC's of the 2 new force guided relays through the feedback of the safety relay making the 2 new relays 4NO 1NC on each.