Best Relay for a Motor

[Darkwood]

Isn't it strange that similar threads appear on other sites and once rebuked the OP moves on until someone gives them what they want to hear

I take it he's been doing the rounds then, I just think on this occasion the OP is ignorant of the regulations that cover what he wants to acheive and believes the regulations he works to are enough, I haven't suggested at any point the OP isn't competent in his own field.
From the info gathered I personally wouldn't have bought off the shelf units complete with control pendants to convert but instead bought the motor rigs without controls and designed from their - running them either of a single VSD or 4 separate with coupled speed ref' to ensure all motors behave the same.

Its not cheap but he says their is a budget... Sorry but H&S don't allow corners to be cut because of funding, million pound bands, millions taken on the tickets yet skimping on a few grand to have a safe control system to meet regulations, :nonod: I have personally never known a budget not be revised for safety if your case is presented correctly - it could be argued the insurance could be invalid if found to not meet regulations thus no concert/gig!.. bet the limiting budget would suddenly be relaxed.

 

[Lucien Nunes]

As I understand it, you want to substitute single-phase utility hoists with integral pendants, in place of conventional rigging hoists designed for external control, for what would otherwise be a standard multi-motor truss controlled from a normal riggers' handset. I presume the reason is one of economy or lack of available 3-phase supply? You recognise the interfacing your handset with the original wiring of the alternative hoists involves relays of a certain minimum specification, hence your question, although that was worded to suggest a single hoist.

If you know the spec of the original control circuit, then it is a simple matter to spec a relay that will function electrically. I don't think you've stated this yet? The problem arises, as others keep suggesting, that the choice of relay is dependent not only on the electrical requirements of the hoist but also the degree of safety it needs to provide to ensure that the complete multi-hoist system functions as intended. What would be the risk involved if one relay welded shut and caused one hoist to run while the others were stopped? What if one motor started up in the opposite direction, stalled, or reversed while in motion (a single-phase motor may be more prone to this than conventional 3-phase rigging hoist motors)? These are factors concerning the integration of the hoists into a system that demand an overall risk assessment outside of the scope of what we can advise on a forum. You state that you are competent to do this, and I am not personally doubting you, I just don't think we can make any useful recommendation about the choice of components from a distance, for such a critical application.

 

[Darkwood]

On that last note, I think the OP is now well informed that he shouldn't be trying to mess with such systems as he has failed to convince me he has any knowledge of the requirements and regulations surrounding what he wants to do.

In the interests of the safety of the OP and unfortunately the safety of Justin Beiber as well, I'm closing the thread.