Adrian Brentnall wrote:

On 18/08/2019 23:19, The Natural Philosopher wrote:
On 18/08/2019 22:03, Adrian Brentnall wrote:
HI Folks
As the subject says - can't seem to find a contact that operates off
12volts on the coil, and is rated to switch 40+ amps @ 240v a/c.

Thats a fairly non DIY type of 'thing'

Yes - I know it's stretching the definition of DIY grin.

It's for a 'safety' relay on a glass-fusing kiln - will be wired
in-series with the Big Relay that switches mains to the heating elements.
In the event of the Big Relay failing 'on' (which has been known to
happen), the kiln controller (12v out) can drop out the safety relay and
avoid a melt-down. Safety relay needs to be rated to break 15 - 40A at
240v (several different kilns with differing specifications).



Does such a thing exist - or do I have to use a a slave relay from the
12v to switch a 240v coil?

https://uk.rs-online.com/web/p/contactors/7648882/

If you dont mind ante-ing up a ton

Yes - that's rather more than I was hoping to pay understatement - but
thanks.
It may be just as simple, and much cheaper, to switch a small relay with
the 12v and use the contacts on that to switch mains to the Safety
contactor - which can then be a £30 jobbie.

There seem to be a lot of 12v-coil 'contactors' which are targeted at
the DC, high-current market -
but Id want something that could interrupt 40A / 240v safely.


Thanks

As far as current is concerned, a relay will have a much easier time
interrupting 40A AC than it would 40A DC. It may be worth looking at
the detailed ratings of the DC devices, because if they are rated
adequately for 240V the current should not be a problem for them.

--

Roger Hayter