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.

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

Thanks
Adrian

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.

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

Thanks
Adrian

https://uk.rs-online.com/web/p/contactors/7447582/

but you don't want to be paying their prices!

There are plenty of similar contactors, from many manufacturers, that
are rated the same or higher.

SteveW

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'


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



Thanks
Adrian


--
€œPeople believe certain stories because everyone important tells them,
and people tell those stories because everyone important believes them.
Indeed, when a conventional wisdom is at its fullest strength, ones
agreement with that conventional wisdom becomes almost a litmus test of
ones suitability to be taken seriously.€�

Paul Krugman

On 18/08/2019 22:26, Steve Walker 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.

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

Thanks
Adrian

https://uk.rs-online.com/web/p/contactors/7447582/

but you don't want to be paying their prices!

There are plenty of similar contactors, from many manufacturers, that
are rated the same or higher.

SteveW

Thanks Steve
No - I certainly don't want to be paying that sort of money (£138 !) -
only needs to be single-pole anyway...

I did the obligatory search on Google, and trawled CPC / Farnell without
much success..

I think it'll turn out a lot cheaper in the long run to use the 12v to
switch a little din-mounted relay, and use that to switch the 240v to a
£35 40A contactor. Also kinder on the circuit that's driving it..

Thanks

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

Adrian Brentnall formulated the question :
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).

I assume the concern is the Big Relay's contact becoming welded up?

Why not just have two 240v relays, both being switched on by the
control supply and both having their contacts wired in series? Even if
the contacts of one weld up, its very unlikely both would weld up.

I have a circuit which actually uses two in series for switching a high
DC current (100+ amps). One is delayed switching, so the other relay
just carries current, rather than switching it.

A separate circuit monitors the main switching relay, so that if it
does break when its coil supply goes off, it prevents the circuit which
normally powers coil, from powering the coil - an LED then comes on, to
indicate a fault. Human intervention is then required, to unstick the
relay.

Another thing you could do is use an electronic zero switching relay,
much less likely to latch up. I have had one here in constant switching
service for a couple of decades.

On 19/08/2019 08:12, Adrian Brentnall wrote:


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

A RCD would be able to interrupt that, put the relay between L & E with
a resistor to make it trip.

You would have to manually reset but thats probably best anyway.


---
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https://www.avast.com/antivirus

On 19/08/2019 08:06, Adrian Brentnall wrote:
On 18/08/2019 22:26, Steve Walker 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.

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

Thanks
Adrian

https://uk.rs-online.com/web/p/contactors/7447582/

but you don't want to be paying their prices!

There are plenty of similar contactors, from many manufacturers, that
are rated the same or higher.

SteveW

Thanks Steve
No - I certainly don't want to be paying that sort of money (£138 !) -
only needs to be single-pole anyway...

I did the obligatory search on Google, and trawled CPC / Farnell without
much success..

I think it'll turn out a lot cheaper in the long run to use the 12v to
switch a little din-mounted relay, and use that to switch the 240v to a
£35 40A contactor. Also kinder on the circuit that's driving it..

Thanks



soldi state relay is cheaper for a simgle pole but a cursory search
unearthed only 24V DC control


https://uk.rs-online.com/web/p/solid...elays/4729121/

Try a search for solid state relays instead


--
€œIdeas are inherently conservative. They yield not to the attack of
other ideas but to the massive onslaught of circumstance"

- John K Galbraith

The Natural Philosopher wrote:

soldi stateÂ* relay is cheaper for a simgle pole

But then you'll need a F-expensive fuse to protect the SSR :-)

On 19/08/2019 10:52, Andy Burns wrote:
The Natural Philosopher wrote:

soldi stateÂ* relay is cheaper for a simgle pole

But then you'll need a F-expensive fuse to protect the SSR :-)

How expensive can a 60A mains fuse be?

anyway you STILL need that.


--
Future generations will wonder in bemused amazement that the early
twenty-first centurys developed world went into hysterical panic over a
globally average temperature increase of a few tenths of a degree, and,
on the basis of gross exaggerations of highly uncertain computer
projections combined into implausible chains of inference, proceeded to
contemplate a rollback of the industrial age.

Richard Lindzen

In article ,
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.

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


Try a standard car relay? Costs a couple of quid. See if it survives.
Obviously, take safety precautions in case it doesn't. But assuming it is
in a suitable housing for safety purposes, chances are it will be OK.

--
*No radio - Already stolen.

Dave Plowman London SW
To e-mail, change noise into sound.

The Natural Philosopher wrote:

How expensive can a 60A mains fuse be?

£15 to £20 for a 40A semiconductor fuse, Dad went through a similar
issue with SSRs instead of contactors on his kiln.

dennis@home presented the following explanation :
A RCD would be able to interrupt that, put the relay between L & E with a
resistor to make it trip.

Interesting idea!

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

In article ,
Dave Plowman (News) wrote:
In article ,
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.

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


Try a standard car relay? Costs a couple of quid. See if it survives.
Obviously, take safety precautions in case it doesn't. But assuming it is
in a suitable housing for safety purposes, chances are it will be OK.

I'd be dubious about puttting mains voltage into a car relay. I'd be
unhappy about the insulation.
You certainly could get relays to do the job, I've used them on projects,
but switching 40A is probably a bit much for any of them. I think you are
into the 'contactor' realm.

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

In article ,
charles wrote:
Try a standard car relay? Costs a couple of quid. See if it survives.
Obviously, take safety precautions in case it doesn't. But assuming it
is in a suitable housing for safety purposes, chances are it will be
OK.

I'd be dubious about puttting mains voltage into a car relay. I'd be
unhappy about the insulation.

Really? Most have all the bits mounted on a plastic base. I'd be surprised
if that wouldn't insulate 240v. Obviously it would be unsafe if not in a
suitable enclosure for mains. To protect the terminals etc from prying
fingers.

--
*Never kick a cow pat on a hot day *

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:

In article ,
charles wrote:
Try a standard car relay? Costs a couple of quid. See if it survives.
Obviously, take safety precautions in case it doesn't. But assuming it
is in a suitable housing for safety purposes, chances are it will be
OK.

I'd be dubious about puttting mains voltage into a car relay. I'd be
unhappy about the insulation.

Really? Most have all the bits mounted on a plastic base. I'd be surprised
if that wouldn't insulate 240v. Obviously it would be unsafe if not in a
suitable enclosure for mains. To protect the terminals etc from prying
fingers.

If it were in a box attached by a plug and flex I'd agree it was
reasonable, and easy to make safe against electric shock. Although if
it is supposed to break the circuit for safety some reassurance over
contact spacing, internal lead spacing and the dielectric strength of
the plastic used would be nice. And some note on the box to say it was
not to be used with a motor or other inductive load.

However, if it is 40A it sounds as if it is to be wired-in and
effectively part of the electrical installation. In that case I think
one should only use type approved parts for mains voltage and the
expected current.



--

Roger Hayter

On Sunday, 18 August 2019 22:03:18 UTC+1, 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.

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


There's one in every pre pre-engaged starter motor car.
Off you go, down to your local car breakers.

On 19/08/2019 13:48, Dave Plowman (News) wrote:
In article ,
charles wrote:
Try a standard car relay? Costs a couple of quid. See if it survives.
Obviously, take safety precautions in case it doesn't. But assuming it
is in a suitable housing for safety purposes, chances are it will be
OK.

I'd be dubious about puttting mains voltage into a car relay. I'd be
unhappy about the insulation.

Really? Most have all the bits mounted on a plastic base. I'd be surprised
if that wouldn't insulate 240v. Obviously it would be unsafe if not in a
suitable enclosure for mains. To protect the terminals etc from prying
fingers.


Where is the arc suppression built in on 12v car relays?

On Sun, 18 Aug 2019 22:03:16 +0100, 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.

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

Yes as others have already said, at a price.

Many industrial contactors in more recent years have been modular and you could
mix and match coil voltages into a common contact base, easily adding auxiliary
contacts and indicators.

For the coil 24v 48v 110v and 240v are common across a wide range of
manufacturers, 12v remains extremely rare.

--