Mains contactor expected lifetime?

As much as a millivolt?

Dont be silly.

You simply have no clue do you?

Coils like that are what we used to use to resonate at 10-20Mhz, in conjunction with less capacitance than you would see between the leadout wires going to such an element.

Oh good, I can join your club.

No.

No John, sorry, you cant.

You are talking total drivel. TurNiP is right.

I suspect that there is an error in that calculation.

Well you are the expert on that...

I find your disagreement comforting.

First, I can't find that part listed. :)

Anyway, your 7kW load will be virtually resistive so it works out at just over 30A at 230vAC. A 40A contactor is fine. The lifetime is going to be the mechanical life of the system. :)

I'd thought about using a solid-state relay instead - but I'm not

I've come across resistive heating systems that used a mechanical contactor followed by a SSR. The mechanical unit is necessary because a SSR can never be regarded as "off" from a safety perspective, so any emergency stop or fault condition has to operate the mechanical device.

IC40/2 : 2p 40A modular contactor - 8.4kW resistive @230vAC

Typical info for an ABB contactor of similar design & rating: Max electrical switching freq with AC-1 load: 300 cycles per hour Electrical durability with AC-1 load: 150000 cycles Mechanical durability: 1000000 cycles

Well I've just had half a bottle of Famous Grouse.

And I say it's resistive (the kiln not the Famous Grouse).

Bloody 'ell.

When I was at uni my cleaner told me Grouse was a 'good' whisky.

It may be compared to Tesco Value Potcheen, but I still prefer Isle of Jura.

And I once had a bottle of Littlewoods Sherry in one evening, not sure if that was the evening I clambered fearlessly on the parapet of a fifth-floor tenement roof or not.

Owain

====snip====

It's not the maximum instantaneous voltage so much as the maximum instantaneous current. In this case, a mostly resistive load with a small element of inductance, the two are almost the same thing.

It's the interruption of ca 29 amps of current that creates an inductive back EMF to trigger an arc. However, the use of an AC supply allows for a much smaller contact separation distance than that needed when using a

In fact the 'auto extinguish' feature of AC supplies is so effective that a much cheaper 'toggle effect' can be used in light and socket switches, one where the end (ab)user can, with some dedication to the task, defeat the toggling action to admire the SFX and, in some cases, the 'light show' from behind the plastic switch plate.

The old fashioned "Tumbler" light switches used on DC supplies had a more foolproof toggle action, along with a contact separation measurable in centimetres rather than the millimetres of a modern light switch.

Well no, there is no 'inductive EMF' in the case of a resistor. However mains voltages are enough to strike one anyway. fact any voltage is, if the gap is small eniough.

Yup. Which is why many relays are derated for DC load operation.

Yup. Never said you wont get arcing, just that 'inductance' was a red herring.

No, that's wrong. the inductance is the same whether the frequency is