Unobtrusive Isolators close to Ovens but needing very long cable runs, are such runs OK.

[Nickfromwales]

A robot in cyberspace says this:

 

13

 

 

 

A latching contactor relay (or bi-stable relay) maintains its state without continuously powered coils. A momentary pulse "sets" the contacts closed, while a reverse polarity pulse or a separate mechanical/electrical reset pulse "resets" them to the open position. This saves significant energy and prevents buzzing or drop-out during power dips. [1, 2, 3, 4, 5]

 

Why Latching Contactors are Used

Standard relays and contactors are "fail-safe," meaning they require constant power to hold a circuit closed. Latching contactors are highly beneficial in specific applications: [1]

• Energy Efficiency: Ideal for systems that stay on for long durations, as no power is consumed to keep the contacts engaged. [1, 2]

[Mattg4321]

Or get a normally closed contactor. 

[Nickfromwales]

1 hour ago, Mattg4321 said:

Or get a normally closed contactor. 

I have some odd, inbuilt aversion to this needing any kind of constant (continuous / maintained) signal or feed to function, and am favouring something that flip / flops with a single ‘hit’.

 

I may need therapy……but I do also like belts, braces, and for my phone to continue to remain silent each and every night.

[Mattg4321]

7 hours ago, Nickfromwales said:

I have some odd, inbuilt aversion to this needing any kind of constant (continuous / maintained) signal or feed to function, and am favouring something that flip / flops with a single ‘hit’.

 

I may need therapy……but I do also like belts, braces, and for my phone to continue to remain silent each and every night.

It’s a fair point if you want it to

go off and stay off in the event of the smoke detector circuit going down. 

[Nickfromwales]

2 hours ago, Mattg4321 said:

It’s a fair point if you want it to

go off and stay off in the event of the smoke detector circuit going down. 

Madness I know (IRL) and that was my exact concern.

 

If I can buy one thing to be a maybe, or another that’s a definite, and the price isn’t hundreds apart, then I’ll go definite each and every time.

[joth]

On 07/07/2026 at 23:16, Nickfromwales said:

Criticism / objections (or applause) welcomed

Aside from the whacky surprise it leaves to any future electrician working on it, I'd be concerned fire alarms come with a "test monthly" sticker or similar, and this thing frobbing off so regularly will decrease lifetime of the rcbo and relay base, and increases odds it gets forgotten and not re-enabled

 

 

[Nickfromwales]

3 hours ago, joth said:

Aside from the whacky surprise it leaves to any future electrician working on it, I'd be concerned fire alarms come with a "test monthly" sticker or similar, and this thing frobbing off so regularly will decrease lifetime of the rcbo and relay base, and increases odds it gets forgotten and not re-enabled

 

 

The benefit outweighs these ‘odds’, as the MVHR not supplying a fire with a plentiful feed of fresh air (to aid combustion) would be my preference; the significance of this was enough for me to consider it robustly, pros and cons, before suggesting it to my client.

 

Any future electrician would be informed by the owner, before they took any tools out, and would also encounter printed labels on the CU stating the additional measures required. 
 

However, if that all failed, the absolute worst case scenario THEN, would be the owner eventually realising that the lMVHR wasn’t on then they’d simply go and reset it.

 

Number of people who test their smoke detectors monthly?  . Not so sure but I’d bet that It’s a VERY low percentile…..  …..like single digits.

 

Only the relay would wear, not the RCBO🙂, and this will likely be tested and approved for 1000’s of operations. In actuality, it’ll fire maybe 2-5 times per decade.

[Spinny]

Can MVHR be used to distribute gaseous fire suppression ?

[JohnMo]

Why is MVHR running any different from open trickle vents when you have a fire. The fire consumes as much oxygen as it can, the fire becomes a low pressure zone, sucking air via opening anyway. Running or not it will suck air through the MVHR or from other rooms via the plenum. If you want MVHR to not contribute to fire air supply you need a fire dampers also.

[Nickfromwales]

1 hour ago, Spinny said:

Can MVHR be used to distribute gaseous fire suppression ?

Nope!! B Regs have an aversion to death inducing systems being installed in residential dwellings lol.

 

Waking up to a home being fully filled with Halon would not go well……

[Nickfromwales]

1 hour ago, JohnMo said:

Why is MVHR running any different from open trickle vents when you have a fire. The fire consumes as much oxygen as it can, the fire becomes a low pressure zone, sucking air via opening anyway. Running or not it will suck air through the MVHR or from other rooms via the plenum. If you want MVHR to not contribute to fire air supply you need a fire dampers also.

Turning off a mechanical fan that is forcing air into rooms, for the sake of £100, is worth the extra effort imo.

 

All ground floor plaster-in vents have intumescent fire collars on them.