Why are RCDs so massively over-expensive?

[treezleef]

Hi,
We are going into business making RCDs. We cannot undertsand why this massive gap in the market has been missed? All existing offtheshelf RCDs are >£30 and massively over-engineered!!!.

Our method is a simple version of a "Fluxgate current sensor".

That is, we use the fluxgate principle, but dont bother with the feedback, and dont bother using a "square law" core Torroid (we just use a standard , cheap as chips, AC CT torroid)

Its for 32Arms mains distribution boxes, that need an RCD.
They must detect >30mA of imbalance current (between line and neutral) , and 6mA or more of DC "leakage" current.

....seriously ....all you have to do is you get your mains line and neutral running through the torroid aperture.......then you simply shove a square wave voltage into the sense coil (the sense coil "secondary" that's wrapped round the torroid).......then the voltage that gets looked at, is simply the voltage across a low value resistor in series with the sense coil.....(its put in series with the coil "gnd" connection and ground)........and you then see either a symetrical waveform if no DC and no imbalance...or otherwise its non symetircal..........in fact, all you have to do is buffer it, filter it, add a small offset voltage so its positive all the time......then read it into an ADC....and its job done. Why is not everybody doing it like this?.....no feedback is needed.
No "square law" core is needed.

So why is nobody doing this?
Why is everyone paying >£30 for an offtheshelf RCD? (i am speaking about RCDs that dont contain the contactor, but just give the signal)

..the way described is inaccurate a bit, but you easily calibrate that out in production....just measure the coil core characteristics of the parts before building them up....

(this is for a sensor which will detect 30mA imbalance current in 32Arms wires...and also detect 6mA DC and more.)

 

[timhoward]

Will regulation 536.4.203 affect your business plan?
As the default position is we wouldn't be allowed to fit your RCDs in another manufacturers consumer unit.

 

[treezleef]

thanks, you mean in BS7671?...we dont have that standard, we cant afford them.
Also, If it works, why cant it be fitted in any equipment?

 

[Strima]

thanks, you mean in BS7671?...we dont have that standard, we cant afford them.

But you can afford to set up for research, manufacturing, testing, compliance, product registration, advertising, distribution etc?

 

[nicebutdim]

Currently under £75 delivered. A drop in the ocean in the overall cost of bringing a product to market - especially if one wants to ensure that product has a market.

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[snowhead]

I was going to explain the complications and expense of getting a new product from a new company approved and to market but then I found the 3 phase art gallery exhibition bus bar and earthing for domestic house threads, so I won't be wasting any time on this thread.

 

[treezleef]

Currently under £75 delivered

Thanks, i have an article, available to all on the web, (from an international university) which shows an RCD signal circuit being done with <$5 of components (and that unnecessarily comprises feedback and a "square law" torroid core, so it would be even cheaper than that when the feedback is gotten rid of, and a non "square law" core is used).....the contactor would be additional to that, but as you can see, its well under £75.

 

[nicebutdim]

Thanks, i have an article, available to all on the web, (from an international university) which shows an RCD signal circuit being done with <$5 of components (and that unnecessarily comprises feedback and a "square law" torroid core, so it would be even cheaper than that when the feedback is gotten rid of, and a non "square law" core is used).....the contactor would be additional to that, but as you can see, its well under £75.

£75 is how much a copy of BS7671:2018 costs.

How many RCDs do you expect to sell and what applications are you intending your products be used in?

 

[Lucien Nunes]

It is true that detecting the imbalance is cheap and simple. Opening the circuit reliably under fault conditions is harder and more expensive, as it requires chunky metal contacts, complicated trip-free toggle mechanisms, arc chutes...

But maybe you don't have to actually open the circuit. Playing back a 5-second audio sample is cheap enough and if you use the speaker assembly from a mobile phone you can leverage mass production economy. So when you have a leakage, the RCD shouts out load and clear to come and turn the main switch off as there is a fault. Bonus is that it can remind you to press its test button on schedule (RTCs are cheap too).

I mean, if 'don't touch the busbars' is OK in an art gallery, surely a talking RCD is OK in a DB?

 

[Simon47]

All existing offtheshelf RCDs are >£30 and massively over-engineered!!!.

No they aren't. There are LOTS on the market for a lot less than that.
And only over engineered if you consider actually doing the job reliably isn't important.

 

[treezleef]

Thanks, but a type B RCD , that can detect 30mA imbalance, and >6mA DC, is way more than £30

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shop.evchargersdirect.co.uk

 

[Electrics]

Weird trolling.

 

[Simon47]

Thanks, but a type B RCD , that can detect 30mA imbalance, and >6mA DC, is way more than £30

Ah, the old "shift the goalposts" technique. In your original complaint you said "All existing offtheshelf RCDs are ...".

 

[treezleef]

Thanks, but the original post does say, admittedly at the bottom.....

(this is for a sensor which will detect 30mA imbalance current in 32Arms wires...and also detect 6mA DC and more.

...but yes, my apologies, as that bit should really have been at the top...i will edit the OP. Thankyou for spotting it....just tried to "EDIT" it, but it wont let me, too long after the event. Do apologise for that. That line should have really been at the top.

The OP does also say...

They must detect >30mA of imbalance current (between line and neutral) , and 6mA or more of DC "leakage" current.

...but yes, you are right, that bit of wording , that you kindly pointed out, was not intended

 

[telectrix]

could you not have a hammer on a magnetic pendulum that an imbalance will cause the pendulum to deflect and the hammerhead hit a OFF button? cheap as chips.