What type RCD for energy saving lights?

[ericmark]

In the main the RCD in a CU has just 4 connections two in and two out, so test button connects from line out to neutral in to cause the imbalance, however for a 10 mA RCD socket test button to trip a 100 mA trip feeding it clearly it would not only need to be connected to earth but take 50 times the rated current, needs to be 50 mA to trip a 100 mA trip.

 

[bernardgreen]

 

[JohnW2]

In the main the RCD in a CU has just 4 connections two in and two out, so test button connects from line out to neutral in to cause the imbalance ...

Yes, sorry, I wasn't clear. I was talking specifically about active RCDs (such as you mentioned) - we've been through this before and it seems that, unlike the 'usual' test button arrangement you (and flameport, and bernard) describe (which one sees in the usual passive RCDs) many (most? all?) active RCDs introduce an L-E path when one presses the test button.

We have speculated that one reason for this could well be so that pressing the test button checks for the presence of an 'effective earth' as well as RCD functionality, per se.

Mind you, as I discovered with some experiments I reported here a year or two ago, there are also at least some active RCD (sockets) in which (by some mechanism!) the RCD cannot be reset in the absence of an adequate earth connection - so one could not even 'test' one of those in the absence of an adequate earth!

Kind Regards, John

 

[bernardgreen]

The "Functional Earth" connection in RCDs became necessary when electronic tripping was introduced. In the event of loss of Neutral due to a fault in the supply Network there was no supply to the electronics and hence no trip could happen.

 

[JohnW2]

The "Functional Earth" connection in RCDs became necessary when electronic tripping was introduced. In the event of loss of Neutral due to a fault in the supply Network there was no supply to the electronics and hence no trip could happen.

Yes, indeed, but it is fairly controversial (and most RCDs don't have them), essentially because the probability of a neutral supply fault and an L-E fault (both very rare occurrences, individually) in an installation happening simultaneously is so close to zero!

However, this hasn't really got anything to do with what I was discussing - which is the way in which the test circuitry of an active RCD appears to work.

Kind Regards, John

 

[ericmark]

If the test button for a 30 mA RCD gives approx a 30 mA imbalance it really does not matter that much if line - neutral or line - earth, but the standard seems to be with multi RCD's in series to have three times stages, so 10, 30, 100, 300 mA and they should trip between 1/2 and full rating, so the trip current maximum needs to be if line earth no more than 15, 50, 150 mA so it only trips one device when tested, with line - neutral it does not matter so much, however only way to test a caravan or boat RCD is with test button line - neutral as other wise the shore RCD will trip first, so you do want the button some where near the tripping current as it may be only way to test it.

I have looked at many RCD's for voltage, the loose Wilex was marked 230 volt bit of a surprise as would have expected maximum voltage, but on the side so once fitted can't read, rest were in boards so could not see any voltage, however since above 50 volt is low voltage and comes under low voltage rules one would think they would work between 50 and marked voltage, which is a problem for a test button to work without tripping next size up.

Not even sure what current the RCD tester uses, is that a simple resistor or does it actually use 30 mA?

In the early days no one relied on the RCD, even TT supplies had water pipes and gas pipes so line - earth fault would rupture a fuse, but as the water and gas pipes have been replaced with plastic were are starting to rely on the RCD, the ELCB-v was discontinued because unreliable, but seems the replacement is also unreliable, I have seen a bosch boiler manual that states use type A RCD, but not seen any other domestic appliance which states use type A.

 

[flameport]

Bosch washing machine requires Type A:

from https://www.bosch-home.co.uk/produc...ashing-machines/WIW28301GB#/Tabs=tab-3276279/


Type B RCD recommended for this Vitodens 100-W boiler, which according to them is their best-selling gas condensing boiler, and is a Which? Best Buy 2019:

From these PDF instructions: https://viessmanndirect.co.uk/files//aa22877b-8b78-4293-a83e-a7ec00f58658/WB1C Install Serv.pdf
That document is dated 2012, the requirement for these things isn't new.

 

[JohnW2]

Bosch washing machine requires Type A:

Interestingly, it does not seem to actually 'require' an RCD at all - merely saying "When using a residual current circuit breaker, only use...."

The bolier instructions are also interesting, since (per what I recently mentioned), the recommendation seems to be for an RCD which will respond to DC "(fault)" currents.

Kind Regards, John

 

[EFLImpudence]

Surely,

IF an appliance actually required an RCD for ITS own protection, then the manufacturer should fit it to the appliance - like they do with fuses.

 

[JohnW2]

Surely, IF an appliance actually required an RCD for ITS own protection, then the manufacturer should fit it to the appliance - like they do with fuses.

As always, that is certainly an argument.

However, at least in the case of the washing machine, it could be that what is being said is that, if/when the WM (and other things) are protected by an RCD, then that RCD should be a Type A, to avoid the risk of the protection (by the RCD) of other things being impaired by the presence of the WM?

Remember that, as I said, the WM instructions said nothing about an RCD being 'required' - it merely indicated what type should be used IF one had one.

Kind Regards, John

 

[EFLImpudence]

Yes, I was verifying your point by implying that, as no appliance comes with an integral RCD, none must actually require one.

 

[JohnW2]

Yes, I was verifying your point by implying that, as no appliance comes with an integral RCD, none must actually require one.

Indeed. I find it very hard to think of any way in which any appliance could "require an RCD for ITS own protection" - i.e. I cannot think of how earth leakage, per se, could harm an appliance.

On the other hand, as I said, I can see the theoretically possibility that an appliance might impair the protection enjoyed by other things if it shared with them an RCD 'of the wrong type'.

Kind Regards, John

 

[EFLImpudence]

I expect they are writing new regulations for separate circuits as we speak.

 

[ericmark]

Is a washing machine portable? If we follow the recommendation any non portable appliance over 2 kW should have a dedicated supply, so hardly matters if it has a type A or AC as it only supplies the washing machine, however we all know the appendix may say dedicated supply, but it rarely gets one, but why would the regulations tell you do do something which if following the regulations would not be required?

 

[JohnW2]

Is a washing machine portable? If we follow the recommendation any non portable appliance over 2 kW should have a dedicated supply, so hardly matters if it has a type A or AC as it only supplies the washing machine ...

That would not be true if one accepts and extrapolates from the implication of the boiler instructions above (that "energy efficient equipment" can generate DC fault currents) and one wants the RCD to satisfactorily protect the one appliance that it is meant to be protecting.

Kind Regards, John