5kw Air-conditioning unit wiring

[ericmark]

Good point raised by @flameport it says

When installing the earth leakage protector, make sure it is compatible with the inverter (resistant to high frequency electric noise) to avoid unnecessary opening of the earth leakage protector.

so

RCD Type B: RCD for which tripping is achieved as for Type F and in addition:
(a) for residual sinusoidal alternating currents up to 1 kHz

This to my mind causes a problem, much depends on the consumer unit make and model, but getting a type B is expensive and not available as single width RCBO as far as I am aware. This advert says £114 and it seems to be three modular wide, for Wylex part number NSPE-5580 looking at £600.

Taking a chance with non type B is all well and good if it does not supply anything else, but don't want a fault on the AC stopping a second fault on a socket stopping it from tripping, so with that information there seems no way you can supply from the ring final, I was unaware of the RCD requirement.

 

[JohnW2]

Good point raised by @flameport it says

When installing the earth leakage protector, make sure it is compatible with the inverter (resistant to high frequency electric noise) to avoid unnecessary opening of the earth leakage protector.

Yes, it is interesting, not the least because it refers to an issue opposite to that which flameport usually stresses (and I think you have been known to mention) about the inappropriate use of Type AC RCDs.

The usually voiced concern that in certain situations (e.g. when there are DC components of the current waveform), a Type AC RCD may fail to operate 'when it should' in response to a residual current. The instructions you quote refer to the possibility that an RCD of an inappropriate Type may suffer 'unnecessary opening' (which I take to mean 'operating when it shouldn't) in the presence of 'high frequency noise'.

You go on to suggest that this means that a Type B RCD would be needed, and you support that by quoting:

RCD Type B: RCD for which tripping is achieved as for Type F and in addition:
(a) for residual sinusoidal alternating currents up to 1 kHz]

... which I take to mean that it will trip in response to residual sinusoidal alternating currents up to 1 kHz. However, that is not the issue which the instructions posted by flameport are talking about - and I personally haven't got a clue as to whether or not a Type B RCD is any more "resistant to high frequency electric noise [which may otherwise cause 'nuisance tripping'] than is any other Type of RCD (e.g. Type AC), are you?

On the face of it, if a Type B will trip in response to high frequency residual currents, whereas other types of RCD won't, that would tend to suggest (at least, to me) that the Type B was probably less "resistant to high frequency components" (than, say, a Type AC), wouldn't it?

Kind Regards, John

 

[ericmark]

I was worried about the use of type AC RCD's in my own house, when reading the packet it said type B I had not realised until after they were installed they were type AC. However my thoughts now are 1) The RCD is extra protection as a TN supply, and 2) With 14 RCBO's (RCD and MCB combined) two independent faults stopping it for tripping when required is slim.

So I have all type AC curve B RCBO's in my home, and I am not rushing out to charge them.

However for me to take a calculated risk, is very different to telling some one else to take the risk, be is a Bosch central heating boiler which says used type A or an AC saying use type B. Specially as we have not idea if a TT or TN supply. With a TN supply as long as a dedicated supply with it's own RCBO I would not be unduly worried, if it trips the supply it will only trip the supply to the AC not anything else, and if it freezes the RCD/RCBO then again only the AC supply affected. And to be frank never seen a type B single module width RCBO best I have seen is type A two pole switching but only one pole over load sensing. This means to fit a type B would likely mean a henley block and a dedicated consumer unit for anything better than type A.

With a TT supply we rely on the RCD, so this is a very different kettle of fish, I have looked for the cost of the RXF50B2V1B Air Conditioner in vain, but adding £600 for the RCD would clearly bump up the price some what, and one starts to look at the electric cars with their charging points and devices which allow the use of type A RCD's.

Personally I wonder if a special RCD is really required or is it the manufacturer being careful no claims can be made from them if some thing goes wrong, the type B I found were 40 amp, did not find one big enough to cover whole CU, so to comply is not easy, big question is how many electricians read the instructions to find "When installing the earth leakage protector, make sure it is compatible with the inverter (resistant to high frequency electric noise) to avoid unnecessary opening of the earth leakage protector."? Had it said use a type A, F, or B then yes an electrician would possibly see that, but I did the normal thing of find in document RCD which comes up with nothing, as they call it an earth leakage protector.

In my own house I would use a dedicated circuit and a type A RCBO, but at work I would use a type B, as there is always some one who will point out one has made a mistake, and it is a watch my back situation. Although we have a electric vehicle charging point and I have not seen any special RCD's for that, but maybe they are in the point its self.

 

[JohnW2]

Personally I wonder if a special RCD is really required or is it the manufacturer being careful no claims can be made from them if some thing goes wrong ....

Quite probably the latter - just as we see with manufacturers 'requireing' unnecessary isolators and fuses. Fortunately, the change in wording of BS7671 means that we can now over-ride such 'instructions' with common sense, and still be 'compliant'.

,... to comply is not easy, big question is how many electricians read the instructions to find "When installing the earth leakage protector, make sure it is compatible with the inverter (resistant to high frequency electric noise) to avoid unnecessary opening of the earth leakage protector."? Had it said use a type A, F, or B then yes an electrician would possibly see that ...

I very much suspect that they couldn't do that (specify a particular type of RCD) since I suspect that they have not got any more of a clue than have you or I as to what type of RCD (AC, A, F, B), if any, is "resistant to high frequency electrical noise" (which may cause 'nuisance trips').

I've been moaning for a very long time about the paucity of useful information about the various types of RCD. Everything I've read, like the 'descriptions' in 531.3.3 of BS7671, indicates what waveforms of residual current will result in a (desired) trip - including, for all other than Type AC, waveforms with a superimposed DC component (of specified magnitude). However, nowhere have I yet found any information about how "resistant" any (if any) of the Types are "resistant" to characteristics of current (normal or residual) (such as "high frequency noise") which may result in nuisance trips.

Hence, as above, I for one (and quite probably also the manufacturers) have not got a clue as to which, if any, of the available Types of RCD would satisfy the requirement to be "resistant to high frequency electrical noise".

Kind Regards, John

 

[ericmark]

Hence, as above, I for one (and quite probably also the manufacturers) have not got a clue as to which, if any, of the available Types of RCD would satisfy the requirement to be "resistant to high frequency electrical noise".

I think most of use are the same, and with RCBO's it really is not much of a problem, we have a limited number of items supplied from same unit, and should it not trip, or should it trip erroneously, it is not too hard to track down why. The problem is where half the house goes through one RCD.

Last house I had two RCD's for whole house fitted around 1992, in the main no problem, then I would have a bout of tripping, no faults found and it would go away again, thunder storms could cause them to trip, and resetting one could cause other one to trip, but without anything changing it would stop tripping for a few years, I blamed spikes on the line, possibly some one on the estate using a welding set.

So this house all RCBO's, they are in error type AC, however type A is the best you can get with RCBO's, so asking for type F or B means a separate enclosure it will not go in the main consumer unit, to fit more than two stand alone two module wide RCD's in a modern consumer unit is not going to be easy and retain the type testing, with car recharging points all the special disconnection equipment is built into the charging pod, so a standard type A RCD is all that is required.

I would say any domestic equipment should be made as not to require any better than type A, any additional filters, or automatic disconnection equipment should be built into the appliance.

This all does raise the question should inspecting and testing include testing for DC and high frequency AC? But returning to the originally question it does seem a dedicated supply is required, from it's own RCBO type A so it will not impact on the rest of the house, I would say £600 for the protection devices is OTT, if it trips a type A then simply would regard it as faulty, and want it repaired or modified under warranty, it is unreasonable to expect the use of a type B RCD.

 

[JohnW2]

I think most of use are the same, and with RCBO's it really is not much of a problem, we have a limited number of items supplied from same unit, and should it not trip, or should it trip erroneously, it is not too hard to track down why. The problem is where half the house goes through one RCD.

I'm not sure that is true.

In discussions about types of RCDs, what we usually discuss is the theoretical risk that a DC component of current, or a non-sinusoidal residual current may prevent an RCD tripping when it should. If that is the case then, far from being "not much of a problem", it could be very much a problem (potentially a 'threat to life') even if it were an RCBO on a dedicated circuit serving just one load.

I would say any domestic equipment should be made as not to require any better than type A, any additional filters, or automatic disconnection equipment should be built into the appliance.

Again, I'm not sure that it as simple as that. "Automatic disconnection equipment within the appliance" would not be enough, since that would only be relevant in terms of faults within the appliance. What would be needed (but probably not practical) would be that domestic equipment should be made such that it could not result in DC components or other waveform features in the current drawn that could impair the functionality of an RCD protecting the entirety of one or more circuits, due to faults in other loads or other parts of the circuit(s).

This all does raise the question should inspecting and testing include testing for DC and high frequency AC?

If testing an RCD of a type that should trip in the presence of DC components or with high frequency residual currents, then the answer is presumably 'yes'.

However, as I said, the instructions that flameport and you quoted do not relate to a requirement to trip with high frequency AC but, rather, to not trip ('nusiance trip') due to the presence of high frequency 'noise'.

Kind Regards, John

 

[ericmark]

Does it matter, the question was can it be supplied from the ring final, and it seems answer is no. I can see the poor guys eyes glazing over as he reads our posts.

 

[JohnW2]

Does it matter, the question was can it be supplied from the ring final, and it seems answer is no. I can see the poor guys eyes glazing over as he reads our posts.

Indeed. It doesn't matter at all to the OP. I was respionding to your statements, (particularly your statement that an RCBO which didn't operate when it should because it was the wrong type was "not much of a problem") which I believe were incorrect and therefore might mislead people who read them.

Kind Regards, John

 

[ericmark]

The question is answered in the instructions

Make sure to use a dedicated power circuit. NEVER use a power supply shared by another appliance

And for other questions started a new thread https://www.diynot.com/diy/threads/...r-than-type-ac-or-a-rcd.573336/#ixzz6yWj2BhQT

 

[JohnW2]

The question is answered in the instructions

Make sure to use a dedicated power circuit. NEVER use a power supply shared by another appliance

That doesn't address the other instruction which says:

When installing the earth leakage protector, make sure it is compatible with the inverter (resistant to high frequency electric noise) to avoid unnecessary opening of the earth leakage protector.

Kind Regards, John