Nest Thermostat Y-Plan Install

[stem]

The correct fuse is the one that protects the cable. With 1.5mm cable that would be 13a.

I'm sure he was referring to the manufacturers instructions, because he had a little bag of 3A fuses he carried around specifically for that purpose. I seem to remember he said that a CORGI inspector had pulled him up previously. So yes it was a long time ago.

I remember seeing a PCB where the boilers wiring terminals were soldered onto the printed circuit board before any internal fuses. So the connection was through the PCB 'foil' (if that's the right word) In this case the foil had 'blown' instead of the 13A fuse which was still intact. I soldered a link across the blown bit, and fitted a 3A fuse to the FCU. I guess that it wasn't dangerous as the circuit had been interrupted and made safe, but it would have been easier to change a blown 3A fuse than repair a PCB.

They seem to have different standards in the rest of Europe though. I worked in Italy a few times in the 90's and I bought a lamp which from memory had 0.75mm2 cable rated at 6A, and an unfused plug that went into their radial sockets that I think were protected by a 16A circuit breaker. The Italian guys I was working with (electrical engineers working on a new factory installation) didn't see a problem with it.

 

[winston1]

Manufacturers instructions are guidance only and don't have to be followed. They are at times wrong as well.

Perhaps someone had put the wrong fuse in the boiler. PCB foil should not blow before the internal fuse any more than before an external one.

Lamps with 0.75mm cable are available here as well and it is perfectly legal to fit an unfused 15 amp BS546 plug on it on a 15 amp radial circuit. Do you think such a lamp will take 15 amps?

 

[ericmark]

Manufacturers instructions are guidance only and don't have to be followed. They are at times wrong as well.

Perhaps someone had put the wrong fuse in the boiler. PCB foil should not blow before the internal fuse any more than before an external one.

Lamps with 0.75mm cable are available here as well and it is perfectly legal to fit an unfused 15 amp BS546 plug on it on a 15 amp radial circuit. Do you think such a lamp will take 15 amps?

If following the rules, bulbs should have built in fuses so they will fail if there is ionisation in the bulb, so if used on a 15 amp radial the lamp should if rules followed still be fused, OK I know Ikea sold bulbs without built in fuse, so I would guess there are also other makes, but that is breaking the rules.

Also as you well know 0.75 mm² cable is not rated at 13A and in the UK it should have a limit of 6 amp, so in real terms 5 amp fuse, although 3 amp is the preferred size, the Europlug is rated 2.5 amp, there is no socket defined by EN 50075 only the plug, and it seems some sockets it can fit in are 10 amp and some are 16 amp. The German "Schuko"; Type F in not permitted in this country because it is reversible and often does not have shutters.

For portable appliances the plug must be provided etc. However a boiler installation is not by any stretch of the imagination a portable appliance, so the manufacturer has every right to expect it to be fused to the size recommended in their instructions, and if their instructions are not followed then one can expect problems including burning out of printed circuits, although with a portable appliance the fuse in the plug is only to protect the cable, since not a portable appliance the manufacturer can stipulate what fuse is used in either a FCU or Plug.

Yes you don't have to follow the instructions, but if you don't then you must do your own risk assessment, a quick check and motorised valve rated 2.2 amp and 6 watt, clearly 2.2 amp is max fuse size, (from Screwfix website) to have any fuse larger than 5 amp is asking for problems.

 

[EFLImpudence]

If following the rules, bulbs should have built in fuses so they will fail if there is ionisation in the bulb, so if used on a 15 amp radial the lamp should if rules followed still be fused, OK I know Ikea sold bulbs without built in fuse, so I would guess there are also other makes, but that is breaking the rules.

Ok, so alright for bulbs to have fuses rated at many times their current.

Also as you well know 0.75 mm² cable is not rated at 13A and in the UK it should have a limit of 6 amp, so in real terms 5 amp fuse, although 3 amp is the preferred size

What if it is a 6A load?
Is it fitted to appliances that can cause an overload?
Weren't there recent threads pointing out that that is the flex used on kettles and fitted with 13A fuses?

the Europlug is rated 2.5 amp, there is no socket defined by EN 50075 only the plug, and it seems some sockets it can fit in are 10 amp and some are 16 amp.

Does it come fitted to appliances that can draw more than 2.5A?

The German "Schuko"; Type F in not permitted in this country because it is reversible and often does not have shutters.

Why not if fitted to a 16A circuit with a socket that does have shutters.

For portable appliances the plug must be provided etc. However a boiler installation is not by any stretch of the imagination a portable appliance, so the manufacturer has every right to expect it to be fused to the size recommended in their instructions, and if their instructions are not followed then one can expect problems including burning out of printed circuits,

No, they don't and one shouldn't.
They should make their appliances fit for purpose knowing they will be on circuits of all types.
Likely they do not expect the same where fusing down is not done.

although with a portable appliance the fuse in the plug is only to protect the cable, since not a portable appliance the manufacturer can stipulate what fuse is used in either a FCU or Plug.

Why? What is the difference?

Yes you don't have to follow the instructions, but if you don't then you must do your own risk assessment, a quick check and motorised valve rated 2.2 amp and 6 watt, clearly 2.2 amp is max fuse size,

(from Screwfix website) to have any fuse larger than 5 amp is asking for problems.

What if the instructions are different elsewhere?

The demand for 3A fuses on things like boilers and extractor fans is solely because there are such things - and/or the manufacturer thinks they are required in the UK.

Like manufacturers who state in their instructions that an RCD must be fitted ?
Some shower manufacturers wrongly say the shower must be protected and others correctly that it is the circuit which requires the RCD.
They are merely quoting an electrical requirement that might actually not be applicable (rare nowadays with RCDs obviously); it has no bearing on the working of the appliance.

Also like the Gas Regulations demanding bonding conductors whether electrically required or not.

 

[stem]

Perhaps someone had put the wrong fuse in the boiler.

The bit of the PCB in question was directly from the live supply terminal which was soldered on to it. So, before it reached the boilers internal fuse. Interestingly when power was restored the fault hadn't been rectified (long story) so this time the fuse (now 3A) did blow, without any further damage to the PCB.

The fault turned out to be that the pump wires had been incorrectly connected and the live had been inserted into the earth terminal creating a shot circuit between the live wire and pump / pipework. This also means that the boiler's internal wiring responsible for switching the pump wasn't protected by the boilers internal fuse.

Lamps with 0.75mm cable are available here as well and it is perfectly legal to fit an unfused 15 amp BS546 plug on it on a 15 amp radial circuit. Do you think such a lamp will take 15 amps?

Personally I wouldn't want to leave it like that, but as per my earlier experience in Italy, the majority of Europe do and they seem to survive. Its over 60 years since we installed 15A sockets with unfused plugs in our homes here. And your example above contradicts what you said earlier.

The correct fuse is the one that protects the cable. With 1.5mm cable that would be 13a.

In this case, the correct fuse for 0.75mm2 wouldn't be 15A.

Here, the aforesaid lamp would come from the manufacturer with a 3A fuse in the plug.

When it comes to central heating systems, I haven't found any advantages of fitting a 13A fuse over a 3A fuse, only advantages of fitting a 3A. If offers better protection for connected components. The manufacturers of boilers / programmers / thermostats et al, state that a 3A fuse should be fitted [all are wrong of course ] so why fit a 13A.

 

[winston1]

However a boiler installation is not by any stretch of the imagination a portable appliance, so the manufacturer has every right to expect it to be fused to the size recommended in their instructions, and if their instructions are not followed then one can expect problems including burning out of printed circuits,

So once again I point out that exactly the same boilers are used in Europe usually connected to a 16a MCB, often via a schuko plug, with only a 16a MCB for protection.

 

[winston1]

Here, the aforesaid lamp would come from the manufacturer with a 3A fuse in the plug.

3amp fuses in circuits with incandescent lamps is too small. They will blow before the internal fuse on the lamp. This means on failure you have to replace both the fuse and lamp (effectively doubling the cost). A 5a fuse is better as only the internal lamp fuse then blows.

 

[DetlefSchmitz]

The fault turned out to be that the pump wires had been incorrectly connected and the live had been inserted into the earth terminal creating a shot circuit between the live wire and pump / pipework. This also means that the boiler's internal wiring responsible for switching the pump wasn't protected by the boilers internal fuse.

That does sound as though the boiler PCB design hadn't taken into account the possibility of a shorted pump. I can understand why you would want to put fuses outside, knowing that this kind of design was in place. But it shouldn't have been necessary if the boiler was designed correctly.

 

[ericmark]

When in a commercial situation we took delivery of a new machine, the manufacturers would stipulate protection required, in some cases it required semi-conductor fuses, the fuse was often not inside the equipment as it would be difficult to access, and often the equipment would be commissioned by the manufacturer or their agent who would ensure any fuses or trips were actually installed.

It is no different with domestic, to have a control, fuse, or other device external to the appliance is acceptable. However there is one big difference with domestic, the appliance is in control of an ordinary person, this means any distribution board needs type testing i.e. we have to use a consumer unit. And we also have laws which for example require that portable appliances must be supplied with a 13A plug attached in the UK, and since at moment still in the EU the same item must be suitable for rest of EU so a plug used in other EU countries can be fitted with causing danger, so if the appliance needs a fuse, this fuse must be in the appliance and you can't rely on the one in the plug. But this only applies to a portable appliance, it does not apply to boilers, water pumps, motorised valves, and thermostats used in central heating.

There is no reason why the fuse fitted in a FCU can't be relied on to afford protection. There may well be extra fuses in the boiler, but that does not remove the need for external fuses.

I have as an electrician made errors, I fitted a type B MCB instead of a fuse to a machine, so one the fuses were expensive, and two easy for wrong fuse size to be fitted, however it transpired the semi-conductor fuse acts faster than a type B MCB so when the heating element when short circuit it took out the solid state relay as well, returning to fuses the relay was protected. I had thought I knew better than the manufacturer, but in that case I was wrong.

Many other cases I did improve on what manufacturers requested, but if one gets it wrong, one has to face the music. So if the manufacturer in their spec as @stem pointed out on another thread says the appliance required a type A RCD (Bosch Worcester) can we really say come on that's OTT I am fitted a type AC as that is what comes in the consumer unit, or does it actually need a second type A RCD fitting?

I will admit I don't even know what type is fitted to this house, I will guess type AC, they are 30 mA at 40 mS that is all I looked at when fitting, but I don't have a modern gas boiler so not an issue. But be it a 3 A fuse or a type A RCD manufacturers do say what should be fitted, and to ignore what they say could result in problems for the installer.

 

[stem]

@jay83 sorry, we seem to have branched off from your Nest install project. Don't let it put you off posting back if you need any further help with it. I'm sure you will be able to come to your own conclusion as to the size of fuse you will fit.

 

[winston1]

When in a commercial situation we took delivery of a new machine, the manufacturers would stipulate protection required, in some cases it required semi-conductor fuses, the fuse was often not inside the equipment as it would be difficult to access, and often the equipment would be commissioned by the manufacturer or their agent who would ensure any fuses or trips were actually installed.

It is no different with domestic, to have a control, fuse, or other device external to the appliance is acceptable. However there is one big difference with domestic, the appliance is in control of an ordinary person, this means any distribution board needs type testing i.e. we have to use a consumer unit. And we also have laws which for example require that portable appliances must be supplied with a 13A plug attached in the UK, and since at moment still in the EU the same item must be suitable for rest of EU so a plug used in other EU countries can be fitted with causing danger, so if the appliance needs a fuse, this fuse must be in the appliance and you can't rely on the one in the plug. But this only applies to a portable appliance, it does not apply to boilers, water pumps, motorised valves, and thermostats used in central heating.

There is no reason why the fuse fitted in a FCU can't be relied on to afford protection. There may well be extra fuses in the boiler, but that does not remove the need for external fuses.

I have as an electrician made errors, I fitted a type B MCB instead of a fuse to a machine, so one the fuses were expensive, and two easy for wrong fuse size to be fitted, however it transpired the semi-conductor fuse acts faster than a type B MCB so when the heating element when short circuit it took out the solid state relay as well, returning to fuses the relay was protected. I had thought I knew better than the manufacturer, but in that case I was wrong.

Many other cases I did improve on what manufacturers requested, but if one gets it wrong, one has to face the music. So if the manufacturer in their spec as @stem pointed out on another thread says the appliance required a type A RCD (Bosch Worcester) can we really say come on that's OTT I am fitted a type AC as that is what comes in the consumer unit, or does it actually need a second type A RCD fitting?

I will admit I don't even know what type is fitted to this house, I will guess type AC, they are 30 mA at 40 mS that is all I looked at when fitting, but I don't have a modern gas boiler so not an issue. But be it a 3 A fuse or a type A RCD manufacturers do say what should be fitted, and to ignore what they say could result in problems for the installer.

All very well but as I have said several times:

So once again I point out that exactly the same boilers are used in Europe usually connected to a 16a MCB, often via a schuko plug, with only a 16a MCB for protection.

 

[EFLImpudence]

The fact remains that the UK only has plug fuses because of the 30A/32A ring circuit because of the reasons for its introduction.

Do people really think that manufacturers - be they in Turkey or China - fit integral fuses in their products destined for Europe and the rest of the world but intentionally remove them from products destined for the UK?

I have no FCUs nor fused plugs in my flat. The few products I brought with me have not suffered by being fitted with unfused reversible plugs.

What about wall warts? Perhaps they should not be used on 32A circuits.

What about manufacturers' instructions that demand an RCD or isolation switch? Do they do this because it protects the product or is that merely what they think the regulations require?


I have just bought a new printer. The instructions come in fourteen languages and even the English (first in the booklet) makes no mention of a 3A fuse. The only safety instruction is "Use only with the power cord supplied by HP" - two-pin reversible plug - so were I to take it back to England, I suppose I would not be allowed to swap the plug for a UK one and vice versa I would not be allowed to use it here without the fuse that would have been in the plug?

 

[ericmark]

We are talking about a boiler, or central heating system, it really does not matter where in the world it is fitted, if the manufacturer says supply with 3A fuse and a type A RCD 30 mA and 40 mS that is possible anywhere in the world, nothing in the instructions says it needs plugging in to 13A socket or 16A socket, it could be something like this

it does not need to be a British FCU.

Just because some one does this

it does not mean we should copy it, some people do seem to do daft things around the world.

 

[EFLImpudence]

We are talking about a boiler, or central heating system, it really does not matter where in the world it is fitted, if the manufacturer says supply with 3A fuse and a type A RCD 30 mA and 40 mS that is possible anywhere in the world,

The point you keep missing is that for the same product they do not say it elsewhere.

 

[winston1]

We are talking about a boiler, or central heating system, it really does not matter where in the world it is fitted, if the manufacturer says supply with 3A fuse and a type A RCD 30 mA and 40 mS that is possible anywhere in the world, nothing in the instructions says it needs plugging in to 13A socket or 16A socket, it could be something like this

it does not need to be a British FCU.

Just because some one does this

it does not mean we should copy it, some people do seem to do daft things around the world.

Boilers in Europe are invariably plugged into the standard socket for the country. I have never seen any form of inline fuse. Not sure what your picture is, it's a bit small.