Potterton boilers with fused neutrals

[kme]

Just read the current PE mag. Guy has sent in a photo of a NEW potterton boiler, which has the Phase and neutral outgoing terminals fused at 2A.

PE contacted Potterton, Who`ve said they`re made like this, and shipped out all across Europe. Apparently, they meet CE standards.

How strange is it that we can`t / mustn`t / shouldn`t have a fused neutral, yet a boiler manufacturer supplies them as standard for the external control equipment. I wouldn`t have thought it would meet current standards. but they`re selling `em!!!!!

KME

 

[jl-heating]

potterton spit *

 

[Justanotherusername]

Some time this is done if the units are used in the US with domestic supply being 2 phase 110VAC so giving 220VAC but both need fusing to earth.

Hope this makes a bit of sense.

Chris

 

[Andy™]

ive came accross this myself and wondered how they get away with it. ill read the story in PE later

 

[sparkyt]

just wired a potterton combi this morning, i had to look twice and yes the supply L and N are fused! and they are wired with a poxy flex which doesnt enter the boiler through any of the glanded inlets but a great big hole full of pipes.

 

[kme]

I know what you mean, Chris; but surely can`t be meeting CE standards???

Complete carp, AFAIAC

 

[green-hornet]

It does not and should not conform to our standards for reasons we all know.

I have not read the article but will do there may be an explanation as to why.

Thanks goes to Chris from ECD Ltd for his answer, I was unaware of that, but now I know.

 

[Andy™]

could this justify being refused to connect, or a code 1 on a PIR?

whilst it would be very easy to bypass the neutral fuse with a terminal block, in doing so you have gone against what the manufacturer has installed, so any failure and they will use that as an excuse

 

[green-hornet]

[quote name='Andy

 

[DarkInferno]

I'm sorry I don't understand why they shouldn't fuse the neutral, (I can't see why they /should/ but I'm playing devil's advocate here) this is on their PCB and is to stop damage to the boiler, not provide protection against shock.

If its a L-E short, then the phase fuse will blow first as it will have the L-N + L-E current.

If it is a L-N short then either fuse will blow admittedly, however as the fuse is encased, behind a plastic panel that states something along the lines of 'danger, supply must be isolated before removed' and the entire boiler is pretty much bonded to earth.

I fail to see the harm.

(I also can't see how you would bypass it with a terminal block if it is on the PCB, take the insulation off it and ram it into the fuse-holder?)

I'm sure I'm missing something here..

 

[Andy™]

I think thats what I would do or refuse to connect it and ask them why its fused.

i have sent them an email asking them why they make boilers with fused neutrals, even though its dangerous. their reply will be posted when i get it (their email is [email protected] if anyone else wants to complain/email them)

 

[Lurch]

I'm sure I'm missing something here..

I think you might be. If the fuse was for internal controls only then you could argue that it is up to them what they do. This double fusing is for the external controls so is double fusing our wiring which is obviously against BS7671.

Luckily I only work with people who know what they're doing so don't have to wire Pottertons.

 

[PBC_1966]

Some time this is done if the units are used in the US with domestic supply being 2 phase 110VAC so giving 220VAC but both need fusing to earth.

It's not 2 phase, it's single-phase 3-wire.

 

[The Godfather]

On a personal note, a fuse in the Neutral has to be a very dangerous scenario, we'd like to see further clarification of this and why Potterton have done so

The Boys

 

[kme]

I`ll see if I can scan and post the letter..... stand by.View attachment 410

 

[DarkInferno]

I think you might be. If the fuse was for internal controls only then you could argue that it is up to them what they do. This double fusing is for the external controls so is double fusing our wiring which is obviously against BS7671. Luckily I only work with people who know what they're doing so don't have to wire Pottertons.

But as the boiler wiring instructions and those diagrams show the Neutral (and Earth/Live, its SL only) for external controls /must/ always be taken from the fcu.

6. Remove the link between terminals 1 & 2. The 230V
supply at terminal 2 must be connected to the thermostat.
The switched output from the thermostat must be
connected to terminal 1 (Figs. 60 & 61). If the room
thermostat being used incorporates an anticipator it MUST
be wired as shown in Figs. 60 & 61.

NOTE: The 230V switched signal for external controls
(Frost Stat - Room Stat - Timer) must always be taken
from terminal 2 at the boiler. Live, Neutral and Earth to
power these controls must be taken from the Fused Spur.

 

[Lurch]

But as the boiler wiring instructions and those diagrams show the Neutral (and Earth/Live, its SL only) for external controls /must/ always be taken from the fcu.

Right, after seeing the letter with associated picture the OP is slightly misleading.

The neutral fuse is only for the internal controls. The neutral to the clock would be taken from the same neutral terminal that the feed is connected to so the external controls neutral is not fused. Is this right?

If so, I see no problem, well, I can see what Potterton will say. 'Our boilers aren;t for you oiks to prod and poke about in, therefore BS7671 doesn;t apply'.

It is and isn;t a problem, I'm fairly certain this isn;t the only piece of equipment with fused neutrals internally.

 

[kme]

But as the boiler wiring instructions and those diagrams show the Neutral (and Earth/Live, its SL only) for external controls /must/ always be taken from the fcu.

BUT, no-one has ANY control over which fuse will "blow" under fault conditions.

If the Neutral fuse flows (50% chance?) then the controls don`t work; although they`re still live.........

NOW do you see the danger??

Immaterial where the supply comes from. Yes, they`re from the FSU. The Boiler is fed from the SFU, so the external controls, by virtue of their connection to the boiler, are (indirectly) fed from the FSU.

For a L-N fault - there is no guarantee which fuse would go first. If it really didn`t matter, we wouldn`t bother doing polarity tests!

KME

 

[DarkInferno]

BUT, no-one has ANY control over which fuse will "blow" under fault conditions.If the Neutral fuse flows (50% chance?) then the controls don`t work; although they`re still live.........

NOW do you see the danger??

Immaterial where the supply comes from. Yes, they`re from the FSU. The Boiler is fed from the SFU, so the external controls, by virtue of their connection to the boiler, are (indirectly) fed from the FSU.

For a L-N fault - there is no guarantee which fuse would go first. If it really didn`t matter, we wouldn`t bother doing polarity tests!

KME

If the live internal fuse blows the controls won't work and there will still be a live to them... I fail to see your point.

 

[kme]

Right, after seeing the letter with associated picture the OP is slightly misleading. The neutral fuse is only for the internal controls. The neutral to the clock would be taken from the same neutral terminal that the feed is connected to so the external controls neutral is not fused. Is this right?

.

I only see them saying that you need to remove the link. They do NOT say that you must take your supplies from the unfused side of the connections. We`ve all done boilers with a couple of zone valves nearby 0 you shove one neutral in either side, to keep cable connection manageable.

I don`t read the info the same way as you did, mate.

KME