Socket outlet Or Fused Spur

[sparkwright]

Quantum storage heaters - they INSIST the off peak supply must be in 2.5mm2 flex - even though 1.5mm2 would be ok for most sizes.

And they INSIST the 24hr part must be a switched FCU and NOT a plug and socket.

And if there is a fault with the heater, and the two requirements above have not been met, they will NOT honour the guarantee or help in any way.

 

[EFLImpudence]

As Winston keeps saying...

 

[EFLImpudence]

Quantum storage heaters - they INSIST the off peak supply must be in 2.5mm2 flex - even though 1.5mm2 would be ok for most sizes.

What if you used 4mm²?

Obviously nonsense.

 

[Harry Bloomfield]

Yes, but H was making the point that a dedicated 6amp circuit may eliminate the need for a fuse in the double pole switch unit.

No, I was suggesting that a 6amp MCB offers much better protection than a 3 amp fuse.

 

[endecotp]

The boilers I work on require an earth connection to enable the boiler pcb to recognise the gas /air has lit and the flame is established.

...

Immediately after the sparking ceases the controller feeds AC up the H T lead to the ign pin tip where upon it passes through the flame and changes from AC to DC which confirms to the controller that the gas is lit.

So you're suggesting that the current flows from the electrode, through the ionised gas, through the burner metalwork to the gas supply pipe, back to the gas meter, down the earth wire from the gas meter to the main earthing terminal at the consumer unit, then down the boiler circuit's CPC back to the boiler.

This doesn't seem likely to me. I think it's more likely that the burner metalwork is connected within the boiler to its electrical earth. In fact I'd say that would be a requirement, as no boiler is likely to be double-insulated.

Have you tried operating one of these boilers with the supply earth connection disconnected?

Of course there is value in checking for earth continuity to the socket or FCU, e.g. as part of an EICR.

 

[Harry Bloomfield]

Thanks for the replies.

The boilers I work on require an eartconnection to enable the boiler pcb to recognise the gas /air has lit and the flame is established.

If I understand things correctly a heating/hot water demand to the boiler controller (pcb) which brings the fan on.
After a second or two the valve opens and the gas is pulled into the fan, mixed with air and forced out through the burner surface where it is ignited by a burst of sparks between the ign pin (spark electrode) and the burner face.

The current involved in the sensing is miniscule, besides which the boiler control PCB senses between the pin a ground internally, so the earth loop impedance has absolutely no bearing on the flame detection system.

I therefore suggest, that your testing of the earth loop impedance at the boiler is entirely pointless, other than to provide your electrical mates with work.

Just to be clear, the fridge, space heater, oven and water heater in my tourer caravan - all are able to operate on bottled gas. All need a 12v battery supply to work, none need an actual connection to earth at all - everything will work quite happily sat on rubber tyres, with no 240v anywhere near.

 

[EFLImpudence]

Not sure I really understand the concept described but - wouldn't an RCD trip with such an arrangement?

 

[Harry Bloomfield]

Not sure I really understand the concept described but - wouldn't an RCD trip with such an arrangement?

It is a really tiny current, far too small to trip an RCD, besides, it is neither L to E, nor N to E. The boiler PCB's control supplies are entirely isolated from the mains supply.

 

[endecotp]

Not sure I really understand the concept described but - wouldn't an RCD trip with such an arrangement?

If the current did flow through the pipework etc. then it would contribute towards tripping, but I guess it would be much too small to actually trip. Like how a small current flows to earth through interference suppression capacitors in many power supplies.

But if the circuit is completed by a low-resistance earth connection inside the boiler (as I’m sure it must be), then no.

 

[amstel]

Could I just ask a question please regarding RF lighting's answer in post 3,..."personally I prefer to install an FCU as it allows the circuit to not have RCD protection".
I dont see why a fused plug top and socket needs RCD protection and a FCU doesn't? hopefully somebody will explain.
Thanks.

 

[BS3036]

Sockets always need RCD protection because that is what the regulations say. The reasoning is that you could plug anything in that has e.g. a frayed cable or some internal fault which might injure someone if they touch it. A fixed installation using an FCU is 'less likely' to have such an issue. Even an FCU will need an RCD if the wiring is done in certain ways, but may theoretically be avoided.

 

[amstel]

I have a washing machine and dishwasher both on their own dedicated circuits under the kitchen worktop, both on 16amp mcb's, if I changed the plug top/socket to a fixed FCU with a flex outlet, would that comply? thanks.

 

[Harry Bloomfield]

Deleted..

 

[EFLImpudence]

I have a washing machine and dishwasher both on their own dedicated circuits under the kitchen worktop, both on 16amp mcb's, if I changed the plug top/socket to a fixed FCU with a flex outlet, would that comply? thanks.

Why would you want to do that?

 

[amstel]

Because as it is, I think it should be rcd protected? not sure. Thanks.