Fuse size?

[Engineer54]

Not sure where your all getting your information from, as to plug top/FCU fuse protection. Fuses within these accessories are there purely to protect the flexible cable connected to them. Protecting the equipment in any way is purely coincidental!!

If the manufacturer of an appliance requires a form of OL device to protect components within an appliance, then it should be provided by the manufacture. So in essence, the installation circuit wiring is protected by a suitable rated MCB, Fuse etc, located in the CU/DB. Appliances with a manufactures factory fitted lead/flex with a fusible plug top or is connected to the power source via a fusible connection unit, the fuse is protecting the lead flex, ...Not the appliance!!

 

[Guest111]

Not sure where your all getting your information from, as to plug top/FCU fuse protection. Fuses within these accessories are there purely to protect the flexible cable connected to them. Protecting the equipment in any way is purely coincidental!!

If the manufacturer of an appliance requires a form of OL device to protect components within an appliance, then it should be provided by the manufacture. So in essence, the installation circuit wiring is protected by a suitable rated MCB, Fuse etc, located in the CU/DB. Appliances with a manufactures factory fitted lead/flex with a fusible plug top or is connected to the power source via a fusible connection unit, the fuse is protecting the lead flex, ...Not the appliance!!

Normally in the installation manual for the boiler it states that the appliance must be fed via a 3A fuse and a double pole isolator with a minimum contact separation of 3mm.

 

[SirKit Breaker]

You did the right thing. The MCB is there to protect the cable, and the fuse in the spur is there to protect the appliance flex, but by default is will also protect the appliance.

I agree, the 6a MCB would most likely trip before the 13a fuse, but by fitting the correct fuse you have it all covered.

And as an earlier post stated, you will maintain any warranty.

Cheers.......Howard

 

[clematis432]

Agree with Engineer54, in my particular boiler the PCB,relays,etc (24V circuit) are protected with a 100mA fuse and the pump,fan,solenoids,etc (240V circuit) are protected by a 2A fuse. (both boiler manufacturer,s fuses). This surely puts to bed the idea that the 3A/13A fuse, & 6A mcb protective devices forementioned are not intended to protect the appliance, only the circuit cabling. Nicsin02 posted a worthwhile topic, though don,t think anyone would disagree that the 3A fuse is more appropriate.
Congrats to lively and knowledgeable participants in this forum,as an ex leccie, I love to browse it.

 

[D Skelton]

in my particular boiler

This surely puts to bed the idea that the 3A/13A fuse, & 6A mcb protective devices forementioned are not intended to protect the appliance

In your particular boiler no, you're probably right, however some of the cheaper boilers come with only the 3A fuse in the plug to protect them. As do most appliances.If fuses weren't meant to protect appliances as well as the cable, then every appliance utilising flex with a csa of 1mm or over would automatically come with 13A fuses?? But they don't do they? In fact, if I'm not mistaken, most boilers are fed with 1mm flex so surely a 13A fuse would be ok as it protects the cable feeding it??Somehow I think the legal requirement to protect boilers with 3A fuses has got more to do with protecting the boiler than the cable.

 

[MarkieSparkie]

In your particular boiler no, you're probably right, however some of the cheaper boilers come with only the 3A fuse in the plug to protect them. As do most appliances.If fuses weren't meant to protect appliances as well as the cable, then every appliance utilising flex with a csa of 1mm or over would automatically come with 13A fuses?? But they don't do they? In fact, if I'm not mistaken, most boilers are fed with 1mm flex so surely a 13A fuse would be ok as it protects the cable feeding it??Somehow I think the legal requirement to protect boilers with 3A fuses has got more to do with protecting the boiler than the cable.

It may be of interest that The Code of Practice for In-service Inspection and Testing of Electrical Equipment:3rd Ed, Table 15.6 lists 1.25mm[SUP]2[/SUP] as the minimum CSA for an appliance cord or flex protected by a 13A BS1362 fuse and 0.5mm[SUP]2[/SUP] minimum for a cord or flex protected by a similar 3A fuse.

 

[MarkieSparkie]

Comparing data for a 6A BS 60898 Type B MCB or BS 61009 RCBO from BS7671:2008+A1:2011 Fig 3A4 with a 3A BS1362 Fuse from the Bussman catalogue datasheet:
6A MCB requires a prospective overload current of 30A to trip in the conventional time.
3A Fuse requires a prospective overload current of between 12 and 18A in the conventional time.
[FONT=&amp]Therefore discrimination is likely to be achieved in this case.[/FONT]

 

[clematis432]

In your particular boiler no, you're probably right, however some of the cheaper boilers come with only the 3A fuse in the plug to protect them. As do most appliances.If fuses weren't meant to protect appliances as well as the cable, then every appliance utilising flex with a csa of 1mm or over would automatically come with 13A fuses?? But they don't do they? In fact, if I'm not mistaken, most boilers are fed with 1mm flex so surely a 13A fuse would be ok as it protects the cable feeding it??Somehow I think the legal requirement to protect boilers with 3A fuses has got more to do with protecting the boiler than the cable.

"Some of the cheaper boilers come with only the 3A fuse in the plug to protect them" ??
I find this hard to believe, and if so, the manufacturer of that boiler would surely be negligent in their protection of the boiler components, PCB in particular.

 

[D Skelton]

It may be of interest that The Code of Practice for In-service Inspection and Testing of Electrical Equipment:3rd Ed, Table 15.6 lists 1.25mm[SUP]2[/SUP] as the minimum CSA for an appliance cord or flex protected by a 13A BS1362 fuse and 0.5mm[SUP]2[/SUP] minimum for a cord or flex protected by a similar 3A fuse.

Very true, it also says it in the regs. Oh well 1mm/1.25mm, both the same thing really

 

[D Skelton]

"Some of the cheaper boilers come with only the 3A fuse in the plug to protect them" ??
I find this hard to believe, and if so, the manufacturer of that boiler would surely be negligent in their protection of the boiler components, PCB in particular.

Not if the PCB is built to handle 3A. Like I said in my first post in this thread, I've seen PCBs fried because the boiler was protected by a 13A fuse instead of a 3A fuse.

 

[Engineer54]

Irrespective of what a manufacturer states on the appliance or boiler or what have you, the 1362 fuse in a plug-top or FCU is there purely to protect the flexible lead/cable and NOT the appliance itself. As i have stated earlier any protection to the appliance by a 1362 fuse rating, is purely coincidental.... Any appliance protection requirements are down to the manufactures themselves. Obviously it is down to the end user to fit an appropriate sized 1362 fuse to the plug-top or FCU...

 

[Rauer]

As above !!!! I don't understand why everyone seems to think its to protect the appliance!!

 

[clematis432]

Not if the PCB is built to handle 3A. Like I said in my first post in this thread, I've seen PCBs fried because the boiler was protected by a 13A fuse instead of a 3A fuse.

PCB,s are not built to be protected by a CIRCUIT fuse of 3A or any other size. Leave that to their designers to protect it. A short circuit in a PCB will "fry it" normally anyway whatever the protection. I have also seen PCB,s fried, and with lower than 3A protective devices.

 

[D Skelton]

So if boilers are to have their own protection fitted internally by the manufacturer, why is it that the last boiler I took apart had no fuse apart from the 3A in the plug it came with? I'm not doubting what any of you are saying, but I find it hard to understand how the componets would be protected if you say they are not built to handle 3A and yet the only protection they have is 3A?

 

[Engineer54]

I find it hard to understand how the componets would be protected if you say they are not built to handle 3A and yet the only protection they have is 3A?

That question is best asked to the boiler manufacturer, rather than to the forum.... It'll be interesting to see what they have say too!! ...lol!!