Mains adaptor - to fuse or not?

Rockingit · Sep 25, 2022

Here's a Sunday puzzler for you all.....

I've a large rental stock of properly made up mains adaptors for use in Europe and elsewhere - so typically something like a Schuko >1m 3c H05 / H07 1.5mm flex > twin 13A duraplug trailing socket, variants for other countries, USA and so on.

[ElectriciansForums.net] Mains adaptor - to fuse or not?

The other day I spotted this

Luceco SRGDSU62PB | Extension Lead 6G USB 2m | Rexel UK

Get Extension Lead 6G USB 2m at wholesale prices at Rexel UK - your electrical distributor. Join Now!

www.rexel.co.uk

and thought 'that's a good idea' so ordered a couple in to see what they're like and to chop the 13A plug off and swap for a Schuko / Swiss / Eddison / Hubbell / 16A......

However..... All the above outlets rely on protection in the circuit, not a fuse in the plug. Because of the built-in USB chargers in this unit, should this still have a 13A fuse in circuit??? Interested to hear people's take on this. Also.... BS7671 doesn't really apply here (even though of course we continue good advice and best practice) because of being used overseas.

mainline · Sep 25, 2022

Rockingit said:
Here's a Sunday puzzler for you all.....

I've a large rental stock of properly made up mains adaptors for use in Europe and elsewhere - so typically something like a Schuko >1m 3c H05 / H07 1.5mm flex > twin 13A duraplug trailing socket, variants for other countries, USA and so on.

The other day I spotted this

Luceco SRGDSU62PB | Extension Lead 6G USB 2m | Rexel UK

Get Extension Lead 6G USB 2m at wholesale prices at Rexel UK - your electrical distributor. Join Now!

www.rexel.co.uk

and thought 'that's a good idea' so ordered a couple in to see what they're like and to chop the 13A plug off and swap for a Schuko / Swiss / Eddison / Hubbell / 16A......

However..... All the above outlets rely on protection in the circuit, not a fuse in the plug. Because of the built-in USB chargers in this unit, should this still have a 13A fuse in circuit??? Interested to hear people's take on this. Also.... BS7671 doesn't really apply here (even though of course we continue good advice and best practice) because of being used overseas.

It needs a fuse as it could be plugged in a 32 amp ring final.

Rockingit · Sep 25, 2022

mainline said:
It needs a fuse as it could be plugged in a 32 amp ring final.

They don't typically exist outside of the UK - I think you misunderstand my post

Rockingit · Sep 25, 2022

To clarify - the source of supply will typically be a 16A or 20A radial in most settings, Schuko plugs are rated at 16A.

Pretty Mouth · Sep 25, 2022

I would have thought the built in USB charger would be ok without protection from a 13A fuse. The ones built into socket outlets rely on the circuit protection, which could be 32A.

Comparing time/current curves,a 16A MCB offers similar protection to a 13A fuse anyway.

ipf · Sep 25, 2022

Pretty Mouth said:
I would have thought the built in USB charger would be ok without protection from a 13A fuse. The ones built into socket outlets rely on the circuit protection, which could be 32A.

Comparing time/current curves,a 16A MCB offers similar protection to a 13A fuse anyway.

Charger wise, of course, without 1362 fuse is the norm....phones, power tools, etc....unless you have a fork lift truck

......or a car, maybe.

Can't see any problem with 16amp protection at circuit source.

Lucien Nunes · Sep 25, 2022

A 13A BS1362 fuse won't protect a small 5V SMPSU in any meaningful way. If the USB supply module is made to a decent standard, it will have a fusible resistor or SMD fuse or similar on the board, appropriate for the fraction of an amp that the circuit needs. If it doesn't, and any of the usual faults occur that more or less short the mains input, it will go bang with or without the 13A fuse. A C20 upstream might lead to a bigger bang.

OTOH the multiple mains outlets could lead to a total load in excess of 13A being connected and that is where the lack of a 13A fuse might make a practical difference. Although a BS1363 double socket outlet must be designed for a total load of at least 20A, that doesn't apply trailing sockets and many stipulate a maximum fuse rating of 13A. That will partly or mainly be due to the use of 1.25sqmm flex, but the internal contacts, rivets etc will have been value-engineered with the 13A limit in mind. Probably no worse than a Schuko power strip with a Schuko plug but officially out of spec for a 13A one.

mainline · Sep 25, 2022

Rockingit said:
They don't typically exist outside of the UK - I think you misunderstand my post

I did misunderstand.
This one
If used in the UK with an unfused plug, then it would need a fuse because it has at least 3 mains outlets.
Also, I would have thought chopping the plug off would void any manufacture's warranty.

· Trusted quality, manufactured and certified to BS1363-2
· Two USB Ports - (2.1A shared) to power and charge your devices
· Six sockets - allows you to connect four items safely into one outlet
· Power and Surge Indicator - shows that the sockets are connected and protected
· Fuse: 13A

Rockingit · Sep 26, 2022

Lucien Nunes said:
A 13A BS1362 fuse won't protect a small 5V SMPSU in any meaningful way. If the USB supply module is made to a decent standard, it will have a fusible resistor or SMD fuse or similar on the board, appropriate for the fraction of an amp that the circuit needs. If it doesn't, and any of the usual faults occur that more or less short the mains input, it will go bang with or without the 13A fuse. A C20 upstream might lead to a bigger bang.

OTOH the multiple mains outlets could lead to a total load in excess of 13A being connected and that is where the lack of a 13A fuse might make a practical difference. Although a BS1363 double socket outlet must be designed for a total load of at least 20A, that doesn't apply trailing sockets and many stipulate a maximum fuse rating of 13A. That will partly or mainly be due to the use of 1.25sqmm flex, but the internal contacts, rivets etc will have been value-engineered with the 13A limit in mind. Probably no worse than a Schuko power strip with a Schuko plug but officially out of spec for a 13A one.

That was basically my take on it - a theoretical 3A difference between a 13A fuse and a circuit OCPD of 16A is negligible in practice.

G1ZQC_David · Oct 7, 2022

Rockingit said:
Here's a Sunday puzzler for you all.....

I've a large rental stock of properly made up mains adaptors for use in Europe and elsewhere - so typically something like a Schuko >1m 3c H05 / H07 1.5mm flex > twin 13A duraplug trailing socket, variants for other countries, USA and so on.

View attachment 101910

The other day I spotted this

Luceco SRGDSU62PB | Extension Lead 6G USB 2m | Rexel UK

Get Extension Lead 6G USB 2m at wholesale prices at Rexel UK - your electrical distributor. Join Now!

www.rexel.co.uk

and thought 'that's a good idea' so ordered a couple in to see what they're like and to chop the 13A plug off and swap for a Schuko / Swiss / Eddison / Hubbell / 16A......

However..... All the above outlets rely on protection in the circuit, not a fuse in the plug. Because of the built-in USB chargers in this unit, should this still have a 13A fuse in circuit??? Interested to hear people's take on this. Also.... BS7671 doesn't really apply here (even though of course we continue good advice and best practice) because of being used overseas.

To be honest, these overseas countries don't use fused plug protection at all. So U.K. regs do not apply.
As for the USB 5V units, they should have a Fuse-able resistor inline with one leg on the circuit board, (Most do).
So if the USB 5V went pop, it will blow the onboard protection.
David (G1ZQC) Lincolnshire.
"Quote" Don't let the Grey smoke out!