Fuse rating - UK Vintage Radio Repair and Restoration Discussion Forum

ITAM805 · 18th Jan 2019, 5:20 pm

I was given a batch of 1.1/4" fuses, they are voltage rated on the end caps as 125V or 250V, but the current rating is odd.

The 250V reads 'S MDL 8/10' and the 125V 'SS MDX 6.1/4'. What are they anti-surge, slow blow?

Many thanks

G6Tanuki · 18th Jan 2019, 5:48 pm

Those are Bussmann time-delay fuses - have a look at:

http://www.cooperindustries.com/cont...nicfuses3.html

and http://www.cooperindustries.com/cont..._MDL_MDL-V.pdf

ITAM805 · 18th Jan 2019, 5:57 pm

Many thanks G6, that's them

snowman_al · 18th Jan 2019, 6:47 pm

If you have not guessed already, they are 800mA (8/10A) and 6.25 Amp (6 1/4A) That is the Americans for you ;-)
They are called 'dual element' fuses, I think the idea is for the solder to melt on prolonged over current. Then the spring pulls the two halves apart.
Alan

ITAM805 · 21st Jan 2019, 2:29 pm

Thanks for the info Alan. I did wonder if the 6 1/4 was 6.25A but not the 8/10A, not having dealt in fractions for many a long year!

trobbins · 26th Jan 2019, 12:22 pm

Just a note that as those fuses are from USA and are UL rated, they aren't designed to operate continuously above 80% of rating. In contrast, IEC rated fuses are designed to operate continuously at up to 100% rating.

emeritus · 26th Jan 2019, 1:20 pm

Interesting: I hadn't realised that rating fuses by blowing current was a UL standard. I had thought that rating fuses by blowing current rather than carrying current was peculiar to automotive fuses.

ITAM805 · 26th Jan 2019, 2:07 pm

Many thanks trobbins. I had to look up 'UL rated' and didn't realise there was such a diverse range of types!

trobbins · 26th Jan 2019, 2:10 pm

UL 284-14 is the north american standard, and is noticeably different to the IEC 60127-2 standard. For most, a fuse is really the final last gasp of protection before fire and brimstone, but for many applications a fuse may be able to be 'designed' to provide much more selectivity as to what fails and when. There is an info doc in the sticky on Fuses that goes in to some detail on that.

18th Jan 2019, 5:20 pm	#1
ITAM805 Nonode Join Date: Jul 2010 Location: Folkestone, Kent, UK. Posts: 2,172	Fuse rating I was given a batch of 1.1/4" fuses, they are voltage rated on the end caps as 125V or 250V, but the current rating is odd. The 250V reads 'S MDL 8/10' and the 125V 'SS MDX 6.1/4'. What are they anti-surge, slow blow? Many thanks Attached Thumbnails

18th Jan 2019, 5:48 pm	#2
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,995	Re: Fuse rating Those are Bussmann time-delay fuses - have a look at: http://www.cooperindustries.com/cont...nicfuses3.html and http://www.cooperindustries.com/cont..._MDL_MDL-V.pdf

18th Jan 2019, 5:57 pm	#3
ITAM805 Nonode Join Date: Jul 2010 Location: Folkestone, Kent, UK. Posts: 2,172	Re: Fuse rating Many thanks G6, that's them

18th Jan 2019, 6:47 pm	#4
snowman_al Octode Join Date: Dec 2018 Location: Llandeilo, West Wales, UK. Posts: 1,092	Re: Fuse rating If you have not guessed already, they are 800mA (8/10A) and 6.25 Amp (6 1/4A) That is the Americans for you ;-) They are called 'dual element' fuses, I think the idea is for the solder to melt on prolonged over current. Then the spring pulls the two halves apart. Alan

21st Jan 2019, 2:29 pm	#5
ITAM805 Nonode Join Date: Jul 2010 Location: Folkestone, Kent, UK. Posts: 2,172	Re: Fuse rating Thanks for the info Alan. I did wonder if the 6 1/4 was 6.25A but not the 8/10A, not having dealt in fractions for many a long year!

26th Jan 2019, 12:22 pm	#6
trobbins Heptode Join Date: Oct 2009 Location: Melbourne Australia Posts: 901	Re: Fuse rating Just a note that as those fuses are from USA and are UL rated, they aren't designed to operate continuously above 80% of rating. In contrast, IEC rated fuses are designed to operate continuously at up to 100% rating.

26th Jan 2019, 1:20 pm	#7
emeritus Dekatron Join Date: Jan 2012 Location: Brentwood, Essex, UK. Posts: 5,337	Re: Fuse rating Interesting: I hadn't realised that rating fuses by blowing current was a UL standard. I had thought that rating fuses by blowing current rather than carrying current was peculiar to automotive fuses.

26th Jan 2019, 2:07 pm	#8
ITAM805 Nonode Join Date: Jul 2010 Location: Folkestone, Kent, UK. Posts: 2,172	Re: Fuse rating Many thanks trobbins. I had to look up 'UL rated' and didn't realise there was such a diverse range of types!

26th Jan 2019, 2:10 pm	#9
trobbins Heptode Join Date: Oct 2009 Location: Melbourne Australia Posts: 901	Re: Fuse rating UL 284-14 is the north american standard, and is noticeably different to the IEC 60127-2 standard. For most, a fuse is really the final last gasp of protection before fire and brimstone, but for many applications a fuse may be able to be 'designed' to provide much more selectivity as to what fails and when. There is an info doc in the sticky on Fuses that goes in to some detail on that.