I bought this fuse (and its holder) for my battery fuse and disconnect:  https://za.rs-online.com/web/p/products/7038655

It is a Bussmann 125A NH00 size fuse that is rated for 500Vac - if you check the specs for it you will see it is also rated for 250Vdc.

Similarly the popular Jean Müller Keto disconnector also uses this NH00 fuses - also a 500Vac fuse, and I can't find its equivalent Vdc rating.

So my question is - are all the size NH00 500Vac fuses 250Vdc equivalent? 

7 hours ago, admiral said:

So my question is - are all the size NH00 500Vac fuses 250Vdc equivalent? 

I don't believe that you can assume that. If you can't find a DC rating for it, don't use it for DC. DC is so much harder to interrupt than AC.

7 hours ago, admiral said:

So my question is - are all the size NH00 500Vac fuses 250Vdc equivalent? 

The DC fuses are filled with a kind of silica or quartz which acts as an extinguishing agent for the arc. The AC fuses will not have this. So I agree with @Coulomb, can't just assume this.

Ok, I agree that is a safe way to look at this.

I would like to find the DC rating for the fuses used in the Jean Müller Keto disconnector - these fuses:  https://thepowerstore.co.za/products/nh-fuse-link-125a-for-keto-00

It is not on the Powerstore website as far as I can see.  I searched for the SKU (N5014607), and got to this page:  https://www.jeanmueller.de/produkte/jean/en_GB/1322637050548/NH fuse-link 500V combi indicator M00 GL 125 ISM/PR/N5014607/additionalInfos/index.xhtml#product_tabs

There is no information on DC equivalent voltages there.  I am truly curious as to what fuse should then be used with the Keto disconnector?

Just get another brand of fuse of the same size (fortunately they are standardised) that does have a DC rating. It may be that the manufacturer of the fuse holder never had DC in mind; vastly more AC fuses are sold than DC, because power distribution is all AC.

@Coulomb - I agree that is the correct way to go;  i.e. to get a fuse with a DC rating.  I was just curious as to how the Jean Müller setup (Keto) works with fuses that does not have a clear DC rating - and it is generally suggested as a good battery disconnect on this site.

In my case - I bought this fuse:  https://za.rs-online.com/web/p/products/7038655  I bought it from a local supplier (Electroparts in Cape Town).  It does have a DC rating according to that RS Online site.  However, if I search for it on the Bussmann site it does not have a DC rating there?  I.e. here:  http://www.cooperindustries.com/content/dam/public/bussmann/iec-electrical/resources/data-sheets/bus-iec-ds-10164_nh500voltsfuselinks.pdf

@SilverNodashi - I think you mentioned somewhere that the NH fuses are ok?

1 hour ago, admiral said:

However, if I search for it on the Bussmann site it does not have a DC rating there?

It's a concern. They do look as though they are well capable of breaking 60 VDC, but I'd certainly like to see it on the latest datasheets.

I wonder if it has something to do with the Cooper Bussmann to Eaton Bussmann transition.

Yes, in this case I'd like to be more than double sure!  And like I said - even the Jean Müller fuses are not clearly marked for DC use (that I could find).

6 hours ago, admiral said:

Yes, in this case I'd like to be more than double sure!  And like I said - even the Jean Müller fuses are not clearly marked for DC use (that I could find).

I don't have the link now, but there are definitely DC fuses on the Jean Muller website. I also contacted Segen Solar, which is (one of ?) the importer of Jean Muller. They said you can ask your local shop to order the DC fuses from them. Not sure about the price or lead time.

I also agree that if no DC data exist, do not use the fuse for DC. Littlefuse has an excellent whitepaper on fuses.

On 2019/05/20 at 10:01 AM, admiral said:

@Coulomb - I agree that is the correct way to go;  i.e. to get a fuse with a DC rating.  I was just curious as to how the Jean Müller setup (Keto) works with fuses that does not have a clear DC rating - and it is generally suggested as a good battery disconnect on this site.

In my case - I bought this fuse:  https://za.rs-online.com/web/p/products/7038655  I bought it from a local supplier (Electroparts in Cape Town).  It does have a DC rating according to that RS Online site.  However, if I search for it on the Bussmann site it does not have a DC rating there?  I.e. here:  http://www.cooperindustries.com/content/dam/public/bussmann/iec-electrical/resources/data-sheets/bus-iec-ds-10164_nh500voltsfuselinks.pdf

@SilverNodashi - I think you mentioned somewhere that the NH fuses are ok?

Here is the Jean Muller DC rated NH-link fuses:

https://www.jeanmueller.de/produkte/jean/en_GB/N_DC/Fuse-links for DC applications/index.xhtml

Apparently Segen Solar do have them (or can order them). Just ask your local solar shop to order the correct fuses from Segen.

Great thank you @CarlT

I contacted Bussmann as well, and they have confirmed the fuse I initially mentioned is 250Vdc rated.  But, it is really important to confirm the fuse(s) you're getting are indeed rated for DC.  The arc a DC circuit can make is very impressive, and also impressively scary.

On 2019/05/23 at 3:10 PM, admiral said:

Great thank you @CarlT

I contacted Bussmann as well, and they have confirmed the fuse I initially mentioned is 250Vdc rated.  But, it is really important to confirm the fuse(s) you're getting are indeed rated for DC.  The arc a DC circuit can make is very impressive, and also impressively scary.

Something else to consider is the current vs time curves of the fuse.

Do not expect a 100A fuse to blow at 100A, especially not immediately.

For my Pylontech, coupled with my MP II, I will probably use 50A DC fuses. The ones I'm looking at have the correct curves and should blow before the BMS needs to switch off the battery due to high current.