Fuse Size

[Alwayslearningelec]

This is a 400A spare switch with 400A fuses. Need to fuse it down to 150A. How would I know if 150A fuses would fit in these slots( doubt it)? Could I use fuse reducer of some sort? Thanks.

 

[tom baker]

Bussman makes fuse reducers

 

[Alwayslearningelec]

Bussman makes fuse reducers

Yes. But more than likely id need them and they would be able to be used in this situation?

 

[BillyMac59]

The switchgear manufacturer could tell you if a 150A fuse is a straight fit or if fuse reducers are required.

 

[norcal]

225A would be the smallest fuse, as Tom Baker said, fuse reducers.

 

[LarryFine]

Take a fuse with you to the supplier, or measure one (with a non-metallic ruler).

 

[jim dungar]

The switchgear manufacturer could tell you if a 150A fuse is a straight fit or if fuse reducers are required.

Actually it is UL that would tell you. They set the amperes rating versus fuse clip sizes.
The ranges for the typical Class H and Class R, in the OP, are:
Below 30A
31 to 60A
61 to 100A
101 to 200A
201 to 400A
Fuses reducers are available to put smaller fuses into larger fuse holders.

 

[BillyMac59]

And I'm sure that UL has passed that info, thereby giving their approval, to the manufacturer. That info could be readily gleaned from their website, hence my suggestion.

 

[jim dungar]

And I'm sure that UL has passed that info, thereby giving their approval, to the manufacturer. That info could be readily gleaned from their website, hence my suggestion.

It would come from the fuse manufacturer not the switchgear manufacturer.
These size ranges have been around for more than 100 years. Isn't this stuff taught to apprentices?

 

[petersonra]

Are fuse reducers even listed? I might be mistaken but I seem to recall they aren't.

I guess as long as they are not a bolt in application you are ok with class j fuses, but you don't have class j fuses.

 

[petersonra]

Here is an interesting possibility. I didn't even know such a thing existed until I looked.

A2D-R - Reducer Fuses - Class RK1 - Time-Delay Fuses | Mersen

A2D-R - Reducer Fuses - Class RK1 - Time-Delay Fuses | Mersen

ep-us.mersen.com

 

[tom baker]

When I started at one job, all the fused switches had the maximum size fuse installed…a 60 amp fuse that should of been 7 1/2. I got very familiar with fuse reducers

 

[don_resqcapt19]

Here is an interesting possibility. I didn't even know such a thing existed until I looked.

A2D-R - Reducer Fuses - Class RK1 - Time-Delay Fuses | Mersen

A2D-R - Reducer Fuses - Class RK1 - Time-Delay Fuses | Mersen

ep-us.mersen.com

That document includes the following statement:

"Replaces traditional temporary-use only Fuse Reducer accessories"

There was an attempt to in a code rule that said that, but it was rejected. Some fuse reducers are listed products and the code change was rejected because the listing standard does not say that they are only for temporary use. As I recall it was Mersen who submitted the PI for this change, and it is interesting that they do manufacturer UL listed fuse reducers.

The following part numbers are the Bussmann fuse reducers that are UL listed.
213, 213-R, 216, 216-R, 226, 226-R, 242-R, 2621, 2621-R, 263, 263-R, 2641, 2641-R, 2642, 2661, 2661-R, 2662, 2662-R, 2664, 2664-R, 616, 616-R, 626, 626-R, 642-R, 663, 663-R, SA, SA

It appears that either 242-R or 2642 would be the fuse reducer needed for this application.

Bussmann also has other fuse reducers that are not listed products.

 

[Dennis Alwon]

I see an A6D 150 / 400 I think this fits where a 400 amp fuse would fit....

A6D150/400R | Mersen Electrical Power: Fuses, Surge Protective Devices, Cooling & Bus Bars

ep-fr.mersen.com