Fuses

[Mike01]

What is the difference between class ?R? and class ?J? fuses they are rated 0-600A available 250 or 600V and the size is different the ?J? smaller than the ?R? but is there any difference in their operation they are both labeled as current limiting and sometimes time delay so why one over the other? Another question standard breakers are rated at 80% for continuous loads (I believe I said that right) do you rate fuses the same way or are fused manufactured for 100% continuous load? Just curious on the second question I have herd different responses from different people and would just like your opinions thanks.

 

[cschmid]

who are the manufacturers of the fuse(s)?

 

[kingpb]

The fuse and switch should be sized for 125% unless the fuse-switch combination is rated for 100%.

Class J fuses provide a higher degree of current limiation over the RK1 and RK5fuses, They are also smaller.

 

[Mike01]

right?

right?

so than you treat fuses just like breakers unless they are rated for 100%.

 

[cschmid]

J fast-acting fuses
? CJ HRCI-J - HRCI-J fast-acting fuses are industrial duty fuses with the excellent current-limiting characteristics of fast-acting HRCI-J fuses to limit damage to equipment and installations by the thermal and magnetic energy associated with a large short-circuit fault current. Overload characteristics limit cable damage due to low
overload currents.

R-rated fuses
for motor circuit protection
? JCG - Indoor/enclosure R-rated medium voltage,
current-limiting fuses for motor circuit protection.

? JCH - Indoor/enclosure R-rated medium voltage,
current-limiting fuses for motor circuit protection.
? JCK - Indoor/enclosure R-rated medium voltage,
current-limiting fuses for motor circuit protection.
? JCK-A - Indoor/enclosure R-rated medium voltage,
current-limiting fuses for motor circuit protection.
? JCK-B - Indoor/enclosure R-rated medium voltage,
current-limiting fuses for motor circuit protection.
? JCL-A - Indoor/enclosure R-rated medium voltage,
current-limiting fuses for motor circuit protection.
? JCL-B - Indoor/enclosure R-rated medium voltage,
current-limiting fuses for motor circuit protection.
? JCR-A - Indoor/enclosure R-rated medium voltage,
current-limiting fuses for motor circuit protection.
? JCR-B - Indoor/enclosure R-rated medium voltage,
current-limiting fuses for motor circuit protection.

Fuses may have to be treated like circuit breakers but they are not equal in trip values... all fuses are not equal and the above information is off the cooper-Bussman web site..

 

[jim dungar]

so than you treat fuses just like breakers unless they are rated for 100%.

Yes, the application of enclosed fuses is the same as that of enclosed circuit breakers.

Class J fuses tend to be faster acting than class R.

 

[Jraef]

An more expensive of course. That's why some people use over sized Class J fuses just as fault current limiters in HIC applications where they want to have circuit breakers for low level fault trip reset capability. In fact, I think it was GE who used to actually have Class J fuses inside of their current limiting breakers wasn't it?

 

[jim dungar]

J fast-acting fuses

R-rated fuses
for motor circuit protection

You have confused medium voltage R-rated fuses with Class R fuses which are 600V maxiumum.

 

[davidr43229]

What is the difference between class ?R? and class ?J? fuses they are rated 0-600A available 250 or 600V and the size is different the ?J? smaller than the ?R? but is there any difference in their operation they are both labeled as current limiting and sometimes time delay so why one over the other?

There are 2 Classes of R fuses. RK-1 & RK-5, The RK-1 are more current limiting. The RK-5 can be sized for most applications at 125% - 150%. The RK-1 Time current cruves are NOT the same as the RK-5, and RK-1 should be sized at 150% to 175% of the FLA of the application. Class J burn warmer, due to the size reduction, and should be sized also to 150%-175% of the FLA. The advantage of the Class J is size. Many manufacturers have Class J Buckets that are doubled up in Switchgear. Said a different way a 2 Class J buckets or panels take up the same space as 1 Class R bucket.

who are the manufacturers of the fuse(s)?

It doesn't matter who manufactures the fuses, they all have to fall under the UL standard ie: time current, Current limitation & size, heat rise Umbrella.

do you rate fuses the same way or are fused manufactured for 100% continuous load?

Most fuses are rated to continously carry rated current either at 100 or 110% at 25 degrees C. Breakers are rated at 40 degrees C. I rarely give advice to rate at 100%. Devices with inrush can not handle this percentage. Purely resistive 115%

 

[cschmid]

you are right the typre R are meduim voltage fuses...what I was after in a hurry was the web site he could check them out on but was unable to locate what I was after in short notice. I believe below says it better than I can..
Just got home and grandsons (3 of them) just got here. now for the important things in life... have a great weekend

http://ecmweb.com/news/electric_specifying_right_fuse/

Class R fuses. These non-renewable fuses are made in 250VAC and 600VAC ratings, with current ratings from 0A to 600A. Class R fuses are available with DC ratings. They have an interrupting rating of 200kA rms symmetrical and are separated into two separate classes, RK1 and RK5. RK1 fuses are available with interrupting ratings of 300kA.

Both RK1 and RK5 fuses are current-limiting and meet standard-prescribed maximum peak instantaneous let-through current and maximum I2t let-through energy requirements.

Actually, Class RK1 and RK5 fuses are Class K-1 and K-5 fuses with ferrules and knife blades modified to conform to Class R rejection requirements. The grooved ring in the ferrule and the slot in the knife blade, when used in conjunction with special fuseholders designed to accept Class R fuses only, prevent interchanging of any other fuse class with the installed Class R fuse.

All Class R fuses must be labeled ?Current Limiting.? They may be labeled ?Time Delay,? indicating that they meet the optional time-delay test by not opening in less than 10 seconds at 500% of fuse ampere rating.

Class J fuses. These non-renewable fuses are current-limiting and conform to 248-8. Current ratings of UL Class J fuses range from 0A to 600A, and the voltage rating is 600VAC. Class J fuses are available with DC ratings. The interrupting rating is 200kA rms symmetrical. Fuses with 300kA interrupting ratings are available. Time-delay labeling is available if the fuse meets the UL optional time-delay test requirements of a minimum 10-sec opening time at 500% of fuse current rating.

 

[davidr43229]

1.

All Class R fuses must be labeled ?Current Limiting.? They may be labeled ?Time Delay,? indicating that they meet the optional time-delay test by not opening in less than 10 seconds at 500% of fuse ampere rating[/QUOTE
Per UL248-12 April 14, 2004
8.3 Verification of overload operation
Part 1, Table 4
Test 1 ? 1.35 In
Test 3 ? 2.0 In
Test 5 ? 5.0 In for time-delay fuses only. For 250 V ac fuses rated 30 A or less, the clearing
time may be 8 s minimum.
2.

Fuses with 300kA interrupting ratings are available. Time-delay labeling is available if the fuse meets the UL optional time-delay test requirements of a minimum 10-sec opening time at 500% of fuse current rating.

Additionally the CLass J has to hold :135% <60A: open within 1 hr; >60A: open within 2hr
200% Specific max. opening times by case size


Just my $.02