E-Rated VS R-Rated Fuse

Status
Not open for further replies.
E

Electriman

Senior Member
Location
TX
Greetings,

I have a 2.4 kv motors that I am protecting it via a 12R fuse. The fuse is fed using a 2/0 cable from upstream. So to protect the cable I have to use a 200E rated fuse. But the problem I have 200E fuse is not coordinated with 12R rated fuse and it does not allow the motor to start. Do you have any recommendation?
 
Electriman said:
Greetings,

I have a 2.4 kv motors that I am protecting it via a 12R fuse. The fuse is fed using a 2/0 cable from upstream. So to protect the cable I have to use a 200E rated fuse. But the problem I have 200E fuse is not coordinated with 12R rated fuse and it does not allow the motor to start. Do you have any recommendation?
Click to expand...

Interesting. A fuse.protecting the motor. Fuses commonly don't protect the motor, they are applied to protect the distribution system from a motor failure taking the motor off line should the motor fail well as the moor control. Motor protection is provided by an overload relay. Years ago it was done thermally but modern overload protection is done with a programable electronic relay.
Also, please describe what you ment by the E-rated fuse not allowing the motor to start.
 
templdl said:
Interesting. A fuse.protecting the motor. Fuses commonly don't protect the motor, they are applied to protect the distribution system from a motor failure taking the motor off line should the motor fail well as the moor control. Motor protection is provided by an overload relay. Years ago it was done thermally but modern overload protection is done with a programable electronic relay.
Also, please describe what you ment by the E-rated fuse not allowing the motor to start.
Click to expand...

I recommend to read this article.
http://www.littelfuse.com/products/fuses/medium-voltage-fuses/medium-voltage-fuses/e-rated.aspx

R-rated fuses are widely used to protect motor feeders in medium voltage along with over load relays.

http://www.littelfuse.com/products/fuses/medium-voltage-fuses/medium-voltage-fuses/r-rated.aspx
 
Electriman said:
It is 600 hp and it is a pump. The motor fuse is 12R.
Click to expand...

A rule of thumb is 1000% flc for 8-10 sec
the 12R is marginal
an 18R is recommended for 600 HP
http://www1.cooperbussmann.com/pdf/9eeffb1f-bed9-4110-87e5-f1ae5c335e77.pdf
flc 133 x 6 x 1.6 ~ 1300 A from the 12R curve ~0.03 sec
600%/800 A for 100 sec

The feeder ampacity must be > OL setting
the feeder fuse can be sized for short ckt only since the OL protects the conductor for toc
look at the curves and pick one that will carry 1300 A for 8 sec or so
 
Electriman said:
I recommend to read this article.
http://www.littelfuse.com/products/fuses/medium-voltage-fuses/medium-voltage-fuses/e-rated.aspx

R-rated fuses are widely used to protect motor feeders in medium voltage along with over load relays.

http://www.littelfuse.com/products/fuses/medium-voltage-fuses/medium-voltage-fuses/r-rated.aspx
Click to expand...
FYI, I have plenty of background on medium voltage motor protection and control as I sold medium voltage motor starters for years. You have missed the point that the OP omitted data regarding the application which he provided later.
As I stated fuses do not protect motors but are used to take the motor off line should the motor fail. Originally medium voltage motors used CTs to drive thermal overload relays which had a N/C contact in series with the motor starter coil to drop the motor starter off line should the N/C open. Now these MV starters used programable SS OL relays to more closely parallel the overload characteristics of the motor.
The R rated fuses are used with MV motor starters and if they do blow you most likely have a serious motor failure issue.
The E rated fuse is used for transformers as Nd feeders. As I asker the OP what is the issue with his 200 E-rate fuse issue that prevents the motor from starting?
The most custom MV starters that I had ever sold were qty(3) 2300v reversing autotransformer starters that included a zero speed switch to prevent the starter from being reversed until the motor had slower to an acceptable speed.
I have also sold countless fused MV fused load interrupter switches commonly used on the primary of transformers as well as feeder protection. It is important to be informed of the complete application information such the correct fused can be selected and proper ratings provided.
I could share my experiences with applying fused MV load interrupters as disconnects for PF capacitor banks.
 
Ingenieur said:
A rule of thumb is 1000% flc for 8-10 sec
the 12R is marginal
an 18R is recommended for 600 HP
http://www1.cooperbussmann.com/pdf/9eeffb1f-bed9-4110-87e5-f1ae5c335e77.pdf
flc 133 x 6 x 1.6 ~ 1300 A from the 12R curve ~0.03 sec
600%/800 A for 100 sec

The feeder ampacity must be > OL setting
the feeder fuse can be sized for short ckt only since the OL protects the conductor for toc
look at the curves and pick one that will carry 1300 A for 8 sec or so
Click to expand...

Thanks
I can go for 18R fuse.

About that E rated fuse, it is supposed to protect the cable that feeds the starter. Remember that I have a 600 hp motor, then I have the starter the 12R fuse is inside the starter so I can't change it since it is coming from a vendor. The starter is 50 ft away from the motor.

To feed the starter, I have to run cable from a power pole 550 ft away from the starter. So I plan to use a fuse disconnect switch to protect the cable.

So my question is should I use a E rated fuse to protect the cable or R-rated fuse? Remember there is no OL relay to protect the cable. The ol relay is inside the starter which is very near the motor.

If I use a E-rated fuse then there is no way to find a fuse to protect the cable (200E) and coordinated with the 12R or 18R fuse inside the starter.

Can I use an 18R fuse instead of 200E fuse?
 
templdl said:
FYI, I have plenty of background on medium voltage motor protection and control as I sold medium voltage motor starters for years. You have missed the point that the OP omitted data regarding the application which he provided later.
As I stated fuses do not protect motors but are used to take the motor off line should the motor fail. Originally medium voltage motors used CTs to drive thermal overload relays which had a N/C contact in series with the motor starter coil to drop the motor starter off line should the N/C open. Now these MV starters used programable SS OL relays to more closely parallel the overload characteristics of the motor.
The R rated fuses are used with MV motor starters and if they do blow you most likely have a serious motor failure issue.
The E rated fuse is used for transformers as Nd feeders. As I asker the OP what is the issue with his 200 E-rate fuse issue that prevents the motor from starting?
The most custom MV starters that I had ever sold were qty(3) 2300v reversing autotransformer starters that included a zero speed switch to prevent the starter from being reversed until the motor had slower to an acceptable speed.
I have also sold countless fused MV fused load interrupter switches commonly used on the primary of transformers as well as feeder protection. It is important to be informed of the complete application information such the correct fused can be selected and proper ratings provided.
I could share my experiences with applying fused MV load interrupters as disconnects for PF capacitor banks.
Click to expand...

Thanks for sharing your info.

What is OP?

I have explained the application and information in the previous post but if you need anything else let me know.
 
Electriman said:
Thanks for sharing your info.

What is OP?

I have explained the application and information in the previous post but if you need anything else let me know.
Click to expand...

"OP" stands for either Original Poster (the person who started the thread) or Original Post (the initial post of the thread.)
It is usually clear from context which of the two is meant.
 
Ingenieur said:
A rule of thumb is 1000% flc for 8-10 sec
the 12R is marginal
an 18R is recommended for 600 HP
http://www1.cooperbussmann.com/pdf/9eeffb1f-bed9-4110-87e5-f1ae5c335e77.pdf
flc 133 x 6 x 1.6 ~ 1300 A from the 12R curve ~0.03 sec
600%/800 A for 100 sec

The feeder ampacity must be > OL setting
the feeder fuse can be sized for short ckt only since the OL protects the conductor for toc
look at the curves and pick one that will carry 1300 A for 8 sec or so
Click to expand...

Sir,

In the equation above, what is 1.6? I understand that 6 is for inrush current but I don't know how you got 1.6.

Thanks,
 
Status
Not open for further replies.
Top