THERMAL MAGNETIC TRIP UNIT SETTINGS

[GOERGE]

Greetings everyone
I have a eaton JD 35k breaker 3 pole catalog number JD3250F...... I understand this is a 250 amp breaker... or is it ....Is it the Frame that is rated at 250 amps ... but not the breaker ??
This is a thermal magnetic trip unit... i do not understand the dials and settings..
There are three dials one for each leg... the dials go from 5 on right to 10 on left
I have seen other breakers that have a scale in percentage of the amp rating of breaker i understand those .
these i do not understand because ...one there is no clear amp rating for this breaker...and two the scale I do not understand
Can someone please shed some light on this breaker and procedures on meaning of dials
Thank you
Goerge

 

[infinity]

According to your catalog number from Eaton it's fixed at 250 amps:

https://www.eaton.com/us/en-us/skuPage.JD3250F.html

https://www.eaton.com/us/en-us/skuPage.JD3250F.specifications.html

 

[david luchini]

The dials adjust the instantaneous trip setting from 500% to 1000% of the trip unit rating.

 

[BMANN06]

The dials adjust the instantaneous trip setting from 500% to 1000% of the trip unit rating.

What he said, this type of ACB is generally used in a motor starter bucket/cell. You would use this breaker and set the trip rating to protect your conductors (in the event of a short circuit) and premise a motor to start without a nuisance trip, and the motor protection would come from the Overloads in the starter.

 

[zog]

Greetings everyone
I have a eaton JD 35k breaker 3 pole catalog number JD3250F...... I understand this is a 250 amp breaker... or is it ....Is it the Frame that is rated at 250 amps ... but not the breaker ??
This is a thermal magnetic trip unit... i do not understand the dials and settings..
There are three dials one for each leg... the dials go from 5 on right to 10 on left
I have seen other breakers that have a scale in percentage of the amp rating of breaker i understand those .
these i do not understand because ...one there is no clear amp rating for this breaker...and two the scale I do not understand
Can someone please shed some light on this breaker and procedures on meaning of dials
Thank you
Goerge

The F in the JD3250F stands for Frame, so the breaker itself can have up to a 250A rating. This breaker has a trip unit that will have it's own ratings which determines the trip settings, the dials are multiples of the trip unit rating.

 

[zog]

What he said, this type of ACB is generally used in a motor starter bucket/cell. You would use this breaker and set the trip rating to protect your conductors (in the event of a short circuit) and premise a motor to start without a nuisance trip, and the motor protection would come from the Overloads in the starter.

This is a MCCB not an ACB

 

[david luchini]

What he said

The dials adjust the instantaneous trip setting from 500% to 1000% of the trip unit rating.

this type of ACB is generally used in a motor starter bucket/cell. You would use this breaker and set the trip rating to protect your conductors (in the event of a short circuit) and premise a motor to start without a nuisance trip, and the motor protection would come from the Overloads in the starter.

Wait, that's not what I said.:happysad:

 

[Jraef]

The links are to depictions and tech data for only the FRAME, there are no trip units shown. Ostensibly because you asked about the dials, the breaker in front of you must have them, which would be on the trip unit that goes into that hole in the front, above the lugs. The thing is, we don’t know what trip unit you might have. It could be thermal-mag, it could be mag-only. In either case the three separate dials are always the Magnetic Trips providing only the Short Circuit protection, thermal trips are what provide the Over Current protection and on MCCBs must be fixed in order to be UL listed.

That is, unless it is a Motor Protection Circuit Breaker (MPCB), in which case you would have one additional dial that you set as the thermal trip point. MPCBs can only be used in motor circuits in a manner similar to a Manual Motor Starter, with the adjustable thermal trip acting as the Overload Protection.

 

[GOERGE]

Thank you to all that answered..... I got my answer from Eaton
Turns out this is 175 amp breaker
Breaker frame rated at 250 amps
Breaker size is labeled right below dials ...the In amps
The dials are adjusted for each leg for inrush circuit in multiples of ten
What through me off was this breaker is feeding a 80 amp load three phase with number 4 wires
I thought the dials were to scale down the amp rating of breaker... THEY ARE NOT.....
AND SOMEONE BEFORE ME PROBABLY THOUGHT THE SAME THING
THIS is a big hazard and i am correcting situation for this customer !!
Thanks Again

 

[david luchini]

What through me off was this breaker is feeding a 80 amp load three phase with number 4 wires
I thought the dials were to scale down the amp rating of breaker... THEY ARE NOT.....

#4 conductors on a 175A breaker is a problem, unless this is some type of motor load or air-conditioning and refrigerating equipment load.

 

[Jraef]

#4 conductors on a 175A breaker is a problem, unless this is some type of motor load or air-conditioning and refrigerating equipment load.

Absolutely. Inverse-Time (Thermal Magnetic) breaker can be sized up to 250% of motor HP FLA per 430.52 if used in a motor starter circuit that has another overload relay or protection built in. So if it's a motor with 80A FLC, the T-M breaker feeding a motor starter, VFD or Soft Starter could be up to 200A and be perfectly allowable because in a motor controller, the OL relay or protection is also protecting the cables. The breaker is being used only for Short Circuit protection (and disconnecting means)..

 

[BMANN06]

Absolutely. Inverse-Time (Thermal Magnetic) breaker can be sized up to 250% of motor HP FLA per 430.52 if used in a motor starter circuit that has another overload relay or protection built in. So if it's a motor with 80A FLC, the T-M breaker feeding a motor starter, VFD or Soft Starter could be up to 200A and be perfectly allowable because in a motor controller, the OL relay or protection is also protecting the cables. The breaker is being used only for Short Circuit protection (and disconnecting means)..

Wait is that what he said or that what i said ..

 

[BMANN06]

This is a MCCB not an ACB

My mistake, i use the term ACB for any open air contacts in a circuit breaker, (small or large) oil circuit breakers or vacuum type breakers i change the letters. I'm just a dumb electrician ... if you put more than 3 letters in front of the breaker ... ima hit the manual.

 

[Bret Hull]

Thank you to all that answered..... I got my answer from Eaton
Turns out this is 175 amp breaker
Breaker frame rated at 250 amps
Breaker size is labeled right below dials ...the In amps
The dials are adjusted for each leg for inrush circuit in multiples of ten
What through me off was this breaker is feeding a 80 amp load three phase with number 4 wires
I thought the dials were to scale down the amp rating of breaker... THEY ARE NOT.....
AND SOMEONE BEFORE ME PROBABLY THOUGHT THE SAME THING
THIS is a big hazard and i am correcting situation for this customer !!
Thanks Again

So did you have to take individual inrush readings on each leg and divide them by 10, and that's the setting number 5-10 on the dial?