4160-480 transformer loading 480 Motor

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tjonak

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I need your help determining if the system found at an Industrial site I visited is Ok. I have never come across this before, and have been scouring the code trying to make sense of it. There is a 4160 Motorpact MCC feeding a 4160 Primary 480 secondary transformer about 200' from the MCC. That secondary side of that transformer is tied directly (10' away) to a cooling tower water pump. I did not see any secondary OCP coming off of that transformer, nor did I see any disconnecting means within line of sight of that motor. What code section do I need to look in to verify if this is acceptable practice or not?
 
How old is this installation?
There are several NEC sections that are different depending on if the installation is industrial with trained maintenence.
 
The site is about 6 years old. I did find that as far as the disconnecting means is concerned, that 430.102(B)(1) Exception (2) that would probably alleviate the requirement for a disconnecting means. Is that the trained maintenance requirement you are referring to?
 
Seemingly that would apply and depending on the specifics 240.21(C) could allow the transformer secondary to be protected by the properly sized primary OCP device.
A number of engineered industrial applications fall under Code rules not commonly in place.
 
tjonak said:
I need your help determining if the system found at an Industrial site I visited is Ok. I have never come across this before, and have been scouring the code trying to make sense of it. There is a 4160 Motorpact MCC feeding a 4160 Primary 480 secondary transformer about 200' from the MCC. That secondary side of that transformer is tied directly (10' away) to a cooling tower water pump. I did not see any secondary OCP coming off of that transformer, nor did I see any disconnecting means within line of sight of that motor. What code section do I need to look in to verify if this is acceptable practice or not?
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What, if anything, is providing overload protection to the motor?


SceneryDriver
 
augie47 said:
Seemingly that would apply and depending on the specifics 240.21(C) could allow the transformer secondary to be protected by the properly sized primary OCP device.
A number of engineered industrial applications fall under Code rules not commonly in place.
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It is protected by the Sepam 42 controller, which from my understanding is the motor controller. It the has CT's and such sending data into the relay. I do not know if the Sepam controller also offers overload protection.
 
Jim (Dungar) is back. He can likely provide more insight,.
 
I have to agree with Augie, a delta-delta transformer is one situation where primary protection can also protect secondary conductors. You still would need motor overload protection in addition to SC/GF protection.
 
tjonak said:
It is protected by the Sepam 42 controller, which from my understanding is the motor controller. It the has CT's and such sending data into the relay. I do not know if the Sepam controller also offers overload protection.
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Yes a Sepam is capable of providing overcurrent protection of the motor. Is there a single Sepam or two of them?Are there CTs on the transformer secondary? Does the motor have internal RTDs?

Off the top of my head I can't recall ever protecting a secondary side motor using only primary side CTs. Effectively the transformer will have a small soft start function due to its inrush plus then the motor starting current.
 
jim dungar said:
Yes a Sepam is capable of providing overcurrent protection of the motor. Is there a single Sepam or two of them?Are there CTs on the transformer secondary? Does the motor have internal RTDs?

Off the top of my head I can't recall ever protecting a secondary side motor using only primary side CTs. Effectively the transformer will have a small soft start function due to its inrush plus then the motor starting current.
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There is one single Sepam protecting it. The internal RTD's from the 480V motor are ran back to the Sepam. There are no CT's on the Secondary of the transformer, only on the primary, contained in the Motorpact Bucket.
 
tjonak said:
There is one single Sepam protecting it. The internal RTD's from the 480V motor are ran back to the Sepam. There are no CT's on the Secondary of the transformer, only on the primary, contained in the Motorpact Bucket.
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Depending on your relay, you should be able to create a custom time current curve using upto 4 or more segments.
 
jim dungar said:
Depending on your relay, you should be able to create a custom time current using upto 4 segments.
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Alright.
So thus far, we agree that the following code articles apply;
240.21(C) for allowing protection on the Primary side,
430.102(B)(1) Exception (2) for allowing there to not be a disconnecting means within line of sight of the motor.
However, by looking at the onelines I just found, it appears the transformer is Delta Wye, not Delat Dealt. So wouldn't mean 240.21(C) would not apply?
cooling tower one line.PNG
 
I would also like to add, that I genuinely appreciate everyone's support and input so far. This is my first time posting on MH forum, and I have already learned so much, thank you all!
 
240.21(C) would apply because your transformer secondary line currents are not directly linked, via the transformer turns ratio, to the primary side line currents.

I don't know if your installation would qualify for some of the 'special' industrial rules at the end of section 240. I am doing this from memory so I can't quote a specific paragraph.
 
petersonra said:
He indicated there are RTDs in the motor running back to the relay. That should be adequate for overload protection.
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I have never considered RTDs as being equal to an NEC motor running overload protection, but maybe I have led a sheltered life?
 
jim dungar said:
I have never considered RTDs as being equal to an NEC motor running overload protection, but maybe I have led a sheltered life?
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isn't the whole reason for overloads to prevent the motor from over heating?

Part III. Motor and Branch-Circuit Overload Protection
430.31 General. Part III specifies overload devices intended
to protect motors, motor-control apparatus, and motor branch circuit
conductors against excessive heating due to motor overloads
and failure to start.
Click to expand...

However, unless the motor exceeds 1500 HP, it does not seem like RTDs are a NEC approved method.
 
tjonak said:
Alright.
So thus far, we agree that the following code articles apply;
240.21(C) for allowing protection on the Primary side,
430.102(B)(1) Exception (2) for allowing there to not be a disconnecting means within line of sight of the motor.
However, by looking at the onelines I just found, it appears the transformer is Delta Wye, not Delat Dealt. So wouldn't mean 240.21(C) would not apply?
View attachment 2563423
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1. Since your system is grounded, the EGC/SSBJ shall be run with all circuits. secondary side of the transformer is also required to be grounded.
2. Since Xformer is delta-Wye, primary and secondary conductors are required to be protected IAW 240.21. You can't use primary OCP to protect secondary conductors (see 240.21 (C) (1).)
3. 430 is for motor load requirement which is not related to required on 240. However, you can using 1 OCP to achieve both requirement.
 
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