Transformer primary protection

[hhsting]

I have car wash site which has 208V single phase vacuums fed from circuit breakers all 20A in panelboard. The 208/120V three phase panelboard feeds only vacuums, has 150A main breaker and it is fed from transformer.

The transformer is 45kva primary 480V three phase secondary 208/120V three phase.

The primary of the transformer is protected by GV3P65 Schneider electric. Please see below link specs and data sheet GV3P65:

GV3P65 - TeSys GV3 Manual Starter and Protector, thermal magnetic circuit protector, rotary knob, 48 to 65 A, EverLink BTR | Schneider Electric USA

Schneider Electric USA. GV3P65 - TeSys GV3 Manual Starter and Protector, thermal magnetic circuit protector, rotary knob, 48 to 65 A, EverLink BTR.

www.se.com

I am not sure regarding transformer primary protection normally there would be breaker. Question can the transformer primary be protected by the above GV3P65 Schneider Electric?


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[pisani168]

Primary protection does not necessarily need to be a breaker fuses are good to or protective relays. The manual for the motor starter switch states that it should be used for motors only. So, I do not recommend using it for a transformer.


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[hhsting]

Primary protection does not necessarily need to be a breaker fuses are good to or protective relays. The manual for the motor starter switch states that it should be used for motors only. So, I do not recommend using it for a transformer.


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Ok but GV3P65 is in motor control center. Their is feeder from GV3P65 to transformer primary. What if I place 60A enclosed circuit breaker or 60A fused disconnect between GV3P65 and transformer? That would not solve the problem?


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[hhsting]

Primary protection does not necessarily need to be a breaker fuses are good to or protective relays. The manual for the motor starter switch states that it should be used for motors only. So, I do not recommend using it for a transformer.


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Do you know of any breaker whose manufacturer instruction list to be used in transformer?


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[pisani168]

I can’t really advise you what CB you can use. I assume that you want to take advantage of the code to provide protection for the secondary conductor by means of the primary protective device.
With that being said, if you have a 480/208 delta / wye gnd, the ratio is 2.3. That means, in case you want to install a 60A MCCB e.g. Cutler Hammer HFD 60A, you are within the 125% that code allows.
2.3 x 60A = 138A. Your conductor on the secondary side must have an ampacity of at least 138A (75C table). I would give you the exact references but I’m too lazy to grab my code book.

It makes sense to download the CB TCC and verify that the XFMR inrush is below and to the left of the tripping curve.


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[hhsting]

I can’t really advise you what CB you can use. I assume that you want to take advantage of the code to provide protection for the secondary conductor by means of the primary protective device.
With that being said, if you have a 480/208 delta / wye gnd, the ratio is 2.3. That means, in case you want to install a 60A MCCB e.g. Cutler Hammer HFD 60A, you are within the 125% that code allows.
2.3 x 60A = 138A. Your conductor on the secondary side must have an ampacity of at least 138A (75C table). I would give you the exact references but I’m too lazy to grab my code book.

It makes sense to download the CB TCC and verify that the XFMR inrush is below and to the left of the tripping curve.


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Post #1 is what’s shown on plan. I am trying to stop this by seeing if it does not comply per NEC 2014. I don’t see any violation except NEC 2014 Section 110.3(B). Instruction indicate to use on motor but it’s used on transformer instead.

I do have secondary breaker for transformer secondary conductors. Secondary Main breaker in panelboard is 150A and secondary conductors are 1/0 phase.

So NEC 2014 Section 240.21(C)(1) says three phase transformer such as my case primary delta to secondary wye grounded secondary conductors cannot be protected by transformer primary breaker?


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[Jraef]

The device you show is only UL listed under UL 508 for Type E and F motor controllers. It cannot be used here in the US for any other purpose (they can use it in IEC countries for this however).

We must have something listed as Branch or Feeder Circuit Protective Device, so that means UL489 for circuit breakers or UL98 for fused disconnects. Either one is fine, but in any case, they would need to be AHEAD of that device, because it cannot be used as a branch or feeder by itself.

I'm guessing someone bought this system from overseas, because it was cheaper than one made here in the US. Am I right? I love it when people do that and pay no attention to whether it can be installed here, "that's someone else's problem".

If this was made here, it's likely not UL listed, because UL would not have allowed that use.

If it was built here and they put a UL508A label on it, someone should call UL...

 

[kwired]

One other problem you might have is if load isn't very balanced on all three poles, it may trip because it looks like a phase loss condition to the overload unit - it was designed to protect three phase motors.