Protection for VFD with MCCB 3

[pisimatza]

Hi

Got a question, for those who use European standards. Question is at quotation level. I got to protect VFD, with MCCB. Designer asked for 50 KA, coordination type 2, and both thermal(0.8-1 In) and magnetic protection. After u, can i use class 10 of thermal protection, with MCCB for motor protection (Surion type-GE, )? Designer wants curve C, but this is nonsense. Curve C is for MCBs only, and at 50 KA (and for some cases 200 A), theres no MCB.

Thanks for reply .

 

[electricuwe]

I would not worry about the abbreviations MCB or MCCB, but just comply with the request regarding the protection requirements.

 

[HCBFlash]

I'm not quite in synch with the abbrev's, but I'm guessing you are considering the use of a "motor circuit protector", a thermal magnetic circuit breaker with adjustable settings for both overcurrent and short-circuit protection.

AB, ABB, Siemens, Telemcanique/SquareD, and others should be able to accomodate those curves.

Just stay clear of Moeller.


flash

 

[ScottyUK]

MCB is Miniature Circuit Breaker and has four response curves defined A - D. A is pretty uncommon now.

The same curves are not available on a MCCB although an MCCB with an electronic tripping unit should be able to give at least as much flexibility in setting the tripping characteristic. Where's the problem?


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If we learn from our mistakes I'm getting a great education!

 

[jraef]

I agree with ScottyUK. There are no pre-defined trip curves designated by letters for MCCBs. And besides, a trip curve C is just for general purpose loads, nothing special really. A VFD will have it's own thermal and instantaneous trip characteristics for protecting the motor, the MCCB is there mainly just to protect the VFD and the cables going to it.

 

[gepman]

MCP I believe is Motor Circuit Protector (similar to a Cutler-Hammer HMCP), MCCB is Mold Case Circuit Breaker (similar to a Cutler-Hammer HFD, i.e. UL489 breaker), MPCB (not used in above discussion) is Motor Protection Circuit Breaker (similar to an Allen-Bradley 140M). I didn't know what MCB was until ScottyUK stated it.

I would have to pull out my copy of UL 508E to see if Type 2 coordination applies to VFDs. I know it does apply to contactors. I also thought that the combination had to be tested in order to qualify as Type 2 coordinated.

I would use either a MCCB or a MPCB to protect the VFD. If you look at A-B VFD manuals they list the recommended protection for each type. I would assume that other manufacturers of VFDs do the same. A-B's 140M is listed for Type 2 coordination with their Bulletin 100 contactors. I don't know about other manufacturers ratings.

The designer may have specified it wrong which isn't uncommon.

 

[dpc]

MCP = Motor Circuit Breaker in NEMA/ANSI land.
MCB = Miniature Circuit Breaker in IEC land.

These are two different things. I believe Scotty's assessment is correct, since the OP referred to European standards.

In the US, it would be a code violation to use an MCP upstream of a VFD to protect it, since an MCP can only be used as part of a combination starter for control of a motor.

 

[jraef]

Yes, let's not get off track. The OP specifically stated "European standards" which means IEC conformity, let's not muddy things up for him with NEMA terminologies. They are different, let's just leave it at that unless someone wants to start a new thread.

 

[dpc]

DOH! Correction to my last post- MCP = Motor Circuit PROTECTOR.

dpc

 

[jraef]

I started an FAQ on the terminology isses. Please feel free to email me with comments or additions.

faq237-1402



JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> faq731-376

 

[pisimatza]

Thanks Jraef, good point there. The protection circuit breaker is used for cable and VFD protection(not heavy start conditions), so MCCB does not protect the motor. So no motor protection circuit breaker.
ScottyUK : I expected from the projector something what makes sense, not curve type C for MCCB. U really can get close to this curves A B C D , with an electronic trip unit(anyway in practice no-one did that before). And for MCCBs there are trip classes: 5(for "light" loads), 10A, 10, 20, 30(last onme for heavy duty).

 

[gepman]

If MCCB is a UL 489 Molded Case Circuit Breaker I think that you are getting motor overload trip classes confused with a circuit breaker trip curve.

Don't expect something to make sense from the specifier unless they know the standards. Besides Type 2 coordination does NOT apply to VFDs as far as I can tell (it is meant for circuit breaker/motor starter (contactor) combinations) and the two components must be tested together to verify that they meet Type 2 coordination (i.e. no damage so that the contactor can be used again after a fault). See

http://www.automation.rockwell.com/uk/enews/type2_about.htm

for more information on Type 2 coordination.

Regarding MCB's, has anyone seen a 3 pole Miniature Circuit Breaker rated for 480V and UL 489 rated (so it can be used ahead of a motor contactor)?

 

[jraef]

Yes, they exist. Bad idea, but they exist. But please don't hijack someone else's thread, just start another.

 

[gepman]

I should have made myself more clear. I wasn't trying to hijack his thread. pisimatza had mentioned possibly using MCB's to protect the VFD. If they are not UL489 rated then that would not meet NEC, which was my point that I didn't state very clearly. I have never seen an MCB that was UL489 rated and 480V rated. Of course pisimatza didn't mention voltage or country of installation, only "European" which I am not sure if it is IEC components for install in US or in some other country.

 

[jraef]

Again, why would the OP have been specific about European standards if he was at all concerned about UL issues? Geez, we ask people posting questions to be geographically specific and then flog them with answers that are irrelevant anyway.

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[ScottyUK]

pisimatza,

I know you can get an electronic tripping unit to behave in a similar manner to the MCB curves. The tripping classes you refer to are specific to MCCBs which are intended for motor protection duty. The tripping class is more commonly found on a thermal overload relay.

Type 2 coordination has already been discussed above by the NEC guys. I wonder if the 'C' referred to is the setting for magnetic trip element? On breakers where it is adjustable the settings are (from memory) designated by letters from A-H. A setting of C would be a fairly low magnetic trip setting.


jraef,

LOL.




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If we learn from our mistakes I'm getting a great education!