1.- I have the following configuration to protect a 50HP, 3P, 480V motor: one CB model TED134150WL
(150AF/100AT) installed in the MCC + a cable to feed a panel box located in the same room + (a panel box with: a CB model TED134150WL + O/L + soft starter + by pass contactor) + cable to feed the motor + motor installed in site. The CB (150AF/100AT)installed on the panel box is protecting the motor? the CB installed in the MCC is protecting the cable? Is it that configuration according to NEC request?

2.-.- Could a fixed electromechanical trip have and adjustable magnetic element?



3.- How can I specify a CB, How many parameters I have to specify, eg: I have a Load 50kVA, V=480, In= 65Amp,3P, How can I specify the frame, and thermal-magnetic trip for that load.



4.- How can I specify an instantaneous current value for a CB with a fixed thermal-magnetic trip.



5.- Motor Circuit Protection: How I have to specify a MCP for a 50HP motor, 480V, 3P, what values of current I have to know and what MCP parameters they represents.



6.- If I have a MCP + O/L protecting a motor in site and the feeder of that motor is protected by a CB (with a fixed thermal-magnetic trip) installed on a MCC: is it That arrange accepted by NEC?

Technically, the 2nd MCCB is a redundant SCPD (Short Circuit Protective Device), it could have been a non-fused disconnect or a molded case switch, since you already have a feeder MCCB in the MCC that is protecting the cables all the way through the circuit. The local controller needs only have a disconnect method and lock-off capability since it appears as though you don't have another disconnect near the motor. As to the NEC issue however, the NEC has no problem with you having redundant SCPDs in a circuit, that is your prerogative.

Some fixed thermal-magnetic breakers do have adjustable magnetic trips on them, however I do not think the TED frames are like that. Every manufacturer is different, and within manufacturer's offerings there are different series of products that offer either version.

Typically, thermal-magnetic MCCBs are rated for a maximum of 80% of their stated rating as a continuous load, unless you specifically ask for (and pay extra for) a "100% rated" breaker. So determine your amp load, divide by .80 and pick the next breaker size up from that. the caveat to that however is that the breaker must be capable of protecting the cables, so I always determine the cable size first based on the NEC rules for a particular type of load, then pick out the proper breaker based on that. For instance, the cable sizing rules for motor loads are different than those of other loads, you follow article 430 for motor loads, I think 220 for all others.

and You can use the rules in article 430 to determine the magnetic trip value you need based on the complex rules and exceptions; make sure you read the exceptions by the way. But keep in mind that what you want to specify and what you get may end up being 2 different things. An MCP, or more correctly a Manetic Only MCCB, can ONLY be used in a LISTED combination starter assembly put together and tested in series by the manufacturer of the controller. You cannot buy them separately and install whatever you like. The MCPs are not UL listed by themselves, they are only UR, meaning UL Recognized, to be used in another LISTED assembly. So in reality, when you specify a combination starter for a given motor, the manufacturer of that combination starter will have already determined the correct MCP that goes in to that starter. They CANNOT deviate from that submitted combination (and provide the UL listing). With the new rules in article 409 of the NEC regarding SCCR (Short Circuit Current Ratings) being an absolute requirement now, this is no longer in the hands of local engineers.

Yes, technically it is fine. Where this would be valid is if you had one set of conductors going from the MCC to the controller, then a smaller set of conductors going from the controller to the motor. The controller, being the MCP + OLR, is protecting the smaller conductors. The MCCB in the MCC is protecting the larger ones. IF however, the conductors were the same size all the way through, the MCP would again be redundant; it could have been a plain switch.

Bottom line, all your answers regarding the motor branch circuit are in article 430 of the NEC. The NEC allows you to overdo just about anything, but you would be wise to consider that having too many trip points can be a coordination issue in that you may not know where a fault happened until you figure out which device tripped. If time is money in your application, you may want to consider consolidating.

Now, all that said, there is a particular case involved in your application that deviates slightly from all that. I don't know of any manufacturer who has UL listed their Soft Starters in combination with a mag-only MCCB (MCP). The simple reason for this is that the higher magnetic trip ratings of the MCPs are not necessary because the soft starter will eliminate the inrush current. So most soft starter manufacturers just use the more readilly available thermal mag MCCBs, which facilitates their being able to more easily attain an SCCR rating without testing the combination (very expensive for them).

Clear as mud eh?

Thanks very much jraef

I have a lot of confussion with that subject let me try to explain again.

My problem is that the client is requesting to change the main circuit breaker located in MCC to a motor circuit protector, so I have to reply him... but I have another concern about that design

The system is the following:
1.- MCC: we are installing a main circuit breaker MCCB thermal magnetic (fixed) of 150AF/100AT model TED134150WL
2.- Cables: from MCC to Soft starter panel box: 3x4AWG MC-HL
3.- Soft Starter panel box, (located close to MCC) that panel contain inside the following:
3.1 another circuit breaker MCCB thermal magnetic (fixed) of 150AF/100AT model TED134150WL
3.2 a soft starter device
3.3 a by pass contactor
3.4 O/L over load rated 1.25FLA
3.3 additional control connection for start/stop
4.- Cables: from Soft starter panel box to motor: 3x4AWG MC-HL
5.- Load: motor 50HP,3P,480V,60Hz,1.15sf

I know that the Soft Starter is minimizing the inrush current actually is working at initial 200%FLA up to 350% FLA and the motor reach the speed.

According to your last paragraf I agreed with you about the "higher magnetic trip ratings of the MCPs are not necessary", but...
What can I do for improve the configuartion system?

What circuit breaker I have to change?

What configuration I have to have in order to protect the motor and conductor from short circuit current + ground fault + overload if I have the by pass contactor? The by pass contactor is using to protect the soft starter for continuos working, it is not supposed used for a DOL start the motor.

The setting for CB & MCPs: What that means the set 100AT, what trip is that if the instantaneous trip is for short circuit fault current value.

Thanks again and I apologize for my english

M.B.

That would be illegal! You CANNOT use a Motor Circuit Protector anywhere except as part of a tested listed enclosed assembly. It is not rated to be used as a feeder breaker in any way.

That part number is for a 150AF, 150AT breaker, i.e. it is a 150A breaker, not a 100A.
Possibly too small of cables for that breaker. I show #4 90deg C wire, 3 conductors in a raceway as being good for 95A max. You would need at most a 90AT breaker for that. Unless you know that those cables you are using are rated for 150 amps or more for some reason. Even if the breaker is rated 100A, that technically is too big for those conductors.

Again, that part number is for a 150A breaker, not a 100A. Might not be a problem here however because in this location, the breaker is just a disconnect and short circuit device. So if it is a 150AT breaker, the mag. trips should be fixed at around 675A. The motor FLA should be 65A, so 675 / 65 = 1040%, which does not exceed the NEC rules and exceptions for maximum instantaneous trips for a motor that size. In the Motor Starter assembly, the Overload Relay is now providing closer thermal protection for your wires.
No problems here, other than I assume you mean 1.25 X FLA on that overload relay.

Other than the possible wire sizing problem, I don't see a problem with the components that needs "improvement". Where is that directive coming from?

Neither, as long as that cable checks out to be rated for 150 amps or more. The wire is adequate for the motor (FLA x 125%), and technically the OL relay is going to be protecting the conductors at a lower level than the breaker in the MCC anyway, but per the rules, the cables from the MCC to the motor starter are only being protected by the breaker in the MCC, and that is where you need to do your homework on that conductor rating (or possibly you posted the wrong part number on the breaker).

The bypass contactor has nothing to do with anything regarding the breaker sizing. Don't concern yourself with it. Your conductor issue is the only problem I see.

100AT is shorthand for "100 Amp Trip" and is referring to the thermal trip setting of that MCCB. The magnetic trip setting on a TED is fixed, I can't remember at what value but it is usually 4.5 x FLA, so 675A in your case if it is a 150AT, or 450A if it is a 100AT. If that were an Across-the-Line (DOL) starter, that mag trip setting may end up being a little too low, but with the soft starter, no problem. No need to change it there.

So to summarize, you need to check to see if your wire is rated at a greater amperage than what the NEC says (since I don't know what type of wire it is). If it is rated for 100A, you need to then check for sure to see if that MCCB in the MCC is really a 100AT breaker or a 150A as the part number indicates. If the breaker really is 150A, or if the breaker is 100AT an the wire is really only rated for 95A, you need bigger wire. Or if you don't want to change the wire, you need a smaller breaker in the MCC.

The rest of your system is fine.

Keep in mind, I am offering you tips here, not to be substituted for having this looked at by a qualified engineer that can visit the site and see all the issues involved. If this seems like too much for you, consider bringing someone else in.

Thanks again Jraef

I am proceeding to change the main cb to:CB adjustable instantaneous trip, 480V, 150AFrame, 90AT adjustable, 18kAmps in order to protect the cables along its route.

When you said "If that were an Across-the-Line (DOL) starter, that mag trip setting may end up being a little too low, but with the soft starter, no problem", are you refereing to a DOL mag-trip of 6*FLA as minimum

The thermal trip setting of a MCCB is calculate: 1.25*FLA*1.2
In this case I have a FLC=65 Amp (NEC) and FLA=55Amp motor nameplate
AT=65*1.25*1.2=97.5 and AT=55*1.25*1.2=82.5 which one I have to use for specify a CB

Thanks again for your support

M. Bravo