Ckt Bkr is Tripping: Feeder for 40 HP Elevator.

[sspeare]

DESCRIPTION OF CIRCUIT:
Elevator motor is 40 HP, 208 Volt/3-phase. Motor FLA from NEC Table is 114 Amps. Breaker sizing: 114 FLA x 2.5 = 285 Amps, round up to 300 Amp. Circuit Breaker #1 is in the Main Dist Panel "MDP". CB #1 is a 300 Amp thermal magnetic breaker, as follows: Siemens JD Frame, model number JXD63B300. CB #2 is inside the elevator machine room. CB #2 serves as the NEC-required disconnect and OCP device. CB #2 is enclosed, and is exactly the same rating and model as CB #1. The cable between CB #1 and CB #2 is copper: 3-#2/0 phase conductors with 1-#4 equipment ground.

THE PROBLEM:
What I'm hearing from the field is: "the breaker is tripping." I have not managed to find out which breaker, or if it's both breakers. The electrician says the instantaneous trips are factory-set at the minimum. The electrician is asking me "how high" to set the adjustable instantaneous trips for these 2 breakers in series. I'm telling him to check for faults first.

QUESTIONS:
1) Am I in trouble because these breakers in series are "fighting" each other with their instantaneous trips?

2) Should I replace the CB in the machine room with a fusible switch?

3) Assuming we can't locate a fault, what can be done?

 

[waross]

First, find out which breaker is tripping.
Is the breaker tripping every start?
It could be a bad breaker or a bad motor. That covers over 99% of the possibilities.
Google "Megger". Check the motor circuit for faults.

1) Probably not.
2) Why.
3) Get a more experienced electrician. Call a motor repair shop and ask them to send out a motor expert.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[crisleon]

Well, I am not sure if I understand your note. However as far as I can understand I just try to advice you in your 3 questions and others.
1) You have to know which CB tripped, it is absolutely necessary for going farther. I can't understand this electrician who don't know which one tripped. Waross is right - take an electrician who knows how to deal with basic electrical procedures.
2) CBs working in series it is nothing strange. If the #1 is upstream in the MDP, it must protect your cable - the feeder going to the downstream device (to the elevator panel inside the machinary room) and busbars of the panel as well. Downstream of them the circuit is protected by the CB #2 - and it must be very sensitive becaus it protects the motor. I don't know this Siemens' CB (JXD63B300), but I am afraid that thermal magnetic relay is not sufficient for the proper protection of the motor (there are a few possible causes to damage your motor).
3) You should check and consider to exchange CB #2, but into direction towards supersensitive motor protecting unit. To exchange it with fuses is completely not possible, it would be a big mistake.
4)CB #2 must trip first in case of short-circuit failure downstream the panel's busbars and it should then trip immediately. In case of overload the motor it is mandatory that it should also trip as first - fuses are not able to do it, forget about such a possibility.
5) It were better if it would be possible to set the delay on the uspstream CB #1. If it is not possible - you should consider to change its protecting relay or even the whole breaker. I suppose that it probably would be posssible to set this delay at the time 0,3sec. or even more (to get the time distinction between tripping of # 1 and #2). However without the detailed schematic and parameters of circuits, cables and switchboards - I cannot say anything more.
Probably this elevator and the motor are very important to you, so you should take the experienced electical man to solve exactly your problem on your site.
Regards
CL

 

[sspeare]

Thank you -- Please don't mind my CAPITAL letters -- I'm not shouting. Here are my ANSWERS to waross & crisleon:

ANSWERS to waross:

First, find out which breaker is tripping. I WILL.

Is the breaker tripping every start? I WILL FIND OUT, IF I HAVE TO BEAT IT OUT OF THEM.

It could be a bad breaker or a bad motor. That covers over 99% of the possibilities. I'LL HAVE THE ELECTRICIAN TEST BOTH CB #1 and CB #2. ALSO WILL HAVE THE ELEVATOR CO CHECK OUT THEIR MOTOR.

Google "Megger". I WILL.

Check the motor circuit for faults. I WILL.

ANSWERS to crisleon:

1) I'LL FIND OUT WHICH CB TRIPS FIRST.

2) CB #2 IS IN IT'S OWN SEPARATE ENCLOSURE INSIDE MACH RM. ON THE LOAD SIDE OF CB #2 IS THE ELEVATOR "SOLID STATE SOFT-START" CONTROLLER. THE ELEV CONTROLLER HAS INTEGRAL OVERLOAD PROTECTION. I'LL GET MORE INFO ON THIS CONTROLLER. BOTH OF MY CBs (#1 IN MAIN PANEL & #2 IN SEPARATE ENCLOSURE IN MACH ROOM) HAVE ADJUSTABLE INSTANTANEOUS TRIPS: FROM APPROX 2 - 12x THE BREAKER RATING.

3) ARE YOU SUGGESTING REPLACING CB #2 (MACH RM) WHAT I CALL A "MOTOR CIRCUIT PROTECTOR" (MCP), THAT CAN HAVE EXTREMELY HIGH INSTANTANEOUS SETTINGS, BUT DOES NOT HAVE OVERLOAD PROTECTION? I WILL LOOK INTO THAT.

4) I UNDERSTAND.

5) BOTH OF MY CBs (#1 IN MAIN PANEL & #2 IN SEPARATE ENCLOSURE IN MACHINE ROOM) HAVE ADJUSTABLE INSTANTANEOUS TRIPS: FROM APPROX 2 - 12x THE BREAKER RATING. I'LL HAVE THEM ADJUST CB #1 TO HAVE A LONGER TIME FOR INSTANTANEOUS TRIP, THAN THE INST TRIP FOR CB #1. DID I GET IT RIGHT?

I WILL POST THE TIME-CURRENT CURVE FOR THIS BREAKER, ALONG WITH A SCHEMATIC OF THE ENTIRE CIRCUIT. WILL HAVE TO WAIT UNTIL TOMORROW WHEN I'M AT WORK.

Again, thanks very much to both of you. Your answers are valuable, to put it mildly.

 

[crisleon]

Well, "MOTOR CIRCUIT PROTECTOR" sounds quite good, similarly as SOLID STATE SOFT-START CONTROLLER. If this MCP is equipped with real protection of the motor, I may withdraw some my previous claims and reservations referring to the CB #2 (after getting your scheme and parameters maybe I'll be able to say more).
I think that you may also ask the engineer supervising such lifting aparatus (elevators), especially of electrical specialty. In Poland such a supervision is mandatory (in charge of the govermental office and authorities), I don't know how it is organized at your country.
Regards
CL

 

[jraef]

Before you start replacing things or spending money on motor shops, realize one thing:

A LOT of elevators, especially hydraulic, use Y-Delta motor starters. They are notorious for causing nuisance tripping of circuit breakers. During the transition from Y-to-Delta the motor is off-line and when it reconnects, there is an inherent phase shift. When that phase shift lines up just right with the phase angle of the incoming line, it can create a voltage spike in excess of what any legal setting would be on a magnetic trip. In other words if all the factors happen to hit just right, here is nothing you can adjust to fix it. The real solution is to get rid of the Y-Delta starter and go to Solid State. There are specific Solid State Starters made exclusively for the elevator market for just this reason (and the fact that there are special requirements and listings necessary for elevators).

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[sspeare]

ALL:
Please see the PDF I uploaded, which is 5 pages. It has data for the breakers - CB #1 and CB #2 are identical. I did some markings on the TCC. Both breakers are thermal/magnetic - also known as inverse-time.

To jraef: the elevator motor starter/controller is supposed to be "Solid State, Soft-Start." I will verify w/elev co.

To crisleon:
I did not mean to mislead you about CB #2. I was just asking IF a Motor Circuit Protector "MCP", which has instantaneous only for short-circuit only protection, might be an appropriate replacement for my existing thermal/mag CB #2 in the Machine Room. All of this assumes the "soft-start" elevator controller has overload protection built-in.

Again, thank you all.

 

[sspeare]

I don't see the uploaded file, I'll try again ......

 

[jraef]

You cannot use an "MCP" (Mag-Only) circuit breaker at all unless you are the manufacturer of the starter and the entire starter is UL listed as a combination unit. Many people are unaware of this but it is a fact that cannot be ignored. Don't do it.

That said, the Mag Trips of a JXD63B T-M breaker are the exact same Mag Trips as a JXD63L Mag-Only breaker, so nothing is going to change in that respect anyway. It's possible that the settings are too low, but if it is a Solid State Soft Starter, that's probably not true either.

By the way you cannot adjust the "time to trip" on a Magnetic trip, only the level. The NEC permits you to set the level at a maximum of up to 1700% of the motor FLC if you can prove that it will nuisance trip at lower levels AND it is an "Energy Efficient" design (as most new motors are now). So in theory you could have the JXD Mag Trip on #2 set at 1900A, which on that breaker is setting #5. But read on.

The first thing you must do is determined the starter type for absolute sure, no guesses. It makes all the difference. If it is a SS starter, then most likely you have a bad SCR. If you don't has a solid state soft starter (some people call Y-Delta a "soft start" when in fact it is not) then the likely sources of problems go up and require a little more investigation.

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[sspeare]

OK, I will drop the "MCP" idea. Also, I will find out for sure if we have a "solid state soft-start" controller.

Thank you.

 

[crisleon]

Do you know now which breaker was tripping first?
I have no idea how to help you. CB#2 is crucial for the safety of your motor. CB#1 should trip later than CB#2, so the time setting here would have the desirable effect (if possible anyway to set anything on it).
In my opinion the thermo-magnetic realay in CB#2 is not sufficient to properly protect it in case of overload or some failures of supply (the lack of one phase or the sag of the feeding voltage).
You may ask the producer of the lift (or similar one) or another consultant how to protect this motor in better way (has the soft start unit another protection of this motor?) or how to set the protection unit. You cannot undertake the snap decision. Our advices on the distance may be not valid to you.
Regards
CL

 

[jraef]

Good point about not knowing for sure if the starter has OL protection, but it's a fair assumption that it does. I know of no soft starter mfrs any longer who do not build in the OL protection for the motor, it's just too cheap for them not to be including it.

But then again, we don't really know anything for sure about the starter at this point.

sspeare, are you in the US or Canada? I only ask because if so, there are VERY SPECIFIC requirements for elevator controllers that must be met which are above and beyond the normal NEC requirements, none of which would have allowed the installation to have taken place without motor OL protection in the starter. Although that's assuming it was inspected, most (if not all) Fire Marshalls will not permit an elevator to be used without a permit, which would entail that inspection.

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[sspeare]

- The elevator controller has integral overload protection.

- CB #2 is the NEC-required disconnect/OCP near the door in elev mach room. The line side of CB #2 is the feed from CB #1, which is in the main distribution panel. The load side of CB #2 feeds the elevator controller.

- The elevator is in the USA.

- CB #2 was tripping - only.

- Electrician has now adjusted the instantaneous trip on both CBs to 7X the breaker rating. We will see what happens.

 

[jraef]

Just to emphasize again though, if you truly do have a Solid State Soft Starter, the instantaneous trips should never trip unless there is a problem with it. That would most likely be a shorted SCR, or if it has a Bypass Contactor, the contacts are welded. Simply cranking up the dial may be the precursor to a bigger, and much more expensive, failure.

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[sspeare]

jraef, yes I understand what you're saying: an instantaneous trip indicates a major problem. I was not able to slow the electrician down before he adjusted the instantaneous trip. My next step is to have them look for a fault. Thanks.

 

[crisleon]

Sspeare: "Electrician has now adjusted the instantaneous trip on both CBs to 7X the breaker rating. We will see what happens".
I am not sure if I understand you, however I can't abstain from the caution: it may be a mistake. To "see what happens" may be not proper strategy.

Look: 7x rating = 7 x 300A = 2100A (nearly in the middle between the "HIGH instantaneous setting" and "LOW instantaneous setting" (see at the enclosed chart I-T). If the short-circuit current will be greater (say: Isc=2800A), then the tripping will follow instantaneously.
However if the Isc will be lesser (say: Isc=1200A), then the tripping will not follow properly early (the thermal relay reacts with the delay).
You should know this simple relation which must be assured:
the setting Iset on the relay < the short-circuit current Isc. If this relation will not be fulfilled the CB may switch off the failured circuit too late.
You have to know the calculated or measured short-circuit current Isc and then you may set Iset on ths relay. If so far nobody calculated it (nobody knows it) you should set the CB's relay (CB#2) in the lowest position (to avoid bigger problems in case of low-current short-circuit failure). Setting on the CB#1 may be different.
Isc may be calculated by means of the analize of the whole circuit (starting from the transformer or even from the source of voltage up to the place of the short-circuit) or - quite precisily - by means of dividing the phase supply voltage (120V for example) per the measured resistance of the short-circuit loop.
Be careful, don't omit anything which may cause bigger problems to you. Please, take a good local consultant to ask for a good advice.
Regards.
CL

 

[sspeare]

crisleon, excellent advice, I will keep after this problem. First thing will be to calc/measure the available short circuit current. Thanks very much.

 

[waross]

Is this a new installation or a failure of an existing installation.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[sspeare]

It is a relatively "new" installation. It operated OK for approx 3 months. No problems on start-up.

 

[WoodrowJWeen]

Does this breaker perhaps have a shunt trip coil that is supposed to be activated by the fire alarm system? We use this setup with heat detectors next to sprinklers in the elev mach rm & top of shaft in order to do a code required shutdown of power before the sprinklers dump water on the elev equipment. Maybe this shunt trip coil is being accidentally activated. Just a guess.