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3 Phase Motor

12/14/2018 12:35 PM

What are the IEE regulations regarding the connection of a 3 phase induction motor please.

FLC = 14A

Voltage = 415 V

Power = 7.5 kW

Can it be connected just using a circuit breaker and a contactor without an overload relay.

If it can be connected in this way what should be the size of the circuit breaker.

There is also a heater, how long the heater should be left on when the motor is not running.

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#1

Re: 3 Phase Motor

12/14/2018 1:29 PM

Your local AHJ would take precedence over the IEE (Is this the old IET?) which would take precedence over the motor OEM recommendations. But the best place to start is with the motor OEM and then work your way up the alphabet chain for compliance.

What is the heater heating? The motor? There is a lot this forum doesn't know about your installation.

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#2
In reply to #1

Re: 3 Phase Motor

12/14/2018 1:35 PM

It is heating the motor.

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#8
In reply to #2

Re: 3 Phase Motor

12/15/2018 1:26 AM

The motor anti-condensation heaters are designed to be on at all times the motor is not running. It is not normal to measure the motor moisture to decide whether the heaters stay on or not.

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#3

Re: 3 Phase Motor

12/14/2018 2:49 PM

After connecting, as required by the local codes, the motor should rotate in the correct, desired direction. Centrifugal pumps will still operate, but at about 30% efficiency if running backward.

There is no reason to leave the motor heat on after shutdown.

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#4

Re: 3 Phase Motor

12/14/2018 5:34 PM

Without knowing where you are in the world, we cannot answer definitively. But as a general rule, you are required to provide 3 things for any motor:

  1. A means to turn it on and off.
  2. A means of protecting it from overload conditions
  3. Protection of the entire circuit against short circuit current.
  4. A means of isolating it from power while working on it.

Those four elements can be separate, they can be all in one device, or they can be in any combination. #2 can be done INSIDE of the motor itself and often is on very small motors but I would not expect to find that on a 7.5kW motor. A properly sized fuse or circuit breaker can, in theory, be used to provide both #2 and #3, but it is VERY difficult to accomplish without compromising one or the other.

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#5

Re: 3 Phase Motor

12/14/2018 11:41 PM

You said..

"What are the IEE regulations regarding the connection of a 3 phase induction motor please."

If you know about them, then why have you not read them? If you are studying electrical engineering, why are you asking us?
You have the answer in the regs!
Strange you ask about a heater and how long should it be left on! Have you not seen a motor run under load? If you have, you would have noted that it gets hot, and the fan at the back and the fins on the body are there to remove the excess heat (I am presuming we are talking about a standard motor and not force vented)

Ergo, once running there is no need for a heater, unless there is something you've not told us!

I'm not going to spoon feed you the answer, as you again know about overloads, then find out how they work and then find out how MCB's work, and you decide which is the best to use.

If you are trying to install this motor yourself, don't!
Find a real electrician to do it!

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#6
In reply to #5

Re: 3 Phase Motor

12/14/2018 11:55 PM

It will have been easier to answer the question if you knew which I doubt than coming up with this garbage,

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#9
In reply to #6

Re: 3 Phase Motor

12/15/2018 2:02 AM

And if you were as clever as you think you are you would not be asking such a dumb series of questions that a 2 yr apprentice or university student could answer!

But while we are here, why do you think I or anyone else should answer your inept questions?

You know about electrical regulations, did you not read them?

My conclusion is you couldn't be bother! Easier to be spoon fed the answer, and that in my many years of experience is both stupid and a utter waste of time for the person giving the answer, as you will not learn a thing from being spoon fed.

It is also dangerous, as you have neither the practice knowledge or manual experience to apply yourself to the answer.

So in reply, it was not my intention to answer your question, but it was easier and infinitely more interesting to question you on your ability to work out the answer yourself.

Judging by your reply, I have annoyed you because I didn't. and your lack of replies to my questions means I have hit the nail squarely on the head and I assumed correctly

No cigar for you.. and get someone else to do your homework!

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#11
In reply to #9

Re: 3 Phase Motor

12/15/2018 3:38 AM

You seem to have made a big fuss out of my question.

The reason why I brought this question is that I came across a installation where the motor above circuit included a 16 A circuit breaker and a 16A contactor without any overload protection. Therefore, all I was asking whether the installation was correct by electrical standards as it did not include an overload protection to set the current to motor full load current. (service factor).

Also, I looked at motor manual and it did not specify how long the space heater should stay on apart from the fact that it should be turned off when the motor is running.

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#16
In reply to #11

Re: 3 Phase Motor

12/15/2018 11:16 AM

You said

You seem to have made a big fuss out of my question.

No I have not... you Sir are the one making the fuss! I have tried to get YOU to think about your problem rather than spoon feed you the answer.

You said,

The reason why I brought this question is that I came across a installation where the motor above circuit included a 16 A circuit breaker and a 16A contactor without any overload protection. Therefore, all I was asking whether the installation was correct by electrical standards as it did not include an overload protection to set the current to motor full load current. (service factor).

Again, as I said as you know about IEE standards, did you read them? No answer!
Some very clever folk, look at this forum and several have answered. However, while I IMHO do not think its good for you to do that, as you will go away thinking one answer fits all problems, I prefer to get you to think.
You ain't done that either!

You said

Also, I looked at motor manual and it did not specify how long the space heater should stay on apart from the fact that it should be turned off when the motor is running.

This part tells me you have ZERO plant and machine experience.
Did you think about calling, writing to the motor manufacturer? No!
Did you ask someone senior to you are you afraid of loosing face as you don't know something, and its easier to ask a bunch of faceless guys on a forum?

You Sir are scary because of your arrogance and obvious lack of experience and knowledge about which you speak!

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#24
In reply to #16

Re: 3 Phase Motor

12/18/2018 1:57 PM

I hope you have learnt something from the discussions.

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#25
In reply to #24

Re: 3 Phase Motor

12/18/2018 5:28 PM

...as well.

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#27
In reply to #24

Re: 3 Phase Motor

12/20/2018 4:30 AM

You are funny...... can't counter my comments as they are on point, so you revert to insults!
What do you think you can possibly teach me? You are arrogant and somewhat stupid to even think you can teach me IMHO.

Grow up! You asked for help, it came not as you expected, on a plate, but in the form of making you work towards getting your own answer!

I gave you the BEST possible advice that anyone should have... go figure it out yourself.. and THEN come back to confirm your findings!

Now off you go, there's a good little boy and do your own homework!

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#19
In reply to #11

Re: 3 Phase Motor

12/15/2018 2:15 PM

Unless the motor has internal overload protection such as thermostats wired to the contactor, it is not protected properly. As a typical squirrel cage induction motor, it is also unlikely to be impedance protected.

Your training served you well, and to seek out possible alternatives to your normal experience is commendable.

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#26
In reply to #11

Re: 3 Phase Motor

12/18/2018 5:45 PM

<...motor manual...did not specify how long the space heater should stay on apart from the fact that it should be turned off when the motor is running....>

That's because the motor manufacturer cannot have any clue as to the on/off cycle of the motor, which is, after all, installation-specific and cannot in any event be a property or feature of the motor!

John: 11, 35.

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#23
In reply to #6

Re: 3 Phase Motor

12/18/2018 10:59 AM

How rude.

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#7

Re: 3 Phase Motor

12/15/2018 12:17 AM

The heater should be be left on as long as necessary to remove any excess moisture that may be in contact with the windings.

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#10

Re: 3 Phase Motor

12/15/2018 2:31 AM

Assuming a standard squirrel cage design, the motor may be supplied with an internal thermal switch (klixon), which can be acceptable overload protection. The klixon, when it opens due to high temperature in the stator winding, will de-energize the contactor. These used to appear even on small inverter duty motors, where the risk of overheating due to low (fan) speed is high.

However, even down to 2kW motors normally get replica type overload protection, which will inexpensively protect your investment from other events, like single-phasing or unbalanced power, that will crisp your motor in short order.

NEMA provides a method for larger motors where the motor manufacturer can designate whether the motor is self protected or not with a Type designation, 1, 2 or 3, which then tell you the degree of protection the device (i.e. thermostat) gives you.

IEC provides a method to evaluate motor internal protection, TP code on the nameplate, see this useful location:

https://electrical-engineering-portal.com/basics-of-built-in-motor-protection-for-beginners

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#12

Re: 3 Phase Motor

12/15/2018 6:40 AM

British Standard IET Wiring Regulations BS7671:2018 require that motors be protected against overload (clause 552.1.2), other clauses require general protection against short-circuit and fire. Reference is made to BS EN60947, which includes motor starters & 511.1 states every item of equipment shall comply with relevant requirements of the applicable British or [EU] Harmonised standard.

FLC of 14 amp is typical for 7.5 kW 415V 3000 rev/min motor. I am not aware of a 14 amp breaker or fuse - 16 amp being a standard size. Also, while the standard MCB or fuse is designed to protect cables, there are overload relays designed to fit on contactors specifically to suit motors (which also protect against "single phase" (2 wire operation)).

At first sight, 16 amp breaker is non-compliant and could easily be marginal for starting current. Short circuit protection is obligatory & usually involves a fast magnetic trip.

It is possible "circuit breaker" is an MCCB or other device with a suitable overcurrent curve & adjustable setting or motor has an integral overheat device but this is invisible to CR4. Modern practice for smaller motors can integrate isolator, overload/short-circuit protection and contactor in one unit.

What make & type is your "circuit breaker, what is written on it??

Bearing in mind the cost of a "clip-on" motor overload for a typical contactor, leaving it out is a dangerous economy.

Heaters should be on always when the motor is stopped, unless you actually have a dry indoor motor location which makes the heater redundant & cost of running a heater 24/7 unnecessary.

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#13
In reply to #12

Re: 3 Phase Motor

12/15/2018 7:29 AM

Thank you for your reply.

The MCB is 5SY 43 D16 Siemens and the contactor is 3RT1026-1B.

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#17
In reply to #13

Re: 3 Phase Motor

12/15/2018 12:31 PM

Salih,

I note that overload compatible with contactor is

3RU1126-4AB0

While the tripping current for "D" type MCB in BS7671 is similar to curve for this overload at 3 x setting & up, at 1000 seconds overload is 1.2 x setting [3 pole] 14 amps = 16.8 amps; while MCB is ~1.5 x 16 amps = 24 amps. Overload trip is ~400 seconds @ 1.2 In with two pole load - no such protection with MCB.

I do not think the the motor is adequately protected against overload. There is a tolerance down on the MCB tripping value but you would have to inject the MCB from an O/C test set to convince it is low enough - a replacement MCB could have the maximum per BS7671 fig.3A6.

Both contactor & overload are obsolete - Siemens would have to be asked if replacement overload 3RU2126? can be fitted on old contactor type.

67model

P.S. I could send ref. for curves, but do not have time this moment.

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#22
In reply to #17

Re: 3 Phase Motor

12/17/2018 7:08 PM

OK, the operating curves.....first Siemen's overload, found at ...

https://support.industry.siemens.com/cs/document/5353140/tripping-characteristics-4nep6511921-01?dti=0&lc=en-WW

Second MCB characteristic, it is a Schneider curve but all MCBs align with BS EN60898/61009-1 Fig. 3A5 of IET Wiring Regulations, 2018.

Note there is a far higher tolerance on MCB compared to motor overload. The marks close together on 3 x In line of overload curve are the +/- 20% tolerance of the overload. The square mark to right of lower one is 16 amp MCB Maximum adjusted to compare with 14 amp setting of overload.

The lower marks [at approx 20 seconds] are for the minimum times @ 3 x In for MCB. It looks as if MCB often gives better protection (which may seem OK if motor has very short start time). However, the maximum test limit for the MCB standard on its curve is 1.45 times x In for 3600 seconds (which aligns with the requirement of at least 50 years in IEE Wiring Regs that "close" circuit excess current protection must operate in 1 hour at 1.45 times circuit rating). The motor overload curve has a much shorter trip time at small overloads.

That comes out at 1.66 times motor full load, which will surely cause twice the designed temperature rise [N.B. few motors will stall at 2 x FLC]. In many cases, the driven equipment at twice normal power, could be on fire before the motor trips - motor protection is to protect both motor & driven equipment & regulations are driven by many years of experience of unwanted fires & consequences.

This is, of course, why motor starters incorporate overloads designed for motors, in addition to cable protection by fuses/breakers.

67model

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#21
In reply to #13

Re: 3 Phase Motor

12/17/2018 5:22 AM

That information plus the sight of the installation including feeder cable size, routing and length, will enable design an installation that is compliant with the locally-applicable coding.

If in doubt, consult a qualified local Electrical Engineer.

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#14
In reply to #12

Re: 3 Phase Motor

12/15/2018 7:34 AM

And the motor has no integral overheat device.

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#15
In reply to #12

Re: 3 Phase Motor

12/15/2018 9:24 AM

Is the space heaters are actually designed to be always on, even for a long time like 6 months if the motor is not running or you have to check specific motor instructions.

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#18
In reply to #15

Re: 3 Phase Motor

12/15/2018 2:02 PM

typically they are, though you might want to compare the cost of 6 months of heat versus drying the motor out after the 6 month period. If you need it available at a moments notice, then leave them on.

You may find that a week with the heaters on before you use it will be satisfactory, certainly enough time to drive out whatever moisture entered the insulation, bearings well greased to exclude moisture there.

your environment will also tell you something, which we cannot see from here, if I may shamelessly quote other CR4 parties. If you are on the deck of a North Slope oil rig, then it makes sense to leave them on. If you are in a temperature controlled indoor space, then it makes no sense to turn them on at all.

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#20

Re: 3 Phase Motor

12/17/2018 4:54 AM

As this is an existing installation:

  • The breaker is there to protect the wiring.
  • The overload, were it there, is there to protect the motor against overcurrent on mechanical overload.
  • BS7671 gives full protocols for co-ordination between protective devices to assure safety of the installation in jurisdictions where British Standards apply.

In summary the existing installation is non-compliant to BS7671 and deserves the installation of a motor overload device to protect the motor.

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