3 Phase Motor

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.

It is heating the motor.

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!

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.

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!

I hope you have learnt something from the discussions.

...as well.

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!

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.

<...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.

How rude.

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

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.

Thank you for your reply.

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

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

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.

And the motor has no integral overheat device.

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.

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.

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.