Motor Rating Plate Full Load Current And Power

OK. A properly-protected(?) motor runs continuously(?) at its full load current without showing any signs of distress(?). Definition of a problem is a real difficulty here.

yes sir, its protected, thts y its arised. the OLR provided was for 5.25kw, 415V is 12A, so its tripped after one hour. i hope either the rating plate is wrong it may 9kw or the pf of the motor is .6, is it possible? not much datas are available.

Oh,look! Further information!

• The overload relay [OLR] needs to be selected and set to the full load current as stated on the motor plate. Please explain the reason that this has not been done in this particular case. Please explain what steps are being taken to correct this issue.
• Please explain why this information was not presented in the original post.

Dear, we r attending the subject for maintenance only. its installed long time back, since it is smoke fan hope never its operated, might be tested but OLR will trip by long time operation only, the rating plate may notice by every one. bcos motor is in roof and starter panel is in ground floor, if the FLA is not given to the panel manufacturer they will provide OLR based on their standard selection for the rated kW, thts 10-12A, its the practice. would you please reply to only one question that, is it possible to draw 15.5A current by a 5.25kW, 415V 3phase motor?

Evidence:

• The motor is rated 15.5A by the manufacturer.
• The measurements indicate 15.5A.

So the answer is "yes".

The concept of the fan motor tripping during a crucial event is abstruse.

u mean to say, I=15.5A, V=415V, so

pf = 5250/1.73/415/15.5

motor is designed for pf= 0.48?, can u pls. explain wt the reason for such a design.

The motor manufacturer can do this over the telephone. Make the call; it's well overdue.

The 15.5 FL amp is the design rating, it should draw a little better than 13 amps when running...but you don't size the ol at running amps, you size it above that rating, 15.5 or slightly greater...

Improving the PF on a motor for emergency use only, is not cost effective....

Anonymous Poster #1 did not select the overload relays; Anonymous Poster #1's switchgear manufacturer selected the overload relays. What Anonymous Poster #1 needs to do is replace the overload relays with ones that are correctly ranged for the connected motors, and set the trip point to the full load current as suggested.

It seems that the forum is having some difficulty in getting that message through to Anonymous Poster #1. The blame card is beginning to appear in Anonymous Poster #1's hand; blame is not a useful concept in Engineering.

For that reason:

<unsubscribes>

I highly recommend listening to this!

Were the O/L's fitted by the OEM or you? Fire pumps are rated far higher than normal, I'm not sure about smoke extraction fans.

fire pump and smoke fans can be considered as similar application, both are critical and will operate on fire, should not stop at any circumstances. OLR is fitted by the panel manufacturer only

<...OLR is fitted by the panel manufacturer only...> So what? if it's the wrong size then why should who fitted it matter a jot? Just fit the correct size!

its not a matter of replacement, done it. the thing is normally for a motor rated 5.25kW 3phase, 415V may take around 10A current only but here it is 15.5A. curious about the reason of such a design of motor and application thats all. if some one knows about it please share.. i think some one who knows about motor design only can explain it, i am not expert in this subject.

<...some one who knows about motor design only can explain it...>

• Please describe the outcome of the telephone discussion that has taken place with the motor manufacturer.
• Please explain the apparent disinterest in overcoming the current problem despite the above responses to the original post.

Quite. GA.

Current = power/volts/√3/cosφ/efficiency. You forgot to include efficiency. To get your figures the PF and efficiency are on the low side, but not unreasonable.

5.25kW is non-standard. Standard rating is 5.5kW

That appears to be a motor built as part of an axial fan assembly. (?).

I cannot identify most of the NP data because of the poor photo.

Some of the Flakt Woods motors are designed special to run at 400 C for 2 hours etc.

That is a very special motor. I would use the NP amps because it is a special duty motor.

my concern was only the thing, a motor with 5.25kW, 415V, 50Hz is drawing 15.5A. theoretically with the formulae, P=rt3VIcosphi, I = 5250/1.73.415/.8 = maximum of 10A, if we consider efficiency .8, it will be a maximum of 11A only. then how it is mentioned in the plate as 15A and consuming 15A. is the rating plate is wrong or is there any special motor in this category? i couldnt find any reference. unfortunately nobody could give any proper reply. , just think if the rating plating not available in the motor, v can measure voltage 415V, current using clamp meter 15.5A, how to calculate the power..rt3VIcosphi ths all. just calculate it will never b 5.25kW

But you're just guessing at the power factor and efficiency. They could be considerably lower, particularly if it's a special motor. Also why calculate current at 415 V? The nameplate is likely to be based on worst case, 380 V.

Don't blame the forum for not giving you a "proper" answer! You can see the motor, nameplate and fan. We can't.

my concern was only the thing, a motor with 5.25kW, 415V, 50Hz is drawing 15.5A. theoretically with the formulae, P=rt3VIcosphi, I = 5250/1.73.415/.8 = maximum of 10A, if we consider efficiency .8, it will be a maximum of 11A only. then how it is mentioned in the plate as 15A and consuming 15A. is the rating plate is wrong or is there any special motor in this category? i couldnt find any reference. unfortunately nobody could give any proper reply. , just think if the rating plating not available in the motor, v can measure voltage 415V, current using clamp meter 15.5A, how to calculate the power..rt3VIcosphi ths all. just calculate it will never b 5.25kW

Well, you are ASSUMING both the PF of the motor and it's Efficiency. Obviously if the resultant I value is 15.5A at that rated shaft kW of 5.25, the PF and Eff values are not what you are assuming they are. As mentioned, this is not a motor that runs all the time, so it's likely that they sacrificed energy efficiency and design PF to attain higher reliability. The motor design may be based on .7PF and 60% Efficiency for all you know, but why would anyone care if it is doing its job of evacuating smoke during a fire?

Again, as long as the operating current is not exceeding the FLC on the nameplate, you don't have a real problem here, just maybe a curiosity.

thank you, any how first time im seeing this kind of motor and i believe what u said, still will search for more references, bcos b4 i worked in switchgear design, never seen such type of motor. overload we were providing always as per the typ-2 co-ordination chart only. is there any benefit in cost wise for the motor manufacturer or the customer by making such a non standard design. we 650 motors in our project, only 5 of them is having this design. thanks

And BTW, you've slipped efficiency in there. You wouldn't like to acknowledge #18 by any chance?

yes dear i admit it, and well said clearly in #22 also. my question, 100% its a non standard product with .6 effiency or .6 pf, first of all no one will go for a non standard product unless there is no any special request. the standard pf and efficiency of motors are .8 only.

if some one go to select that either the manufacturer or customer should get cost advantage. since it is a non standard product most probably no chance. second chance is it may be a special design which is required for fire smoke fan application which im not technically aware and some one who working in motor design can answer, since it is a new subject for me looking for the answer of y y y y, thank you all.

But I said it first . #22 was in reply to your #20, which was the first time you mentioned efficiency.

I thought we'd established that it's a non-standard motor.

I don't know what you're getting at in your 2nd para, but good if the forum has helped clarify your thoughts.

If you use an oscilloscope with voltage and current probes you can measure the phase displacement of the current. It takes some head scratching to figure out because the current probe measures current in one phase and the voltage will be probably across L1-L2. I believe there are instruments that you can rent that have three current probes and three voltage probes that will give you the consumed power, and the phase shift.

With some thought and basic measurements you can characterise the motor. It is a good academic exercise if you can get the time and $ to pursue. It would be a good learning exercise. I would also tap the manufacturer - I am sure they can provide more details on their fan assembly. (I would not be surprised if the motor is actually running at greater than NP power - but it is a 3 hour rating at 300C, not continuous at 40C, and the NP power is possibly misleading). If I am correct, you cannot disengage the motor from the fan to measure the magnetising current running NL. Just another peace of data for the motor. Most fans I have seen run the motor at 100% of its rating.

I would be inclined to say the difference is due to the fact that you refer to 5.25kW - which is the nameplate power delivered by the motor - but then you use VA to do the sums.

415v x 15.5a is 6.43kVA - which would be the 'kW' you consume (and pay for) if you take efficiency into account - as others have said (#18).

Hello,

A you mentioned, it is certainly different. Can you kindly once again share the clear view of the name plate showing all the details legibly.

Can you also let me know the type of starting and the type of connection of the motor wdgs.

Thanks in advance

sure, let me try for clear photo, the starting type is dol, connection is delta.