15 KW motor to connect

[Bright.Spark]

I just got a job to connect a 15 KW motor up. The run is 40 meters and to my calcs I could get away with 6mm armoured but that's with a volt drop of 9.6 volts! Just after a few opinions as to if I should run the 6mm or just go for a 10mm? The cable will be clipped direct. Cheers fellas.

 

[Guest123]

Is this a single phase motor??? also what is it for???

 

[Bright.Spark]

Oh sorry its a 3 phase motor. Its for a compressor.

 

[lamb]

Take into account pf and starting characteristics for the cable and switchgear

 

[Guest123]

Ok so working out 3 phase current is slightly different to single phase


The calc is P/(V x root3 x power factor)

which gives in your case 15000/(400 x 1.732 x 1) (assuming a power factor of unity although around 0.85 is more accurate

= 21.65A per phase. Even at 0.85PF it's only a shade over 25A.

So your cable needs to be able to carry a minimum of 25.65A under it's normal service conditions, assuming 0.85PF.

I would use 6mm SWA protected by a 32A C curve MCB.


Edit....in addition your max VD would be 5% of 400V = 20V, so your 9.6V is fine.

 

[Bright.Spark]

Cheers lenny, thanks very much mate. That's my first job of this week ready.

 

[benji]

what type of control gear (starter) have you got?

yours benji

 

[Bright.Spark]

Its a compressor. It already has a flex coming out of it with l1 l2 l3 and an earth so all the starter is internal. I'm just gona run the cable and put an isolator up.

 

[lewlec]

Its a compressor. It already has a flex coming out of it with l1 l2 l3 and an earth so all the starter is internal. I'm just gona run the cable and put an isolator up.

hi
if you do end up connecting it up make sure you check the rotation of the motor, when i first started i did a similar job to yours and when i ran the compressor it all worked great untill the fly wheel came flying off causing £100 worth of damage!...gutted. hope this is of use to you

regards
gary

 

[Des 56]

hi
if you do end up connecting it up make sure you check the rotation of the motor, when i first started i did a similar job to yours and when i ran the compressor it all worked great untill the fly wheel came flying off causing £100 worth of damage!...gutted. hope this is of use to you

regards
gary

Going off the thread a little so excuse me


Now that is some sound advise for trainees and some sparks who rarely touch 3 phase jobs

It should be written into your brain as essential things a spark should remember to do


If you dont wire and connect 3 phase motors and want to be assured if you did so ,a little question for you
What would you do if it was reversed?

 

[Sintra]

Good point.

 

[chris gray]

ive done very little motor work, but am going to give an answer and see wether im right or wrong and in return learn.
would i rotate a pair of phases? swap l1 and l2 over? would i do this at the motor, isolator or the board?

 

[Bright.Spark]

Fellas it was a nightmare today lol. Firstly the 32Amp C breaker kept tripping so I rang the manufacturer and they said I needed at type D! By this time it was 4 o'clock and I was giving up hope. Luckly a wholesaler came through and I quickly connected it up to my horror I found that the compressor was running the wrong way! I read the instructions and it said that an LED will come on if the motor is in reverse so I left the motor for 2-3 mins and the nosie wasnt better so I shut it off and rang the manufacturer where they told me the LED dont work and I should never believe screen readouts. Luckly the belts had come off the pulleys so there was no major damage but just be warned anyone connecting a compressor, if you think the rotation is wrong then stop the motor and try the other way! All sorted now thank god!

 

[Guest123]

Got it sorted though...happy days.

Good learning curve...if a little steep.

 

[lewlec]

hi

glad your sorted... dont u just hate it when things like that happen!

regards
gary

 

[mechelec]

Fellas it was a nightmare today lol. Firstly the 32Amp C breaker kept tripping so I rang the manufacturer and they said I needed at type D! By this time it was 4 o'clock and I was giving up hope. Luckly a wholesaler came through and I quickly connected it up to my horror I found that the compressor was running the wrong way! I read the instructions and it said that an LED will come on if the motor is in reverse so I left the motor for 2-3 mins and the nosie wasnt better so I shut it off and rang the manufacturer where they told me the LED dont work and I should never believe screen readouts. Luckly the belts had come off the pulleys so there was no major damage but just be warned anyone connecting a compressor, if you think the rotation is wrong then stop the motor and try the other way! All sorted now thank god!

most three phase equipment will have an arrow on a pulley to show correct rotation check before running. I always try to find this and flick the starter to check rotation. Some large compressors and other equipment will be wrecked running in reverse. most submersible three phase pumps have an arrow to show the direction the pump will try to turn (reaction direction) when the starter is momentarily flicked.