Calculating volt drop, cable selection and mcb selection on an 3kw motor

[daiplayer]

If your talking about load balancing over phases.....then....Yeah...kind of...but that would be in the inititial design of the heater itself......not considered during the heater installation...

Seeing as it a three phase supply...You consider that the load in q has already been balanced by the Maker of it.

Installers may need to consider balancing when installing single phase items...into a premesis that uses/ are provided by three phases...( ie,, three single phase (identical heaters) would be installed on a phase each ?


Correct me on this if im wrong though guys..

 

[daiplayer]

Correct



You've identified Cg, but need to identify Ca. Table 4B1. Mineral, thermoplastic @ 35degrees = 0.93 factor.

Dammit...i had tha to start !!! ....then changed my answer cos i thought it would fall between the bracket ( 30 - 70 degrees ?)

 

[pushrod]

Ib = Power / SQUARE ROOT of three x Uo = 36.1 A

is that per phase?

The 36.1A figure is the design current for each line (L1, L2, L3) it is not a total value that is then shared between 3 cables if that is what you are asking

edit : you have to be a little careful with terminology because the phase current (Ip) only equals the line current (Il) when connected in star. If in delta, as it would most likely be in a motor, then Il = √3* Ip

When designing for cable size it is just the line current that you are interested in.

A complex subject (which i am rapidly forgetting) but just to be aware that phase current and line current are slightly different and are not always the same value.

 

[telectrix]

The question is about a 25KW 400V heater.

sorry, my fault for not reading all the posts. was going from original thread title 3kw motor. DOH!

 

[daiplayer]

The 36.1A figure is the design current for each line (L1, L2, L3) it is not a total value that is then shared between 3 cables if that is what you are asking

edit : you have to be a little careful with terminology because the phase current (Ip) only equals the line current (Il) when connected in star. If in delta, as it would most likely be in a motor, then Il = √3* Ip

When designing for cable size it is just the line current that you are interested in.

A complex subject (which i am rapidly forgetting) but just to be aware that phase current and line current are slightly different and are not always the same value.

Much better explanation than mine...

 

[i=p/u]

il get there someday

 

[daiplayer]

il get there someday

You in training are you ?

 

[Dan]

Just bumping some threads in the Electrical Wiring Theories and Regulations forum category here on our Electricians Forums. If this specific topic isn't current, just ignore it, it'll drop off the list in no time. However, if it's something you'd like to contribute to, feel free to reply and bring it back into current discussion.