OP
daiplayer
how the hell do i find a list of cb's/ select them from the OSG ????????? ...or have i just overworked my brain ????????? lol
Discuss Calculating volt drop, cable selection and mcb selection on an 3kw motor in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net
how the hell do i find a list of cb's/ select them from the OSG ????????? ...or have i just overworked my brain ????????? lol
Much respect to you Widdler for putting so much time and effort in. One very small point which doesn't affect the outcome at all. The question said
So wouldn't that mean ref method B [42 from table 4A2?] not ref method C, so table 4D2A column 4 = 1.5mm² carries 16.5A
or am i wrong ?
Selected reference method was C (No. 57).
In questions where it states within building materials, it refers to direct in masonry.
It's all down to interpretation of reference methods, the syllabus I use have in this example gone with the above. But your opinion of reference method B can also be justified.
It's one of the biggest debates I have with my guys.
that q has really baffled me....Is the MCB ratings differnet when talking about 400v/ triple pole ? if so how do i find out which type to use and therefore do the resulting equations become affected ?
Selected reference method was C (No. 57).
In questions where it states within building materials, it refers to direct in masonry.
It's all down to interpretation of reference methods, the syllabus I use have in this example gone with the above. But your opinion of reference method B can also be justified.
It's one of the biggest debates I have with my guys.
Cheers for the reply, on reflection 57 is probs a better fit
I suppose we all have to carry our thermal resistivity meter in our kit as well
Thanks for keeping my brain ticking over!
The question is answered with the exact same approach and formula bar one. The design current (Ib).
With Three phase (400V), we use the following formula:
Ib =Power (P)
√3xUL
Not sure what other posters think but Widdler deserves that for this thread, it was good of you to help that lad out the way you did. Top man
Not sure what other posters think but Widdler deserves that for this thread, it was good of you to help that lad out the way you did. Top man
frozen peas???come on set the sum out clear as ice, peas
how do you get 36.1A for a 3kw motor?
you set sum out for me and paste orig question in too. thank you if you could aint done 3phase before
you set sum out for me and paste orig question in too. thank you if you could aint done 3phase before
is that per phase
Ib -
Ib = Power / SQUARE ROOT of three x Uo = 36.1 A
In = Greater than Ib = 40A breaker
It : = In / Cg = 40 / 0.82 (table 4c1) ......It = 48.78 A
Correct
You've identified Cg, but need to identify Ca. Table 4B1. Mineral, thermoplastic @ 35degrees = 0.93 factor.
Ib = Power / SQUARE ROOT of three x Uo = 36.1 A
is that per phase?
sorry, my fault for not reading all the posts. was going from original thread title 3kw motor. DOH!The question is about a 25KW 400V heater.
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.
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