What is the regulation in BS 7671 to size the MCCB for a motor? Is it 1.5 times the motor full load amperes?
Motor MCCB
- Thread starter Loyal1
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don't think you'll find a reg for that.
What makes you think its 1.5x FLC?
What makes you think its 1.5x FLC?
Let me put it this way, what is the general practice to size the MCCB for the motors?
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Are you blagging your way through an industrial installation or something mate?
A breaker for a motor should be above but as close to the nameplate rating as possible, use a type A curve if available, but if not a type B will suffice.
A breaker for a motor should be above but as close to the nameplate rating as possible, use a type A curve if available, but if not a type B will suffice.
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I don't think this guy should be given any answer except "If in doubt consult a qualified electrician".
//www.diynot.com/forums/viewtopic.php?t=226196
//www.diynot.com/forums/viewtopic.php?t=226196
go to college, read lots of stuff to do with electrics, develop a strong knowledge of electrical theory, have a reasonable command of maths, gain plenty of practical experience, then ....
or consult an qualified electrician?
whats actually happening here? Are you trying to do this yourself, are you trying to pick fault with the person who is doing this for some reason?
Agreed, but please explain to me what this forum is all about, and what is the goal of all you guys here?
You need to base your decision on various parameters.
- Use generic type start up currents
eg 3 - 5 x FLC for star/delta starting 7 - 10 x FLC for DOL
Or in the case of more onerous loads manufacturers data for the particular motor and/or equipment.
Some MCCB manufacturers list motors that can be started various ways for their particular breaker sizes
If none of this makes any sense leave well alone otherwise you will have egg on your face everytime the breaker trips out when it starts up !!
EDIT: But by the questions you are asking I feel you are out of your depth and should steer clear
- Use generic type start up currents
eg 3 - 5 x FLC for star/delta starting 7 - 10 x FLC for DOL
Or in the case of more onerous loads manufacturers data for the particular motor and/or equipment.
Some MCCB manufacturers list motors that can be started various ways for their particular breaker sizes
If none of this makes any sense leave well alone otherwise you will have egg on your face everytime the breaker trips out when it starts up !!
EDIT: But by the questions you are asking I feel you are out of your depth and should steer clear
theres a clue in the name of the website - www.DIYnot.com, i don't generally think industrial applications should be carried out as a diy project, do you?
idle away slack periods inbetween questions and answers with architects and engineers, often helping people with easy-to-remedy problems and advising people who are clearly out of their depth to seek the services of a professional before they cause harm to person, property and livestock.
Sometimes gaining a few little tit-bits of information from other professionals amongst us. The witty banter.
All provided without any fees
, good here, innit? What do you think the purpose of this forum is? And what are the details of the task you are asking about?
Are you an electrician?
Can you answer the questions already asked before you go too much further?
Yes I am electrician, and I thought I could consult other electricians on this forum to seek advice. But apparently this is not what this forum is about.
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Buddy, with the greatest of respect, having seen your questions such as "What's the point in measuring EFLI on a circuit protected by fuses/breakers?", we feel that you are not knowledgeable to be embarking upon such sizeable industrial projects.
Besides, this isn't (despite how it may appear) an electricians' forum, it's a DIY forum.
Are you really a pro spark?
it would depend on the motor type and what it's use is..
if it's inverter controlled then next size up from the rating should be fine as the inverter will deal with any overloads and soft starts etc.
if it's for a DOL motor with variable load then 1.5 - 2 x the rating and a thermal overload in the contactor/starter will suffice.
you might want to consider a C or D type breaker dependant on the start up requirements and subject to meeting the EFLI requirements.
if it's inverter controlled then next size up from the rating should be fine as the inverter will deal with any overloads and soft starts etc.
if it's for a DOL motor with variable load then 1.5 - 2 x the rating and a thermal overload in the contactor/starter will suffice.
you might want to consider a C or D type breaker dependant on the start up requirements and subject to meeting the EFLI requirements.
It was even worse than that...
Yeah, right.
How big is this motor? Why do you want to supply it with an MCCB anyway?
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