Unless you have figured out a different way of working it out...clearly you need to take into account pf but the MCB would be sufficient for taking that into account anyway.
Why would you put it on a 32A breaker FFS...?? rate the protective device properly, that is why they are typed!!
Its from the tech' tabulated tables from Schneider with regards to inrush currents and there mcb's fitting the mcb you suggest will invariably give nuisance tripping maybe only occasionally but in design you should avoid this and i for one would rather use a mcb rating calculated by the manufacturer of the mcb than a crude general theme of type C for motors and type D for transformers ...i often have type B's on motors without issues by using the tabulated manufacturers guidelines so zs can be achieved when meeting it can be problematic if using C or D. Lastly how can power factor be accounted for in mcb design its too much of a variable and would mean the time curves would be inaccurate - bad pf will see more current drawn to do same work and mcb's are monitoring the current so you lost me on that comment...so yes PF is vital to correctly choosing your mcb and when needed should be in your calculating. If the PF was already accounted for then why do we have a 1.8 factor when calculating inductive lighting...... well part of that factor is to allow for the PF below unity associated with inductive lighting as well as control gear loses and possible harmonics which can add to current drawn.
DW, A properly designed circuit that was installed as per design would not require a 32A MCB, properly calculated the MCB would be at a sufficient rating to give O/L protection, fault current protection and comply with disconnection times whilst still accounting for inrush currents.
With regards the pF, my comment related to the fact that using a C or D rated MCB would account the the vagaries of variable pF caused by the operation of the machine and fluctuations on the supply that impact it. Clearly if I was designing a circuit from scratch for this this installation i would find out the stated pF from the machine manufacturer and then design the circuit correctly taking into account the length of run and all other factors that would determine cables sizings etc to ensure full 7671 compliance.
I will agree to disagree here, when using mcb's on motor circuits manufactures guidelines must be referred to to ensure nuisance tripping is not ever going to be an issue due to inrush.... and with said compressor been a fixed load and as long as you dont fit it as a plug and socket arrangement the the cabling can be wired as per load and cable calcs and the mcb can overrate the ccc of the cable meaning no additional costings and would still fall within the BS7671.... the number of times ive corrected others installs because the mcb's are nuisance tripping because they stuck basic calcs and believing that the mcb only need be rated the next size up and typed as a (c) in the case of a motor. It dosn't work like this as the trip threshold of the next size up mcb is often too low regardless of type fitted....this is especially the case with compressors as they start on load.
Just with regard to accommodating the power factor of the motor, it might be a consideration that the PF improves significantly as the motor load increases so with a variable load the run current may increase but the energy consumption in kVAr would increase somewhat less.
I see your point Marvo but by habit and also leaving no room for error using the stated PF is the safe option for me, the only issue here on MCB is the trip threshold is variable i.e. a type C would be between 5 to 10 times In so when designing for a motor you should always use the lowest value, 5 in this case and with a standard motor taking up to 10x cuurent on start up then usually you can only guarantee no tripping either fit a type D after confirming it wont also trip or increase MCB rating which usually allows for a lower type.
Merlin range dont recommend you fit type C for motors and only type D unless you refer to their tables of increased mcb rating ... It really turns all the 'what you learned at college on its head' well nowadays it does they still teach them type C for motors and type D for transformers.....wish it was that simple.
I will agree to disagree here, when using mcb's on motor circuits manufactures guidelines must be referred to to ensure nuisance tripping is not ever going to be an issue due to inrush.... and with said compressor been a fixed load and as long as you dont fit it as a plug and socket arrangement the the cabling can be wired as per load and cable calcs and the mcb can overrate the ccc of the cable meaning no additional costings and would still fall within the BS7671.... the number of times ive corrected others installs because the mcb's are nuisance tripping because they stuck basic calcs and believing that the mcb only need be rated the next size up and typed as a (c) in the case of a motor. It dosn't work like this as the trip threshold of the next size up mcb is often too low regardless of type fitted....this is especially the case with compressors as they start on load.
And do you know how many motor installs I have done in the last 32 years...I work with motors continually, and most a lot higher rated than 5.6kW and I have never had any issues with using Type C or D MCB's when the calcs have been done with accurate information. I am used to dealing with motors that start under load that make the 5.6 spoken of seem like the piggy back starter. Your also likely forgetting that at this rating I would think the starter will be YΔ. As for your satisfaction of over-rating the CC of the cable..on that we will have to disagree because I will never agree with that being satisfactory or acceptable.
And do you know how many motor installs I have done in the last 32 years...I work with motors continually, and most a lot higher rated than 5.6kW and I have never had any issues with using Type C or D MCB's when the calcs have been done with accurate information. I am used to dealing with motors that start under load that make the 5.6 spoken of seem like the piggy back starter. Your also likely forgetting that at this rating I would think the starter will be YΔ. As for your satisfaction of over-rating the CC of the cable..on that we will have to disagree because I will never agree with that being satisfactory or acceptable.
Well this says it all you are clearly a man stuck in his own ways and if it not your way then its wrong.... firstly the compressor has its own overload protection so how the hell can an over rated mcb to the ccc of the cable be an issue.... this is why they introduced this regulation to save the wasteful costs of larger cables.
I also have spent many decades doing motor supplies well above the example the OP gives and what concerns me here is you think that star delta affords you a lesser rating of mcb which you are incorrect the spike from the change over from star to delta means you must treat the mcb rating the same as if it was direct on line ..... i realise you picked your name as outspoken on here but look at the evidence so far you have been re-educated on numerous occasions so far but you seem to be a little stubborn to accept it. Im not pulling you for a debate im pointing out when i think you are wrong and im not by far the Mr know it all and will accept when im wrong and hold my hands up but from you joining this site i see you find it difficult to accept if you may be wrong.... wouldn't surprise me if you have been kicked off other sites as usage of terms like ffs etc etc show a short temper and a intolerance to differing opinion.
Please dont get me wrong i believe you are well educated and good at your job from your posts but you come across as a bloke who refuses to be wrong..... from the opening on this debate your calcs disagreed with the OP motor plate and you got sarcy then edited about PF then you refute the use of a 32 amp mcb when im quoting from schneiders own tables which was the mcb brand you recommended, then you have a self opinion of the regulation regarding omiting overload protection of a fixed load just because you have never factored it into your designs yet it used often on large scale project to save costs on fixed motor supplies and even stated for it use on motor circuits in the IET guidlines to circuit design. I can only say if you have a problem with this regulation take it up with the IET and stop throwing your negative opinions about it in numerous threads where its completely acceptable to apply it (yes ill agree domestic isn't really a place for it but it can be applied in certain circumstaces).... .
I sit back on new members with who give a lot of input to assess them and realising your character i only contradict you if i can give good back-up but yet this still seems to not change your opinion if you are unwilling to be flexible and accept contradiction without a negative response or a derogatory comment you are in my books a lost cause stuck in your ways. Ive given responses on this thread and can back everyone of them up with Spec's, tables ill happily forward regarding trip thresholds and mcb recommended ratings... like it or not they are in black and white and IMHO over-rule any of your responses.
Don’t apologise to me. It’s funny watching the squabble going on. All I can say is I’m glad neither of you worked on our MCC’s. Nothing would be working.
With respect Tony your MCC's are a whole different ball park and mcb's wouldn't be a suitable upfront device to start with as would the motors i normally fit (30kw+) this little debate was only with regards to the OP set-up.
Don’t apologise to me. It’s funny watching the squabble going on. All I can say is I’m glad neither of you worked on our MCC’s. Nothing would be working.
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