Machines and motors 3 phase. can someone help me with my calculations please.

[michaelw6]

Hello guys, and girls.
Here's the issue!
I am installing a new milling machine into a factory, the machine is specked at 32a 3 phase.
more info suggests its a 7kva machine with a 75a surge and 20kva.
so Ive calculated its basically a 5.6kw 10.64a running and 16kw 30a surge. thus the 32a mcb.

The confusion started when they were going to connect it to an existing 32a supply already installed but upon further investigation i found, yes it was a c32 and 32a isolator but the singles in the trunking were 4mm.
Now by my calculations over a 50m run this should never have been 4mm not in singles more like 10mm??
If i do a cable calc on swa armored it said 4mm (I'm using cable mate to do the calcs as its been a while since ive gone old school) now should i just rewire in a 4mm armored clipped direct?.
The cable size in the singles goes up due to the amount of other circuits in the trunking.
Ive always been taught to go worst case scenario, but am i charging the customer to install a cable that is not required?
Maybe its that the surge does not last long enough to worry about?!
Any help much appreciated but if i cannot get a final solution think ill go with my gut and put in the armored...

 

[telectrix]

what was running on the 4mm singles before? KW/current rating?

 

[michaelw6]

Un sure there was nothing there when i got there.
it may be old. the building and wiring is about 20 years old.

 

[telectrix]

darkwood is your best bet with this, but 7kVA is nowhere near 32A, more like 15A. are you sure they are not referring to 32A OCPD?

 

[michaelw6]

sorry thats 7kva running
20kva surge
who or whats darkwood!!

 

[Darkwood]

Your understanding of inrush for the motor and MCB ratings is wrong, firstly I assume the whole machine may have a KVA rating of machine, you calcs in you opening post don't make sense tbh so my questions are:-

Where are you getting the KVA rating from and the Surge rating (Inrush I assume you mean here)?
What is the rating of the main motor in KW or HP (motors are not given in KVA)
Is the supply to the machine direct - IE... not to socket outlet or has any means of been unplugged and used for other equipment?
Why do you believe it requires a 32amp (c) - and what brand is the mcb?

A few just to get the ball rolling?

 

[telectrix]

sorry thats 7kva running
20kva surge
who or whats darkwood!!

that ^^^^^^ is darkwood, a knowlegeable bloke on motors ^^^^^^.

 

[michaelw6]

ok.
the info i have is from the manufacturer.
they said 32a mcb required.
the info they faxed over said
75a surge 20kva
7kva running.
thats all the info i have and that its a
ymt goodway gls200

 

[netblindpaul]

ok.
the info i have is from the manufacturer.
they said 32a mcb required.
the info they faxed over said
75a surge 20kva
7kva running.
thats all the info i have and that its a
ymt goodway gls200

Is it one of these?
GLS200 - YMT Technologies

 

[Darkwood]

Ok .. seems the manufacturer doesn't understand the info' thats sometimes required but going on what they have given we will guess at a 5.5Kw motor, if its a standard induction motor then we would be looking approx 10-11amps FLC. Been a small milling machine this is really all I need to say a 32amp (b) or (c) will surfice (taken from a Schneider trip curves for motor inrush), if your Zs is comfortable then opt for the type C.

As for you cable query - if this is a dedicated load and only supplys the machine you can assume the machine is a fixed load of say 15amps to be on the comfortable side so class your supply cables as ommited for O/L protection and see with standard cable calc's what you get - check if possible by onsite measurement that your Zs value complies to the mcb you wish to use, Remember you could use a type B but mcb manufacturers may vary in there recommendation for motor to mcb rating plus we are assuming the motor is a 5.5kw ( Check with the company ).

 

[netblindpaul]

DW,
If it is the machine that I have linked to, then it has Fanuc drives.
It will therefore have a step down Tx. these damn things are a stupid pain in the arris.
Forget the machine rating, they have such an inrush that even a D type of the right rating for the Tx won't hold, trust me, I have the T-Shirt!

 

[Darkwood]

Looking at the link here and if indeed Netblindpaul has the correct one then the info you gave is incorrect, it may be the case that full load of machine is 32amp with an 11kw motor - I think before you go any further we need to establish which model and size you are getting and download the spec for it.

 

[michaelw6]

well the supplyer said 32a.
cable calcs are ok if done on a 16a mcb?
im pritty sure though the mcb will not hold on a 16amp. we had an issue last year if i recall with one of there other machines brought over from there other factory having thi issue.

 

[michaelw6]

that is the model on the spec sheet indeed.

 

[michaelw6]

the suppliers were not helpfull at all it was several phone calls and faxes to get this info out of them!

 

[Darkwood]

DW,
If it is the machine that I have linked to, then it has Fanuc drives.
It will therefore have a step down Tx. these damn things are a stupid pain in the arris.
Forget the machine rating, they have such an inrush that even a D type of the right rating for the Tx won't hold, trust me, I have the T-Shirt!

Yep just posted and seen it, had fun myself with these but were drive controlled and wound for 100hz so for the OP I have to agree and say the advice given is likely incorrect given the new info.. A good chat with tech' of the supplier is the best bet here.

 

[netblindpaul]

OK, mistake 1, it is NOT a milling machine!
It's a LATHE.

Next, forget the machine ratings, you need the interposed Tx rating.

DW, the Fanuc's are 230V 3ph, 50Hz normally, it's the Tx inrush that is the killer.

 

[netblindpaul]

Oh & supplier tech will only be able to recite the OEM spec, they will have no clue, these guys have no clue about BS7671, I used to be one.

 

[michaelw6]

we have rang and spoken to a few different people but like i said this is all the info i got.
netblindpaul, they said the surge presumably inrush was 75a 20kva 380v
I will try again tomorrow to call and ask for the "interposed Tx rating"
see what they say.

 

[netblindpaul]

Well there is a clue in your last post 380V, we don't have 380V in the UK.
It's not the Tx rating only you need, you need the full spec, rating, LCRZ, and the other parameters so be able to calculate the inrush.
I made this mistake once, only once, I fitted a D type sized to the Tx. rating, never again.
I ended up with a D type 2 or 3 ratings above the Tx draw.
That was a mess.

 

[michaelw6]

update: the customer spoken to the supplier and no joy they have to find out as they dont supply details like that?! FFs how hard is this gonna be!
think im just gonna spec for a 6mm 5c armoured 30m run on a 32C europa is the consumer unit. if it keeps tripping i can refer to the supliers last email they spec the 32a supply.
thinking if i go one bigger on cable size just incase. cannot do no harm.