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cable size & breaker capacity

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mommu79

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can any one help me to select a cable size & breaker capacity for the instalation of a new cnc automatic drilling machice,
rated power is 3*380v ac + pe , 60 hz with 100 A slow fuse rating.
 


Hello mommu79,

what is the power of the Motor?

I look for my data chart. Slow blow up fuses are use for 40kW motor power with direct starting or for 50kW with star / delta starting connection.

Motornennströme.jpg
Datasheet © by Klöckner Moeller, Bonn; Schaltungsbuch 1964

Here look for the datasheet or the specification plate of the machine. So you find the power for the breaker capacity.

For this current you need a cable size of 25mm² for each wire. If it is a long line better you use 35mm².

regards

Rainer
 
Hello Mr.rfredral, Thank u very much for your reply.From the chart i got an idea about the fuse rating.for the cable,actual required length is 17 meters,so as you advise better i will go for 35mm².
Also please help me,that the customer is requesting to fix one breaker in the main distribution board and other near the machine,tell me weather it is advisable to have the same rating breaker ?
 

Hello mommu79,

for a cable length of 17 meteres you can use 25mm². Only if it is going up to 50 m or longer the use 35mm².

Two circuit breakers in series is not good. Put a circuit breaker with 100 A slow blow fuses in the main distribution board and a safety disconnection switch near the machine.

For example, like this one.

**broken link removed**

I show you this products from Moeller & EATON, because it is the well known firm here in Germany. Maybe you can find a contact in your country here.

Regards

Rainer
 
If fuses for rated current are wanted near the machine for some reason, higher rated fuses can be installed in the power distribution, because they don't need to provide overcurrent protection, only short circuit protection.
 
FvM said:
If fuses for rated current are wanted near the machine for some reason, higher rated fuses can be installed in the power distribution, because they don't need to provide overcurrent protection, only short circuit protection.
Click to expand...

why aren't we consider voltage when we are near the device
 

Hello FvM,

ok, you can put two circut breakers in series, but then the first one must be 1,6 times more then the second one. So, when the second one is 100A the first must be 160A.

With a cable of 25mm² the max. current ist 125A. So a short circuit will not blow up the fuse of 160A only the cable. :evil:

This was the reason, why I wrote to use only one breaker and a switch.

This was the problem, when I make the installation of my workshop. The way from the main distributions board to my workshop is 50m. I need 25A here. so I must set the fuse in main distributions board to 35A. Therefore normaly 4mm² cabel is necessary, but about the voltage dropping I must need 6mm².

Regards

Rainer
 
With a cable of 25mm² the max. current ist 125A. So a short circuit will not blow up the fuse of 160A only the cable.
Click to expand...
A fuse of 160A will provide suffcient short circuit protection in most cases (certain condition regarding grid impedance and cable length have to be checked). The cable between the power distribution and the overcurrent protecting fuse must not involve connectors or T-junctions in this case. See DIN VDE 0100-430 respectively IEC 60364-4-43.
 
Re: cable size & breaker capacity

Can any one provide me a chart for cable sizes & their capacity,it will be helpful for me to install other machines..

- - - Updated - - -

also pls be informed that right now we dont have supply from electricity board,we are going to use generators only,so the above mentioned capacity will also suit the generator power or some modifications has to done ?
 

Hello mommu79,

here I give you a chart for cable sizes and the fuses you need. Please use "Gruppe 2".

Kabelbelastung.jpg
Datasheet © by Klöckner Moeller, Bonn; Schaltungsbuch 1964


Regards

Rainer
 

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