Calculate 3 Phase MCB size

[dtec dave]

Hi..I should probably know this but don't do too much 3 Phase stuff!!

Can anyone give the formula for working out the size of a 3 phase MCB?

I have a 12kw 3 Phase fryer to install.

Cheers

 

[loz2754]

12kW divided by 3
Divide result by U⁰ (230V) to give amps per phase

 

[loz2754]

 

[dtec dave]

So further to this, I need to calculate the cable size for a 40amp 3 phase MCB. Do I just base it on the CSA per phase i.e 6mm?

 

[Spoon]

So further to this, I need to calculate the cable size for a 40amp 3 phase MCB. Do I just base it on the CSA per phase i.e 6mm?

In a way. There are differences. E.G. if you look at Table 4D4A you will see that for a cable clipped direct, the max current is 49A for single phase but 42A for 3 phase.
All other installation criteria's have got to be taken into account as well.

 

[westward10]

Where have you got 40A from.

 

[dtec dave]

Where have you got 40A from.

40 amps to supply 4 way board.

Way 1 12 kw Fryer..3 phase 16 amp mcb (Thinking diversity will bring it below 16amps)
Way 2 6 kw Grill...3 phase 10 amp mcb
way 3 L1 16 amp socket circuit
L2 10amp for 2.2kw water heater
L3 Blank
Way 4 L1 Blank
L2 6 amp Lights
L3 16 amp socket circuit

I'm really struggling for power as the site is maxed out so can't go over the 40 amp 3 phase supply.

Hope the above looks ok...someone will tell me if not. Just at planning stage at mo.

 

[westward10]

I see never realised this was all being considered from your first post. The fryer is 17-18A and should be on a 20A device.

 

[telectrix]

total oad estimate including sockets is c.25kW. split ove 3 phases this equates to 8.3kW per phase, assuming loads are closely balanced. c. 36 A per phase, so 40A per phase should just cope.

 

[Strima]

I'd look at moving some loads off L3 onto L1 depending upon the load balancing at the supply.

Although the fryer and grill are high loads once up to temperature this will drop as they start cycling through heating and cooling.

What sort of lighting is installed? I doubt it would be 6 amps, I'm guessing a small commercial kitchen so probably a couple of floro tubes and other lighting so around 2 amps.

What loads are plugged into the socket outlets?

Is the eater heater instantaneous?

 

[dtec dave]

In a way. There are differences. E.G. if you look at Table 4D4A you will see that for a cable clipped direct, the max current is 49A for single phase but 42A for 3 phase.
All other installation criteria's have got to be taken into account as well.

I'd look at moving some loads off L3 onto L1 depending upon the load balancing at the supply.

Although the fryer and grill are high loads once up to temperature this will drop as they start cycling through heating and cooling.

What sort of lighting is installed? I doubt it would be 6 amps, I'm guessing a small commercial kitchen so probably a couple of floro tubes and other lighting so around 2 amps. Yes, just a couple of led strip lights, 8 led lamps and 2 emergency lights

What loads are plugged into the socket outlets? Just hand held kitchen appliances, fridge, freezer etc

Is the eater heater instantaneous? No, under sink 10l heater