3 phase supplies for table & band saw

[Marine electrical fitter]

Hi all,

I have been asked to install individual three-phase supplies for a band saw and table saw.
Having trouble figuring out the correct cable / breaker sizes required (I’m a marine electrical fitter and it’s been a long time since doing this sort of works).
I currently have an Eaton memshield three-phase distribution board, 415V with 100A main switch.
Length of run to the saws is approx. 50m.
Band saw is 415V 3p+E 1.1kW.
Table saw is 415V 3p+E 3.5kW.
Each come with a 16A red 4 pin plug on 2.5mm 4 core braided cable.
Was considering using armoured cable clipped direct to the wall to an individual RCD protected industrial socket outlet with isolation.
Any advise on what I’m missing / formulas and calculations required would be much appreciated.

 

[Spoon]

Welcome to the forum mate.
Calculate the max amps current draw for each item.
Select an appropriate breaker for each item. Or look in the manuals and see if they suggest a size.
Then pick a cable size/type for each breaker. Take into account installation method, voltage drop, grouping factors (if applicable), environment...ect... the usual stuff.
Don't forget Part P. As they are new circuits then this work is notifiable.

 

[brianmoooore]

If the plugs are staying on the tools, you're not installing a table saw and a bandsaw, you're installing a couple of 16A 3 phase sockets, and the calculations should be for those sockets.

 

[davesparks]

16A sockets would be best served by a 16A MCB's.
If the machines are supplied with 16A plugs fitted then you can only assume that is what theanufactirer intends for them to be supplied by.

Overload protection will be provided within the motor controls inboard the machine.

 

[brianmoooore]

16A sockets would be best served by a 16A MCB's.
If the machines are supplied with 16A plugs fitted then you can only assume that is what theanufactirer intends for them to be supplied by.

Overload protection will be provided within the motor controls inboard the machine.

Only thing to be decided is 16A type B, C or D.

 

[Spoon]

16A sockets would be best served by a 16A MCB's.

If the items don't pull no were near 16A then is there much point in sticking in a 16A breaker and cable sized for it?
As long as the supply is no bigger than 16A then the socket will be ok.

 

[brianmoooore]

A 16A socket is a 16A socket. The design has to accommodate whatever someone else decides to plug in there, long after the table and bandsaws may have gone.

 

[Rockingit]

If the items don't pull no were near 16A then is there much point in sticking in a 16A breaker and cable sized for it?
As long as the supply is no bigger than 16A then the socket will be ok.

Given the wide availability of 16/3 devices, lack of challenging cable sizes... I can't seen any compelling argument for making life hard and trying to go smaller!

A 16A socket is a 16A socket. The design has to accommodate whatever someone else decides to plug in there, long after the table and bandsaws may have gone.

Agreed!!

 

[Fazz711]

As said.
You are installing 16A sockets.
You have to cover them in the design process.

 

[davesparks]

If the items don't pull no were near 16A then is there much point in sticking in a 16A breaker and cable sized for it?
As long as the supply is no bigger than 16A then the socket will be ok.

Yes you could use an MCB sized more closely to the load, but the savings are unlikely to be very much.
The advantage of making it a 16A circuit is that you can easily plug an alternative machine into it without having to alter the circuit.

 

[davesparks]

A 16A socket is a 16A socket. The design has to accommodate whatever someone else decides to plug in there, long after the table and bandsaws may have gone.

As said.
You are installing 16A sockets.
You have to cover them in the design process.

There is no requirement for a socket to be fed from an OCPD equal to its rating, as long as the OCPD is not greater than the socket's rating it is fine.

It is quite common in the entertainment industry to find 400A outlets fed at 315A.

 

[loz2754]

It's unlikely Part P will apply, as I doubt this is in a dwelling.

 

[Lucien Nunes]

As above, consider them as generic socket outlets, but there's no harm in doing a sanity check of the three factors would typically make it worth considering the specific loads expected to be plugged into them. One is when they make up a fair chunk of the available supply to the DB and you need to start looking at design load and diversity. For a couple of 16's on a 100A DB, not so relevant.

Another is if the cables are especially long and voltage drop is a limiting constraint. With motor loads the starting current is relevant, you don't want machinery with induction motors that struggles to start against load because starting current wasn't taken into account by the installer of the generic 16A sockets. But even for a 3.7kW motor (aka 5hp) the FLC is 8A or so, giving you 100% overload within the design VD of the socket circuit, and saws don't normally start against load. So if the circuit is specced for 16A it should be fine for the table saw.

Then on a related note, whether you need C- or D-curve protection to prevent tripping on starting currents and whether this pushes you up a cable size to achieve the necessary Zs. I would protect with C types by default, unless there was a major cost issue with the cable and the nature of the expected load really didn't demand C's. No reason to think you would have any issues with C here, for the same reason that the FLC is only 50% of the In anyway.

 

[Spoon]

It's unlikely Part P will apply, as I doubt this is in a dwelling.

Something for the OP to confirm. The machines are not partially big so I was thinking they may be part of a small workshop attached to a house, as a hobbyist.

 

[Rockingit]

It is quite common in the entertainment industry to find 400A outlets fed at 315A.

Get around the provincial venues and you'll regularly find PLOC outlets fused at 200!