Three Phase!!

[scotteng]

hello all!!
I have never touched 3 phase before, never had any training and have little knowledge...so tend to stay well clear!

Just out of curiosity, i was asked today to quote for running a new 3 phase circuit from a 3 phase board to accomodate a 3 phase fryer! I declined to quote as im not competant in that area, but it did make me think what cable would you use for 3phase?? running from the board to the appliance, ive only ever seen 5 core cable in swa...is that whats used??

cheers!

 

[seasickstevie]

...I have never touched 3 phase before,

Best not

 

[electronicsuk]

Three phase has been discussed to death on here many times, so I'll keep my answer short. It's possible to use 3-core to carry L1, 2 and 3 for balanced loads such as motors where no neutral is required, then earth via the steel wire armour.

If you move up to 4-core, this will give you enough cores for the three phases plus neutral for unbalanced loads, or alternatively you could use it with a balanced load and use the remaining spare core as an earth in tandem with the armour.

Obviously, 5-core will get you L1, L2, L3, E and N.

As you say, it's almost always some variety of SWA or SY, singles in conduit/trunking, or busbar systems used for distributing 3ph.

 

[briwire]

If you were to do the job, you need to see how many conductors the appliance requires. 3 for just 3 phase or 4 if a neutral is also needed. Many electricians also prefer to use a 5 th core for a good earth rather than rely on the armouring and its terminations.

3, 4 and 5 core SWA is readily available and is treated the same as with single phase. The restrictions are the environment, temperature etc that will determine the final cable to the appliance.

 

[Lectrician]

The installation method would depend on many other considerations, not just if it is three phase or not.

You would likely install the circuit in the same way as the other circuits on the kitchen, if these have been done correctly.

PVC conduit and trunk is not uncommon in commercial kitchens. (not mmt2 type stuff!).

SWA could be used.

I would always run a neutral, even if the appliance only needed the three phases. It is there for the future. A frier will typically require a neutral anyway - the elements will typically be wired in a star configuration, and a neutral is required (although would work with out, you would still generally connect the neutral).