Garage Lift / Supply

[pjscotland]

Sorry guys I'm completely new here and have been searching the net for an answer to this for days now and cannot find anything suitable so thought I'd come ask the experts direct.

Here's the Background.

I'm currently in the throws of a garage extension to allow me to put in a car lift. I have bought a car lift and it's 3ph electo/mechanical with a 3.3kw motor. I have contacted a drives company and they have advised that I can run this with a digital phase convertor fed from a suitable 32a supply. Now this is where my question comes in.

At present I have a radial supply into the garage fed from a 32a MCB on the main house CU. The armoured cable feeding the garage is 4mm, so far so good ! Inside the garage there is a 5 way distribution board with the various 6 & 20 a breakers in there feeding the ring main in the garage and the lighting circuits, but I need a 32 a supply so here are my 2 thoughts.

1. Can I piggy back the incoming supply at the garage 100a isolator and run another length of 4mm cable in paralell to a seperate 32a switch isolator to feed the phase convertor / lift. That way the lights and sockets in the garage will still be protected via the MCB's in the 5 way distribution board, and the sepperate 32a supply will be protected directly for the 32a breaker inside the main house ?

2. Can I put a 32a breaker in the garage distribution board and simply run 4mm cable from that to the new 32a switch isolator to feed the phase convertor / lift ? I'm not sure if this is correct as technically both the main fuse in the house and the fuse in the garage distribution unit will both be the same rating ?

I should point out that the lift will only be used occasionally and will not be up and down like a ------ draws all day long / every day, and when the lift is in use the only other draw on the incoming cable will be the lighting circuit (6 x 58w fluro's)

Is what I'm proposing possible, or do both options fail into the catogory of bad practice and if that is the case what do you all suggest I do to overcome my problem ?

 

[pjscotland]

I think I'm going to have to up the cable into the garage and replace the breaker in the main CU to 40a.

PITA but what else can I do as I still don't have any firm answers on starting currents etc

 

[High Tower]

The KW rating on the motor is normally the maximum demand, so to include start up currents, as this is the "maximum demand" for the purposes of design currents.

So, change the 3phase motor for a single phase item, a much cheaper option, complete cable calcs to bs7671 to confirm that cable is sufficint for total loading with diversity applied, and consider replacing breaker/(s) on the circuit concerned for type c

also if the ramp is connected at any point to a switch fuse then the fuse will need to be changed for a HRC fuse (High rupture current)

 

[pjscotland]

Sorry High Tower,

Are you saying that if I replaced the 3ph 3.3 kw motor with say a single phase 3 kw motor I will never ever pull no more than 3 kw ?

So worst case senario would be I have my 4x4 on the ramp half way up and I decide I wanted to take it up further I would never see more than the maximum 3 kw ?

I'm no expert, but this is something I'm struggling to comprehend.

 

[High Tower]

Forget single phase and three phase if you currently have a 3.3 hp motor driving the ramp which is geared then swapping it out for a 3.3hp single phase motor will do the job exactly the same and will be cheaper and consume less current than a phase inverter only difference is for instance a 3kw motor single phase will pull a touch over 13amps and a 3 phase of same wattage will pull 7.5 amps so a single phase motor will still output the same hp which is what. Is required to drive the gearing in the ramp regardless of weight as the ramp will be designed to lift a certain tonnage with that amount of hp

 

[davelerave]

I think I'm going to have to up the cable into the garage and replace the breaker in the main CU to 40a.

PITA but what else can I do as I still don't have any firm answers on starting currents etc

hey i connected a few car lifts lately-you'll prob need just 'C' type sized according to motor hp/kva

as already said OCPD and cable are sized according to FLA

as far as starting current/kva goes motor should start at 90% of rated voltage and may start at 80% of rated voltage -so that's 20% VD max during startup or thereabouts