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 ?

 

[benji]

What,s the cable route length from c/u to garage c/u &what type of route ie underground or what?

but i think your looking at a new cable

yours benji

 

[pjscotland]

Total length from house cu to garage cu would be in the region of 15m.

It is buried

 

[DiscoDave]

you will be looking at a new cable and it will have to be a good size for your 32A supply as you are planning on a phase inverter.

Have you already got yourself a phase inverter or indeed priced them up? they are not cheap! You do have a few options, if it is a hydraulic lift the cheapest option is to replace the pump motor for a single phase one, even if it's a cable type you might be able to change the motor but this would probably end up being bigger and need more current to spin the load.

On the other hand once the inverter is bought, installed and commissioned you then have the world of three phase power tools open to you. your advantage here being that a lathe or milling machine that may not be up to spec for modern manufacture may be of use to you, and a good price as the three phase tool market is fairly limited to industrial buyers!

 

[pjscotland]

I've been quoted £500 for the invertor, but now it looks like a new supply cable into the garage so the price looks like it keeps going up.

Maybe I'm approaching this all wrong, maybe I should be looking at a 3ph installation either direct from the leccy board as the main pole feeding the neighbourhood is just 30m away in the back field or alternatively just looking to get a cheap 2nd hand 3ph diesel gennie as I will only be using the lift sparadically.

Anyone know what size kva gennie i would need to run a 3.3kw motor allowing for starting current etc ?

 

[DiscoDave]

cheap second hand genny may be more the ticket, can't help with the calcs tho i'm affraid!

 

[mogga]

as its only requiring power to move and it will be infrequent IMO Id go with a genny Im assuming this isnt going to be a profesional garage and will be used part time? 3ph gennys arent as expensive as a leccy board 3ph(If they wuill give you one )

 

[pjscotland]

I can basically pick up a 6kva genny for about the price of the invertor (approx £500) but is 6kva going to be big enough or do i need to take into account starting currents and will I need to be looking at 20kva and then the price really starts to ramp up to well over a £1000 ?

I basically don't know enough about genny sizing, and how stop / start motors effect the sizing.

I already set the ball rolling with the leccy company so as the quote will cost nothing I may as well persue that avenue at the same time

But I agree, with the limited use a genny would probably be the cheapest option if I don't need a huge one, if I need a large genny due to starting currents then I may need to look at other ideas which are presently
a) the use of a gearbox and smaller rated motor
b) using a hydraulic motor and running that off a small 240v single phase Power pack

All the same any idea's are always welcome so please keep them coming as right now I'm gutted that I can't get this to work with my current set up

Paul

 

[High Tower]

I've done these before just change the motor to acsingle phase

 

[pjscotland]

The motor is 3.3kw, how do I run siomething that big off single phase ?

 

[High Tower]

its not about total wattage its about HP, what hp is the three phase motor?, And more to the point 3.3kw is just shy of 15amps so shouldnt be a problem

 

[pjscotland]

The motor is stamped 3.3kw, which through conversion equals 4.4 hp unless I'm missing something here, like I say this is all slighty confusing to me.

 

[High Tower]

Remove the exsisting motor on top of the ramp post, and replace with something SIMILAR to this CMG Single Phase Motor - 3.0kw 4 POLE - CS/CR - MTC [M2400300-MTC] - £292.60 : Single Phase Electric Motors | Three Phase | Electrical Inverter Drives | Suppliers | UK this is a 3kw single phase, with a bit of fettling something like this would be a easy fit, even a 4kw motor would be available. a 4kw would only pull 17.5 amps ish so your 4mm cable would cope no problem

 

[pjscotland]

ignoring my ignorance, what about starting current?

I was under the impression that starting current is 4x that of running current albeit briefly.

Or does this not apply to single phase ?

Or because it's so brief does it not have any effect ?

 

[mogga]

how did you get on ?? or did you get it wrong n get stuck under a weekend project?