Compressor wiring

[ronan]

I am currently wiring my shed , i extended the shed a few years ago and am only getting around to wiring it properly now , i was given a 3hp compressor and am now getting around to plumbing in the air main and want to do the electrical circuit too.
Do i need a direct online starter ? Where the compressor was before (in my late uncles shed) it was wired in with one.
What size wire do i need from the consumer unit ? And what size trip ?

Thanks

 

[FranV8]

You shouldn't need a DOL starter - the starting/stopping should be done off the pressure switch on the compressor.

I think it's technically a 16 Amp supply recommended for one of these, which means either fixed wiring or a suitably larger plug and socket. Many people run 3Hp from a 13 amp supply, although some people will blow fuses over the time (inital current inrush when the comp starts from stationery)

Wire size I won't comment on, but it will ahve to consider the distance from your consumer unit and what other loads you put on now/future. I'd allow for bigger than you want now, you're bound to want to put more toys in the shed that need more juice over time.

There are sparkey's on here that can help though. Of course you'll likely need to get the installation done or signed off by a qualified electrician anyway...

 

[eil]

If it was wired up through a contactor before at your uncles, well there must have been a good reason for having it done like that. i am guessing that its and old 3 hp motor and not the modern psc type you have. My old Brookes 3hp motor draws 16amps when running, I have it wired up through a contactor and overload, there is less load on the pressure switch contacts like that, as well as more protection for the motor.

 

[tigler]

A DOL is good working practice, probably the reason it was originally installed with one. It has the added benefit of having an overload cutout to protect the motor.
Cable gauge is very dependant on the length of run, upto say 25 mtrs you will be ok with 4mm sq, any longer or if you envisage more load in the future, go for 6mm sq. Go for a 32 amp type C MCB.

 

[ronan]

My uncle worked in the maintenance unit for a major hospital , his best friend was the maintenance manager and he was the head sparks before he became manager, there was plenty of surplus electrical stuff of the best quality lying around so i'd say thats why there was a dol used.
The compressor is only about 12 feet from the cu in the shed , as for more toys in the future , my shed is too small for anymore which is a killer because i really want a small milling machine , a tom senior or something like that .

 

[madkayaker]

DOL is required for a motor bigger than 0.75KW.

 

[tigler]

That can't be right, I have a Hydravane with a 1.1 KW motor, runs totally fine off a 13 amp socket, I have a big hammer drill with a 1 KW motor, that couldn't be used off a DOL by virtue of it's application.

 

[madkayaker]

will dig the regs book out and give you the number if you like but it right

 

[ronan]

I don't mind fitting one even if its not strictly neccessary , i'd rather do things properly first time and not have to worry in the future. Are all dol's the same or are they sized for the load ?

 

[madkayaker]

sized for load

 

[ronan]

I found the information label on the compressor today , along with the usual stuff eg voltage , hertz , it has for amps : 14,60

I take it that this means 14 amps while running and 60 amps during the motor starting inrush , am i correct ?

 

[brightspark]

I found the information label on the compressor today , along with the usual stuff eg voltage , hertz , it has for amps : 14,60

I take it that this means 14 amps while running and 60 amps during the motor starting inrush , am i correct ?

full load amps will be 14 and 60 amp starting load is about rite for a 3hp motor

 

[ronan]

full load amps will be 14 and 60 amp starting load is about rite for a 3hp motor

What mcb would be suitable to run the compressor , i already bought a 32 amp type "c" one , is this too large an amperage ?

 

[tigler]

No, that is the appropriate size for the circuit.