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Hi,

I'm looking for some guidance from more experienced hands. Have a friend who just bought a 2.2kw air compressor which is obviously blowing the fuse in the plug due to the start-up current. Manufacturers information suggests a 30a single phase motor DOL for the power rating whilst the person who sold it said it needs a 15a fused spur.

The compressor won't be installed on its own circuit with a type c circuit breaker so wondering what the best route to take given a fused spur off the ring is limited to 13a also? Someone suggested an unfused spur to a 16a single phase 2P+E connector and plug like you see at caravan parks which could cope with the start up current but any guidance much appreciated.
 
you could fit a 16A type C MCB in the ring, in an enclosure ,instead of a 13A FCU. then hard wire the compressor into that.
 
A little confused here, you say the manufacturer suggest fitting a DOL starter, doesn't this compressor already contain its own integral control?... or am I getting it wrong, a 2.2 kw single phase would have the effective inrush of a 5.5 to 7.5 kw 3ph so yes a 30amp front end type c would be recommended although you could use a permanent 16amp connection.
 
The Hager commercial catalogue (I happen to have to hand) has 2.2kW DOL single phase protection as 50A C/D MCB, or 40A fuse. Pretty brutal!
 
I agree but he sort manufacturers guidance which usually refines the worst case scenario those charts are based on. The higher the mcb the more problematic complying with ELI which makes advice difficult without having more info.
 
My own experience is mostly small motors (<= 1kW) under electronic servo control, there the protection is more about stopping fires if/when the electronics fail.
 
I tend to cap at 39kw but that's just because of the industries I serve and tend to be drive controlled so minimal concerns of massive inrush.
 
Try a 13A time delay (slow blow) fuse in the plug ? ?

I know this was said tongue-in-cheek but for those not familiar with fuse specs, normal 'slow-blow' cartridge fuses will not have the breaking capacity (nor will they correctly fit a 13A plug) and must not be used for this application.
 
Based on the 30A fuse suggestion then it looks like a 32A C-curve MCB and matching circuit would be needed, either hard-wired to an isolator or a 32A commando style plug/socket (and of course RCD/RCBO use in that case, also if buried cables < 50mm, etc).
 
SIngle phase motor driven air compressors like the one you mention most often use capacitor start and capacitor run type induction motors. For these motors, in order to have sufficient starting torque to quickly run up to speed without labouring the voltage at the motor terminals must not drop much. A consequence of too much voltage drop along the supply to the motor is a longer start time which will stress the start (and run capacitors) leading to reduced life. It is clear when they have failed when the motor fails to start and the overload trip operates through high stalled current - often the windings are damaged too because they have overheated.

As a for instance, my brother-in-law has a 2.2kW compressor in his workshop which was regularly failing. It was fed by a 30 to 40m run of doubled up 4mm2 singles - solution add in a third single for both L and N. If I remember correctly fed from a 32A type B mcb but would need to confirm this. I advised a new run of 16mm2 singles but we decided to see how triple 4mm2 singles performed first.

Do you volt drop analysis and calculations carefully. I cannot remember what the allowable voltage drop is for a CSCR motor driving an air compressor- someone will know. I think my BIL's run suffered 235 to 210V on start-up. (Of course some of this external due to Ze and he is fed by a pole transformer some 200m away).

See this:

Maximum voltage drop limit - Electrical Installation Guide - https://www.electrical-installation.org/enwiki/Maximum_voltage_drop_limit
 
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