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Wiring For An Air Compressor


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The limits of my knowledge are narrow, but not that of the internet, and especially here.  So advise me, please, on domestic electrical wiring?

 

I have an air compressor, runs off the mains.  It's wired via a switched flex outlet, not a three pin plug, ever since I got fed up with the racket it made and enclosed it in a sound proof box in the far corner of the garage.     A drum of air hose reaches everywhere I want it, in or outside.  Ideal, except that every so often it blows the fuse in the wall outlet, which I have carefully sited so that it is a looooooooong stretch to get at the fuse and replace it.  

 

I'd like to replace the outlet with one that includes a circuit breaker, which I could reach and reset with one finger press.    But all I can see on the 'Net are RCDs, that break at tiny currents.   So my Qs are:

1/  Why does the fuse keep going? 

2/  Am I endangering the wiring further back by running the compressor and repeatedly replacing fuses?

3/ Will an RCD flex outlet do the job I want it to?

4/ Better suggestions please!

 

Thanks!

John

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Is this a 3hp compressor? I think that is as big as you can get on a plug-in connection.

Bit of a worry why the fuse blows, I presume a 13a one?? or is it wired through a switched fused spur?

https://www.tlc-direct.co.uk/Products/BG850.html?ad_position=1o2&source=adwords&ad_id=45425533757&placement=&kw=&network=g&matchtype=&ad_type=pla&product_id=BG850&product_partition_id=174048899587&test=finalurl_v2&gclid=CMT74OmIgNECFcW4Gwod5EoItQ

 

If the compressor is rated very close to the 13A fuse rating, i suppose you could try a 16A mcb. That can be put in its own enclosure, but I doubt it would be regarded as the correct solution. If the compressor is 3hp, it may (just may) have a fault so ought to be checked over. It does have a RCD somewhere??

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Don't know if this helps, but I have a similar problem with the Lavor Steam Pressure Washer I have.

 

Its right on the 13 amp limit, in fact a service engineer a few years back said that he thought a lot of the time they actually pulled 14 amps at start up, so one batch of fuses might just tolerate it, whilst another batch would just blow one after the other, which was a pain as you'd hit the on button and bang would go the fuse, he showed me a trick which was to hold the gun trigger open when hitting the start button as it gives the pump motor a bit of a soft start.

 

I also noticed that quite often that after getting over the start hurdle, that after 10-15 mins use it would quite often blow a fuse, but that this was far more frequent if I used an extension cable. His advice was change the cable to the Washer to a heavier one, and buy the heaviest duty extension cable I could and keep it as short as possible. He explained that the Washer was right on the limit of 13 amps, and that the cable, and especially an extension cable were also close to the limit, and that in use they get a little warm and introduce a little resistance which can be enough to just tip the load over the top.

 

I changed the cable to the washer to a heavier grade, and bought a short heavy duty extension. Most of the time I now don't get a problem, but still before I use it I always check I have a spare fuse to hand just in case.

 

Will be interested to see what other suggestions you get for the compressor wiring, as it sounds as though it will be the right solution for me to try as well

 

Alan

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Hi JohnD

 

My guess is you sould not have a fuse next to the compressor.

 

I have a D ratted fuse in my main fuse box, cant remember the amarge possibley 40 amp.

 

the point is, most large electric motors allways draw a lot of currant on start up, If memery serves, the D rated motor fuse in the main fuse box works on a delayed principle.

 

than it acts like any other fuse would

 

 

One other question totaly off topic, but you do have access to drain the compressor of air of the night time (I never leave a compressor full of air over night)

 

found this for you

http://www.boost-energy.com/faqs/what-breaker-or-fuse-should-i-fit

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A "Switched Fused Spur"  That's what it has now.  13A cartridge fuse.   So simple to replace, except for being on the wall behind the compressor enclosure.

 

The compressor has a circuit breaker on it, as part of its electronics .  Tiny little switch on the 4x4" box on the side of it.    That has gone off in the past.

It's similar to this, direct drive and yes, 3hp.   https://www.machinemart.co.uk/p/clarke-raider-15500-3hp-50-litre-air-compress/

 

Is it that the motor draws a lot more current at start up than when running?

Even so, I'd be a bit shy of fitting a higher rated fuse - aka 16A mcb - on it.    Can I get a 13A mcb built into a flex outlet?    All I can find at 13A have cartridge fuses. 

John

 

PS Wow! the advice piles in!    The electrical supply was fitted by a pro electrician.  I have taken the supply to a double three-pin socket. which never powers more than a radio, to power my compressor.    I think there are CBs back in the junction box, I'll trace it back, but they don't blow, it's the fuse.  Maybe because as said above, the motor on the compressor does pull a big current on start up, but not long enough for the CBs to blow.   So if I have CBs in the main supply box -  don't need a fuse?  J.

Edited by JohnD
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OTU,

useful idea about the steam washer, but the compressor is now immobile in its sound suppressing box (I was warned that direct drive compressors are very loud!), with a short power cable, and inacessible until I take the front off.  I've made the air supply mobile by the hose drum.

 

Urge,

I regret that I often forget to turn it off, so it starts to run at night, startling the neighbours.   Better now in its sound proof (ish) box.   But I should drain the tank of condensation more often, so when I do, I spray WD40 into the air intake.  Why not leave it pressurised?

 

John

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I never leave mine full of air as there is water in air

 

and having spent agess preping something for paint, I dont want water or oil anywere in my air lines, 

 

filters can only do so much

 

leave the tank empty and open, let the tank dry and breath, but dont leave the power on or it will be running all night and it wont switch off due to the tank being open

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My 3hp compressor runs off a 13amp plug. Now it's old i have to turn it over by hand a few times and put a fan heater on the motor to warm it up before I try to start it otherwise it will blow the fuse in the plug. Once it's running and warmed up there is no problem. It's the initial start and draw of current that kills it.

 

Mark

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^^^This.  Compressors have a high breakaway torque requirement so the motors will pull ABOVE it's normal full load current briefly (milliseconds) on start-up.

 

This is a recognised issue and in industrial installs motor rated fuses or motor rated breakers are used which are designed to withstand short-term surges.

 

Volt-drop can also be a problem as under starting situations, lower available voltage at the motor will actually increase it's current draw.  This is why long or undersized cabling (be it permanent or an extension lead) can increase fuse blowing as can any iffy connections.  If it's got worse recently, it may also be an indicator that the motor capacitors are getting a bit weary.

 

Nick

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Yes, Urge, I did!  Thanks!

 

I've traced the wiring back to the distribution box (?) in the garage.   There, the circuits are protected by old fashioned ceramic fuse bodies with renewable fuse wire.  The wire looks, by comparison with a cardful I have in store, to be 15A.    There is an "RCCB" protecting the circuit that the compressor runs off.    Is this like Residual Earth Current protection?  Does it protect the wiring or only (!) the user?

With those, do I really need a 13A fuse in the cable outlet?

 

.I presume that the capacitors are in that black box on the side of the compressor, Nick?    Is there any way that, armed with a Multimeter, I can test them?

 

This isn't a new problem, but I think it may be more common in cold weather, which matches Mark's finding.

 

That distribution box (right word?) in the garage is a metal box with the fuses inside.    As it happens and despite its age (114 years), our house has a bank of contact breakers for everything in there. Must be a later fitting.  They have 'gone' on occasion, and make restoring function so simple, once the fault is dealt with, and reliable.     Maybe a good policy would be to employ a proper electrician (no offence, anybody -  I'm the improper electrician!) to do the same for the garage.

 

John

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OK thought I'd have a chat with our tame electrician (if there is such a thing), and he has a simple inexpensive solution.

 

Single MCB enclosure  eBay £5

16amp MCB C or D type  eBay £3

 

Wire the Enclosure into the Ring alongside your existing double socket (or replace it)

 

Wire the compressor into the MCB enclosure.

 

As options, if the circuit isn't already RCB protected, get a double enclosure box plus an RCB  extra £10

 

If its a pain having the compressor wired into the Enclosure, then get an industrial in line 3 pin plug and socket (like they use on site equipment/cara vans) wire the socket into the MCB enclosure, and then you can plug and unplug the equipment when you want.

 

Ring main should already be on a 32amp fuse/circuit breaker so a 16amp supply point isn't a problem. However if its a single spur supply to the existing socket DONT do this.

 

Alan

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John, the RCCB protects against earth faults (if the amount of current on N and L is different by more than a few mA, ie it is leaking, it trips) so it protects you. The fuse protects the equipment, or rather importantly, the cables.

 

Ifyou have a 15A fuse just feeding that circuit, you could change the switched fused spur to just an outlet plate, ie a cooker type switch. or as above a 16A outlet and socket.

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Whats the advantage of the cooker type switch?    I have one of those next to the work bench, it runs the pillar drill.  I fitted it, and AFAICR, if it has a fuse, it's a 13A one.    No fancy RCCB etc.

 

OTU

that's so far out of my knowlddege zone that I think I really will get an electrician in!

 

After Xmas!

J

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Cooker switch is unfused (rated at 40A or so) and then you would be relying on your old consumer unit (fusebox) for protection.

https://www.tlc-direct.co.uk/Products/MKK5105.html?ad_position=1o2&source=adwords&ad_id=45425533757&placement=&kw=&network=g&matchtype=&ad_type=pla&product_id=MKK5105&product_partition_id=174043016947&test=finalurl_v2&gclid=CJTokt6GgtECFYcK0wodvawF1w

 

 

Ideally a new garage consumer unit would be good, with a rewire. Personally I would use RCBO's (a bit like your MCBs at home, but with a built in RCD/earth leak protection) so if one circuit has an issue with earth leakage, only that one circuit trips. Downside is they are £30 each as opposed to £3 for an MCB.

With a rewire I would have a dedicated 16A supply for the compressor, with the cooker type switch or 16A plug. Plus a ring main or a few other radial circuits. Depending on what else has a serious current draw.

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