Wiring for a compressor

[dunny]

Thanks Eric.

As I said the next step is to get a spark in. The workshop (and hence compressor and MIG) will only be in use occasionally but it still has to be right.

Will see what the spark says when he comes. I am hoping I can get him here in the next couple of working days.

D

 

[Iggifer]

Has Her Maj had her home rewired yet ? I heard the wiring was in a terrible state

I don't believe so, I'm sure it was going to be a 25 year project or something. Imagine the hoops you'd have to jump through to get that contract!

 

[Echo the husky]

You can guarantee whoever gets that job will be a salesman who has no skill or care when it comes to wiring.

 

[Iggifer]

I would imagine their is a company somewhere that has the Royal Warrant and they'll be pretty much guaranteed to get the job, although, to get subbies in, I imagine they'd have to go through quite a few background checks!

 

[ericmark]

All the new circuits will come under Part P in England and Wales

Not just new circuits - Part P applies to any work whatsoever on fixed electrical cables or fixed electrical equipment located on the consumer’s side of the electricity supply meter which operate at low or extra-low voltage and are—

OK Mr Pedantic you know jolly well I am referring to notifiable work do we actually have to put notifiable in every time.

My point is it is getting harder to find some one who has done both domestic and industrial work. In the old days electricians would move from domestic, to commercial to industrial as the demand changed. Today the domestic electrician often can't do industrial stuff as he lacks the safety clearance and the industrial electrician can't do domestic because he's not a scheme member. Firms may do both but very few sole traders will have experience at both bar for a few who are getting old in the teeth.

 

[ban-all-sheds]

I would imagine their is a company somewhere that has the Royal Warrant and they'll be pretty much guaranteed to get the job, although, to get subbies in, I imagine they'd have to go through quite a few background checks!

Like making sure they do not own any blowlamps.

 

[ban-all-sheds]

OK Mr Pedantic

Ever the cry of the careless and the inaccurate who think that when their carelessness and inaccuracy is pointed out criticism should be deflected to the messenger.

you know jolly well I am referring to notifiable work

Then don't conflate that with the requirements of P1.

do we actually have to put notifiable in every time.

Every time? Certainly not.

Only when we mean to say that the work is notifiable.

 

[Iggifer]

I would imagine their is a company somewhere that has the Royal Warrant and they'll be pretty much guaranteed to get the job, although, to get subbies in, I imagine they'd have to go through quite a few background checks!

Like making sure they do not own any blowlamps.

Yup, but I heard the queen loves a bit of HEP2O and JG speedfit clipped direct anyway.

 

[SimonH2]

My mate has an older version of that compressor in the garage - and running the grit blaster we can keep it running continuously. And no, you can't hear anything else when it's running !

Had "a few problems" to start with - specifically getting it to start. Of course, when it was new, it was "tight" so took more current to start than now it had "a few hours on it". But the design isn't great - if it's the same, then permanent capacitor 2 pole motors which My dad suggested have poor starting characteristics.

The issues we saw were that when cold in particular, the first motor would fire up and get up to speed. After a few seconds, the second motor fires up - and the voltage sags such that it doesn't run up properly and either the supply fuse blows or the overload trips. This is where the "poor starting characteristics" bit comes in - a switch start 4 pole motor would probably have started up fast enough to have avoided the problem.

This was running it from a 30A rewireable fuse - I'd say you'd stand no chance of starting it off a B32 MCB. The 30A cartridge fuse in the house got a bit of 5A fuse wire added alongside it in the holder to provide some discrimination

Someone from Machine Mart came out to it, and fitted slow start dump valves. There's a T-piece in the line from compressor to non-return valve. The slow start valve p1ss air out until a certain pressure is reached - which in practice means the compressor is run up to speed - and thus unload the motor for a few extra seconds. That was generally enough except in the coldest weather.

One other mod it's had, the second compressor isn't unloaded when it stops. There's a solenoid valve which is powered up during the delay between first and second motors starting (pneumatic delay switch on the contactor) so it gets unloaded before it starts. This failed eventually - and as an alternative I fitted some plumbing so the pressure switch unloaded valve unloads both compressors - with a non-return valve in the tee so the first to start doesn't pressurise the second.
For the technically minded ... Live supply goes via pressure switch, then to coil of first contactor and common of the delay switch mounted on it. NC on delay switch goes to unload valve on second compressor, and NO contact goes to coil on contactor for second compressor.

The wiring isn't complicated, and it wouldn't be hard to rewire it so the second motor ran off a separate supply (and hence separate fuse).

 

[dunny]

They recommend a 45A fuse but I suspect it will still be the same motor set up. Did MM charge for the modification?

 

[bernardgreen]

Also, you will need to seek permission from the DNO for this additional load, especially as your supply is "overhead". They will not want all the lights in the other houses on the same supply dimming everytime you start the compressor!

I am aware of a situation where complaints from several house owners about their lights dipping has finally led to one of their neighbours being told by the DNO to cease using a piece of equipment ( not known what this is but belioved to be a metal working equipment ) or face disconnection. ( no children or vulnerable adults in the house )

 

[Adam_151]

I would imagine their is a company somewhere that has the Royal Warrant and they'll be pretty much guaranteed to get the job, although, to get subbies in, I imagine they'd have to go through quite a few background checks!

Like making sure they do not own any blowlamps.

Yup, but I heard the queen loves a bit of HEP2O and JG speedfit clipped direct anyway.

A lot of sites are going down the route of no hot works these days. Generally crimped fittings on copper tube are the way its done. Normally the clerk of works keeps his eye open for the push fit (which is normally not permitted by the job spec) creeping in where it wont normally be seen!

 

[Echo the husky]

Ah Mapress fittings, I love installing those. Nice and quick, even the 4" sizes! Far more expensive than end feed though...

 

[ban-all-sheds]

You must have a big tool.

Spoiler

 

[ericmark]

Even in industrial situations compressors cause problems. I remember one which was part of a batching plant, it would blow a fuse but when tested no fault found. In the end I was sent to sit and watch the compressor and what I found was the exhaust value was leaking and causing over time the pressure in the cylinder to increase seen as the crank slowly moved until bottom dead centre and then when the de-load valve tried to open the inlet valve it failed because there was too much pressure in the cylinder.

It was cured by holding the de-load valve open all the time other then when in run, rather than just when in star, so pressure could not build up.

My point is the start of even three phase motors is not as easy as one first thinks. The de-loading of compressors is complex with timers galore even with just one motor. It is de-loaded to start, it is then de-loaded when pressure is reached, and after a delay if pressure does not drop motor stops. Add a second motor and then the de-loading system becomes more complex.

I have looked at the idea of running multi compressors on a system it was not as successful as hoped but the compressors were at opposite ends of the factory, however it is not easy to modify compressors. With a lathe then adding an inverter to get a soft start with no lamps dimming is not too hard, but with the compressor it requires more skill even the selecting of inverters needs some skill, I did get it wrong on one job, all the specs said it should work but in practice it failed. In the end I found a motor with a built-in inverter and ASii coms but it was expensive.

In real terms you don't want to know the problems. What you want is for some expert to assess what you have and come up with a way of getting what you want, be it a liquid fuelled compressor, an extra large receiver or other method what you need is for an expert to assess it all and tell you how much it will cost. We still have no idea why you want the air so we could never give you an answer.