Earth sleeve

[JohnW2]

Is this actually a serious discussion? I can't tell. Are we just talking about a standard plumbing Flexi pipe?

I presume so I was also a bit surprised!

Kind Regards, John

 

[EFLImpudence]

I don't now any secrets and presume it guards against abrasion - oh, and it looks nice

 

[Risteard]

According to Wiki ROI regs banned uninsulated CPCs in 2013

That isn't correct.

The Amendment to the Wiring Rules was only issued last year, and it does not come into force until late 2017.

 

[Mikefromlondon]

efl and John, so I was right in my initial thinking the braid was for some sort of physical protection, such from bulging and bursting, as opposed to for maintaining electrical conductivity, when years ago it was a requirement to earth all pipes and sinks and tubs, so fair enough it is essentially for physical protection. Its just that since we have been discussing about non insulated earth wire that we ended up discussing about earths in general.

 

[flameport]

years ago it was a requirement to earth all pipes and sinks and tubs,

Although plenty of people have done such things, it was never a requirement.

 

[Mikefromlondon]

I don't now any secrets and presume it guards against abrasion - oh, and it looks nice

Just changing subject slightly, One thing I could never understand, serious tuners add powerful turbo chargers to boost intake, and they then have to use mega inter coolers, now my understanding is when air is being compressed it heats up, (physics) so these mega turbos boost anything up to 3 bars or even 4 bars, and then have to pass it through inter cooler where by removing heat, the air must lose boost pressure, so is there any point in boosting too much as you end up loosing final boost pressure due to cooling so this one thing i have never understood properly, that car enthusiast pay a hell of a lot of money for larger turbos and then having to use massive intercooler to take away heat, and you end up lower temperature that must mean you have lowered boost pressure, so why not use a smaller booster (turbo) and not then having to use an intercooler.

 

[EFLImpudence]

Not an expert but -

Well, you want it boosted - that is more by mass forced into the cylinder - but not heated and expanded because cooler air is denser and contains more oxygen by volume.

I suppose that logically means it is less boosted than it might be but it is the amount of oxygen that is the critical factor.

It must be a balance between mass and volume.

 

[JohnW2]

.... so why not use a smaller booster (turbo) and not then having to use an intercooler.

Because you would then end up with a lower pressure (at the desired injection temperature) than you wanted. As you have implied, it's all down to the laws of Physics.

As you say, if one adiabatically compresses an ideal gas, the increase in pressure one sees consists of two components - one due to the actual compression (squeezing the gas into a smaller volume) and the other due to the increase in temperature consequent upon that compression.

Numerically, the ratio of pressures before and after adiabatic compression will ('ideally') be equal to the ratio of volumes before and after compression raised to the power of the 'adiabatic index' (which is approx 7/5 for air). Hence, if one adiabatically compresses the air into one quarter of its volume at atmospheric pressure, the pressure immediately achieved will not be 4 bar but, in fact, will be 4^(7/5) bar, namely about 6.96 bar. If one then cools the compressed air back to ambient temperature, the pressure will then fall to the 'originally expected' 4 bar.

However, assuming that one is aiming for 4 bar, if one initially compresses the gas by a factor of less than 4:1, then the pressure after cooling back to ambient temp will be a lot less than the 'desired' 4 bar (in fact, about 2.7 bar).

I realise that, in practice, one would not want to cool the air right down to ambient temp, but the same general argument applies. The pressure one ends up with (after cooling) will simply be the 'volume compression ratio' adjusted for the pressure change as a result of the (desired, after cooling) increase in temp from ambient to 'after compression and cooling'. Again, if one 'tries to be clever' by compressing less (so as to reduce the amount of required cooling), one will end up with a pressure (at the desired temp, after cooling) less than one wanted.

Kind Regards, John

 

[Mikefromlondon]

I get it now John, thanks, sorry to drag you into this. But yes fully understands it now. I thought there must be a catch in this somewhere, otherwise why would anyone want to hang a great big shining aluminium Intercooler in front of their wagon and blocking its radiator!

 

[ericmark]

Volumetric efficiency the more dense the air is the more the cylinder can draw in.

However twin and earth with no id sleeving on the bare copper there is nothing to say that cable can't be used for other than earth bonding, but where it has the yellow/green covering then not permitted to over sleeve.

 

[JohnW2]

However twin and earth with no id sleeving on the bare copper there is nothing to say that cable can't be used for other than earth bonding ...

... except that, unless in conduit etc., regs do not allow a single-sinsulated live conductor (particularly when the sheathing of T+E may not even be 'rated as insulation').

... but where it has the yellow/green covering then not permitted to over sleeve.

In terms of BS7671, that's only true of singles. There is nothing in BS7671 which says that over-sleeving of G/Y is not permitted in multi-core cables (such as T+E), even if many/most of us would probably not regard it as a very desirable practice.

Kind Regards, John

 

[JohnW2]

I get it now John, thanks, sorry to drag you into this. But yes fully understands it now. I thought there must be a catch in this somewhere, otherwise why would anyone want to hang a great big shining aluminium Intercooler in front of their wagon and blocking its radiator!

You're welcome. It's really just a case of the temperature rise being an unavoidable (and largely unwanted) 'side-effect' of the compressing, such that one has to 'undo' that side effect, returning one to the situation that one would have had if that 'side effect' had not existed.

One can think of sort-of electrical analogies. Increasing the power supplied to a load (not one designed to produce heat!) may result in unwanted temperature rises resulting in the need to expend effort and energy in implementing cooling. Someone might 'try to be clever' by reducing the power supplied (e.g. by reducing supply voltage), thereby reducing the temp rise and removing the need for cooling - but then, of course, the load might well not function as required. Just as with the turbo-charging, one therefore has to accept, and 'deal with' the 'side effect' of temperature rise, as a price to be paid for achieving the desired end result.

Kind Regards, John

 

[Mikefromlondon]

I think I have understood it now, so what you are saying is when Turbo spins, it compresses the incoming air let us say to our intended target value of 3 bars, but as air starts to get compressed it also heats up, in doing so its pressure increases further so instead of getting 3 bars, it may have gone up in pressure to say 4 bars, so we now cool it down by passing it through an intercooler where the temperature drops down and and we are back in business at 3 bars what we intended. Got it I think.

Of course if you look at it from another point, heat is produced when air ( or any gas) is compressed, so if we were to trap this compressed air in a canister, initially it would get heated up and then lose its temperature, and eventually the canister cools down to ambient or surrounding temperature, but still has that compressed air in it. Intercooler helps cool air quickly so that it can be used immediately in cylinders of car engine, whereas a canister can take all its time to cool off slowly.

 

[JohnW2]

I think I have understood it now, so what you are saying is when Turbo spins, it compresses the incoming air let us say to our intended target value of 3 bars, but as air starts to get compressed it also heats up, in doing so its pressure increases further so instead of getting 3 bars, it may have gone up in pressure to say 4 bars, so we now cool it down by passing it through an intercooler where the temperature drops down and and we are back in business at 3 bars what we intended. Got it I think.

Exactly.

Of course if you look at it from another point, heat is produced when air ( or any gas) is compressed, so if we were to trap this compressed air in a canister, initially it would get heated up and then lose its temperature, and eventually the canister cools down to ambient or surrounding temperature, but still has that compressed air in it. Intercooler helps cool air quickly so that it can be used immediately in cylinders of car engine, whereas a canister can take all its time to cool off slowly.

Again, exactly. I was talking about an adiabatic compression (i.e. a process that happens so quickly that there is no time for any heat to be lost) - which is essentially what will be happening in a turbo-charger. As you say, that's why one has to use a cooler rather than wait for it to cool down itself - if one tried the latter, the engine would probably only be able to do one stroke every hour or so (hardly a 'go faster' technique ).

Kind Regards, John

 

[EFLImpudence]

I think you both are missing the point that, as well as the compression, what is important is the oxygen content.

Air is 29% oxygen at all temperatures but - if because of expansion due to the temperature - the air has expanded to, say, twice the volume then actual amount of oxygen, per unit of volume, will be halved.

Look at climbing a mountain - the air at the top is still 29% oxygen but you will find it difficult to breath as the air is a lot thinner (less pressure - it has expanded) and so contains an actual lesser amount of oxygen per lung-full than at ground level (more pressure - it is compacted).


Edit - should be 21%