Aircon Condenser outside Earthing Equipotential Zone

Now here's one to get your thinking caps on for...

Modern mains supplies (Domestic and Commercial) are all to often CNE...Combined Neutral Earth.....where the 'Earth' supplied by the electricity supplier is tapped from the Neutral.
The normal approach is to define an "equipotential zone" of the building. The 'earthed' metalwork within the zone is all at the same potential, but it might not be at true earth, especially in fault conditions.

Metalwork taken outside the zone (eg water pipe for an outside tap) should have a plastic isolating section inserted, to prevent someone operating the tap from providing a better earthing path under fault conditions.
Supplies to outbuildings outside the zone are supplied without the main zone earth, and are then protected through an RCD and locally earthed.

So what about airconditioning units? Should they be treated as being outside the zone? The condensing unit and pipework is earthed metal....does this equate to the example of the tap above? Should the system be supplied through an RCD with a separate earth?
Whats the thoughts?

No:)

we make sure they are well bonded to the building and the eelectrical systems within the building:)
That is the best we can hope for:) bring out a separate earth bond for the unit frame work at least the size of the mains conductors:)

Kind Regards Andy:)

Hi
Mr Electrocoolman not 100% sure about the content of your post, would it be possible for you to clarify your statements with preferably a regulation number or your source of this information, in particular the requirements for a supply to a shed or garage and also the insulated insert to the outside tap. I think once these have clarified, we will be in a much better position to comment on your post.

Thanks
Birds

Depends where the Condensors are mounted?

Electrical equipment mounted on the external fabric of a building is still regarded as being within the 'equipotential zone'.

If, for example the units were 'ground mounted' say 5 metres or so from the building then the BS7671 regs are more hazy!

It could be argued that an Earth rod should be fitted and bonded to the exposed metal work, but I feel this is a bit OTT.

As for RCD protection that is not required, fullstop!

Only socket outlets that are likely to provide power to portable appliances for external use HAVE to be RCD protected by a 30mA RCD.

Fixed items of Class 1 electrical equipment only have to have disconection time of 5 secs under fault conditions if attached to the buildingds fabric and cannot be simultaneoulsy touched whilst in contact with ground potential.

If they can be simultaneously touched whilst in contact the discon' times drop to 0.4 of a second.

If the Zs satisfies all these requirements then no RCD is required.

If not then it is!

Clear as mud eh? :D

Modern inverter driven compressors/condensing units cannot be supplied through an RCD.

If you have taken your mains supply from the consumer unit/dist board on a seperate circuit and then taken a PSC reading that falls within the limits I don't see a problem.

The combined neutral/earth goes all the way back to the centre tap of the supply transformer where it is earthed

As far as the plastic isolator within a water pipe that serves an outside tap, I've never heard of this? Can you elaborate?

I feel that the water would act as a current path anyway, so the plastic 'break' would be rendered useless :confused:

Modern inverter driven compressors/condensing units cannot be supplied through an RCD.

Yes they can!

Birds

How do I do that wrap around thing

As far as the plastic isolator within a water pipe that serves an outside tap, I've never heard of this? Can you elaborate?

See GN5 Page 96 9.4.11

PME supplies feeding an outside tap.

If the feed is in copper then it is recomended that a plastic insert is fitted to ensure that a PD is not created between a copper pipe and true earth potential! ;)

BTW Water is an extreamly bad conductor or electricity!

See Here ww.iee.org/Publish/WireRegs/EarthingPlasticPipes.pdf

I've had to leave the first 'w' out of the link above cause thsi forum won't let me post a link untill my post count hits 15 :mad:

Quote:

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Originally Posted by Birds

Modern inverter driven compressors/condensing units cannot be supplied through an RCD.

Yes they can!

Birds

How do I do that wrap around thing

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No they can't:D well they shouldn't being fixed equipment:)

Kind Regards Andy:)

No they can't well they shouldn't being fixed equipment

Why

Birds

Earth is Earth, neutral is neutral. The potential of the two can be different, so there can actually be a difference of potential between earth and neutral.

Quote:

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Originally Posted by Birds

No they can't well they shouldn't being fixed equipment

Why

Birds

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Because BS7671 does not require Fixed Items of power using equipment to be RCD protected as long as the rated disconection times 5secs/0.4secs can be satisfied by using EEBADS.

If the supply is a TT supply then you have no option but to have a Type S 100mA RCD as a Main switch for the WHOLE installation.

Quote:

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Originally Posted by frank

Modern inverter driven compressors/condensing units cannot be supplied through an RCD.

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This is the statement

A few posts later and it looks like they can be supplied through an RCD. The statement was'nt they should'nt, or they dont need to be it was CANNOT.

Question
If a modern inverter was to be supplied through an RCD

(1) would it damage the inverter or compressor or any other component.

(2) would it void the warranty.

(3)Would it affect the RCD in any way (other than possibly causing the RCD to trip)

Birds

There is nothing intrinsicaly wrong with running any item of electrical equipment through an RCD, in so much as risking damage to it's PCB circuitry or any other internal electrical operation.

However you would be ill advised to do so for operational reasons as the system may be prone to nuisance tripping, especialy on a 30mA RCD.

A/C units due to the fact of their mechanical composition of Motors, Compressors, Heating elements, pumps and exposure to moisture etc etc are by their very nature very likely to sucumb to nuisance tripping.

As I've stated previously, fixed items of equipment do not have to be protected by a 30mA RCD and the regs actualy recommend that they aren't due to the reasons already mentioned.

However.............................................

If the electrical installation is TT (Earth Rod) then you have no choice in the matter only in so much as your required to fit a 100mA Type S unit as a main switch at the origin of the installation which, if it's an existing installation will already be there.

BTW a Type S is a 'Time delayed' unit which is far less susecptible to nuisance tripping than a standard 30mA unit.


It's all in the Big Brown Book, and if any A/C contractors are installing their own power supplies then they should make themselves familiar with this or else sub the work out to a Sparx. ;)

If you follow the advice of the manufacturers then they recommend that inverter units SHOULD NOT be installed with RCD protection

Quote:

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Originally Posted by frank

If you follow the advice of the manufacturers then they recommend that inverter units SHOULD NOT be installed with RCD protection

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I was just about to close on this one as it seems that other than possible nuisance tripping its ok to supply through an RCD. Then Frank you throw that one in.Just looked through an installation manual of your favorite manufacturer ,and guess what! Page 9 of an RXS manual.

Warning
(3) Be sure to install an earth leak detector. (One that can handle higher harmonics)


I think we are about done on this now.But more than happy to carry on if the others are not to bored.

Birds

Quote:

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Originally Posted by sinewave

Because BS7671 does not require Fixed Items of power using equipment to be RCD protected as long as the rated disconection times 5secs/0.4secs can be satisfied by using EEBADS.

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Ref 471-08-03:
Protection > Disconnection Times > Special Circuits : "A disconnection time of not more than 0.4s is required for final circuits supplying....fixed equipment outside the Equipotential zone with accessible exposed-conductive-parts."

Surely the best way of ensuring this is to install a RCD in the supply.

Quote:

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Originally Posted by Electrocoolman

Ref 471-08-03:
Protection > Disconnection Times > Special Circuits : "A disconnection time of not more than 0.4s is required for final circuits supplying....fixed equipment outside the Equipotential zone with accessible exposed-conductive-parts."

Surely the best way of ensuring this is to install a RCD in the supply.

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I think this is getting like Sinewaves other forum on SCREWFIX.

Good night and good luck

Birds

Quote:

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Originally Posted by Electrocoolman

Surely the best way of ensuring this is to install a RCD in the supply.

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If a radial supply to an A/C unit is designed properly and is fed from a TNS or TNC-S (PME) earthing system then 0.4 sec discon time can easily be achevied using EEBADS with no need for an RCD.


But as with most supplies 'Touch Voltage' needs to be kept under 50 volts however this is attined.

If instaling on a Farm or Equestrian centre then 'Touch Voltage' drops to 25 volts and Discon time to 0.2 secs! :eek:

Quote:

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Originally Posted by Birds

Hi
Mr Electrocoolman not 100% sure about the content of your post, would it be possible for you to clarify your statements with preferably a regulation number or your source of this information, in particular the requirements for a supply to a shed or garage and also the insulated insert to the outside tap. I think once these have clarified, we will be in a much better position to comment on your post.

Thanks
Birds

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Hi Birds,
the following link might clarify supplies to outbuildings when main supply is PME (TNCS)

http://www.iee.org/Publish/WireRegs/...s_outdoors.pdf

I normally treat garage / shed as TT supply running supply from main consumer unit via a 2pole MCB fitted on supply side of any RCD unit in Consumer Unit....then fit RCD (30mA) and MCBs in shed.

Insulated tap answered by previous post.

Cheers.

Quote:

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Originally Posted by sinewave

If a radial supply to an A/C unit is designed properly and is fed from a TNS or TNC-S (PME) earthing system then 0.4 sec discon time can easily be achevied using EEBADS with no need for an RCD.

But as with most supplies 'Touch Voltage' needs to be kept under 50 volts however this is attained.

If instaling on a Farm or Equestrian centre then 'Touch Voltage' drops to 25 volts and Discon time to 0.2 secs! :eek:

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Agreed, but originally we were not talking about a TN-S supply, but rather a TN C-S (PME) supply where equipotential zones bring special considerations into play when equipment is 'conductive and touchable' and is outside the zone.

The point is that in a fault condition on the supply, the Neutral (and hence 'Earth' of the Equipotential zone) can rise way above the True Earth, thus anyone touching the exterior metalwork can provide a better 'earth path' for the fault current.

So should we consider the supply to the A/C as a special case and make it a TT supply through an RCBO (or RCD/MCB) and provide a local earth?

Alternatively, and perhaps the safer option, we should again supply via an RCBO and we should bond each system back to the main PME point with 10mm and provide additional Earth rods local to each system outside unit.

Apologies for keeping this thread going but hopefully this will clarify the problem.....
Have a look at the following:

http://www.iee.org/Publish/WireRegs/...egulations.pdf

It suggests lines along the latter with bonding and local earth rods, thus helping to limit the touch voltage exterior to the equipotential zone.

Quote:

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Originally Posted by Birds

Good night and good luck

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Hey, Birds, relax, chill. It's only a forum for discussion, it isn't a contest.

Quote:

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Originally Posted by Electrocoolman

Apologies for keeping this thread going .....

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Don't apologise, your knowledge is being spread around - even I'm learning stuff here :cool:

Hi:)
you can fit all the RCD trips you want:) but they will break you heart with nuisance trips, that I can vouch on from experience;)
bond the metal work to the main earth to keep the units within the zone and fit a goos quality MCCB, C rated for motor start up if you like:)

Kind Regards Andy:)

Yawn :rolleyes:

[QUOTE=Brian_UK;54938]Hey, Birds, relax, chill. It's only a forum for discussion, it isn't a contest.

Hi Brian

You're right I must learn to chill and relax! And just veiw the misleading statements without question ,or maybe just agree with whatever, after all is only a discussion so does it really matter if its misleading or not.Early in the post we couldn't fit RCDs to modern Inverter equipment, now we can. look what a disscussion can achieve. Thanks for the advice.

Keep up the good work
From the CHILLED Birds

PS how do you get the little winking icon at the bottom of the page