can someone please explain?

[Dean Williams]

Hi folks
Think i'm having an off day today, but could someone please explain the science behind the reason you would install a larger earth cable to a jacuzzi pump. I know its something to do with fault current, or leakage to earth through water under fault conditions where the fault current would not be enough to trip the MCB but enough to kill u. So how does a larger earth help this.
I ask this because a jacuzzi pump/motor exists in zone 1 and our expert says we need to run in a 16 or 25mm earth for added protection.

 

[Engineer54]

Hi folks
Think i'm having an off day today, but could someone please explain the science behind the reason you would install a larger earth cable to a jacuzzi pump. I know its something to do with fault current, or leakage to earth through water under fault conditions where the fault current would not be enough to trip the MCB but enough to kill u. So how does a larger earth help this.
I ask this because a jacuzzi pump/motor exists in zone 1 and our expert says we need to run in a 16 or 25mm earth for added protection.

I'd like him to explain that one to me too!! lol!!!

 

[Darkwood]

As E54 says id ask him to elaborate and from what Reg does he find that requirement from, the only thing i can think of is Manuacturers guide and would still ring them on this to find the reasoning, i will too keep a wath of this thread to see if a justifiable answer is given.

 

[Inteificio]

I think it has something to do with magic faeries.

 

[needasparks]

Talk of these magic bean cables is interesting, wonder if 25mm bonds to steel kitchen tops work just as well.
I guess its good ole chinese whispers again.
One thing is said and a pen pushing designer somewhere re-writes a reg to make his idea fit into the world

 

[Dean Williams]

the engineer we are using has had 30 years of experience with installing swimming pools and other specialist stuff like petrol forecourts etc. he's designed complex BMS systems as well as HV submains and seems to know his onions. i didnt ask his reasons in case it made me sound thick, after all, i'm the companies testing engineer & QS...!

 

[Sav]

Hi,
I just installed wiring for a hot tub at a job.

The manufacturer requested that the cable was 2.5 and swa and that it was made off into an isolator with a commando socket outlet ( they run the load from tub to commando socket).

The only other thing they requested was that the mcb should be a C type 20A.

Nothing about 16mm earth etc.

Hope this helps,
Sav

 

[Sav]

Is the jacuzzi installed in an outbuilding ?

I ask this as you may need to extended the equipotential zone, due to pipework etc in the out building.

Right, hat on and ducking for cover !!!!!

Sav

 

[needasparks]

Perhaps he thinks jacuzzi is a code word for faraday in engineer talk

 

[leckyant]

the engineer we are using has had 30 years of experience with installing swimming pools and other specialist stuff like petrol forecourts etc. he's designed complex BMS systems as well as HV submains and seems to know his onions. i didnt ask his reasons in case it made me sound thick, after all, i'm the companies testing engineer & QS...!

Dean.............Just ask him for some clarification are you a man(sparky) or a mouse?

 

[Darkwood]

On this occasion he design may be out of the scope of the BS 7671 and subject to other reg's i would ask him without fear of looking stupid and say you cant find and Reg' that would suggest his requirements except if he designed it his requests need to be met as it rises above the BS 7671 as its classed as manufacturers instructions... only reason i can think is hes more use to designing for a larger scale etc from larger supplies to building may require bigger earthing systems but certain areas of the design may mean isolated pipework through insulated gaskets and possible that it been fitted say in a garden may fall out of the equipotial zone and P.D.s may exist between supply earth and the ground it sits on.

 

[Dean Williams]

the way he said it was along the lines of: if water from jacuzzi was to splash onto motor, then water would have a potential which may not be enough to operate mcb/rcbo/fuse, therefore a larger earth is required, typically 16mm or 25mm

 

[needasparks]

Still can't get my head round it needing to be bigger than the phase supply to it.

 

[Dean Williams]

would it have anything to do with the resistance of the water in the jacuzzi, like if the water resistance is lower than the earth resistance

 

[Engineer54]

I fail to see why you would install a bigger CPC than the phase conductors?? What on gods earth is the added protection of a 16/25mm CPC going to give you??

Most Jacuzzi control panels now incorporate integral RCD protection too!!! lol!!

 

[leckyant]

Beats me man. Why don't you suggest 1/2 a dozen 1 milli amp RCDs in series

 

[spark 68]

The only time it may need to be larger CSA that I can think of, is if it is a combined CPC and bonding conductor for PME/TNC-S, and you are extending the zone

 

[telectrix]

the way he said it was along the lines of: if water from jacuzzi was to splash onto motor, then water would have a potential which may not be enough to operate mcb/rcbo/fuse, therefore a larger earth is required, typically 16mm or 25mm

which would seem to suggest that he reckons that copper less than 16mm has a higher resistance than water.

 

[Engineer54]

the way he said it was along the lines of: if water from jacuzzi was to splash onto motor, then water would have a potential which may not be enough to operate mcb/rcbo/fuse, therefore a larger earth is required, typically 16mm or 25mm

Total hogwash!! lol!!

 

[Inteificio]

the way he said it was along the lines of: if water from jacuzzi was to splash onto motor, then water would have a potential which may not be enough to operate mcb/rcbo/fuse, therefore a larger earth is required, typically 16mm or 25mm

So if water (which is a lousy conductor), splashes on to a motor (which would be IP rated), the difference of a few milliohms of conductor width will be affected but the few thousand ohms of water path.

Seems implausible to me, but then again i often overlook stuff.