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Regulation 531.2.2.201
Regulation 531.3.1.201
No requirement to disconnect Or switch the neutral under fault conditions or for protection against electric shock for TT or TN systems unless additional measures are required by part 7 such as caravan installations etc
 
As for inspection and testing I'd approach that isolator 2m from a hottub and clearly see the reason they've converted to a TT arrangement. Possibly applaud the effort made as they've understood the risks exporting a TNCS arrangement.

Its all very well criticising but not one person has stated a different approach regarding the TT. (I would rather not TT the workshop DB.)

I wouldnt be applauding anything about the proposed plan of disconnecting the CPC at the isolator and connecting an earth rod.

I would not be converting any part of the installation to TT if possible, the TNCS earth will always be a better earth, I would prefer to install earth electrodes connected to the MET to guard against the possibility of a lost PEN.
They will eventually, hopefully, actually bring this in to our regulations.
 
You are not exporting TN-C-S, you are using a cpc which is derived from a TN-C-S source.
Yes my error
I wouldnt be applauding anything about the proposed plan of disconnecting the CPC at the isolator and connecting an earth rod.

I would not be converting any part of the installation to TT if possible, the TNCS earth will always be a better earth, I would prefer to install earth electrodes connected to the MET to guard against the possibility of a lost PEN.
They will eventually, hopefully, actually bring this in to our regulations.
I agree that i don't particularly want to use a TT with a less reliable earth. However i presumed thats standard practice regarding a hottub outside the equipotential zone. Thats why I've started the post for advice.
Could i use theTNCS upto the hot tub and just connect an earth rod at the workshop DB as backup? Is this what your immplying?
 
Thats why I've started the post for advice.
Could i use theTNCS upto the hot tub and just connect an earth rod at the workshop DB as backup? Is this what your immplying?

Have you checked the regulations for outdoor swimming pools as they are the closest thing to an outdoor hottub?

I'm not implying anything, I'm sharing my opinion that earth electrodes connected to the MET are the best solution.
I'm certainly not suggesting 'just connect an earth rod' because a single earth rod is never enough to provide a reliably low Ra.
 
I agree that i don't particularly want to use a TT with a less reliable earth.
I guess the real issue is not so much the reliability of the TT's earth as such (you could have two rods in different areas and two wires so no single point of failure) but making sure it will reliably disconnect on a fault.

With a TN-S / TN-C-S you have RCD, magnetic, and thermal actions that will all ultimately trip the breaker, but on TT only the RCD will realistically do it as you simply won't have a low enough Ze.

But if you go for the more traditional TT set up for the workshop with a 100mA S-type RCD incomer and then 30mA RCBO for each circuit then you are not relying on a single RCD to disconnect on a fault.

However i presumed thats standard practice regarding a hottub outside the equipotential zone. Thats why I've started the post for advice.
The subject of TN-C-S and outdoor stuff comes up regularly and always prompts a bit of a heated debate as there are sound points and strongly held beliefs on many fronts! So far hot tubs and similar have not really been a comon subject, but the risk of EV changers for cars had mandated something must be done, but not clear yet if a cheap and easy solution outside of EV kit is going to be widespread.

For now it is "to TT, or not to TT, that is the question"

Could i use the TNCS up to the hot tub and just connect an earth rod at the workshop DB as backup? Is this what your immplying?
A single standard rod will never get a low enough impedance to pull down a PME fault voltage far enough. If you had a couple of rods around the hot tub zone (or some buried mesh, etc) you might be able to keep the step/touch potential gradient down but that would be a major design effort (needing the sort of modelling software they use for lightning protection and earth validation for major installations) to establish its effectivness.
 
What we need is a change of attitude towards protection against a PEN fault/earthing/taking responsibility.

Foundation trenches are a great place for a horizontal electrode, an earth connection to the steel reinforcing is also a great electrode. Its already normal for the reinforcing to be connected to the elctrical earth on big buildings, how much of a change would it be to make this common practice for small buildings?

If building regs changed to require 2 connection points to the rebar to be made available for earthing when any foundation or slab is cast then I think we could easily achieve good earth connections for all installations.
Obviously this wouldn't immediately affect existing buildings, but that's not a reason not to do it for new buildings, and slowly as extensions are built etc the overall effect would be to make everyone safer.
 
Single pole rcbos would not be a departure as there is no requirement which specifies them.
Regulation 531.2.2.201
Regulation 531.3.1.201
No requirement to disconnect Or switch the neutral under fault conditions or for protection against electric shock for TT or TN systems unless additional measures are required by part 7 such as caravan installations etc
You are both missing the point. SP RCBO's would only be a departure where a T/D RCD main switch was installed, not because the regs state SP RCBO's are not permitted, but because a single fault would probably still trip the main RCD. If someone said they were protecting the entire installation with a single RCD and MCB's you would say that is non compliant, the effect of a fault on a final circuit would be exactly the same as a T/D RCD with SP RCBO's.....total loss of power, therefore that arrangement is non compliant as well for the same reason.
 
The usual reason for going 3-core on single phase are one or more of:
  • Not meet the Zs for disconnection times for sub-main OCPD due to high R2
  • Armour not meeting adiabatic limit for fault clearing
  • Not meeting 10mm copper equivalent bonding for extraneous conductive parts on TN-C-S
There probably are other things I have missed and other folk will point out tomorrow...
I know there was another reason:
  • High integrity earthing (high leakage currents) with two CPC
Now can I turn this in to a Spanish Inquisition sketch?
 
You are both missing the point. SP RCBO's would only be a departure where a T/D RCD main switch was installed, not because the regs state SP RCBO's are not permitted, but because a single fault would probably still trip the main RCD. If someone said they were protecting the entire installation with a single RCD and MCB's you would say that is non compliant, the effect of a fault on a final circuit would be exactly the same as a T/D RCD with SP RCBO's.....total loss of power, therefore that arrangement is non compliant as well for the same reason.
I do get your point, mearly pointing out what the regulations say about the neutral on TT and TN systems.
However there’s a difference between a departure and a non compliance, your example is not a departure as to depart is to afford the same degree of safety etc etc.
Completely agree that you would want selectively between rcd’s
 
I do get your point, mearly pointing out what the regulations say about the neutral on TT and TN systems.
However there’s a difference between a departure and a non compliance, your example is not a departure as to depart is to afford the same degree of safety etc etc.
Completely agree that you would want selectively between rcd’s
Agreed I used the wrong terminology....not a departure but definitely a non compliance IMO, been too many weeks not working!
 
I'm about to install a new supply for one on a job, after enquiring the hot tub manufacturer has said it does not require it's own earth electrode and is fine on tn-c-s...

Sparky mate of mine is installing one and the manufacturer for his one have said it must be on TT.

As much of a minefield as sodding car chargers
 
I'm about to install a new supply for one on a job, after enquiring the hot tub manufacturer has said it does not require it's own earth electrode and is fine on tn-c-s...

Sparky mate of mine is installing one and the manufacturer for his one have said it must be on TT.

As much of a minefield as sodding car chargers
Never done myself, and I’m aware of the various issues, but isn’t one of the main concerns is what the bathers are stepping onto when they get out of the tub. That is grass or floor of wooden shed for example?
 
I suspect water heating is the risk, not the pump.

The Matt:e box is quite a reasonable approach but it relies on the volts being out of range and I did see a demo where you might not get enough L-N anomaly to detect a PME fault that has raised N+E to 70V or so above true Earth.

Still, nothing is ever perfect and it is about managing risk levels to a reasonable degree.
 
I'm about to install a new supply for one on a job, after enquiring the hot tub manufacturer has said it does not require it's own earth electrode and is fine on tn-c-s...

Sparky mate of mine is installing one and the manufacturer for his one have said it must be on TT.

As much of a minefield as sodding car chargers
I went for the option of TT at the hot tub. Just sat better with me. I think you have to look at the external influences and siting of the tub. This was not near any other exposed conductive parts and located near retaining walls with soil etc. To me it should be treated as a swimming pool. If smashing a rod in will create a form of equipotential zone around the tub I'm doing it., albeit relying on a RCD for fault protection.
 

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