Whirlpool bath. Is there legal requirement for additional dedicated RCD even if we have Double RCD CU?

[benhurr]

Hi to all. Is there legal requirement for additional dedicated RCD even if we have Double RCD CU?
Our whirlpool bath has ambiguous instructions: first it saying that it has to have separate RCD outside. Then it says "IF separate RCD installed" like if there as an option not installing it.
We have double RCD CU and it has spare switches in case if dedicated wire is needed.

 

[pc1966]

It absolutely must have RCD protection. Given the very high risk of water and electrics together then having a 2nd RCD in series just for the tub is not a bad thing as it reduces the chance of a single failure leaving it unprotected.

Also should there be some fault with the tub that trips them, you will be able to reset the house one without having to determine the tub is at fault and separately isolate it.

Is this a small one that plugs in to a 13A socket or something the needs a dedicated feed? For 13A outlets you can get outdoor rated RCD sockets that might be a simple solution if outdoors, or indoor versions.

EDIT: Also check the specifications, normally domestic RCDs are 30mA rated but you might find the manufacturer recommends 10mA in which case it will need a special choice (you can get 13A RCD sockets with 10mA trip as well).

 

[MJPD29]

As advised above, it is essential, and 10ma may be preferred. Safety first when your sitting in a giant kettle

 

[benhurr]

It absolutely must have RCD protection. Given the very high risk of water and electrics together then having a 2nd RCD in series just for the tub is not a bad thing as it reduces the chance of a single failure leaving it unprotected.

Also should there be some fault with the tub that trips them, you will be able to reset the house one without having to determine the tub is at fault and separately isolate it.

Is this a small one that plugs in to a 13A socket or something the needs a dedicated feed? For 13A outlets you can get outdoor rated RCD sockets that might be a simple solution if outdoors, or indoor versions.

EDIT: Also check the specifications, normally domestic RCDs are 30mA rated but you might find the manufacturer recommends 10mA in which case it will need a special choice (you can get 13A RCD sockets with 10mA trip as well).

It says 30ma and there was a milliseconds specs as well, I even bought 2 of those rcd spurs as soon as I read the manual. It just the other day I noticed that on the other electrician formum they mostly against additional rcds on already protected by rcd circuit. Even argued that it may fail building control etc , others argued that even if it not necessary as long as it is not harmful it is okay) That’s what made me doubt. Looks like the regulations are fairly ambiguous)

 

[MJPD29]

It will not fail building control, where did you see that? You'll need appropriate test gear to ensure the rcd is operating correctly too. If there circuit is already protected by the appropriate rcd then there is no need to add another. The circuit will also need tested and certified to ensure it meets regulations.

 

[benhurr]

yet here people posting that whirlpool bath tub will benefit from extra rcd on already cu-rcd protected circuit. so what is going on? or is it extra safety just for peace of mind beyond reasonable requirements?

 

[benhurr]

It will not fail building control, where did you see that? You'll need appropriate test gear to ensure the rcd is operating correctly too. If there circuit is already protected by the appropriate rcd then there is no need to add another. The circuit will also need tested and certified to ensure it meets regulations.

yet here people posting that whirlpool bath tub will benefit from extra rcd on already cu-rcd protected circuit. so what is going on? or is it extra safety just for peace of mind beyond reasonable requirements?

 

[davesparks]

Looks like the regulations are fairly ambiguous)

The regulations aren't ambiguous on the matter, they require 30mA RCD protection to be installed for various reasons.
In the average domestic installation this means that RCD protection is required for all final circuits at the CU.

Everything else you have read online, here and elsewhere, is people's opinions on what can be done over and above the regulations.

The wiring regulations set a minimum standard, most of us try to exceed that standard.

 

[benhurr]

The regulations aren't ambiguous on the matter, they require 30mA RCD protection to be installed for various reasons.
In the average domestic installation this means that RCD protection is required for all final circuits at the CU.

Everything else you have read online, here and elsewhere, is people's opinions on what can be done over and above the regulations.

The wiring regulations set a minimum standard, most of us try to exceed that standard.

if some electricians confident that extra rcd is required despite being already on cu-rcd circuit and some including you (perhaps) -- not , then this is the evidence of ambiguity (IMHO)

 

[davesparks]

if some electricians confident that extra rcd is required despite being already on cu-rcd circuit and some including you (perhaps) -- not , then this is the evidence of ambiguity (IMHO)

No it isn't, it is evidence that different people have different opinions on going beyond the requirements of the regulations.

Ask any one of those electricians to show you the requirement for a second 30mA RCD connected in series in the regulations and they will not be able to.

 

[benhurr]

No it isn't, it is evidence that different people have different opinions on going beyond the requirements of the regulations.

Ask any one of those electricians to show you the requirement for a second 30mA RCD connected in series in the regulations and they will not be able to.

Would you put a second rcd for whirlpool bath on already protected by cu-rcd circuit?

 

[RichardM]

There is no requirement for a second RCD in fact it makes it more inconvenient for the occupier as both RCDs will probably trip at the same time. If you are concerned about tripping half the house, assuming it's a separate circuit for the bath disconnect the circuit at the C/U on the RCD rail and fit an RCBO. Socket type RCDs even 10mA will not necessarily protect the main RCD, believe me discrimination in RCDs / RCBOs is more luck than science.

 

[davesparks]

Would you put a second rcd for whirlpool bath on already protected by cu-rcd circuit?

No I wouldn't because the second one would be redundant. And depending on the exact make and model used could cause more hassle than good.

If one was installed then the upstream RCD (at the CU) will trip first because the normal cumulative leakage current of the installation will bias it to trip first.

If the one installed downstream is the usual SFCU type then, experience has shown, that pressing the test button on it often causes the RCD at the CU to trip first. This test button is often the only means of switching it off so any time you want to turn it off half the house goes off.

 

[brianmoooore]

If one was installed then the upstream RCD (at the CU) will trip first because the normal cumulative leakage current of the installation will bias it to trip first.

The tripping tolerance of RCDs is +0%/-50%, meaning a 30mA RCD is within tolerance as long as it trips in the required time when subjected to anywhere between 15mA and 30mA of leakage.
There will be a balance of probability that the upstream RCD will trip if considering a large number of installations, but for any individual installation, this cannot be assumed. The tolerance of sensitivity is likely to be greater than any cumulative leakage.