TT System Existing is a multi9 13 way RCD main switch DB

[fattony]

Hi

Ive read a few discussions on the topic but what setup would you recommend for replacing a DB on a domestic TT system?

I've moved house and need to get the meter changed ready for the car charger, I need to upgrade the severely dated DB at the same time.

Existing is a multi9 13 way RCD main switch DB, one of those circuits is a sub main to the garage which I'm intending on adding a car charger to at some point, realistically the only option I see is a 16 way DB, I was looking at this

https://www.cef.co.uk/catalogue/products/5183084-16-way-100a-sp-n-type-a-distribution-board-with-incomer?msclkid=061440893d991f53b24b2659d78aba45&utm_source=bing&utm_medium=cpc&utm_campaign=Smart%20Shopping%3A%20Switchgear%20%26%20Distribution&utm_term=4587368677094774&utm_content=Smart%20Switchgear%20%26%20Distribution&gclid=061440893d991f53b24b2659d78aba45&gclsrc=3p.ds

The intention was to use RCBO's for the circuits which I think would allow me to keep the main switch, I think my next question is on the sub main to the garage, if this is for example a 50A 30mA RCBO in the main DB would I need to install RCD protection in the sub main or should that not be a RCBO and a separate earth ROD installed for the garage, this would prevent a fault tripping a RCD upstream.

Thanks

 

[suffolkspark]

Hi

Ive read a few discussions on the topic but what setup would you recommend for replacing a DB on a domestic TT system?

I've moved house and need to get the meter changed ready for the car charger, I need to upgrade the severely dated DB at the same time.

Existing is a multi9 13 way RCD main switch DB, one of those circuits is a sub main to the garage which I'm intending on adding a car charger to at some point, realistically the only option I see is a 16 way DB, I was looking at this

https://www.cef.co.uk/catalogue/products/5183084-16-way-100a-sp-n-type-a-distribution-board-with-incomer?msclkid=061440893d991f53b24b2659d78aba45&utm_source=bing&utm_medium=cpc&utm_campaign=Smart%20Shopping%3A%20Switchgear%20%26%20Distribution&utm_term=4587368677094774&utm_content=Smart%20Switchgear%20%26%20Distribution&gclid=061440893d991f53b24b2659d78aba45&gclsrc=3p.ds

The intention was to use RCBO's for the circuits which I think would allow me to keep the main switch, I think my next question is on the sub main to the garage, if this is for example a 50A 30mA RCBO in the main DB would I need to install RCD protection in the sub main or should that not be a RCBO and a separate earth ROD installed for the garage, this would prevent a fault tripping a RCD upstream.

Thanks

An rcbo or rcd in the garage and a rod wont stop it tripping the upstream one. If you could get pme then you could use an mcb for the submain, and then add more rcbos in the garage

 

[fattony]

An rcbo or rcd in the garage and a rod wont stop it tripping the upstream one. If you could get pme then you could use an mcb for the submain, and then add more rcbos in the garage

My only thought was I shouldn’t be exporting the Earth from the house hence the 2nd rod.

There is currently a supply to the garage where they have exported the Earth, rcd main switch on this, so I could just fit a mcb in the house and RCD main switch or RCBO in the garage

Thanks

 

[suffolkspark]

My only thought was I shouldn’t be exporting the Earth from the house hence the 2nd rod.

There is currently a supply to the garage where they have exported the Earth, rcd main switch on this, so I could just fit a mcb in the house and RCD main switch or RCBO in the garage

Thanks

Nothing wrong with using 1 rod for the whole installation.

If you're keeping TT, the submain will need an rcd or rcbo infront of it won't it, think about the likely zs readings you'll be getting vs what the protective devices require to operate for fault protection. A 50A type B mcb needs 80% zs of 0.69 to disconnect. You're not getting that from any rod .

 

[Rockingit]

As I understand it, the next amendment being published to BS7671 will likely include the addition of an internal RCD to all EVC devices. However as the supply circuit may well require an RCD as well due to the existing requirements for cable installations when buried this potentially leads to a nuisance trip situation, which I think is maybe what you’re getting at. In this scenario, the minor risk and inconvenience of not knowing which device may trip under fault has been deemed not a nuisance.

 

[fattony]

As I understand it, the next amendment being published to BS7671 will likely include the addition of an internal RCD to all EVC devices. However as the supply circuit may well require an RCD as well due to the existing requirements for cable installations when buried this potentially leads to a nuisance trip situation, which I think is maybe what you’re getting at. In this scenario, the minor risk and inconvenience of not knowing which device may trip under fault has been deemed not a nuisance.

Yes it is really, Thats kind of where I got to in my head after reading SuffolkSpark’s post (thanks for that) I need the RCD to protect the sub main cable, the EVC has a RCD built in and if a fault were to develop then I’d have a multiple of RCD’s to reset.

RCBO is still the best setup as currently a fault will trip all 13 circuits (via the RCD main switch)

From what I’ve read a non RCD main switch is ok if using RCBO but the meter tails need to be secured and glanded?

 

[suffolkspark]

Yes it is really, Thats kind of where I got to in my head after reading SuffolkSpark’s post (thanks for that) I need the RCD to protect the sub main cable, the EVC has a RCD built in and if a fault were to develop then I’d have a multiple of RCD’s to reset.

RCBO is still the best setup as currently a fault will trip all 13 circuits (via the RCD main switch)

From what I’ve read a non RCD main switch is ok if using RCBO but the meter tails need to be secured and glanded?

Yes thats right, use a wiska tails gland, some consumer unit brands also then have a clamp which also holds the tails secure at the main switch. Youll probably want dp rcbo for your ev, so if your garage board will be main switch > mcbs, make sure you use a dp rcbo at least for that garage submain in your main board.

The wylex stubbies are switched neutral which may satisfy this, just check charger instructions, as some have a built in rcd now so its fine, i fitted a podpoint yesterday that didn't, and stipulated 2pole rcbo or rcd.

 

[fattony]

Nothing wrong with just changing this to a traditional split load board and save on the RCBO then really

 

[suffolkspark]

Nothing wrong with just changing this to a traditional split load board and save on the RCBO then really

How will you meet disconnection times without rcbo? What is your Ze?

 

[westward10]

The circuit for EVSE must not share an RCD for other circuits such as dual RCD boards unless one RCD is reserved solely for the EVSE. Your situation of a sub circuit having an RCD particularly if it is for additional protection is clouded as to whether this would be deemed as shared.

 

[suffolkspark]

The circuit for EVSE must not share an RCD for other circuits such as dual RCD boards unless one RCD is reserved solely for the EVSE. Your situation of a sub circuit having an RCD particularly if it is for additional protection is clouded as to whether this would be deemed as shared.

Has this always been the case? Ive seen many ev chargers on dual rcd boards? And in many installs with upfront rcd, i don't do them often, infact yesterdays was my third ever, and they've all been on their own as luck would have it rather than planned

Edit, came in in AM2, theres a little bit about it on hagers website, but then it goes on to saying you can still come off a dual rcd board if its a type A, but the charger still needs another one of its own downstream too

Another thing to keep an eye on at eicrs i guess, the amount of dog ---- ev installs i see

 

[westward10]

Has this always been the case? Ive seen many ev chargers on dual rcd boards? And in many installs with upfront rcd, i don't do them often, infact yesterdays was my third ever, and they've all been on their own as luck would have it rather than planned

Edit, came in in AM2, theres a little bit about it on hagers website, but then it goes on to saying you can still come off a dual rcd board if its a type A, but the charger still needs another one of its own downstream too

Another thing to keep an eye on at eicrs i guess, the amount of dog ---- ev installs i see

Section 722 was introduced in the 18th Ed and yes it has always been the case see Regulation 722.531.3.101 and should merit a Code if carrying out an EICR.

 

[suffolkspark]

So the only solution i can see here is to get pme on so the sub can be an mcb, or feed the ev from house db not via garage board.

 

[westward10]

I would say so yes or use electrical separation. The Regulation is pretty open as to how it applies regarding a sub circuit, does the RCD only apply to that sub circuit or would the downstream circuits be considered as sharing that RCD. If the sub circuit was 30ma for additional protection I would say shared as the downstream would not need further protection although this would strictly be non compliant but needs must on existing installations. If it wasn't 30ma but an RCD was used for fault protection on the sub circuit and downstream circuits were 30ma I'm not so sure this would be deemed shared.

 

[DPG]

Don't forget the SPD also.

 

[fattony]

The circuit for EVSE must not share an RCD for other circuits such as dual RCD boards unless one RCD is reserved solely for the EVSE. Your situation of a sub circuit having an RCD particularly if it is for additional protection is clouded as to whether this would be deemed as shared.

Didn’t know that, learn something new every day

 

[fattony]

One last question regarding the RCD on the meter tails, the meter tails will pass through a cavity wall to the external meter box, my heads telling me I would need RCD protection on this if less than 50mm in the wall but just looking to clarify

 

[fattony]

Regarding the EV, it’s an Ohme charger which I believe has a type A RCD built in, setup would be:

• 50A RCBO to feed garage db
• Garage db has no RCD protection
• 32A MCB from garage db to charger, charger has additional Type A RCD built in