Does SWA need RCD on a TT?

[HappyHippyDad]

I know the answer, at least I think I do as I am now questioning myself! It's just I've seen a few jobs recently where the electrician (or who ever did the job) did not give any fault protection to the armoured cable, so I am wondering if I am missing something?

The most recent example from today is an EVCP which has been installed using SWA cable. The SWA goes directly into the consumer unit where it is supplied from a MCB. There is no relevant RCD protection on this cable. I realise it would not be required for TNCS or TNS as it would have fault protection from the main fuse. However, this is a TT, so there will be no fault protection on the SWA cable.

This is clearly wrong, isn't it?

 

[westward10]

Unless ADS is satisfied by the mcb then it is wrong.

 

[James]

32A B type Max Zs of 1.67 Ohm

would be tricky to achieve with TT earthing.

although with a 100mA time delay rcd it would be easy to achieve ADS

 

[newfutile]

32A B type Max Zs of 1.67 Ohm

would be tricky to achieve with TT earthing.

although with a 100mA time delay rcd it would be easy to achieve ADS

dont you mean 1.37 ohms or 1.1 ish at 80% values.
maybe with many rods mates or structural building earthing but i doubt it.
(RCD) Residual Current Device will comply but can lead to selectivity issues

 

[Risteard]

I know the answer, at least I think I do as I am now questioning myself! It's just I've seen a few jobs recently where the electrician (or who ever did the job) did not give any fault protection to the armoured cable, so I am wondering if I am missing something?

The most recent example from today is an EVCP which has been installed using SWA cable. The SWA goes directly into the consumer unit where it is supplied from a MCB. There is no relevant RCD protection on this cable. I realise it would not be required for TNCS or TNS as it would have fault protection from the main fuse. However, this is a TT, so there will be no fault protection on the SWA cable.

This is clearly wrong, isn't it?

As others point out an RCD will almost certainly be required for fault protection as it is almost inconceivable that a reliably low Earth fault loop impedance will exist on a TT system (though technically permissible). That said the EVSE will nearly always require a maximum 30mA RCD for additional protection at this point. What EVSE has been installed, and is a circuit breaker actually OK for it?

 

[HappyHippyDad]

As others point out an RCD will almost certainly be required for fault protection as it is almost inconceivable that a reliably low Earth fault loop impedance will exist on a TT system (though technically permissible). That said the EVSE will nearly always require a maximum 30mA RCD for additional protection at this point. What EVSE has been installed, and is a circuit breaker actually OK for it?

ohme pro.
It has type A RCD and pen fault protection inside it, but It's the cable leading up to it that I'm concerned with.
The customer got me to quote, then went with someone else, who I'm guessing wasn't an electrician as there are also other things wrong. I was doing a hob install for them, so had a quick look at the EVCP install.

Top entry into a weatherproof box,
No fault protection on cable.
SWA not glanded properly into the CU.
Armour not earthed
I'm guessing... no EIC or notification.

It's just horrible.

 

[Risteard]

ohme pro.
It has type A RCD and pen fault protection inside it, but It's the cable leading up to it that I'm concerned with.
The customer got me to quote, then went with someone else, who I'm guessing wasn't an electrician as there are also other things wrong. I was doing a hob install for them, so had a quick look at the EVCP install.

Top entry into a weatherproof box,
No fault protection on cable.
SWA not glanded properly into the CU.
Armour not earthed
I'm guessing... no EIC or notification.

It's just horrible.

I can't see how the RCD in the Ohme Pro could be to either BS EN 61008 or BS EN 61009.

 

[westward10]

There is a huge amount of EV chargers which incorporate an RCD which are non compliant to BS7671.

 

[Mark1714]

There is a huge amount of EV chargers which incorporate an RCD which are non compliant to BS7671.

View: https://youtu.be/2re1TyHZZJ8?si=kmVydIEtu1A_gn48

This shows how Myenergi are throwing installers of their Zappi under the bus with a change in their requirements for RCD, that was not originally required? in relation to warranty claims.

 

[Risteard]

View: https://youtu.be/2re1TyHZZJ8?si=kmVydIEtu1A_gn48

This shows how Myenergi are throwing installers of their Zappi under the bus with a change in their requirements for RCD, that was not originally required? in relation to warranty claims.

Whilst myenergi may have suggested that it wasn't required, I would argue that BS 7671 always did require it with the wording in the Standard. As such I've never installed a Zappi without a dedicated RCD which disconnects all live conductors. That's not to suggest that they're in the right for dismissing claims unrelated to this issue, however.

 

[Mark1714]

Whilst myenergi may have suggested that it wasn't required, I would argue that BS 7671 always did require it with the wording in the Standard. As such I've never installed a Zappi without a dedicated RCD which disconnects all live conductors. That's not to suggest that they're in the right for dismissing claims unrelated to this issue, however.

I am with you. Their RCD did not comply with the standard. The only one I know that does comply, though I am sure it isn't alone, is the Garo Entity Pro. That is an RCD with a physical test but, along with PEN fault and load management. My concern is for installers who listened to the argument about the fast moving pace of technology covered by the indent in chapter 7 that I cant remember about it, similar to the unicorn device, that was considered a "get out of jail free" card.