RCD Needed on Circuit to Solar Inverter (UK)?

[aesmith]

Hi,

Our solar inverter is connected to a dedicated circuit from an RCBO in a CU in our garage. The RCBO was chosen, supplied and installed by the solar installers. The cable runs up from the CU in plastic trunking, goes through a concrete block wall to the next room, then is clipped to the wall and along a purlin at ceiling height before dropping down to the inverter in plastic conduit.

Since installation last May the RCBO has tripped twice for no apparent reason. I haven't had any feedback yet from the installer, but after the first trip they said there was no indication of any fault with the inverter. I have suggested that they replace the RCBO just for elimination.

However looking at information from the manufacturer, Solaredge, it seems they're not particularly keen on an external RCD. They recommend that if one if fitted it should be 100mA or 300mA, and there's a comment that where "local codes" require a 30mA RCD then there may be nuisance trips.

But before exploring that further I'd just like to confirm the current requirements. From what I've described, does it sound as if RCD protection is required on that particular circuit cable run?

Thanks,

 

[littlespark]

It possibly doesnt need one.

Under the regs, a circuit would need RCD protection if any of the following were true

Supplies sockets not exceeding 32A
Passes through, or serves a room containing a bath or shower
Any circuit with luminaires (lights)
Is buried in a wall less than 50mm deep*

*This is the one that covers basically everything in a newbuild house... but if you say the cable is surface run, even in trunking...... it may not be required.


The installers, however, may have their own procedures that EVERYTHING must be RCD protected whether it requires it or not.

 

[westward10]

Or if required for fault protection.

 

[mainline]

Hi,

Our solar inverter is connected to a dedicated circuit from an RCBO in a CU in our garage. The RCBO was chosen, supplied and installed by the solar installers. The cable runs up from the CU in plastic trunking, goes through a concrete block wall to the next room, then is clipped to the wall and along a purlin at ceiling height before dropping down to the inverter in plastic conduit.

Since installation last May the RCBO has tripped twice for no apparent reason. I haven't had any feedback yet from the installer, but after the first trip they said there was no indication of any fault with the inverter. I have suggested that they replace the RCBO just for elimination.

However looking at information from the manufacturer, Solaredge, it seems they're not particularly keen on an external RCD. They recommend that if one if fitted it should be 100mA or 300mA, and there's a comment that where "local codes" require a 30mA RCD then there may be nuisance trips.

But before exploring that further I'd just like to confirm the current requirements. From what I've described, does it sound as if RCD protection is required on that particular circuit cable run?

Thanks,

What's the model number ?

Most inverters will have an internal rcd
These inverters by construction cannot feed DC fault current into the installation, as required by IEC 60364-7-
712:2002.

I would change the rcd to a type A 100ma, as suggested by the manufacturer.

 

[aesmith]

What's the model number ?

Most inverters will have an internal rcd
These inverters by construction cannot feed DC fault current into the installation, as required by IEC 60364-7-
712:2002.

I would change the rcd to a type A 100ma, as suggested by the manufacturer.

Thanks. It's a Solaredge "Home Hub" inverter model SE6000H-RWBMNBF54.

If the Wiring Regulations say an RCD is needed, doesn't that mean it needs to be 30mA?

 

[aesmith]

Or if required for fault protection.

Sorry I don't think I follow, does that mean if required by the connected equipment?

 

[newfutile]

Type of earthing (ie:TT) could require (RCD) Residual Current Device to meet disconnection times,also buried in walls,passing though bathroom or supplying standard sockets will require one.little spark explains this better above

 

[aesmith]

Thanks. Earthing is TNS. The circuit runs entirely within a detached outbuildings, from the garage into an adjoining utility room where the solar gear is installed. Does passing through a wall perpendicular to the surface count as buried in the wall?

 

[happysteve]

Thanks. Earthing is TNS. The circuit runs entirely within a detached outbuildings, from the garage into an adjoining utility room where the solar gear is installed. Does passing through a wall perpendicular to the surface count as buried in the wall?

No, it doesn't. (It's a fair question though!) You're all good

 

[aesmith]

OK thanks. I don't want to go against the installer's opinions, but I think I will suggest to them that the breaker could maybe be changed to an MCB.

 

[aesmith]

OK thanks. I don't want to go against the installer's opinions, but I think I will suggest to them that the breaker could maybe be changed to an MCB.

Thanks for all the comments. I've had some feedback from the installers, they say they're going to replace the RCBO as current rules say it needs to be "bidirectional". A quick search around for myself, all discussion about bidirectional devices relates to RCDs or RCBOs. Does that mean an MCB can't be used? Or are MCBs inherently bidirectional?

Thanks. I know there's a risk I'm going to come across as a smart alec talking to the installers in this detail, I just don't want to be an incorrect smart alec.

 

[richy3333]

Is it an A or AC RCBO? I've fitted plenty of type A RCBO's on Solar Edge inverters and never had a nuisance tripping issue. Prior to the new requirements they were not Bi-directional.

 

[aesmith]

Is it an A or AC RCBO? I've fitted plenty of type A RCBO's on Solar Edge inverters and never had a nuisance tripping issue. Prior to the new requirements they were not Bi-directional.

Currently it's a Hager ADA332G which I see is described as "Type A(AC & Pulsating DC Sensitive)"

 

[mainline]

Thanks for all the comments. I've had some feedback from the installers, they say they're going to replace the RCBO as current rules say it needs to be "bidirectional". A quick search around for myself, all discussion about bidirectional devices relates to RCDs or RCBOs. Does that mean an MCB can't be used? Or are MCBs inherently bidirectional?

Thanks. I know there's a risk I'm going to come across as a smart alec talking to the installers in this detail, I just don't want to be an incorrect smart alec.

Clause 6 .1 (Standard marking) of BS EN 60898-1:2019 requires that:
If it is necessary to distinguish between the supply and the load terminals, the former shall be indicated by arrows pointing towards the circuit-breaker and the latter by arrows pointing away from the circuit-breaker.
In the case of RCCBs and RCBOs, Clause 6 (Marking and other product information) of BS EN 61008 1:2012+A12:2017 and BS EN 61009-1:2012+A12:2016 both state:
If it is necessary to distinguish between the supply and the load terminals, they shall be clearly marked (e.g. by "line" and
"load" placed near the corresponding terminals or by arrows indicating the direction of power flow).

 

[mainline]

Currently it's a Hager ADA332G which I see is described as "Type A(AC & Pulsating DC Sensitive)"

Many RCBOs do not switch the neutral and so would not be suitable for use to provide additional protection to the AC supply cable to the PV system.

 

[aesmith]

Many RCBOs do not switch the neutral and so would not be suitable for use to provide additional protection to the AC supply cable to the PV system.

Thanks. Back to basics I think I'm clear that the actual circuit cabling doesn’t require RCD protection, and Solaredge don't recommend it. So does the requirement to disconnect both L and N apply if we just had an MCB type breaker? To be honest I'm not sure how we could comply, it's a Hager DB and as far as I can see neither Hager RCBOs nor MCBs disconnect N.

 

[mainline]

it's a Hager DB and as far as I can see neither Hager RCBOs nor MCBs disconnect N.

Hager ADC932R 32A Double Pole RCBO C Curve 6kA 30mA Type A

Also Hager NDN232A MCB