2nd Garage Board

[GarryT]

Hi, Just a quick question on installing a second board for Solar PV in my garage.
I have a 2 way board at the moment with RCD protection for lighting and sockets, supplied from the main house DB (20A 4.0mm cable).
I have previously installed a separate 6.0mm cable from the main DB to the garage for Solar PV.
Couple of questions?
1. I have connected the 6.0mm cable for the Solar PV to a 32A MCB directly off the mains switch in the house DB, (No RCD protection), should this be an RCBO?
2. What protection do I need in the second board in the garage for the Solar PV /Inverter? I know I need SPD protection, do I just need mains switch and 20A MCB? or should that be RCBO also?
Thanks
GT

 

[Tom256]

Hi, Just a quick question on installing a second board for Solar PV in my garage.
I have a 2 way board at the moment with RCD protection for lighting and sockets, supplied from the main house DB (20A 4.0mm cable).
I have previously installed a separate 6.0mm cable from the main DB to the garage for Solar PV.
Couple of questions?
1. I have connected the 6.0mm cable for the Solar PV to a 32A MCB directly off the mains switch in the house DB, (No RCD protection), should this be an RCBO?
2. What protection do I need in the second board in the garage for the Solar PV /Inverter? I know I need SPD protection, do I just need mains switch and 20A MCB? or should that be RCBO also?
Thanks
GT

The first question that needs an answer is what would be the reason for the RCD protection Garry?

Has the Invertor manufacturer asked for such or is it because of the install method on the supply to the gargae board?

 

[GarryT]

The first question that needs an answer is what would be the reason for the RCD protection Garry?

Has the Invertor manufacturer asked for such or is it because of the install method on the supply to the gargae board?

Cable protection for the 6mm cable back to the main DB?

 

[Tom256]

Cable protection for the 6mm cable back to the main DB?

If the Invertor manufacturer confirms simple separation in place (may need this info) and with no rcd requirement on the AC side by the manufacturer then it comes down to how your 6mm cable is installed. {most manufacturers of Invertors do not advise RCD's}

However, if it is needed it could be for what is called 'Additional Protection' or for 'fault protection' should the Zs of the circuit be too high.

Before I go on too long do you understand those definitions / related requirements [Additional Protection / Fault Protection] ?

 

[GarryT]

If the Invertor manufacturer confirms simple separation in place (may need this info) and with no rcd requirement on the AC side by the manufacturer then it comes down to how your 6mm cable is installed. {most manufacturers of Invertors do not advise RCD's}

However, if it is needed it could be for what is called 'Additional Protection' or for 'fault protection' should the Zs of the circuit be too high.

Before I go on too long do you understand those definitions / related requirements [Additional Protection / Fault Protection] ?

Yes I understand the definitions, I was thinking for cable protection, part of the 6mm cable run is concealed in a partition wall.
Just wondering if the inverter has some form of residual current protection?
Found this on the Fox Ess Inverter site.
Installation and Selection of an External RCD device
- An external RCD is required in some countries. The installer must check which type of RCD is required by
the specific local electric codes. Installation of an RCD must always be conducted in accordance with local
codes and standards. Fox ESS recommends the use of a type-A RCD. Unless a lower value is required by
the specific local electric codes, Fox ESS suggests an RCD value between 100mA and 300mA.
- In installations where the local electric code requires an RCD with a lower leakage setting, the discharge
current might result in nuisance tripping of the external RCD. The following steps are recommended to avoid
nuisance tripping of the external RCD:
1. Selecting the appropriate RCD is important for correct operation of the installation. An RCD with a rating of
30mA may actually trip at a leakage as 15mA (according to IEC 61008). High quality RCDs will typically trip at a
value closer to their rating.
2. Configure the trip current of the inverter’ internal RCD to a lower value than the trip current of the external RCD.
The internal RCD will trip if the current is higher than the allowed current, but because the internal inverter RCD

 

[Tom256]

Yes I understand the definitions, I was thinking for cable protection, part of the 6mm cable run is concealed in a partition wall.
Just wondering if the inverter has some form of residual current protection?
Found this on the Fox Ess Inverter site.
Installation and Selection of an External RCD device
- An external RCD is required in some countries. The installer must check which type of RCD is required by
the specific local electric codes. Installation of an RCD must always be conducted in accordance with local
codes and standards. Fox ESS recommends the use of a type-A RCD. Unless a lower value is required by
the specific local electric codes, Fox ESS suggests an RCD value between 100mA and 300mA.
- In installations where the local electric code requires an RCD with a lower leakage setting, the discharge
current might result in nuisance tripping of the external RCD. The following steps are recommended to avoid
nuisance tripping of the external RCD:
1. Selecting the appropriate RCD is important for correct operation of the installation. An RCD with a rating of
30mA may actually trip at a leakage as 15mA (according to IEC 61008). High quality RCDs will typically trip at a
value closer to their rating.
2. Configure the trip current of the inverter’ internal RCD to a lower value than the trip current of the external RCD.
The internal RCD will trip if the current is higher than the allowed current, but because the internal inverter RCD

Busy day , very late/early so to answer quickly.

No automatic need for RCD/RCBO but if the 6mm cable is in a wall less than 50mm without suitable protection and/or wall containing metallic sections then the 30mA RCD / RCBO is needed. Likewise if it runs through a bathroom etc. It is needed for Additional Protection. The protection within the invertor is not going to protect the AC supply cable from the Consumer Unit.
It would have been better had this need for the RCD/RCBO been designed out by the cable run and perhaps that may still be an option for you?

The manufacturer instructions you have posted in the thread state Type A so they are giving assurance of spearation. The RCD MUST be double pole and break all live conductors (includes Neutral).
If two way current flow is likely the device must be bi-directional.
Be aware this can affect RCD/RCBO trip times as power is still available whilst the Invertor shuts down.
The RCD / RCBO MUST not feed any other circuits.
As it has not been mentioned I take it the system is not capable of Island Mode and is a pure grid feed that switches off once AC power loss?

Also, as a side whilst I am typing [and you may be aware], keep in mind the rated current of the consumer unit at source and this feed from the PV needs to be allowed for.
If you have a 100A rated consumer unit with a 100A fuse in the DNO cut out then you have to redesign to allow for the current from the PV system.
The formula for this is:
Rated current of assembly =/> Rated current of overcurrent device protecting the assembly + rated output of invertor/pv.

 

[GarryT]

Busy day , very late/early so to answer quickly.

No automatic need for RCD/RCBO but if the 6mm cable is in a wall less than 50mm without suitable protection and/or wall containing metallic sections then the 30mA RCD / RCBO is needed. Likewise if it runs through a bathroom etc. It is needed for Additional Protection. The protection within the invertor is not going to protect the AC supply cable from the Consumer Unit.
It would have been better had this need for the RCD/RCBO been designed out by the cable run and perhaps that may still be an option for you?

The manufacturer instructions you have posted in the thread state Type A so they are giving assurance of spearation. The RCD MUST be double pole and break all live conductors (includes Neutral).
If two way current flow is likely the device must be bi-directional.
Be aware this can affect RCD/RCBO trip times as power is still available whilst the Invertor shuts down.
The RCD / RCBO MUST not feed any other circuits.
As it has not been mentioned I take it the system is not capable of Island Mode and is a pure grid feed that switches off once AC power loss?

Also, as a side whilst I am typing [and you may be aware], keep in mind the rated current of the consumer unit at source and this feed from the PV needs to be allowed for.
If you have a 100A rated consumer unit with a 100A fuse in the DNO cut out then you have to redesign to allow for the current from the PV system.
The formula for this is:
Rated current of assembly =/> Rated current of overcurrent device protecting the assembly + rated output of invertor/pv.

Thanks for your help on this Tom. I think I may be able to redirect the 6mm cable to avoid the section within the wall, thus negating the need for RCB/RCBO. Reading most threads on Solar PV seem to avoid the use of RCD's because of nuisance tripping.
Thanks Garry

 

[littlespark]

Thanks for your help on this Tom. I think I may be able to redirect the 6mm cable to avoid the section within the wall, thus negating the need for RCB/RCBO. Reading most threads on Solar PV seem to avoid the use of RCD's because of nuisance tripping.
Thanks Garry

You cant just "avoid" the use of RCD's for nuisance tripping... it will depend on how the cable is routed. (ie buried less than 50mm)

What has been changed is the sharing of RCD with other circuits.... They used to just tag the circuit breaker for PV at the end of a dual board with a common RCD over several circuit.... But it was found that, when the rcd tripped, the inverter would continue to power the affected circuits for too long before shutting down itself.... Too long past the 40ms it should take.