Frame bonding and TL electrical separation?

[T0M0]

Hi All,

My assessor suggested there is no need for frame bonding if a TL inverter has electrical separation between DC and AC. This is news to me and wonder if he is getting confused RCD requirements, but he is adamant.

Anybody heard this? Is everybody bonding TL’s and including earth spikes for TNCS etc?

Out of interest, what type RCD’s are being used for TL’s? I have it from SMA that Type A can be used. Wonder if anyone is using Type AC?

Thanks for reading.

 

[BruceB]

Ask your assessor how that follows from the DTI decision tree or what his authority for that is.

 

[T0M0]

Ask your assessor how that follows from the DTI decision tree or what his authority for that is.

Thanks for that. Obviously asked and was advised it was one of the leading inverter manufacturers. I have also asked the same question of said company, awaiting reply!

Manufacturers instruction takes precedence so I'm interested in what others do if not following DTI.

Thanks again.

 

[BruceB]

Let us know what they (SMA?) are willing to put in writing in due course. Inverters are used in so many different places around the world that the standard inverter manufacturer's response on grounding frames is likely to be 'follow the local codes'.
Regards
Bruce

 

[SibertSolar]

@OP - if using a TL inverter (where there is no simple separation between the DC and AC circuits) then a Type-AC RCD should never be used. The reason is that the trip coil in a Type-AC RCD will not cope with any inherent DC leakage current (pulsed or pure) present within the system, whether generated by the inverter, the PV installation itself, or from a fault condition in either case. I've mentioned this a couple of times previously on here - Germany do not use Type-AC RCDs at all in any of their electrical installations, their most "basic" RCD is the Type-A. When German inverter manufacturers, such as SMA, mention not needing a Type-B RCD on their TL inverter spec's/documents, they mean use a Type-A by default. Current industry legislation/guidelines and (some) inverter manufacturer's statements are still under review and "might" change in the near future.

Just fyi but most Type-A RCDs will not cope with more than 6mA of pure or pulsed DC leakage current being present. Where more than 6mA exists, a Type-B is recommended. Always check with the inverter manufacturer as to their official stance on what type of RCD to use for a TL installation and it's always worth asking them what their values/numbers are for the inverter's DC leakage current (amplitude and frequency is always handy to know) being inherently imposed onto the AC side of the circuit under normal operating conditions.

Hope this helps,

Andy