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Temporary Generator RCD Requirement

Gyaneshwar Kumar

Hello, on one of my projects, I have an existing LV feeder pillar (TN-S system) that is normally supplied from an upstream Switchboard via an XLPE/SWA cable with an integral CPC. We are relocating the upstream Switchboard and it is planned to connect small temporary generator (100A TPN) to the feeder pillar to maintain supply to associated loads. None of the loads inherently require any RCD protection.  

My understanding is that for temporary portable generators, Regulation 551.4.4.2 applies which requires every final circuit to be provided by additional protection by means of an RCD. 

My questions is- Would a single 30 mA four-pole RCD installed at the generator outgoing, protecting the entire feeder pillar, satisfy the requirements of Regulation 551.4.4.2, or is a separate 30 mA RCD required for each outgoing circuit?

I don't see why it wouldn't satisfy the intent of the particular clause. Of course, there will be minor risk of nuisance tripping (although unlikely as no high standing leakage current generating equipment connected) and risk of losing supply to entire FP if there is fault on any outgoing but that is acceptable given the constraints of design and temporary nature of this arrangement. 

Any thoughts would be much appreciated. 

Edit: I think I didn't read the clause properly, it says “every final circuit shall be provided with additional protection…”—it does not say that each final circuit must have its own individual RCD. Hence, I believe a single device upstream that all finals pass through is acceptable. 

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    Stupidly left a temporary changeover in a large joinery works to the last minute. Only a matter of plugging the 63A TPN lead from the an existing changeover switch into the genny. Planned for a Sunday night, a dry run was made earlier in the week with the nightshift supervisor given full instruction on the changeover strategy but without connecting load. 

    300mA S-type on generator did what it was paid to do and shut down due to a N/E fault on a piece of equipment. You can switch out the RCD on the genny but try explaining that from your bed to a joiner at 1.00am on a Monday morning! Had to get up, rain beating off the windows and go to site to fix. Won't make that mistake again!

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    Stupidly left a temporary changeover in a large joinery works to the last minute. Only a matter of plugging the 63A TPN lead from the an existing changeover switch into the genny. Planned for a Sunday night, a dry run was made earlier in the week with the nightshift supervisor given full instruction on the changeover strategy but without connecting load. 

    300mA S-type on generator did what it was paid to do and shut down due to a N/E fault on a piece of equipment. You can switch out the RCD on the genny but try explaining that from your bed to a joiner at 1.00am on a Monday morning! Had to get up, rain beating off the windows and go to site to fix. Won't make that mistake again!

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