The application of BS 7288 RCDs

To my mind “supplementary protection" is just the old words for what we now call “additional protection” (BS 7671 itself used to refer to ‘Supplementary protection by residual current devices’ back in the 16th Ed). The fact that they manage to use both the old and new terms in the same sentance doesn't really surprise me given the way such text gets repeatedly modified over time by committee after committee.

SRCDs are only intended to provide supplementary protection downstream of the SRCD

Pretty obvious of course, but sets the context for the next sentence…

SRCDs are intended for use in circuits where the fault protection and additional protection are already assured upstream of the SRCD.

I reckon that was intended to mean something like: SRCDs are intended for use in circuits where the fault protection and (any) additional protection (required by the circuit itself) are already assured upstream of the SRCD. - so acknowldging that SRCDs etc won't provide any protection to supply cables concealed in walls or needing 300mA RCD protection for fire reasons etc. etc..

But standards committees being standards committees are bound to what is actually written in standards rather than what was probably meant, so the BS 7671 committee rather has its hands tied.

That's just my guess though - I could well be entirely wrong.

   - Andy.

It might have been written in the same vein as “the party of the first part, hereinafter known as the party of the first part” or some such Groucho phrase ? 

Chris Pearson: 
 

 

If anybody can think of another reason for fitting a BS 7288 SRCD, do please speak up.

Changing a C2 to a C3 on a EICR?

Thinking of RCD provided for equipment likely to be used outdoors would be a C2 if absent. If SRCD by front door, would that be a C3?

You've been thinking again haven't you Chris?

Z.

If the installation has a RCD it may be a BS4293, which is not listed in the book.

If it is a RCD that is listed in the book it may not be at the origin of the circuit, it may have been inserted part way along it.

There are variations that aren’t “as the book“ that provides a level of protection in a particular location.

 

If anybody can think of another reason for fitting a BS 7288 SRCD, do please speak up.

I have an upfront time delayed R.C.D. in my flat with individual R.C.D. sockets around the flat. This offers a reliable safe solution to losing all sockets in case of an individual faulty appliance.

Also I have seen individual R.C.D. sockets used in a public village hall where you would not want the ring final R.C.D. tripping off and disconnecting the stage performance if the tea urn went faulty in the kitchen.

Z.

     you would not want the ring final R.C.D. tripping off and disconnecting the stage performance if the tea urn went faulty in the kitchen.

Nor, more importantly, vice versa.  ?

geoffsd: 
 

     you would not want the ring final R.C.D. tripping off and disconnecting the stage performance if the tea urn went faulty in the kitchen.

 

Nor, more importantly, vice versa.  ?

I am lead to believe that the stage performers run on E100 not tea leaves..

Z.

I went to the local Nissan main dealers (when we had one) twice because of a tripping RCD.

The first time it was because someone had watered a plant in a pot stood on a floor socket in the showroom.

The second time it was the coffee machine in reception.

On both occasions it literally closed the business down as the servers and phone system went down, they could not sell cars, service them, do MOTs, a tripped RCD that wo not reset stopped every department working.

Generally a 30 mA RCD manufacturered to any of the British Standards will protect users of individual fixed or handheld appliance in a domestic installation, the issue that need to be considered is if it is the correct type of RCD and is it installed in an appropriate manner to serve its intended purpose. 

Given that the new BS8277 RCDs are Type A and double pole they provide just as much downstream protection as any other RCD.

In the examples I gave above if the coffee machine had been protected by a 30 or 10 mA SRCD chances are the main RCD could have been reset and the business would not have been forced to close, but if the socket in the floor box had been a SRCD it wouldn’t have made any difference   and would not have protected anyone using equipment plugged into it.

Supplementary protection upstream to me means for example galv conduit surface run this way the cable from the distribution has additional protection via the conduit with the SRCD providing additional protection further down stream. 

TS