IET announces new amendment to BS 7671 (IET Wiring Regulations)

AJJewsbury:

The product standard ( BS 7288) says they are not suitable for providing Additional protection.

It doesn't quite say that. That would put it in the the same category as a BS for chocolate tea pots. I think what's written could equally be read as "the the device doesn't protect the upstream part of the circuit and that additional protection [for that - if any is required] will have to be provided elsewhere".

I think it's simply not clear.


 

They do not provide isolation as they do not meet the minimum contact clearance.

Oh yes they do - on a SRCD you just pull the plug out (just like for unswitched BS 1363 sockets). Besides is there actually a requirement for devices providing additional protection only to provide isolation? 531.1.1 only talks about devices providing ADS - additional protection is technically a different beast.


  - Andy.

Well, this is interesting. I don't want to disagree with you Andy, simply provide some points for discussion.


First, a couple of points on whether an RCD is always a device providing ADS:

• In a fault where ADS is required, if the RCD in the SRCD operates first, it is the device providing ADS whether we intended it to be or not. Is "additional protection" a form of ADS anyway

• Regulation 411.3.3 is a requirement for ADS, therefore it could be argued that an RCD provided for 411.3.3 is a protective device providing ADS (or part of the ADS solution)

• In TT systems, it often does, almost by definition.

Now on to "isolation". To be honest, we don't know what the purpose of the "isolation" required for a device providing ADS actually is, because BS 7671 (and the international standards HD 60364 / IEC 60364) doesn't tell us in simple terms ... So, I guess, possible options include something along the lines of:

• Enable isolation of the fault downstream after operation of the protective device to effectively remove the fault and enable the electrical installation to continue to be used safely, or to facilitate safe maintenance and replacement whilst maximizing the availability of the rest of the electrical installation (the plug and socket-outlet combination can do that of course - BUT a single-pole device such as a fuse in an SFCU-RCD doesn't isolate an N-E fault, so ???)

• Provide isolation immediately when the protective device because this is required for safety (a plug and socket-outlet combination cannot achieve this aim, removal of a fuse if the SRCD is in fact part of an SFCU-RCD assembly cannot either - therefore BS 7288 device not suitable ... BUT then again it could be argued that a fuse "blowing" does not, strictly, provide isolation ....)

Thoughts?

This is more of an existential crisis than an electrical installation one.


When is an RCD not an RCD?

Andy


If Additional Protection is required and you can't fit an RCBO in the consumer unit just fit an RCD in a 2 module one in an enclosure next to the consumer unit. I did this in my workshop for the sockets as the old metal MEM has re-wirable fuses, not exactly major engineering works! I will replace this when with a BG unit which are on sale at the moment when I have some time, a well engineered die cast aluminium powder coated finish which is IP rated, what is there not to like?

Andy


The BS says these devices only provide "supplementary" protection they require upstream "Additional Protection" if Additional Protection is required. RCDs do not provide protection for upstream only downstream of the device. The unswitchef varaties do not in themselves provide satisfactory isolation. Yes you could isolate by removing the plug from the socket variety or remove the fuse from the SFCU variety which does put them in the catagory of a chocolate tea point.


Do you agree they are not suitable when Additional Protection is required?

In some instances it will be possible to install a small EN 61439-3 consumer unit in a airing cupboard instead of an FCURCD to connect an additional piece of equipment in the bathroom to an existing circuit when it is not possible or sensible to try and install RCD protection at the main fuse board.


Cost wise there isn’t much difference, in fact it could actually work out cheaper if there’s a couple of appliances to connect or more.


But it does seem utterly and completely over the top.


Andy Betteridge

The product standard ( BS 7288) says they are not suitable for providing Additional protection.

It doesn't quite say that. That would put it in the the same category as a BS for chocolate tea pots. I think what's written could equally be read as "the the device doesn't protect the upstream part of the circuit and that additional protection [for that - if any is required] will have to be provided elsewhere".

They do not provide isolation as they do not meet the minimum contact clearance.

Oh yes they do - on a SRCD you just pull the plug out (just like for unswitched BS 1363 sockets). Besides is there actually a requirement for devices providing additional protection only to provide isolation? 531.1.1 only talks about devices providing ADS - additional protection is technically a different beast.


  - Andy.

Alcomax:

If that is correct there should be a recall

Should the new devices to the new standard be withheld from sale until there is a definitive explanation of how and when they can be used?


Andy Betteridge

I have not seen any of the devices to the new British Standard installed, they are only just coming on the market. 

I don't know why these new devices have been designed as they have or why the new version of the British Standard has been written as it has. 

It all seems to be utter and complete nonsense.




Andy Betteridge

If that is correct there should be a recall

I think you are missing the point.  The product standard ( BS 7288) says they are not suitable for providing Additional protection. They were removed from BS 7671 deliberately for this reason. They do not provide isolation as they do not meet the minimum contact clearance. BS 4293 was removed because because it was an obsolete standard just like BS 1361 fuses.


Are you saying that you disagree with the product standard?