Another OSG error I haven't seen mentioned... RCD and zones

[happysteve]

Eh up

We all know about the duff max Zs tables in the OSG (Table B6) and GN3 (Table A4)... in fact, I've only just recently updated my GN3, and I'm pleased to say they have reprinted it and it now has the correct tables in.

I've noticed in my (early-purchased, with dodgy table B6) OSG that it gives information entirely contradictory to BS7671.

And it's not about something obscure, it's about whether a cable buried <50mm deep in a wall, within the prescribed zones, needs an RCD or not. The regs says it does (522.6.202 (i) and the sentence below (ii)). The OSG says it doesn't (section 7.3.2, p77).

Also, the regs gives you an option that a cable shall "be provided with mechanical protection against damage sufficient to prevent penetration of the cable by nails, screws and the like" (522.6.204 (iv)) WITHOUT RCD protection (as with all the other methods of protection mentioned in 522.6.204), whereas the OSG says that cables protected in this way (mechanical protection that is not earthed) DOES need an RCD.

How has this f'kup occurred? Because in this edition of the OSG they re-ordered the "options." In the old green OSG the options were listed "i" to "vi", where "v" was about the zones. So the sentence, "... cables not installed as per i, ii, iii or iv but complying with v must be protected by a 30 mA RCD." In the new yellow OSG the options are listed (a) to (f), but in a different order, with the one about the zones now being (b), with (e) being about unearthed mechanical protection. But the sentence at the bottom reads, "... cables not installed as per a, b, c or d but complying with e must be protected by a 30 mA RCD."

So they changed the Roman numerals to letters, but failed to take into account that they'd re-ordered the list.

Muppets.

I don't think this is a trivial error, either. Many people "learn" the regs using the OSG (I know they shouldn't, but they do) and it's more tempting to look there than an £85 500 page book. So, there are probably people installing lighting/cooker/shower cables <50mm from the surface within the prescribed zones without RCD protection, who think they are complying with the regs.

I can't understand why this isn't in the errata.

Does anyone have a recently-printed version of the OSG? It will have the correct Table B6 (without a supplied errata sheet). Would you mind checking P77, to see if they've fixed this?

 

[Richard Burns]

Unfortunately the OSG and guidance notes are riddled with errors of this sort, I noticed the one you mentioned, total mess up really.
I do not have the latest copy but I doubt they have bothered to get it right as they obviously never proof read anything before printing.

 

[HandySparks]

You're right, well spotted. Unfortunately, I also have an early copy of the OSG, so can't check that they've fixed this. I suspect not, as the only two errata available on the IET website relate to the Zs tables in the OSG and GN3.

IET Wiring Regulations updates - IET Electrical

Incidentally, I see that on the same page, Fig. 7.3.2 of the OSG refers to Reg 522.6.101, which doesn't exist in Amd 3.

 

[Deleted member 26818]

Gave up on the OSG with the 16th.

 

[Midwest]

happysteve, have you got the ISBN number of the copy you have? I was going to purchase a copy myself, but I'll ring Wiring Regs Bookshop, and see if they have an amended copy first.

 

[happysteve]

happysteve, have you got the ISBN number of the copy you have? I was going to purchase a copy myself, but I'll ring Wiring Regs Bookshop, and see if they have an amended copy first.

My OSG with errors (purchased early) is ISBN 978-1-84919-887-5.

My GN3 with corrected table (purchased last week): ISBN 978-1-84919-873-8.

 

[ruston]

Eh up

We all know about the duff max Zs tables in the OSG (Table B6) and GN3 (Table A4)... in fact, I've only just recently updated my GN3, and I'm pleased to say they have reprinted it and it now has the correct tables in.

I've noticed in my (early-purchased, with dodgy table B6) OSG that it gives information entirely contradictory to BS7671.

And it's not about something obscure, it's about whether a cable buried <50mm deep in a wall, within the prescribed zones, needs an RCD or not. The regs says it does (522.6.202 (i) and the sentence below (ii)). The OSG says it doesn't (section 7.3.2, p77).

Also, the regs gives you an option that a cable shall "be provided with mechanical protection against damage sufficient to prevent penetration of the cable by nails, screws and the like" (522.6.204 (iv)) WITHOUT RCD protection (as with all the other methods of protection mentioned in 522.6.204), whereas the OSG says that cables protected in this way (mechanical protection that is not earthed) DOES need an RCD.

How has this f'kup occurred? Because in this edition of the OSG they re-ordered the "options." In the old green OSG the options were listed "i" to "vi", where "v" was about the zones. So the sentence, "... cables not installed as per i, ii, iii or iv but complying with v must be protected by a 30 mA RCD." In the new yellow OSG the options are listed (a) to (f), but in a different order, with the one about the zones now being (b), with (e) being about unearthed mechanical protection. But the sentence at the bottom reads, "... cables not installed as per a, b, c or d but complying with e must be protected by a 30 mA RCD."

So they changed the Roman numerals to letters, but failed to take into account that they'd re-ordered the list.

Muppets.

I don't think this is a trivial error, either. Many people "learn" the regs using the OSG (I know they shouldn't, but they do) and it's more tempting to look there than an £85 500 page book. So, there are probably people installing lighting/cooker/shower cables <50mm from the surface within the prescribed zones without RCD protection, who think they are complying with the regs.

I can't understand why this isn't in the errata.

Does anyone have a recently-printed version of the OSG? It will have the correct Table B6 (without a supplied errata sheet). Would you mind checking P77, to see if they've fixed this?

And the OSG was included in the 16th exam, that was not free from errors either.

 

[happysteve]

Another one: Table A2 (diversity): motors, in "small shops, stores, offices and business premises."

Says: "100% f.l. of largest motor + 0% f.l. of second largest motor + 60% f.l. of remaining motors." So, second motor free, yay!

That middle number should probably be 80%, as it was in earlier editions of the OSG. But it's not like you can look it up anywhere else (apart from earlier editions), if you're not sure.

Duck's sale.

 

[Midwest]

My OSG with errors (purchased early) is ISBN 978-1-84919-887-5.

My GN3 with corrected table (purchased last week): ISBN 978-1-84919-873-8.

I telephoned Wiring Regs Books, as the current OSG they're are selling, still has the same ISBN that your book has. Spoke to one of the sales team, who said there is a corrected table you can download. He didn't know when an updated OSG would be available, as the IET would probably wait until their stock of this print run is sold out.

However happysteve, when I mentioned you finding another possible error, he became very interested! He asked me to send a link to this thread, as he is seeing the IET representative tomorrow, and he would ask him about it. But, just in case you didn't want them to see this directly, and without getting your permission, I cut and pasted some of your original post and emailed them. Hope you don't mind. He said he would reply. If your correct and they would like to thank the original error finder, I could PM you with their details.

PS, only the bit on mechanical protection/RCD. You could tell about the motors yourself, I have the email address.

 

[happysteve]

Cheers for that. Good thinking. Wouldn't have minded either way. Good stuff.

I think I will write to the IET independently. There are a few issues that I am unhappy with, where their professionalism has fallen below minimum standards, and my membership is up for renewal - usually a good time to have a moan!

PS. Thanks for my 100th "thanks" ! Back atcha!

PPS. Have emailed Mark Coles at the IET (who, according to the book, revised, compiled and edited this edition). Thanks Andy78 for his email address.

 

[happysteve]

Update: I received a swift and courteous response from Mr Coles of the IET. It has gone a reasonable way towards dealing with some of my irritations about the organisation.

 

[ruston]

Update: I received a swift and courteous response from Mr Coles of the IET. It has gone a reasonable way towards dealing with some of my irritations about the organisation.

It makes you wonder though, they must read the forums and realize how dissatisfied people are with them. Then they go on to do the same thing over and over again. It is not as though it is a Mills and Boon book, there again.................