Extension Lead maximum length

[pauchacai]

Sure I am missing something obvious here but having recently gotten into PAT I am confused by some of the extra long extension reels available.

The code of practice for in service inspection & test states clearly the maximum allowable length of extension leads in relations to csa of the core (Table 15.4), and goes on to say that any lead exceeding these limits should be fitted with a 30mA RCD. There seem to be a host of 230v leads on high street sale now that do exceed this and have no RCD protection. Quick example - Masterplug 13A 40m cable reel. This, like many, incorporate a thermal cut-out but no RCD, also after quick ref to BS7671 Table 4F3A fall well short of meeting the voltage drop requirements for both 1.25 & 1.5mm cores.

I feel like I must be missing a trick here. Is it the case that as non statutory regs the codes of practice can be swerved for alternate safe practice?

Confused :dunce2: Any help please...

 

[Paul.M]

BS7671 is for fixed wires.

 

[pauchacai]

Cheers. I appreciate the relevance of 7671 and was just using app4 as further example of why these long leads might not be a good idea, after all a cable is a cable and the laws of physics still apply. But getting back to regulation I still can't square the non-compliance with the PAT code of practice?

Still confused

 

[SJD]

Table 15.4 is "Maximum recommended lengths for extension leads", not maximum allowable. The notes go on to say that above the recommended lengths the lead should be fitted with 30mA RCD protection - but if you already have this on the socket you plug the lead into, would that not suffice? Obviously there will be people who use these (and probably outdoors) with no RCD protection, but I'm not sure that should prevent them being sold?

 

[pauchacai]

Nice one. This is one of the failings of these pubs for me they use words like ' should' & 'recommemded' a lot which leaves room for interpretation but I suppose it gives saddos like us something to chat about!

Table VIII.3 page 131 in the cop is more robust though and states "the length of an extension lead should not exceed (the tabulated values)" It does also state in there that any lead exceeding these lengths should be fitted with an RCD so I think that rules out using the fixed installation protection? Perhaps...! Help

 

[SJD]

Yes, the language sometimes is not precise. With a "specification" hat on, I read "should" as desirable but optional (use "shall" to be mandatory). I think sometimes you can read too much into these guides, when they are not always precise, and sometimes have errors.

 

[sparks1973]

so if you already have an RCD at origin....is there anything else that may be issue here eh?...come on guys...VOLT DROP!!

 

[SJD]

Note 1 below the mentioned table does indeed say this may be a problem, I think that was already noted in the original post.

 

[Silly Sausage]

so if you already have an RCD at origin....is there anything else that may be issue here eh?...come on guys...VOLT DROP!!

Lad I know used to be a steeplejack.
Told me once he was several 100 feet up some stack with his 110V drill, extension lead up from the ground, and it was barely spinning!

 

[ackbarthestar]

What might be the expected maximum load on a domestic extension lead? - 8A
What is the maximum volt drop for power tools used on extension leads? - 11.5V

So lets see how long an extension lead needs to be before the volt drop is below the recommended maximum.

L = (11.5 * 1000)/(24.2 * 8) - Flexible cables have several values for the same size depending on which book you read ( PAT COP, GN3, BS7671)

L = 60m

Now calculate in the average nominal voltage supply ( In my area it varies between 239 - 245 and across the hill it varies from 242 - 253V)
So the volt drop will not make that much difference.

I suspect the important thing here will be the disconnection time under fault conditions, which will not be met without the use of a RCD

 

[pauchacai]

Thanks ackbarthestar that's an interesting one (and i thought my user name was odd...!) I am just trying to understand your calculation here and trust me not pick holes in it, if I am being dumb please point it out. I can understand your assumption of design load at 8A but like everything built into these regs shouldn't we always consider the worst case and the average human being out there? So when dealing with a 1.5mm flex fitted with 13A 3 pin we should consider Ib to be 13A...? Also for calculation, despite what our measured voltage may be the harmonized nominal (named) voltage should always be 230v. If we then work on the figure from 4F3B for 1.5mm BS6500 flex of 32 mV/A/m a 60m length would suffer a drop of 25v. Even using Ib of 8A the drop would be over 15v. Honestly if my understanding is out of whack here somebody please put me straight.

This is aside though to the RCD issue which you quite rightly point out. I am fully aware that real life for all of us does not start and end in a book but these Regs are here to guide and govern us i thought, so going back to my OP I am still struggling to understand how these items which seem to defy the code of practice can be manufactured & sold? More importantly for us now, when coming across a 60m lead not fitted with an RCD which has been legitimately bought at a well known retailer are we supposed to snip off the plug and stick a red label on it?

 

[ackbarthestar]

Your calculations according to your figures are correct.

Just a few notes in reply to your concerns.
1/ Its unlikely that a 13A plug will supply a constant 3kW load, unless the plug/fuse/cable is supplying a single item of equipment rated at 3kW. This is where an one might apply diversity.
2/ All calculations are approximate assuming average intermittent usage, such as lawn mowers, strimmers and the like, we are looking at the range not a precise value.
3/ I would agree that if you stuck to the worst possible case then you would end up with short extension cables and light loads
4/The code of practice is a guide, it has nothing to do with the money making adventures of the 'Orange Sheds'.
5/ How many failures do you know of where 240V extension leads have been used? None I suspect. The greatest danger are split leads and direct contact with the live conductors.
6/ The assumption from the Orange shed is all sockets supplying equipment for use outside should have a RCD fitted. Placing RCDs in series such as BS En 61008/61009 with BS 7288 or 7071 can cause automatic nuisance tripping.
7/ It is unwise to cut any plug off of a cable that has been designated by the manufacturer as safe, unless the extension lead shows signs of deterioration due to heating or serious wear and tear.

 

[pauchacai]

Thanks for sticking with this one mate. I note all your previous points and can't argue with any of them. My thinking on a practical sense is much on a par with yours when faced with real world commercial decisions as a sole trader. We all know that we couldn't function without taking account of diversity and so long as the basic rules of protection are followed the worst that will happen is a bit of nuisance tripping and no-one is getting zapped. The biggest issue here seems to be the lack of RCD protection fitted to these reels.

I think with this post I am just holding up the Regs and COP and saying "Oi... what about this then?" Just wanted to get the thoughts of others out there on the tools and testers. I may run it up the IET flagpole just to see what they say, after all they wrote the flaming thing.

Cheers again everyone. Interpretation is a beautiful thing.... Without it i don't know what the wife and I would argue about!