Hi, I am looking for some expert advice regarding which Wago connectors & box to use to create a spur in a final ring circuit with 32A OCP. I have been lifting some floorboards to replumb for new radiators & have discovered several spurs created using screw connector type 30A junction boxes that I would like to take the opportunity to change to maintenance free boxes. I like Wago connectors but I do see that in the manufacturer’s installation instructions some of their boxes are derated from 32A to 20A in a MF situation, so the question is what are the correct connectors & box to use in this situation? And on a wider point why do boxes rated at 32A in an accessible situation get downrated to 20A in a MF situation? Surely the characteristics of the box don’t change just because it is in an inaccessible location, or am I being naïve? Thanks
Which Wago connectors & box to use to add a spur to a final ring main
- Thread starter GaryM90
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The cables on a ring are only required to be rated at 20A, while I don't think BS7671 says anything specifically about the connectors used to make spurs I believe it is reasonable to assume that it is acceptable for them to be rated at 20A, the same as the cables.
As to why the connectors have a lower rating in a maintenance free environment, I believe the idea is if something is not accessible for maintenance it needs higher reliability and in general one way to achieve higher reliability is not to run components at the limit of their rating.
Of course it all gets a bit silly, because in reality most items in domestic installations very rarely get inspected even if they are accessible for inspection. Also most circults in domestic installations are unlikely to be loaded to their maximum ratings for more than a small proportion of the time.
As to why the connectors have a lower rating in a maintenance free environment, I believe the idea is if something is not accessible for maintenance it needs higher reliability and in general one way to achieve higher reliability is not to run components at the limit of their rating.
Of course it all gets a bit silly, because in reality most items in domestic installations very rarely get inspected even if they are accessible for inspection. Also most circults in domestic installations are unlikely to be loaded to their maximum ratings for more than a small proportion of the time.
You could use Hagar J803 boxes
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I personally find it difficult to get excited about the 'ratings' of terminals/JBs etc. (but see ** below), but for those concerned (maybe even 'strictly') about regs and MIs ...
.... whilst it is true that BS7671 allows a ring final protected by a 32A OPD to be wired in cable with a CCC of 20A, the regulation only says that the circuit should be designed such that it is "unlikely" that any part of the cable will be overloaded "for long periods", so it is theoretically possible that part of the cable could sometimes be carrying anything up to 32A, provided that was not for "long periods of time".
I would say that, if one wants to be 'strict', I think that any terminals involved in joints in the ring probably should be "rated" to be able to carry "up to 32A for periods that are not 'long' ", but I rather doubt that 'ratings'/MIs of the likes of 20A-rated (when inaccessible) Wagos would actually say that!
[ ** for those who are concerned about the 'ratings' of connector terminals, I think this is theoretically far more of a potential issue with Wago-like connectors than with the screwed terminals of traditional JBs. In the latter case, nearly all of the 'connection', hence current, is between the two (or more) conductors, with very little current actually travelling through any part of the terminal itself - hence the only real issue is the physical ability of the terminal to satisfactorily accommodate all of the conductors (regardless of how much current they are carrying). However, with Wago-like connectors (or any other 'one conductor per terminal' situation), all of the current has to travel through conductive parts of the terminal. ]
Yes, one imagines that their thinking is something like that. However, the implication is presumably that they believe that their 32A connectors might become significantly 'less reliable' when carrying currents above 20A - which is perhaps a little worrying.
All true. In fact, what is particularly silly is that the reg really relies totally on trust in the installer - since, essentially by definition, if a joint is not "accessible for inspection and testing", no-one else (including any subsequent 'inspectors') are going to know of even the existence of the joint, let alone what it consists of!
Kind Regards, John
I totally agree with John.
And go further.....the contacts in spring loaded terminals ( Wago is just one of many brand names ) can degrade if the spring is heated by current flowing through the connectors.
I'm pleased to hear that.
True, but to be fair, the same can be true of high degrees of temperature cycling in screwed joints. However, in both cases, if the connection is satisfactory in the first place, there really should not be any appreciable heating at the terminals, so the potential vicious circle should never really get started.
Kind Regards, John
Yeah, they seem to be rated at 32 amps even when inaccessible.
See the PDF link at https://www.tlc-direct.co.uk/Products/ASJ803.html
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I have to agree with @JohnW2 however one has to consider real life. You don't want screw terminals so what can you replace them with?
Even with screw terminals once encapsulated in epoxy resin they are unlikely to become loose. I have used many inside a encapsulated joint box buried under 3 foot of soil with no qualms as to them coming loose. Also used crimp terminals, but never tried encapsulating maintenance free terminals in epoxy resin.
In 1980 I first came across the push in spring connector, so they have been around some time, odd but it was in Algeria when I first came across them, working for a Dutch company. Nothing new under the sun.
Even with screw terminals once encapsulated in epoxy resin they are unlikely to become loose. I have used many inside a encapsulated joint box buried under 3 foot of soil with no qualms as to them coming loose. Also used crimp terminals, but never tried encapsulating maintenance free terminals in epoxy resin.
In 1980 I first came across the push in spring connector, so they have been around some time, odd but it was in Algeria when I first came across them, working for a Dutch company. Nothing new under the sun.
I'm not sure what aspect of what I wrote you are agreeing with. However, although you ask what to replace them with if "You don't want screw terminals", I would personally like to see the evidence for that "if" - i.e. the evidence that the long-term reliability of undisturbed screw terminals is significantly less than that of sprung terminals, particularly in domestic installations in which circuits are not often heavily loaded. Ironically, it is when they are accessible that the connections are more likely to be disturbed (hence 'loosening' probably more likely to happen).
I'm not sure that follows. Resin encapsulation may prevent the screws from unscrewing, but it would not prevent the 'creep' in conductors (particularly when subjected to temperature cycling) that can theoretically cause the connections to loosen.
I would think that would probably be inadvisable (maybe 'forbidden' by MIs??), and at risk of producing problems. If resin got within 'the works' of a sprung terminal, there would presumably be potential for it to impair the effectiveness of the spring-reliant connection.
Kind Regards, John
Thank you all for taking the time to give such comprehensive replies.
I may be wrong but I get the impression that amongst professionals you don’t consider that in theory that there is anything wrong with using traditional JBs with screw connectors in inaccessible situations as they are tried & tested over many decades, but in practice regs say u must use MF JBs, which rules out those with screw connectors. If this is the case can I ask if like I am you were lifting floorboards in your own house to replumb a radiator & came across some non maintenance free JBs on the final ring wud you take the opportunity to change them for MF junction boxes or wud you just leave well alone?
On the specific point of using Wago connectors & boxes I have done some research and found that when used with their 773-173 type connectors the Wagobox XLA has a Maximum Current Rating of 32A in a MF situation BUT reference is also made to a Maximum Aggregate Current of 64A. Can I ask how do u calculate the maximum aggregate current & what is it’s significance? I would have thought that if a JB is rated at 32A & the circuit is protected by a 32A breaker that would be the only consideration.
Cheers
Gary
I may be wrong but I get the impression that amongst professionals you don’t consider that in theory that there is anything wrong with using traditional JBs with screw connectors in inaccessible situations as they are tried & tested over many decades, but in practice regs say u must use MF JBs, which rules out those with screw connectors. If this is the case can I ask if like I am you were lifting floorboards in your own house to replumb a radiator & came across some non maintenance free JBs on the final ring wud you take the opportunity to change them for MF junction boxes or wud you just leave well alone?
On the specific point of using Wago connectors & boxes I have done some research and found that when used with their 773-173 type connectors the Wagobox XLA has a Maximum Current Rating of 32A in a MF situation BUT reference is also made to a Maximum Aggregate Current of 64A. Can I ask how do u calculate the maximum aggregate current & what is it’s significance? I would have thought that if a JB is rated at 32A & the circuit is protected by a 32A breaker that would be the only consideration.
Cheers
Gary
For me the bottom line is to avoid having junctions that are not accessible for inspection and/or maintenance.
I would give some consideration to re-wiring that part of the circuit to remove the need for junction boxes.
Are you implying (again) that regulations can be ignored if they do not suit your personal opinion?
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