Component Form Factor & DIN

[Lister1987]

Excuse the ignorance here but why do we have all inserts (RCD/RCBO/SPD etc) and the only thing that is constant address every make and type is a DIN rail?

Why are the sizes not universal allowing cross-brand usage, I mean a Wylex RCD should function the same as a Hager etc and yet you get some that are completely different dimensions to the other (so you see botch jobs to get a part from another brand fit into another brand board etc etc

Just a random question.

 

[Lucien Nunes]

Distribution boards are often relied upon to comply with regulations by being type-tested. The manufacturer builds a selection of typical units and has them tested in such a way that they can prove that any valid configuration, made of their parts following their instructions, will also be compliant. You do not have to send each assembled board off for testing before use. Obviously manufacturers are not going to type-test their units with other manufacturers' components fitted, just as Ford will not test the safety of their cars when fitted with Mercedes wheels. Therefore, mixing parts from different brands results in an untested configuration, which the manufacturers forbid in their instructions, so there's no need to make the components directly interchangeable.

In other applications such as panel-building, there's no type testing by the component manufacturers. You are free to choose from any range, but it pays manufacturers to stick closely to standard formats so that their parts are at least as easy to integrate as any others. Thus, you get MCBs that are generally similar and are interchangeable in some applications, but different enough in detail that they will not fit each others' boards.

Plug-in types specifically for DBs are made to proprietary designs as each maker has had their own ideas on how to arrange the busbar contacts etc.

 

[Simon47]

Basically it's because the manufacturer's don't care. A variation of "standards are great, every manufacturer shoukd have some of their own" It's actually against their interests if a user can pick and choose, better to lock them in with such detail differences.
Extractor fans have a similar problem - try changing the make (or even just model from same manufacturer) and the cable entry will be different - and they even manage to coolude to put the screw holes in place that are different enough not to use the same plugged holes in the wall, but not different enough to be able to drill and plug new holes.

 

[Lister1987]

You'd think though that if part of the standard stipulates DIN rails (assuming here) that BSI(?) would go 1 step further and push for form factor uniformity?

 

[Simon47]

Don't know who currently maintains the standard, but the D stands for Deutsche - making it (translated) German Industry Norm.
I suppose it would make sense for some dimensions to be specified - so the tallest part fits through the cover aperture, and the lower parts don't foul the back of the cover - but terminal positions and characteristics would be a different matter.
I strongly suspect the gross dimensions are specified - after all, I was able to order a timer relay from one manufacturer, a box from another, and a DIN rail mounted blank from another, and they all fitted perfectly together. But since the timer relay was wired with tri-rated flexibles, terminal positions would be irrelevant.
Switch to CUs/DBs like we're discussing here and it's a different matter. I think components for these would come under a different standard (referencing the DIN standard in part). But there's things like, what happens if the terminal positions are standardised, but adjacent devices have different terminal clamps onto the solid bus bar ? Say one had a rising cage clamp, while the next has a fixed box and screw clamp.

Not insurmountable, but it would require a demand from industry (big outfits, not the individuals like us) to fund the standards making process and come up with a standard. The industry would then need to adapt products to meet the new standard - which might mean a new range of devices incompatible with existing installed products, which would impose a huge cost on the manufacturer and distributors.
Given that there's no advantage to any single manufacturer or to all of them collectively, why would any of them be interested in this ?
When I say there's no advantage to any manufacturer, I really mean that I can't see one. Why would (eg) MK be interested in installers/users being able to fit a (eg) Wylex device in an MK board ? Head down that route, and you quickly get to the question of - if the devices are now guaranteed to be physically compatible*, why can't we mix and match devices ? So another can of worms to pour out on the table. Address that, and you end up with manufacturers struggling to differentiate their products - all the same mechanically, designed to be (eg) magnetically tolerant of "foreign" devices either side, etc - and so it ends up being nothing but a race to the bottom of low prices, low margins, and falling standards. Oops, didn't I just describe the current situation
* One of the reasons for currently mandating only using devices from the one set of approved components is because of the risks of (eg) connections not being made properly if the busbar entries don't match between devices.