Universal MCBs

[DetlefSchmitz]

It's the insistence in this country of using copper bus bars which creates the problem. In Germany the MCBs usually have wires going into them. And adjacent MCBs will be on different phases anyway.

 

[martinxxxxxx]

I think anyone charging for electrical work might want to read March 2012 Edition of ECA Today page 56 and it's called Circuit Protection: don't mix and match. before putting anything that fits in

 

[EFLImpudence]

That just boils down to -

"Don't do it or we will invalidate the warranty"

Obviously different makes should not be mixed if they don't fit exactly but, assuming a perfect fit, what possible difference could it make to an mcb or rcbo?

 

[JohnW2]

That just boils down to - "Don't do it or we will invalidate the warranty" ... Obviously different makes should not be mixed if they don't fit exactly but, assuming a perfect fit, what possible difference could it make to an mcb or rcbo?

Without really scraping the 'vanishingly improbable' barrel, and assuming that the devices meet the requirements of the appropriate Standards, then obviously no difference at all. It's just an attempt to persuade people to buy from them. I wonder if it's actually contrary to 'anti-competition' legislation?

Of course, "invalidate the warranty'is a very common, but usually pretty hollow, threat. For a start, although I may be wrong, I doubt that they can use it as a way of wiggling out of their legal duty to supply goods 'of merchantable quality' - and that includes a reasonable lifespan - so the purchaser's "Statutory Rights" probably remain intact. Secondly, when did anyone last have an MCB/RCBO/CU replaced under warranty?

Kind Regards, John

 

[JohnW2]

It's the insistence in this country of using copper bus bars which creates the problem. In Germany the MCBs usually have wires going into them. And adjacent MCBs will be on different phases anyway.

Yes, that's a reasonable point. Although it might seem that hefty lumps of copper are 'better' than wires, if wires and a neutral bar are deemed OK for neutrals, then why not also Ls - it's not as if the currents are any different! However, I don't see us loosing our lumps of copper any time soon!

On the face of it, common sense tells me that these things should be standardised. I suppose one problem with that is that we have this concept of 'type tested' CUs (whatever the point of that is meant to be, other than commercial protectionism) - which would obviously be potentially a bit undermined if interchageability of contents was mandatory. We don't have 'type tested' BS1363 plugs+fuses (e.g. MK plugs are only compliant with BS1363 if fitted with MK BS1362 fuses),so why for CUs?

Kind Regards, John

 

[SaladFingers]

I think that a solid bus bar is better than wires. Less likely to mechanically relax than wires are, since the terminal has a flat and even spot to 'land' upon and fasten.

 

[JohnW2]

I think that a solid bus bar is better than wires. Less likely to mechanically relax than wires are, since the terminal has a flat and even spot to 'land' upon and fasten.

That may be true - but, as I said, if wires and a bar are deemed OK for the Ns, why not also for the L's - same currents!

Kind Regards, John

 

[EFLImpudence]

Altough, there is nothing to prevent us using wires instead of the busbar, is there?

 

[SaladFingers]

I think that a solid bus bar is better than wires. Less likely to mechanically relax than wires are, since the terminal has a flat and even spot to 'land' upon and fasten.

That may be true - but, as I said, if wires and a bar are deemed OK for the Ns, why not also for the L's - same currents!

Kind Regards, John

Well they are, ish. It's down to construction. It's very tidy and effective to have a wire from the load side N of the main switch to the N bar, but from the L of the switch, it's tidy to have a busbar.

Imagine trying to put a wire in, wire out, with loops large enough for the bend radius, wouldn't be nice to work with or look all that nice.

 

[securespark]

if it looks/feels wrong, it could be

Altough, there is nothing to prevent us using wires instead of the busbar, is there?

The manufacturers could argue that if they have provided you with a purpose-built busbar, replacing it with bits of wire would invalidate the warranty.

 

[JohnW2]

Altough, there is nothing to prevent us using wires instead of the busbar, is there?

Theoretically, no - but in practice:
(a)...one would really need (probably two or three) 'Line bars', analoguous to the neutral ones. CUs obviously don't come with one of those, so one would have to improvise somehow, assuming one could find the space. (to attempt to terminate umpteem separate conductors in an RCD or Main Switch would not be very satisfactory).
(b)...FWIW, and if you cared about such things, you would obviously lose the 'type testing' of the CU (and, as above, possibly it's warranty, if that's worth anything)

Kind Regards, John

 

[Spark123]

I think that a solid bus bar is better than wires. Less likely to mechanically relax than wires are, since the terminal has a flat and even spot to 'land' upon and fasten.

That may be true - but, as I said, if wires and a bar are deemed OK for the Ns, why not also for the L's - same currents!

Kind Regards, John

One reason which strikes me is because someone will almost certainly connect the outgoing wires directly to the bar (not to say it isn't possible with a normal busbar, it just takes a bigger idiot). Another reason I can think of is there will be a nice big bang if there is an incidental short between Bar and N or bar and E, you wouldn't want it somewhere that accessible.

 

[JohnW2]

[That may be true - but, as I said, if wires and a bar are deemed OK for the Ns, why not also for the L's - same currents!

Well they are, ish.

Not really any 'ish' about it. The L and N currents for any circuit will be the same (give or take tiny L-E leaks) - if they weren't and if you had RCDs, you'd know all about it!

It's down to construction. It's very tidy and effective to have a wire from the load side N of the main switch to the N bar, but from the L of the switch, it's tidy to have a busbar. Imagine trying to put a wire in, wire out, with loops large enough for the bend radius, wouldn't be nice to work with or look all that nice.

It sounds as if you are thinky about 'hefty' conductors from the L sides of each of the MCBs/RCBOs, but that wouldn't be necessary - you'd just need a conductor appropriaate for the rating of the device (say 1.5mm² for 6A, 2.5mm² for 16A/20A, 4mm² for 32A etc.), going to an 'L-bar'. The only meaty conductor (which could be flexible) would be from the bar to the RCD or main switch.

Kind Regards, John

 

[Spark123]

The conductor size will depend on the upstream protective device and the adiabatic equation, you wouldn't want to be too close to a piece of 1.5mm in a direct short circuit with a 100A fuse protecting it.

 

[JohnW2]

One reason which strikes me is because someone will almost certainly connect the outgoing wires directly to the bar (not to say it isn't possible with a normal busbar, it just takes a bigger idiot).

True.

Another reason I can think of is there will be a nice big bang if there is an incidental short between Bar and N or bar and E, you wouldn't want it somewhere that accessible.

If we were to go down that path in UK (not going to happen!), I presume that CUs would come with L-bars protected by 'covers' or whatever in the same way that busbars currenly are - so I see no real difference. Indeed, if the aforementioned idiot were to remove/omit that protection from a current CU, the exposed busbar would probably present an even greater hazard of the type you postulate than would an exposed 'L terminal bar', wouldn't it?

Kind Regards, John