Are different brands of MCB interchangeable?

[mike]

I need to swap an unused 40A Wylex MCB in a Wylex consumer it for a

32A MCB for a new ring main.

I'd assumed that different brands of MCB were interchangeable until I saw how many different brands at similar prices Toolstation stocked - and that made me think there must be a market for specific makes.

Toolstation don't do Wylex though -- so will other brands do?

Thanks in advance.

[Bob Minchin dangling via a don]

Not many fit mechanically so best to stick with the matching brand.

Bob

[Andrew Gabriel]

In general, they aren't. Even if they mechanically fit, you're going to be running outside the design and test criteria. MCB's have issues with heat and magnetic fields straying from one to another. One manufacturer will ensure their own work correctly when used as specified, but they aren't going to go to the trouble of making theirs work with alien stray fields leaking in from someone else's.

There are some which are well known to be interchangable, such as MEM, BILL, Eaton, because they're really all the same company and production line.

Note that individual manufacturers often have several ranges, and they often aren't even interchangable.

[Tim W]

mike wibbled on Thursday 29 October 2009 19:06

You would be well advised to use the correct part. Some form factors to vary and technically, a Wylex assembly will not have been type tested with other manufacturer's devices in.

Having said that, sometimes the same parent manufacturer makes stuff under different names and those devices may be interchangeable.

[John Rumm]

There is *some* interchangeability, but its certainly not universal. Even in cases where they do fit, you may find small differences in positioning of components that may make getting the fingers on bus bars in the right place, or the projections mounted through the apertures on cases etc.

Although incomplete, an early stab at an interchange chart is available here. Note the chart is incomplete - just because there is no X in a box does not mean that it won't fit!

that using "foreign" parts in a CU will probably violate its type approval (not that means its any less safe, just it has not been tested and proved as such).

Its also a bit of a moving target - makers tend to redesign ranges from time to time and new ranges may be incompatible with old.

[Mike Clarke]

have a Siemens Stratum CU for which it's now well nigh impossible to get parts. Hager RCBO's fit this box and appear to work without any problems. Perhaps it would be worth adding this to your list for the benefit of anyone else unfortunate to have one of these rare CU's.

[John Rumm]

Ta, added.

[Roger R]

I would have thought the Electromagnetic Compatibility (EMC) regulations required these devices to be compatible (not interfere) with each other. Stray fields are certainly covered by the regulations, and should not interfere with adjacent equipment.

I am no expert on these regs and whether individual MCB's can be considered separate pieces of equipment is debatable. As they are an individual item sold separately its quite probable they should comply wherever fitted.

Explanatory note:

R

[ARWadsworth]

> I have a Siemens Stratum CU for which it's now well nigh impossible to get

You star Mike.

I was working on a Siemens Stratum today and I was going to spend tonight looking for a second hand Siemens RCBO on the internet.

Incidentally the Siemens Stratum is identical to one of the old MK CUs (for which you also struggle to get parts).

Thanks

Adam

[ARWadsworth]

B&Q sell Wylex MCBs but you will be about £5 better off by calling into your nearest electrical wholesalers to buy one.

Adam

[mike]

Thanks for all the replies. Seems like an area where a bit of standardisation would actually be useful.

[Mike Clarke]

Glad to know the info was useful.

In my case the need to add extra RCBO's was because of a major kitchen refit. In view of the part P implications I had the wiring done by an appropriately registered sparkie. He was working on a new CU installation nearby before starting our job so called round with a handful of different breakers to try for size in a spare slot. I don't remember what the other ones were but the Hager one fit OK. I'd assume Hager MCB's should fit too.

The main switch was also in a bad state with part of the casing broken off. It had been like that since we moved in but was functional and (reasonably) safe bur scary looking so we had that replaced as well. When he was initially checking things for size he had a Hager and a Wylex one with him, they both looked like they would be possibles when slotted onto a couple of adjacent spare ways to check for size. When he came to do the job it was a Wylex main switch that was in the van so that's what we now have. I'd expect Wylex MCB's to have a similar profile to this so they would probably also be compatible with this CU but I'm not sure about their RCBO's - I can't remember if he tried one for size on the first visit.

Perhaps the Wiki needs updating to highlight the incompatibility between the two different flavours of MK?

[ARWadsworth]

Perhaps I ought to try to remember to write down which MCBs I have seen in different CUs when at work and then I could contribte to that wiki article:-)

Adam