Has anyone else seen problems with Wylex MCBs? I've had about 5 (all NSB32s) fail over the last year or so. They work fine until either tripped or switched-off and then they stay open circuit (or maybe high resistance) even though the lever latches in the ON position. They're becoming expensive fuses!
Are any other manufacturer's MCBs interchangeable?
Dave
Have you bothered to contact the company .Surely that's the first thing you should be doing .Did you keep the failed ones .?
Stuart
I exchanged them at the local factors but I suspect they went into the bin.
Dave
Are you exceeding their breaking capacity? The PSSC (prospective short circuit current) available at your supply may be exceeding the current which the Wylex breakers can break. This is often written on the breakers in the form M3, M6, M10, etc (3000A, 6000A, 10000A respectively). Some of the older Wylex breakers designed to plug in to the older rewirable fuse boxes have rather low breaking capacities (I think I might have seen as low as 1000A on the push button ones, and probably only 3000A on the toggle versions).
I have seen some Proteus MCBs fail like that in the past - they turn on electrically only some of the time when you turn them on mechanically! (that makes for a rather perplexing fault finding session!)
Something else to consider: are you in a big town, or very close to the substation? If so, it could be that your prospective fault current exceeds the breaking capacity of the MCBs. Most MCBs will only break fault currents up to 6kA - above that they may fail to break, or expire in process!
See the recent threads on just this topic.
The OP said
The "or switched off" bit suggests it's not a breaking capacity issue.
The NSB type referred to is M6 (6 kA).
I suggest a call or e-mail to Wylex's technical support dept:
Telephone: 01543 438320 Facsimile: 01543 438321 eMail: wylex[dot]technical[at]electrium[dot]co[dot]uk
Thanks Andy.
Dave
Absolutely right! The last thing that comes to mind is that the MCB has failed when it latches in the ON position OK.
This isn't the problem. Some of the failures have been on circuits which only have domestic HIFI equipment connected.
That's irrelvant -- it's the supply impedance which matters when it comes to exceeding the breaking capacity.
I would expect that would only come into play if you have actually tripped the circuit due to a fault. Simple overcurrent trips or, more likely given the stated load on the circuit, no trips at all, would not result in damage to the MCB even with a very stiff supply.
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