32A MCB melting

[SteveW]

Why would a 32A MCB on a shower circuit after years of successful operation decide to melt put continue to work. This is on the RCD side of the consumer unit. Why did the fuse not trip. Would the fuse have been at fault or is the shower at fault. If this was the old fuses you know the fuse wire cartridge type the fuse wire would have melted. I posted this out of curiosity as I have decided to replace both fuse with a 40A and the shower for a new one. As safety is of issue with kids......

Steve W

 

[andyd]

When MCB's "melt" it is usually because one of the connections has become loose causing a high resistance resulting in a large amount of heat to be generated. I often see this in industrial applications where there is excessive vibration but I have seen it in domestic situations too. The shower could well be OK. A 32A MCB is a bit small for a shower though. You can run a maximum of 7.36 Kw on one. A 40A one is good for 9.2 Kw but if you are increasing the size of your MCB and/or shower you should make sure the cable is up to it.

 

[SteveW]

Cheers andy
The makers of my fuse box only do 40A or the next one is 53A.
The shop where I'm getting the Fuse from say the 40A " with it's tolerance should be ok "
All wiring to and from shower is all 10mm

 

[andyd]

No problem. 10 sq mm cable is rated up to 63A depending on its installation method so you should be fine.