Question?

[hotfingers]

Bs60898 b type breaker 40amp protects a 6mm cable for shower.. Showers rated at 45 amp on max temp,why doesn't breaker trip before cable over heats?? Breaker ok, zs ok,? Surely breaker shud trip first?

 

[Tim]

Check the time current curves in the BGB, you will find your answer there

Tim

 

[Richard Burns]

Cable insulated?

 

[MTI]

Sorry not got the book to hand but the rating of the mcb will protect a cable that can handle that rated current as a minimum eg: 16A 60898 serves a 2.5mm radial and the 2.5mm will easily handle in excess of this. The tables in the regs will give you data as to at what point that mcb will trip depending on your circuit characteristics also. sorry cant be of much more help but someone will give you table numbers pretty quick.
id also be checking out that cable length...i saw a few recently and one this week with a 6mm on 40A 60898...result....melting insulation at mcb terminal!

 

[hotfingers]

Run is no more than 7 m that's exactly the scenario I just went to but burnt cable at pull cord

 

[hotfingers]

I think 6mm clipped direct can handle 45 amps?

 

[telectrix]

it can. your burnt termination is probably a poor connection.

 

[Richard Burns]

Run is no more than 7 m that's exactly the scenario I just went to but burnt cable at pull cord

this is just a loose connection causing resistance at the pull cord, and taking the full current through a resistor it will get hot and burn the cable at that point.

 

[MTI]

Agree with all the above re loose termination high resistance. Visual inspection sometimes requires a little more than a look and testing. I had similar this week although the melting was at the mcb which wasnt loose but a massive shower, decent 15m-20m plus run in 6mm and 40A mcb. I walked in, saw the shower and instantly commented....ooh that shower looks newer than that cable by far doesnt it so to speak...reply, yes a friend swapped it for us last year because we saw it on offer and thought our old one wasnt up to the job....scary

 

[hotfingers]

I hope so checked everything,gave insulation test to make sure cable wasn't damaged anywhere else,zs was 0.26 which is sound checked breaker tested rcd just feel maybe I shouldn't of replaced the pull cord and reenergised due to shower being rated at 46 amps, I presume the breaker at 40 amp would protect in future. Also made sure terminals were wel tight because of exactly what you said loose connection,thanks for your comments!hopefully all b well

 

[hotfingers]

I commented on the rating of the shower straight away told him 10mm shud of been used and said loose connection but was a bit sceptical about re energising with that load on the 6 mm

 

[VoltzElectrical]

6mm2 reference method C = 47 amps, but will take quite lot more than than short to medium term. Certainly the space of the time of a shower.

 

[VoltzElectrical]

shouldn't 60898 run for an hour at 1.5 times it's rate? Something like that.

 

[rmc86uk]

Agree with all the above re loose termination high resistance. Visual inspection sometimes requires a little more than a look and testing. I had similar this week although the melting was at the mcb which wasnt loose but a massive shower, decent 15m-20m plus run in 6mm and 40A mcb. I walked in, saw the shower and instantly commented....ooh that shower looks newer than that cable by far doesnt it so to speak...reply, yes a friend swapped it for us last year because we saw it on offer and thought our old one wasnt up to the job....scary

I didn't know that because a shower looks new and the cable looks old that it didn't comply.

 

[hotfingers]

We,ll put it down to loose connection then,cheers for all your help