Shower tripping

[piz]

Hello I have just installed a new fuse board and when the shower runs the MCB trips within 20-30 seconds
the ins rest is 1000+Mohms the ze is 0.54 ohms
the shower is 9.5kw I know I nees a 40amp breaker but what I cant understand is why it was ok on a 30amp wired fuse before
and it shouldnt trip out so fast even on a 32amp type b MCB
the rcd does not trip
any help would be great Cheers

 

[Spudnik]

Therein lies your answer.

Your shower is pulling near enough 40A

Put an ammeter round the line and see what you are actually pulling.

Dont forget that old 3036 fuses were able to go quite a way above their rating.

 

[piz]

Thanks Jason
I still cant understand should the 32amp mcb trip out so fast

 

[Darkwood]

If you get you red regs out and look at the current/time tripping curves for your mcb it should show you how long it will last at 40amps and as rewirable fuses have a different time curve they wont blow/trip at the same timings.

 

[piz]

Cheers
Having a look now bit confusing but can see a diference
Think I got the right page p249 and p245

 

[Spudnik]

I had a similar problem today.

Simple CU swap.

Several lighting circuits quite a few LV downlights, no schedule.

Switched on all the lights to establish what MCB did what.

After a minute, one popped.

Got out the clamp meter and it was pulling around 6amps, through an old wylex NB 5A MCB.

A 40amp shower will not run on a 32A MCB.

 

[the jock]

A 9.5kw shower will pull up to 45Amps depending on the shower

is it 9.5kw at 230 or 240V

 

[piz]

Hello just to confirm the ampage was 39.7 amps
you were right Jason