8.5kw shower on a 32amp mcb

[DirtyDog368]

Hello All
Can any one provide non sarcastic suggestions as to why an 8.5kw shower has not tripped the 32amp mcb protecting that circuit?

Found this install in a domestic property. It seems to have been there for years, without out issue.

Thanks
DD

 

[Doomed]

Look at the time to trip on overload characteristics of a B?32 MCB.
They don't have teenage daughters then.

 

[suffolkspark]

Its only a few amps over so will last a while, youve surely come across 9.5kw showers exactly the same?

 

[Zdb]

Also was it on the highest possible heat setting? I doubt it

 

[HappyHippyDad]

Im just dealing with something similar.
8.5kW on a 30A breaker. This one is actually tripping it, but only if the temperature is high and they spend too long in there.

As in the first post, have a look at appendix 3, page 370 of the new edition of BS7671 and you will see that it is highly unlikely a 32A breaker will trip with a 8.5kW shower (approx 37A-no calculator to hand).

 

[hasel5]

Mines 8.5 KW shower is on a 30amp Cartridge fuse and been running spot on for 3 years since i moved in do have a spare Fuse sat in cupboard

 

[Yozza19]

Slight variation in input voltages also play apart
Put your clamp metre on it usually about 28-31 a for a 8.5 on the 7-8 heat setting

 

[Deleted account]

If it's a B type it would need to get to about 46amps before it started to think about tripping.
8.5 kW @230v is about 37A.
See page 370. BBB

Remember a B type breaker only needs to disconnect within .4 seconds at 5 times it's rated current

 

[Taylortwocities]

As Yozza indicates. Check your supply voltage. Current varies with voltage for a fixed resistive load (even my mum knows that......)

 

[PEG]

Not all showers function with a fixed resistive load...or so me mum reckons

 

[buzzlightyear]

Mines 8.5 KW shower is on a 30amp Cartridge fuse and been running spot on for 3 years since i moved in do have a spare Fuse sat in cupboard

that needs up grading to 40amp any way .

 

[buzzlightyear]

some manufactures are now making 7.5 kw showers .

 

[Rpa07]

that needs up grading to 40amp any way .

Might be on 4mm T+E Buzz - never assume and you know why!

 

[DirtyDog368]

Gentlemen and electricians
Thank you all for you valuable input.

Merry Chrimbo and be careful with the Christmas tree lights.

 

[wackyracer]

The 8.5kw is usually at 240v, at 230v the same shower is normally rated at around 7.8kw, so would only be over the MCB rating by a couple of amps.

 

[oracle]

Look at the time to trip on overload characteristics of a B?32 MCB.
They don't have teenage daughters then.

My teenage daughter spent so much time in the bathroom I installed PIR switching. Occasional screaming, but fuel costs went down a bit.

 

[coolsparx]

A few years ago I upgraded a shower cable for a customer, it was an 8.5kW shower on a B32 breaker. It wasn’t tripping & had been in for over 4 years, however there was some discolouring on the mini trunking above the shower. The 2.5mm cable was working beyond its limits!

 

[Darkwood]

Like has been expressed, the trip curve characteristics explains why the 32amp doesn't trip but relative to design of the circuit we have a regulation that states small overloads for long periods should not be possible so anyone designing/altering this circuit should never have done that in the first place.