How long for the Fuse to trip

[bigalert]

Need some help please.If a type 1 32a mcb is protecting the circuit supplying a 9.5kw shower, how long would the fuse last before the current draw made it trip.

 

[RF Lighting]

4 hours at a guess

 

[chapeau]

This page

http://www.tlc-direct.co.uk/Figures/Graphs.htm

links to this graph

So looks like even a pretty long shower would be OK.

 

[ericmark]

At 1000 seconds where the chart shows 32A trace crossing 40A line so around 1/4 hour. However there is no exact figure and the more often it reaches the trip point the weaker it will get so over time the delay will gradually reduce.
Type 1, 2, 3, 4 or B, C, D will have no effect on this time. But temperature in the enclosure will so the figure will vary and one may find it will trip within 5 mins when other power consumption has pre-warmed the enclosure.

 

[spark1]

Need some help please.If a type 1 32a mcb is protecting the circuit supplying a 9.5kw shower, how long would the fuse ???? last before the current draw made it trip.

Excuse me for asking , but why do you ask this question ?

 

[mfarrow]

At 1000 seconds where the chart shows 32A trace crossing 40A line so around 1/4 hour.

Or even 10,000 seconds, 2 3/4 hours.

 

[bigalert]

Someone has said they had uprated their shower from a 7.5kw to 9.5kw and after a while showering the fuse trips . They said they were going to uprate it to a 40amp fuse. Having referred to the chart at TLC i told them the circuit needs checking as a 9.5kw shouldn't overload a 32amp breaker or at least not that quickly.

Wanted to check my interpretation of the graph was right.

Will talk to them again tomorrow.

 

[st07]

Excuse me for stating the obvious, but a 9.5kw load @ 230v is 40A~, so surely a 32A mcb is inadequate for the job and a 40A one is required (providing the wiring is up to the job) as stated?

 

[chapeau]

I suppose that in addition to what ericmark has said above..

I don't know what the BS says, but these lines on these types of graphs don't neccessarily mean all devices being measured will work exactly as shown.

It might mean 50% will trip above the line, 50% below. Then we need to know the distribution, is it normal? What is the standard deviation?

If you are making, for example, an aircraft wing, and this was measuring performance, the graphs might be very very accurate for all such wings. For a £5 CB, there might be quite a wide tolerance allowed in the BS. Dunno.

And looking at the graph, I don't actually think the line touches the 40amp value. Of course we don't know what happens outside the range of the graph, and are probably not qualified to judge, but it doesn't appear to touch, ever.....

 

[ban-all-sheds]

If a type 1 32a mcb is protecting the circuit supplying a 9.5kw shower.

You put that right. Ib ≤ In ≤ Iz.

 

[ban-all-sheds]

At 1000 seconds where the chart shows 32A trace crossing 40A line.

I can't see the 32A curve crossing the 40A line anywhere....