installing shower-main fuse

[davesparks]

Ok so I could go round and amp clamp the meter tails during an evening when most demand is being used??

It's not as simple as that.

A clamp meter will give you the current demand at a particular instant in time, which is not much use for assessing maximum and average demand.

To assess the demand you need a current meter which records the demand over a time period, I usually go for two weeks, and then you get a graph of actual usage when you retrieve the data.
From that you can assess the maximum demand, and the average, which allows you to make an assessment of whether the supply is suitable for the new load.

 

[davesparks]

Probably not in most cases but dont we account for situations where even 70% of that load with diversity taken into account exceeds main fuse?

In the world of the textbooks and city and guilds then yes you do have to base everything on strict calculations and suchlike.

But in the real world it's a bit different, you can use knowledge and experience, actual measured values, rules of thumb and that kind of thing.

It's a bit like the supply voltage, in the classroom and textbooks a lovely continental 230V, but in the real world it's a good solid 250V.

In the case of electric showers I always advise the customer that the first thing to do is look at having a pumped shower which uses both hot add cold water feeds, or a thermostatic shower mixer if they have a mains pressure hot water system. Electric showers are a poor alternative!

 

[davesparks]

That can't be true!???

The fuse will certainly be getting warm occasionally I would have thought in that instance,

A service fuse will tolerate quite a bit of overload before it actually goes!

 

[Leesparkykent]

That can't be true!???

The installation is badly designed for sure but its entirely possible. For example a 100A BS 88-3 will handle 200A for around half an hour before it lets go. so if you averaged the showers out a 9.5KW then it could be possible that 5 showers could run for half an hour before the fuse gave up. Then if you consider the fact most wont shower for no where near half an hour and the likely hood of more than a few showers being used at the same time then IMO its totally possible. Its a shyt designed install though.

 

[davesparks]

This is from the UKPN network design guide, it shows what they use for after diversity maximum demand (ADMD) when designing their networks. I think you might find some of the figures quite surprising.
But please note this is the effect of diversity over a group of supplies, not a guide to the requirements of the individual house. But it does give a good idea of reality versus the textbooks.

 

[gazdkw82]

Well I guess I'm going to say the circuit from OP will be fine. But it seems like guess work

 

[Leesparkykent]

Well I guess I'm going to say the circuit from OP will be fine. But it seems like guess work

It will be unless they have a cannabis farm drawing 100A lol

 

[gazdkw82]

It will be unless they have a cannabis farm drawing 100A lol

Well....

 

[Leesparkykent]

Well....

lol :sifone:

 

[telectrix]

rule of thumb. add the In values of thre MCBs and the x 0.4. on OP's figures thats around 30A. in actual fact that' figure itself is pessimistically high. rare i see > 10A on a clamp here at home. when it's > 10A, i tell 'er inddoors to switch buggers off.

 

[Baker1988]

Totally agree with Tel above^^^^

Reading through that was just about exactly what I was going to say haha any way I can't see a problem adding a shower mate my house has 2 showers in as well as the standard stuff.