installing shower-main fuse

[gazdkw82]

my sister has asked if i will install a shower for her when i have sufficient knowledge and experience.

iv been going through some figures as a little practice whilst im not very busy.

This is the CU set up

TNCS supply

------------CCU------------
downstairs sockets - 32A - 32A with diversity
downstairs sockets 32A - 12.8A with diversity
downstairs lights 6A - 3.96 A with diversity
upstairs lights 6 A - 3.96A with diversity
Cooker 32A - 16.6A with diversity
Heating 16A - 13A with diversity

total demand 82.32A

the supply fuse is 80A

before i even consider installing a shower in the future would the supply fuse have to be upgraded by DNO?

am i going about this the right way?

 

[Pete999]

my sister has asked if i will install a shower for her when i have sufficient knowledge and experience.

iv been going through some figures as a little practice whilst im not very busy.

This is the CU set up

TNCS supply

------------CCU------------
downstairs sockets - 32A - 32A with diversity
downstairs sockets 32A - 12.8A with diversity
downstairs lights 6A - 3.96 A with diversity
upstairs lights 6 A - 3.96A with diversity
Cooker 32A - 16.6A with diversity
Heating 16A - 13A with diversity

total demand 82.32A

the supply fuse is 80A

before i even consider installing a shower in the future would the supply fuse have to be upgraded by DNO?

am i going about this the right way?

How have you arrived at these figures?

 

[Leesparkykent]

What you have to remember is that all of them loads are not going to be running at those figures at the same time. If you clamped it you would probably find its no where near those figures the majority/all of the time. IMO it would probably be under 6A most of the time.

 

[gazdkw82]

How have you arrived at these figures?

Those are the mcbs on the board and the diversitys were from OSG

 

[Pete999]

Those are the mcbs on the board and the diversitys were from OSG

Oh OK thanks

 

[gazdkw82]

What you have to remember is that all of them loads are not going to be running at those figures at the same time. If you clamped it you would probably find its no where near those figures the majority/all of the time. IMO it would probably be under 6A most of the time.

6A? You mean 60A?

i haven't even added the shower to those figures. The shower she has is 35A!!

That would put total load at around 120A on a 80A main fuse.

Is that feasible?

 

[davesparks]

6A? You mean 60A?

i haven't even added the shower to those figures. The shower she has is 35A!!

That would put total load at around 120A on a 80A main fuse.

Is that feasible?

No, he means 6A, a domestic installation will have a surprisingly small average demand.
Most appliances are only on for short periods of time, and rarely pull their full rated current for much of that time.

I'm looking at the energy monitor for my house at the moment and the demand is a whopping 0.017kW! That is just the fridge, freezer and modem on.

If I turn the TV and associated crap on then it goes up to 0.050kW.

That's a far cry short of what the calculation would suggest!

The bottom line is that you need to take a look at what is actually used. On a bigger job you'd likely measure the actual demand using some form of data logger, but that's rarely fragrance for a domestic job!

 

[gazdkw82]

No, he means 6A, there's no way a house is going to have an average demand of 60A!

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?

 

[gazdkw82]

No, he means 6A, a domestic installation will have a surprisingly small average demand.
Most appliances are only on for short periods of time, and rarely pull their full rated current for much of that time.

I'm looking at the energy monitor for my house at the moment and the demand is a whopping 0.017kW! That is just the fridge, freezer and modem on.

If I turn the TV and associated crap on then it goes up to 0.050kW.

That's a far cry short of what the calculation would suggest!

The bottom line is that you need to take a look at what is actually used. On a bigger job you'd likely measure the actual demand using some form of data logger, but that's rarely fragrance for a domestic job!

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

 

[Pete999]

6A? You mean 60A?

i haven't even added the shower to those figures. The shower she has is 35A!!

That would put total load at around 120A on a 80A main fuse.

Is that feasible?

You need to remember, how long will the shower be on? not all day a few minuets at most. like wise any other heavy loads, kettle, etc. probably as small a load as has already been mentioned is correct

 

[gazdkw82]

You need to remember, how long will the shower be on? not all day a few minuets at most. like wise any other heavy loads, kettle, etc. probably as small a load as has already been mentioned is correct

I understand and what your saying but there must be actually rule of thumb to achieve a real average figure that can actually be used if there was ever a problem

 

[Pete999]

Didn't do a lot of Domestics gaz, but don't recall hearing of a rule of thumb, maybe one of the Domestic Installers guys could help.

 

[Resu]

I understand and what your saying but there must be actually rule of thumb to achieve a real average figure that can actually be used if there was ever a problem

I have an example that will mix things up We recently installed a fire alarm system in a 14 bedroom guesthouse. The guesthouse was fed from a standard 100A domestic supply. From memory there was 6 ring circuits, 4 lighting circuits, cooker circuit, 2x 3kw immersion circuits and a heating circuit oh and how could I forget 10(!) electric showers ranging from 8.5-10kW each!

The owner said he has never had an issue with the electrics or blown DNO fuses in the 10 years he has owned the property!

Sent from my SHIELD Tablet K1 using Tapatalk

 

[gazdkw82]

I have an example that will mix things up We recently installed a fire alarm system in a 14 bedroom guesthouse. The guesthouse was fed from a standard 100A domestic supply. From memory there was 6 ring circuits, 4 lighting circuits, cooker circuit, 2x 3kw immersion circuits and a heating circuit oh and how could I forget 10(!) electric showers ranging from 8.5-10kW each!

The owner said he has never had an issue with the electrics or blown DNO fuses in the 10 years he has owned the property!

Sent from my SHIELD Tablet K1 using Tapatalk

That can't be true!???

 

[Resu]

That can't be true!???

I wish I had taken a picture of the boards when I was there. I promise you it's true!

Sent from my SM-G935F using Tapatalk

 

[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.