Can I use a 4mm T&E for a 7.5Kw shower?

[louis butler]

The cable is installed in 3 metres of trunking, 3 metres clipped direct, and 5metres in the joist space with no insulation,

 

[chris murphy]

water is not much colder in winter. 18" down in the ground temp. is fairly constant all year round. at about 10degrees.

Hello telectrix,

I have regularly measured the temperature of Mains water to show people the BIG difference in Summer / Spring water temperatures compared to an average cold Winter day or night Mains water temperature - usually relating to them asking why their Combi Boiler or Electric Shower water temperature is not hot enough.

Mains water incoming pipework is supposed to be at least 750mm / 30" below the ground externally to prevent the water freezing in Winter and to prevent the water warming up in Summer / Spring.

However even at that depth below the ground the average Summer temperature measurements that I have found range from about 15 to 18 degrees centigrade.

However on cold Winter days and nights the range has been from about 3 to 5 degrees centigrade - a BIG difference regarding the incoming water temperature to Combi Boilers and Electric Showers which have a limited Heat Up / Temperature rise for the Hot water.

At my own Home on cold Winter days I have often measured the incoming Mains water temperature at only 3 degrees centigrade - Drinking water in my Fridge was 4 degrees centigrade

I have frequently seen Homes that had either inferior models of Combi Boilers or old Combi`s that were doubtless scaled up inside the Hot water Heat Exchanger where the residents have had to run Baths using the Hot tap only and then have to get straight into it before it gets too cold.

Also Homes where usually inferior models or low wattage Electric Showers could not raise the Mains water temperature to more than tepid unless the water flow volume was turned down so low that it was no more than a trickle - no Showering possible.

Chris

 

[Dave OCD]

Told you so Tel . ?

 

[telectrix]

instant showers are a PITA anyway. the only ones any use are hot and cold fed.

 

[Mikegh]

instant showers are a PITA anyway. the only ones any use are hot and cold fed.

Dunno they don't give me too much trouble

I keep a stock of Mira elites that I remove for my own place

Very little wrong with them in reality ,most problems are down to basic flow issues .

 

[Mikegh]

Had the pump motor tripping the RCD on mine recently

90% of the time it's the heater tank

Rushed at it doing a quickfire ir test on the heater with one wire still attached, managed to mistakenly diagnose it with the N still attached

 

[johntheo]

9 kw is the norm around here, mostly pumped but mine is mains as I have 3.5bar constant. They are a bit on the mean side but have nice spray patterns to give ~ 3.7LPM in the winter (5/40C) & ~ 5.9LPM in high summer (18/40C).

 

[wigwamabama]

Hello telectrix,

I have regularly measured the temperature of Mains water to show people the BIG difference in Summer / Spring water temperatures compared to an average cold Winter day or night Mains water temperature - usually relating to them asking why their Combi Boiler or Electric Shower water temperature is not hot enough.

Mains water incoming pipework is supposed to be at least 750mm / 30" below the ground externally to prevent the water freezing in Winter and to prevent the water warming up in Summer / Spring.

However even at that depth below the ground the average Summer temperature measurements that I have found range from about 15 to 18 degrees centigrade.

However on cold Winter days and nights the range has been from about 3 to 5 degrees centigrade - a BIG difference regarding the incoming water temperature to Combi Boilers and Electric Showers which have a limited Heat Up / Temperature rise for the Hot water.

At my own Home on cold Winter days I have often measured the incoming Mains water temperature at only 3 degrees centigrade - Drinking water in my Fridge was 4 degrees centigrade

I have frequently seen Homes that had either inferior models of Combi Boilers or old Combi`s that were doubtless scaled up inside the Hot water Heat Exchanger where the residents have had to run Baths using the Hot tap only and then have to get straight into it before it gets too cold.

Also Homes where usually inferior models or low wattage Electric Showers could not raise the Mains water temperature to more than tepid unless the water flow volume was turned down so low that it was no more than a trickle - no Showering possible.

Chris

And what is wrong with filling a bath from the hot tap only, if you have a combi boiler? Surely it's more ridiculous to use large amounts of gas to heat the bath water, and then turn the cold tap on just to make it cold again?

 

[Davey251086]

6mm or above all day long, cable needs upgrading. Even with 6mm cable im still going out to jobs were plumbrrs have fit 9.5kw showers in with burnt up isolators causing tripping.

 

[DPG]

6mm or above all day long, cable needs upgrading. Even with 6mm cable im still going out to jobs were plumbrrs have fit 9.5kw showers in with burnt up isolators causing tripping.

Burnt out isolating switches is not down to the cable size though.

 

[Mikegh]

Burnt out isolating switches is not down to the cable size though.

No mainly down to cheap isolators, poor install, load switching etc.

The best shower isolator is one u don't switch off or crabtree or equivalent

 

[Davey251086]

Burnt out isolating switches is not down to the cable size though.

I agree a 100 per cent that the main reason a shower switch burns out is down to a loose terminal connection or cheap shower switch especially where we as sparks are cramming a 10mm cable into a 47mm pattress on the wall loosing them in the process.

However from my experience if your over-rate your cable from say a 9.5kw shower on a 6mm cable it can cause heat to dissipate anywhere on the cable. So where theres a big box on the wall full of single insulated cables with no heat to escape you see it travel all up the cable.

Some ive seen so bad the the whole cable has had to be replace. Simarily to where the cable has been bent or weakened through installation. Heat is going to affect the cable where it is most weak first so at joins or switches.

Still it takes a long time for a 9kw shower to cause the cable to burn up as its never running at full load most of the time.

 

[Mikegh]

Don't they run at full load continuous on full power ?

Or am I missing something ?

 

[James]

Don't they run at full load continuous on full power ?

Or am I missing something ?

Only for short durations, it is rare for that to be the case for hours and hours.

 

[Mikegh]

Only for short durations, it is rare for that to be the case for hours and hours.

Ah right I'm probably misinterpreting the post

The shower is on for a short period of time then ?

 

[James]

What I was getting at, is nearly all showers are only used for short durations.
not normal for one to be in use for several hours in one continuous go.