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,

 

[westward10]

You rate the cable for the worst installation method with regard to its current carrying capacity, that would be the trunking. Being contained in trunking reduces its current carrying capacity to below that required for a 7.5kw shower.

 

[Dave OCD]

It would also be false economy as you can be certain that someone will want to replace it with a higher rated unit in the future. For the length of run and cost why not use 10mm and perhaps a 9.5kW shower which will perform a lot better in the middle of winter when the incoming water is really cold.

 

[Dustydazzler]

As a minimum I would run 6mm in for a domestic hot water shower

 

[louis butler]

Yeah I did think it should be a 6mm minimum but this was wired by somebody else so this cable was already in place, so should i have to say to the customer that the cable needs upgrading,
Thanks

 

[James]

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

Sounds like a fairly easy run to replace the cable.
if you are going to put your name on the certificate, make sure that it is compliment otherwise it will always be a nagging doubt in your mind that some day it will come back and bite you.

 

[telectrix]

It would also be false economy as you can be certain that someone will want to replace it with a higher rated unit in the future. For the length of run and cost why not use 10mm and perhaps a 9.5kW shower which will perform a lot better in the middle of winter when the incoming water is really cold.

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

 

[Intoelectrics]

Yeah I did think it should be a 6mm minimum but this was wired by somebody else so this cable was already in place, so should i have to say to the customer that the cable needs upgrading,
Thanks

I would personally recommend to the customer that the cable requires upgrading as it was incorrectly rated for the installation method in the first place. However, rather than a scaremongering approach, I would focus on the benefits such as the possibility of a larger rated shower unit, like Dave OCD suggested.

 

[louis butler]

I would personally recommend to the customer that the cable requires upgrading as it was incorrectly rated for the installation method in the first place. However, rather than a scaremongering approach, I would focus on the benefits such as the possibility of a larger rated shower unit, like Dave OCD suggested.

Ok will do, thanks

 

[Mikegh]

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

If you're using the pumped type the water in the attic is colder in winter

Not sure how common the pumped is the UK ,I think they're mostly mains fed ?

 

[telectrix]

mostly mains fed, but round here the mains pressure is so low that if anyone flushes the bog, all the showers go cold.

 

[Mikegh]

It would also be false economy as you can be certain that someone will want to replace it with a higher rated unit in the future. For the length of run and cost why not use 10mm and perhaps a 9.5kW shower which will perform a lot better in the middle of winter when the incoming water is really cold.

7.5 seems low, don't come across any of that rating
Would be a bit cold in winter as you say

 

[Intoelectrics]

mostly mains fed, but round here the mains pressure is so low that if anyone flushes the bog, all the showers go cold.

My elderly parents live with me, both are very much retired but are keen gardeners. I can guarantee that the minute I get home from work and decide to take a shower they either go water the plants or start washing up... They are both at the house all day, but still chose to use the water right at the moment I take my shower!

This is the down side of mains fed boilers and showers!

They grew up with stored water systems, or rather the boiled water from a kettle on a stove to fill a tin bath once a week jobby, so never even consider me in the shower each day.

 

[telectrix]

My elderly parents live with me, both are very much retired but are keen gardeners. I can guarantee that the minute I get home from work and decide to take a shower they either go water the plants or start washing up... They are both at the house all day, but still chose to use the water right at the moment I take my shower!

This is the down side of mains fed boilers and showers!

They grew up with stored water systems, or rather the boiled water from a kettle on a stove to fill a tin bath once a week jobby, so never even consider me in the shower each day.

so just have a shower at Xmas, whether you need one or not. outside water will be frozen.

 

[Dave OCD]

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

Regardless Tel, a 7.5kW shower is a bit puny and to get a bit of warmth the water flow will be more of a trickle.

 

[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