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

[telectrix]

agreed. a 3 kW kettle takes 2 minutes to boil. a 2kW kettle takes 3 minutes ( for the same amount of water). which costs more?

 

[littlespark]

agreed. a 3 kW kettle takes 2 minutes to boil. a 2kW kettle takes 3 minutes ( for the same amount of water). which costs more?

Depends on how posh the coffee is… do you take milk and sugar?
Is that a home kettle or a Starbucks?

 

[Norah Nabino]

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

Is it just gues work?
I thought some cable calculations are needed to be certain

 

[Norah Nabino]

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

Is it gues work?I thought some cable calculations are involved to ascertain the size of the cable.

 

[johntheo]

Based on a 240V, 7.5kw shower and a total length of 16M of 4MM2 cable and assuming cable resistance at 4.3mohm/M then my (rusty) calcs give a current flow of 30.975ohms and a shower output of 7.368kw and a voltage drop of 2.13V through the cable resulting in a cable heat loss of 65.94watts or 4.12watts/meter of cable.

So is 4MM2 suitable??.

 

[telectrix]

suitable, but not ideal, esp if there's the possibility of insulation being added by the itchy-poo monkeys.

 

[GLENNSPARK]

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.

Somebody recently wanted me to fit a shower switch shed bought from wickes...
It felt light, looked shyte and came complete with a 27mm surface box to mount it on...

I took one look at it and said: "nah....yer allrite love"

Went round the corner and got a decent one weighing twice as much and a 47mm box...

I don't know why people persist in going to these diy stores for electrical stuff...?

 

[telectrix]

Somebody recently wanted me to fit a shower switch shed bought from wickes...
It felt light, looked shyte and came complete with a 27mm surface box to mount it on...

I took one look at it and said: "nah....yer allrite love"

Went round the corner and got a decent one weighing twice as much and a 47mm box...

I don't know why people persist in going to these diy stores for electrical stuff...?

coz they know no better. i will only fit the crabtree or click 50A round jobbies. them square ones suck.

 

[loz2754]

coz they know no better. i will only fit the crabtree or click 50A round jobbies. them square ones suck.

I finally got around to trying the Click round jobby.
I'll never go back...

 

[Zerax]

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?

That's not how it works... you heat less water to make it hot... rather than more water to a lower temperature. The net effect is the same (ish).

 

[littlespark]

Will you lot stop saying “jobby”

There’s Scotsmen here, you know.

 

[telectrix]

jobby,jobby,jobby.

 

[pc1966]

Based on a 240V, 7.5kw shower and a total length of 16M of 4MM2 cable and assuming cable resistance at 4.3mohm/M then my (rusty) calcs give a current flow of 30.975ohms and a shower output of 7.368kw and a voltage drop of 2.13V through the cable resulting in a cable heat loss of 65.94watts or 4.12watts/meter of cable.

So is 4MM2 suitable??.

Only if it keeps cool enough.

That is one of the 3 critical tests for cable choice:

• Current carrying capacity (combinations of resistance, insulation temperature limit, ambient temperature, and thermal insulation "method")
• Voltage drop (resistance and length)
• Zs for Automatic Disconnection of Supply (resistance, length, protective device and supply impedance)

Should I don the Cardinal Ximénez outfit and summon Cardinal Fang now?

 

[DPG]

I love these convos you have to put every detail in about every product or operation. The science behind it or the physics, the calculations like you designing an electrical installation right from your phone.

If you put anything in laymans terms someone is quick to point out a fall or bite ?

Have fun guys another forum i wont be on again.

You lot are way better electricians...well done

I notice you've been back on the forum this evening. I knew you'd be back.

As I say, stick around - there's a lot of knowledge on here.

 

[GLENNSPARK]

Only if it keeps cool enough.

That is one of the 3 critical tests for cable choice:

• Current carrying capacity (combinations of resistance, insulation temperature limit, ambient temperature, and thermal insulation "method")
• Voltage drop (resistance and length)
• Zs for Automatic Disconnection of Supply (resistance, length, protective device and supply impedance)

Should I don the Cardinal Ximénez outfit and summon Cardinal Fang now?

Installation method and ambient temperature takes paramount for most normal fixed wiring applications as it dictates everything else...