Electrical cable for 9kW electric boiler

[Jack155Q4]

He also wants to fit a different switch (to allow termination of the 10mm flex).

Err---

You have a 45A rated switch, which must surely therefore have terminals suitable for 10mm² conductors, and which already has a 10mm² cable on one side of it, so why does this clown think he needs to replace it?

I looked in the switch - moulded writing on it says 10mm from the top and the side exit says 6mm. I really don't know.

Made the mistake of speaking to the boiler manufacturers for their opinion and he said, he would fit it with 10mm. More doubt in my mind.

 

[bernardgreen]

It could that the switch was designed to take 10mm input which could be a long cable and as such requires 10mm to be withing voltage drop limits and 6mm in the ouput for the short cable to the boiler where voltage drop along the cable would not cause a significant reduction in voltage applied to the boiler.

In other words 10mm for the long run and 6mm for the short final run. A circuit can vary in cable size provided the smallest can safely carry the current set by the MCB

 

[ban-all-sheds]

Who would bother f*rting around making a switch like that?

 

[Jack155Q4]

Thanks guys. We have established that 6mm is good for this but is 6mm T&E OK?

Apart from the cable being too thin he also questioned the type saying T&E is not suitable and heat resistant flex should be fitted.

 

[sparkwright]

Can you send pictures?

 

[Jack155Q4]

Yes (the earthing sleeve is due to be fitted when the plumber comes back, hopefully this week):

 

[RF Lighting]

I wonder where your plumber dredged that scrap of cable from.

Apart from it being a bit scruffy, your installation is fine as it is with 6.0mm² cable.

 

[Stoday]

Tell your "electrician" that the equation for heat generation is

Watts = (voltage times voltage) divided by ohms

If the resistance increases and the voltage remains constant then the wattage reduces.

An electrician should know that.

Err...
In this situation, the voltage is the drop over the 250mm connecting cable; the current that set by the 9kW appliance, say a (nearly) constant 39A.

If the resistance increases and the current remains constant then the wattage increases.

Ahem... an electrician should know that.

 

[Jack155Q4]

I wonder where your plumber dredged that scrap of cable from.

Apart from it being a bit scruffy, your installation is fine as it is with 6.0mm² cable.

How do you actually measure this cable? I put a caliper on it and it was about 4.7mm (including the sheathing - this is the wrong way I guess )

 

[RF Lighting]

You need to measure the diameter of one of the copper strands of the line or neutral conductors with your calipers.

Divide that figure by 2 to give you the radius.


then use pi x r² to get the CSA of one strand.

Multiply this by the number of strands in one conductor. (4.0mm² - 16.0mm² T&E has 7 strands)

Or ask an electrician to look at it. He'll tell you that's a 6.0mm² cable

 

[Jack155Q4]

Many thanks. Appreciate all the help!
Jack

 

[securespark]

Is that trunking above the 45A switch?

Is there any 6mm2 cable in that trunking? If so, it's CCC is reduced to 38A.

As for the 10/6mm2 issue, sometimes the back boxes come with cable clamps and they are reversible, one way round is 6mm2 the other 10.

Is it this you refer to?

 

[EFLImpudence]

Is that trunking above the 45A switch?

That would contain the 10mm².

 

[Jack155Q4]

Is that trunking above the 45A switch?

Is there any 6mm2 cable in that trunking? If so, it's CCC is reduced to 38A.

As for the 10/6mm2 issue, sometimes the back boxes come with cable clamps and they are reversible, one way round is 6mm2 the other 10.

Is it this you refer to?

That is 10mm from the CU.

 

[ban-all-sheds]

Tell your "electrician" that the equation for heat generation is

Watts = (voltage times voltage) divided by ohms

If the resistance increases and the voltage remains constant then the wattage reduces.

An electrician should know that.

Err...
In this situation, the voltage is the drop over the 250mm connecting cable; the current that set by the 9kW appliance, say a (nearly) constant 39A.

If the resistance increases and the current remains constant then the wattage increases.

Ahem... an electrician should know that.

Err...

What he said was "If the resistance increases and the voltage remains constant then the wattage reduces."


Ahem... anybody who can read should know that.

If the resistance increases and the current remains constant then the wattage increases.

But the current doesn't remain constant does it. Anybody with GCSE physics should know that.