Blown 15amp fuse

[iggypops]

Hi all a few weeks back i replaced and installed a new Dimplex 3.4kw storage heater.While at B+Q i quizzed their sparky on what cable size to use explaining in the unit there are 15amp fused switches for each heater. He said he had spent two years installing storage heaters.He said 1.5 heat resistant cable would be fine and the 15amp unit would be fine.Now the fuse has blown could it be just an old fuse i think it was.Or could i have another problem.Thanks in advance for any input.

 

[PrenticeBoyofDerry]

Replace the fuse and see, if it blows again any time soon. You could have a problem, if not could well be the fuse's life expectancy has now come to an end.

 

[OwainDIYer]

I would use 2.5mm on a 20A circuit. It's a continuous 8-hour load.

 

[bernardgreen]

A heater rated as 3.4 Kwatt at 230 volts has a resistance of 15.55 ohms

Applying 240 volts to 15.55 ohms results in a current of 15.44 Amps.

As the mains voltage can go as high as 253 volts ( 230 + 10% ) the heater could in worst case take 16.2 amps

So to say a 15 amp fuse is adequate is in-correct.

A lot of "sparkies" in the sheds are only shelf fillers.

 

[iggypops]

Hi changing the cable to 2.5 is not a problem but the unit switches are all marked 15amp what needs to be done to change to a 20amp fuse.Again any guidance would be appreciated.And thanks for your expert advice so far.

 

[ban-all-sheds]

A heater rated as 3.4 Kwatt at 230 volts has a resistance of 15.55 ohms

Applying 240 volts to 15.55 ohms results in a current of 15.44 Amps.

As the mains voltage can go as high as 253 volts ( 230 + 10% ) the heater could in worst case take 16.2 amps

So to say a 15 amp fuse is adequate is in-correct.

Calculations are done using 230V, not worst case 253.

 

[bernardgreen]

As the mains voltage can go as high as 253 volts ( 230 + 10% ) the heater could in worst case take 16.2 amps

So to say a 15 amp fuse is adequate is in-correct.

Calculations are done using 230V, not worst case 253.

Yes but the 15 amp fuse with 16.2 amps flowing through it doesn't do calculations. It eventually blows.

 

[ban-all-sheds]

Calculations are done using 230V, not worst case 253.

 

[ricicle]

Also, have you seen how long it would take a 15A fuse to operate taking 16.2A ?

 

[Spark123]

I suspect that the calculations will still be done at 240v, just the same as electric showers.
What does the rating plate say?

 

[ban-all-sheds]

I suspect that the calculations will still be done at 240v, just the same as electric showers.

Calculations are done using 230V, not 240.

 

[Spark123]

Think about it, if I have a storage heater which is 10ys old and rated at 3.4kw will it suddenly require a bigger circuit if I connected it up today?

Calculations are done at the rated voltage of the appliance, you can convert them down to 230v if you wish, remembering the wattage will be reduced at 230v.

 

[bernardgreen]

mis formed post deleted

 

[bernardgreen]

Think about it, if I have a storage heater which is 10ys old and rated at 3.4kw will it suddenly require a bigger circuit if I connected it up today?

Yes I have thought about it. Whenever and however it is install if it is rated as 3.4Kw at 230 volts then if the installation supplies it with more than 230 volts it will consume more then 3.4Kw and the current will be higher than the current at 230 volts.

Calculations are done at the rated voltage of the appliance, you can convert them down to 230v if you wish, remembering the wattage will be reduced at 230v.

Yes obviously but since the supply voltage is not regulated at 230 volts and may go as high as 253 volts legally and even higher in network fault situations one should take account of such worst case scenarios.

That said the "calculations" and tabulated data of the maximum current in a cable probably do allow for a circuit designed at 230 volts to still be safe at 253 volts and possibly higher.

 

[AndyPRK]

where can you get this magic 15A fuse wire that blows at 16A ?

Is the cable round and flexible
or flat twin and bare earth ?