Water heaters

[cumbriaelec]

Was just carrying out a PAT Test at a garage. Owner asked me to take a look at his new water heater that wasnt working. Eventually found the right fuse in a bit of a hit and miss excercise inside a fuse board were nothing was marked up... Fuse had blown as the water heater had been looped off an identical water heater in an adjacent room... Both water heaters were rated at 3KW so the 25A fuse wasn't going to deal with that when they were both on... 32A fuse will just about do, but the live is only 4mm. The cables are fed from the fuse board through trunking screwed to the extrior of a wall... about twenty metre run... live goes to heater one then loops off to heater two - no live return to board (so radial circuit)... What do you think? Okay to leave with 4mm, or would you up it to 6mm... or maybe turn it into a ring main with another 4mm cable run to the second water heater spur, as the second water heater is much closer to the board...

 

[stoney306]

Was just carrying out a PAT Test at a garage. Owner asked me to take a look at his new water heater that wasnt working. Eventually found the right fuse in a bit of a hit and miss excercise inside a fuse board were nothing was marked up... Fuse had blown as the water heater had been looped off an identical water heater in an adjacent room... Both water heaters were rated at 3KW so the 25A fuse wasn't going to deal with that when they were both on... 32A fuse will just about do, but the live is only 4mm. The cables are fed from the fuse board through trunking screwed to the extrior of a wall... about twenty metre run... live goes to heater one then loops off to heater two - no live return to board (so radial circuit)... What do you think? Okay to leave with 4mm, or would you up it to 6mm... or maybe turn it into a ring main with another 4mm cable run to the second water heater spur, as the second water heater is much closer to the board...

just run out new 4mm supply and back each one up with 20a. happy days

 

[mrloy99]

Was just carrying out a PAT Test at a garage. Owner asked me to take a look at his new water heater that wasnt working. Eventually found the right fuse in a bit of a hit and miss excercise inside a fuse board were nothing was marked up... Fuse had blown as the water heater had been looped off an identical water heater in an adjacent room... Both water heaters were rated at 3KW so the 25A fuse wasn't going to deal with that when they were both on... 32A fuse will just about do, but the live is only 4mm. The cables are fed from the fuse board through trunking screwed to the extrior of a wall... about twenty metre run... live goes to heater one then loops off to heater two - no live return to board (so radial circuit)... What do you think? Okay to leave with 4mm, or would you up it to 6mm... or maybe turn it into a ring main with another 4mm cable run to the second water heater spur, as the second water heater is much closer to the board...

3kw equates to 12.5amp each at 240 volt so 25amp should cover both.
or at 230 volt 13amps each.
I've not come accross a 25 amp fuse before...but 30amp or 32amp fuse will provide protection
for your 4mm cable.(existing)
Your switches(local isolators) however would probably need to be rated for 32amps too-especially
the first one which the full loading is passing through.You might also find that the water heater
hadn't been fully filled with water before the power was applied and the internal thermal fuselink has operated

 

[Des 56]

Not exactly sure of the rating,but if there are 2 water heaters ,you may find that each heater should have its own dedicated supply

Out of interest I just looked in the guide to the building regs
A water heater with excess of 15 litres capacaty should be supplied by its own seperate circuit circuit

 

[Spudnik]

Not exactly sure of the rating,but if there are 2 water heaters and they are over 2 kw,you may find that each heater should have its own dedicated supply

Tricky one as that only really applies when connecting items above 2kW to a RFC.

Although i would still do the same and use either 2 radials or why not double up on the 4mm and create a RFC?

 

[mrloy99]

Not exactly sure of the rating,but if there are 2 water heaters ,you may find that each heater should have its own dedicated supply

Out of interest I just looked in the guide to the building regs
A water heater with excess of 15 litres capacaty should be supplied by its own seperate circuit circuit

Hmmm---Ideally they of course should be on their own circuit--but I dunno if i'd agree with the 15litre bit though.some of these instantaneous heaters and showers only would hold a couple of litres.

 

[tigerpaul]

Run a new 4mm back from heater 2, thus making a 4mm ring. Then a 32A fuse will be more than adequate (assuming you've taken into account your rating factors)

Each heater though requires its own 13A fused spur, then come off that with a 2.5mm heat resistant flex to the heater.

Why would each heater need it's own seperate supply?

3000/230 = 13.04A so shouldn't be a problem..

 

[thepurple1]

I've not come accross a 25 amp fuse before...but 30amp or 32amp fuse will provide protection
for your 4mm cable.(existing)


We use 25 amp AM and gG type fuses all the time