heating element help...

[sparkatus]

Hi Guys

Just wondering if anyone can refresh my memory on something....

When I was an apprentice I remember doing a couple of jobs changing the element in a water tank, the thing I dont remember is , how do you know the element is down..? do you get continuity between live and neutral as I seem to remember ?

Cheers

 

[Zeespark]

Isnt it IR instead of continuity?

AndyGuinness

 

[batty]

Continuity would need to be checked for open circuit and insulation to check element is not going down to earth.

 

[Ian Speirs]

Hi sparkatus, If the element has blown and you do a continuity check, then you would get no return. You could also do a tong test to see if the appliance is taking the correct load. If for example the element is 2000w and you do a continuity check, a healthy element would be around 26.45 ohms. assuming it has a 230v supply. Using ohms law R = V/I. Hope this helps.

 

[Chr!s]

First check Resistance, disconnect line and neutral, select ohms and test between line and neutral terminals of element, resistance = v2/p so 230 x 230/watts of element, so if element is 3kw =17.6 ohms

if r =0 shortcircuit if r= >299 then its o/c

insulation resistance tester, connect too line of element and earth of element, test at 500v needs to be greater than 1 meg(i think!!!!) then test between neutral earth.

regards chris

 

[Evans Electric]

Funny things ,Immersion htrs but the best way is to megger it between L&E .

Also if its still working ,which a lot are , just taking a long time to heat up the cylinder, put the clampmeter on if you know the KW .

Also try reading the res. of the element ,if its open circuit then you have your answer, I don't really trust the ohms reading because of the water .

On older installations (no RCD etc) Imm.Htrs can continue to work without blowing a fuse, even with just two prongs in the water ( the end bit dropped off) . Working like this they can raise the potential difference on the pipework but the resistance of the water interferes with the fuse blowing . Shocks from kitchen sinks etc. can result.

Not to forget the bleedin' obvious of course , check the stat first.

 

[Chr!s]

evanselectric

I don't really trust the ohms reading because of the water ?

If you carry out an insulaion resistance test this would show up.

regards chris

 

[Chr!s]

ian Speirs

Using law R = V/I. Hope this helps.

When calculating resistance using power the equation is R = V2/p

or transposed to

P = V2/R

regards chris

 

[steptoe]

the problem I sometimes find with imm heaters is they are fine until they reach a certain temp then they seem to stop, and unless your water is at that temp when you do the tests all will show up tickity boo.

as said before, check the stat first.

 

[Ian Speirs]

When calculating resistance using power the equation is R = V2/p

or transposed to

P = V2/R

regards chris

:coat Cheers chris, i was getting ahead of myself by calculating the load but never posted it. Guinness